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Article

Phytochemical Profiles and Antimicrobial Activity of Selected Populus spp. Bud Extracts

by
Piotr Okińczyc
1,*,
Jarosław Widelski
2,*,
Kinga Nowak
3,
Sylwia Radwan
4,
Maciej Włodarczyk
1,
Piotr Marek Kuś
1,
Katarzyna Susniak
5 and
Izabela Korona-Głowniak
5
1
Department of Pharmacognosy and Herbal Medicines, Faculty of Pharmacy, Wroclaw Medical University, Borowska 211a, PL-50-556 Wrocław, Poland
2
Department of Pharmacognosy with Medicinal Plants Garden, Medical University of Lublin, Chodźki 1, PL-20-093 Lublin, Poland
3
Institute of Dendrology, Polish Academy of Sciences, Parkowa 5, PL-62-035 Kórnik, Poland
4
Laboratory of Elemental Analysis and Structural Research, Faculty of Pharmacy, Wroclaw Medical University, Borowska 211a, PL-50-556 Wrocław, Poland
5
Department of Pharmaceutical Microbiology, Medical University of Lublin, Chodźki 1, PL-20-093 Lublin, Poland
*
Authors to whom correspondence should be addressed.
Molecules 2024, 29(2), 437; https://doi.org/10.3390/molecules29020437
Submission received: 26 November 2023 / Revised: 11 January 2024 / Accepted: 13 January 2024 / Published: 16 January 2024
(This article belongs to the Special Issue Antibacterial Agents from Natural Source, 2nd Edition)
Browse Figures
Versions Notes

Abstract

:
Buds of poplar trees (Populus species) are often covered with sticky, usually polyphenol-rich, exudates. Moreover, accessible data showed that some Populus bud extracts may be excellent antibacterial agents, especially against Gram-positive bacteria. Due to the fragmentary nature of the data found, we conducted a systematic screening study. The antimicrobial activity of two extract types (semi-polar—ethanolic and polar—ethanolic-water (50/50; V/V)) from 27 bud samples of different poplar taxons were compared. Antimicrobial assays were performed against Gram-positive (five strains) and Gram-negative (six strains) bacteria as well as fungi (three strains) and covered the determination of minimal inhibitory, bactericidal, and fungicidal concentrations. The composition of extracts was later investigated by ultra-high-performance liquid chromatography coupled with ultraviolet detection (UHPLC-DAD) and with electrospray-quadrupole-time-of-flight tandem mass spectrometry (UHPLC-ESI-qTOF-MS). As a result, most of the extracts exhibited good (MIC ≤ 62.5 µg/mL) or moderate (62.5 < MIC ≤ 500 µg/mL) activity against Gram-positives and Helicobacter pylori, as well as fungi. The most active were ethanolic extracts from P. trichocarpa, P. trichocarpa clone ‘Robusta’, and P. tacamahaca × P. trichocarpa. The strongest activity was observed for P. tacamahaca × P. trichocarpa. Antibacterial activity was supposedly connected with the abundant presence of flavonoids (pinobanksin, pinobanksin 3-acetate, chrysin, pinocembrin, galangin, isosakuranetin dihydrochalcone, pinocembrin dihydrochalcone, and 2′,6′-dihydroxy-4′-methoxydihydrochalcone), hydroxycinnamic acids monoesters (p-methoxycinnamic acid cinnamyl ester, caffeic acid phenethylate and different isomers of prenyl esters), and some minor components (balsacones).

Graphical Abstract

1. Introduction

Poplars are high trees that belong to the genus Populus L. of Salicaceae Mirb. family due to the traditional organism systematics of Carolus Linnaeus [1,2], while the (Salix + Populus) clade is also classified into a higher clade of ((Goupiaceae + Violaceae) (Passifloraceae (Lacistemataceae + Salicaceae))) by Angiosperm Phylogeny Group [3]. Different authors distinguished 6–7 sections of the Populus genus, but this classification is evolving [2]. The deeper systematics of the genus Populus is complex and still discussed due to many factors. It is claimed that Populus specimens are difficult to identify accurately. Moreover, most poplars are known for their ease of spreading and crossbreeding [1,2,4]. A typical example is American P. balsamifera L., which quickly spread in Europe and produced intersectional hybrids with Europe-native P. nigra L. (black poplar) [4]. As a result, pure specimens of black poplars are relatively rare today [1,4]. Another issue is differences in statements of species classifications. According to World Flora Online [5], traditionally distinguished species like P. maximowiczii Henry, P. suaveolens Fisch. ex Loudon, and P. koreana Rehder are nowadays recognized as synonyms of P. suaveolens Fisch. A similar situation occurs for P. balsamifera and P. trichocarpa [2]. In summary, different descriptions of Populus species exist in the literature. For this reason, the system of Populus species classification adopted for this work should be defined. In the present manuscript, a traditional division of species described by Bugała in his monograph elaboration and further modified by Korbik [1,2] was used. This decision was made due to the widespread use of traditional names in the literature, even in 2023.
Apart from systematics, the Salicaceae family is known for famous medicinal plants, especially willows (Salix genus). Willow bark contains biologically active compounds, especially salicylate-like phenolic glycosides [6]. This group of metabolites includes glycosides and glycoside-esters (e.g., salicin and salicortin), aromatic acids (cinnamic and hydroxycinnamic acids), and others. It is well known that salicylates exhibit anti-inflammatory activity [6]. Raw herbal materials from Salix species, especially bark, rich in salicylate-like phenolic glycosides, are still used in cold and mild rheumatic diseases. Moreover, the bark of willow species has its monograph (Salicis cortex) in many official pharmacopeias [7,8].
In the case of the poplars (Populus genus), their organs (bark [9], leaves [10], buds [11,12]) also contain anti-inflammatory salicylate-like phenolic glycosides. For this reason, poplar’s organs are also used in folk medicine to treat gout [13]. However, unlike willows, poplars are not widely included in pharmacopeias. Leaves of poplars (Populi folium) are included in the national part of Polish Pharmacopeia [14]. In case of buds, some species such as P. nigra L., P. balsamifera L., P. canadensis Marsh., P. laurifolia Ledeb., and P. suaveolens Fisch. are plant sources of Populi gemmae in the Russian Pharmacopeia [15]. However, the Populi gemmae monograph is absent in European Pharmacopoeia 11 and USP-NF 2023.
Apart from salicylate-like phenolic glycosides, buds of many Populus species are covered by sticky, resinous exudates [1,16], an additional source of biologically active components. The amounts, seasons, and periods of resin production depend on species and environmental factors. Buds of some species (e.g., P. tremula L.) are only resinous for a short period before cracking in spring, while others are sticky almost all year [1]. The composition of Populus resins is very complex but specific for species. For these reasons, a comparative analysis of bud exudates composition may be helpful for chemotaxonomic purposes [16]. At this point, the main components of Populus resinous exudates were defined as phenols, volatile and non-volatile terpenes and terpenoids, and other substances [16,17].
Biologically, resins form a protective layer on buds, making them less sensitive to wetness, cold, and attacks of pathogenic microorganisms and parasites and less attractive for herbivores. On the one hand, poplar resins often contain relatively high concentrations of polar free phenolic acids; however, more apolar components such as flavonoid aglycones and phenolic acids esters are also detected [16,17]. Surprisingly, one of the rarest substances in resins are glycosides, e.g., salicylate-like glycosides. Literature data have reported their presence in extracts from whole buds [11,12,18] but did not focus unambiguously on resins. Thus, one can guess that salicylates may be components of buds’ interior green tissues, not bud exudates.
Resins of the Populus genus are plant precursors of a bee product known as propolis (or bee glue). It is well-known for multiple medicinal activities such as wound treatment, anti-inflammatory, antioxidant, and antimicrobial. These properties were also reported for poplar bud’ extracts [11,19,20,21]. Researchers reported differences between propolis and poplar buds; however, it is impossible to claim if propolis or poplar buds have more potent medicinal properties. Moreover, Apis mellifera L. bees do not use resins from all available Populus species to produce propolis. It was observed that their preferences for local species may be so strong that foreign poplar trees are ignored. Sometimes, non-poplar species (e.g., birch) are preferred over foreign Populus specimens [22]. The factors impacting bees’ decisions remain unknown. It is suspected that components of some Populus species resins may be toxic or repellent to bees. That is why some poplars may contain highly active components not observed in propolis research. Moreover, literature data on Populus buds are limited compared to propolis or poplar leaves research. So far, phytochemical analyses for species other than P. nigra, P. balsamifera, and P. tremula have focused mainly on GC-MS profiling [23,24,25,26,27,28,29,30,31,32], while LC-MS and LC-DAD investigations are more limited [16,18,28,29]. Moreover, the chemical composition of buds is not yet defined for every Populus species.
Our manuscript compares phytochemistry with antimicrobial properties of ethanol and ethanol/water (50/50; V/V) extracts of poplar buds. Populus species were selected due to the high production of resins (the viscosity of buds before cracking was evaluated in preliminary research) and the expected activity. Section 3 (Materials and Methods) contains a complete list of investigated poplar species. Instrumental analysis was performed using LC-UV-ESI-QTOF-MS/MS due to the expected high amounts of polyphenols and only a few similar works. Solvents used in extraction were chosen due to desired components and previous optimization. Ethanol dissolves buds’ resins and their less polar components, such as flavonoid aglycones and hydroxycinnamic acids esters. More polar constituents (e.g., salicylate-like glycosides) from buds’ green tissues were extracted by ethanol with water (50:50, V/V). Antimicrobial activity screening against bacterial (Gram-positive and Gram-negative) and fungal strains was based on previous experience and the expected activity of propolis [33], as well as results for P. nigra and P. tremula buds [20]. To our knowledge, LC-MS-UV-ESI-qTOF-MS/MS analysis and antimicrobial screening were performed for the first time for poplar bud extracts of most Populus species, excluding P. nigra, P. balsamifera, and P. tremula. Moreover, the activity of all extracts against Helicobacter pylori was also tested for the first time.

2. Results and Discussion

Poplar buds, their resins, and propolis are similar, but they are not the same type of plant material and thus should not be replaced by each other. The Populus buds’ composition and activity data are relatively sparse, particularly regarding propolis. Therefore, the extensive comparative studies of the phytochemistry and biological activity of poplar buds conducted in this study constitute a valuable contribution to this field.

2.1. LC-UV-ESI-qTOF-MS/MS Profile of Extracts

Complete results of LC-UV-ESI-qTOF-MS/MS are presented in Table 1 (identification of components in Populus bud extracts by LC-UV-ESI-qTOF-MS/MS) and in the supplement (Table S1. Relative abundance of extracts components and buds’ extraction yield). A selection of chromatograms is given in Figure 1 (LC-MS chromatograms of Populus bud EtOH extracts represent five different chemical groups). The identification of components was based on retention times of chromatographic peaks and UV spectra, and calculated formulas of deprotonated molecular ions as well as MS/MS fragmentation spectra. Due to the different confidence levels, the obtained information was divided into four groups—A, B, C, and D (see Section 3 and Table 1 for details). Confidence levels A and B mean reliable identification, while levels C and D are tentative.
More than 300 unique components were observed in UV and MS chromatograms. Because most of them remained at trace level (MS or UV peak), Table 1 and Supplementary Table S1 were limited to 223 components. Among them, 163 substances were identified (confidence levels A and B) or tentatively identified (confidence levels C and D). The substitution positions of glycerol by hydroxycinnamic acids were proposed by comparison with previous research [33] and literature [17,19,23]. So far, it has been proved that more symmetric hydroxycinnamic acid glycerides dominate over non-symmetric glycerides in GC-MS research [17,19,23]. For example, 2-acetyl-1,3-di-p-coumaroyl glycerol had a higher concentration than 3-acetyl-1,2-di-p-coumaroyl glycerol in P. tremula buds [23] and further in propolis [17,19]). Differences in concentration and ionization were used to identify isomers of caffeic acid p-coumaric acids methylbutenyl ester [33].
Most of these components were phenols and polyphenols, classified as free hydroxycinnamic acids, salicylate-like phenolic glycosides, hydroxycinnamic acids monoesters, hydroxycinnamic glycerides, other polyphenols, and non-polyphenols. In terms of compound numbers, the richest phenols and polyphenols class was flavonoids (73 components), followed by hydroxycinnamic acids monoesters (35 comp.), others polyphenols (22 comp.), hydroxycinnamic acids glycerides (13 comp.), salicylate-like glycosides (9 comp.), and free phenolic acids (6 comp.), respectively. Only four components were classified as non-polyphenols; most unidentified components were probably also non-polyphenols.
Regarding the components’ relative abundance, poplar bud extracts were mainly rich in flavonoids, hydroxycinnamic acid monoesters, and hydroxycinnamic glycerides. Most observed substances easily produced ions in negative mode; therefore, their relative abundance was calculated from mass chromatograms. In contrast, tectochrysin, pinostrobin, and ferulic acid benzyl ester did not produce ions, or the signals were weak under standard conditions. For those substances, the relative abundance was obtained by comparison of UVmax chromatograms in 280 nm.
Chromatographic profiles of ethanolic (EtOH) and water/ethanol (50/50; V/V) (W/E) extracts exhibited qualitative and quantitative differences. EtOH extracts were more abundant in a number of components than W/E, but some substances were present only in W/E. Most observed compounds remained at an ion trace level, and only unidentified component 2 (RT 0.87 min, [M−H]− at 195.0515 m/z) exhibited low and average relative abundance. Moreover, the most common components of EtOH and W/E extracts exhibited higher relative abundance in EtOH. Rarely were W/E extracts more abundant in common substances. For example, pinobanksin was more abundant in W/E of P.LA, P.M×P.B, and P.N3, while in EtOH for the rest of the samples. In summary, ethanol turned out to be a more appropriate solvent than water/ethanol (50/50; V/V) for batch extraction and further chemometric analysis of poplar buds regarding the number of extracted compounds and their relative abundance.
The relative abundance of most components was obtained due to deprotonated pseudomolecular ion intensity in a single chromatographic peak (see details in Section 3). Only pinostrobin and tectochrysin relative amounts were based on UV peak intensity due to their weak ionization in negative mode.
Populus bud extracts were divided into phytochemical groups. The division was based on the presence of dominant components. Domination was determined based on deprotonated pseudomolecular ion intensity (see Supplementary Table S1). Because chromatographic analyses of EtOH extracts had stronger and more numerous peaks of components, they were selected to direct the division. As a result, extracts were aggregated into several subtypes: (1) flavonoid, (2) flavonoid + hydroxycinnamic acid monoesters, (3) hydroxycinnamic acid monoesters, (4) hydroxycinnamic acid glycerides, and (5) mixed ones.
A considerable group of six EtOH extracts was of (1) flavonoid type (P.DE—P. deltoides; P.DE × P.N.—P. deltoides × P. nigra; P.ER—P. ‘Eridano’ (P. deltoides × maximowiczii clone Eridano); P.LAU—P. laurifolia; P.MAX—P. maximowiczii; P.N.3—P. nigra, sample 3). The flagship compounds in this group included pinobanksin 5-methyl ether, pinobanksin, chrysin, pinocembrin, galangin, and pinobanksin 3-esters (acetate—main—followed by propanoate, butanoate or isobutanoate, and pentanoate or isopentanoate isomer II). Pinocembrin and pinobanksin 3-acetate usually occurred with the strongest signal among these components. The hydroxycinnamic acid monoesters were similar to the previous type but not always present, even if they gave lower peaks (except metoxycinnamic acid cinnamyl ester in P.N.3 and P.ER).
Most EtOH extracts (10/27) were in (2) flavonoid + hydroxycinnamic acid monoesters type (P.BA—P. balsamifera; P.CA—P. cathayana; P.KOM—P. komarovii; P.M×P.B—P. maximowiczii × P. × berolinensis (P. laurifolia × P. nigra ‘Italica’), P.×PE.1, P.×PE.2—P. × petrovskiana (P. laurifolia × P. deltoides), sample 1 and 2; P.×RA—P. × rasumowskyana (P. laurifolia × P. × wobstii); P.SU—P. suaveolens; P.SI—P. simonii; P.TA.1, P.TA.2—P. tacamahaca, sample 1 and 2). The main flavonoids in this group included pinobanksin, chrysin, pinocembrin, pinocembrin chalcone, pinobanksin 3-acetate, and pinostrobin chalcone; the main hydroxycinnamic acid monoesters were caffeic acids derivatives (butyl or isobutyl isomer I, 2-methyl-2-butenyl, 3-methyl-2-butenyl, 3-methyl-3-butenyl ester, benzyl, phenethyl). Most of these substances, except caffeic acid butyl or isobutyl ester isomer I, were present in all EtOH in this group.
The next group gathered two extracts with the domination of hydroxycinnamic acid monoesters. Both of them originated from P. nigra (P.N.1 and P.N.2). The main hydroxycinnamic acid monoesters in this group were derivatives of caffeic acid (2-methyl-2-butenyl, 3-methyl-2-butenyl, 3-methyl-3-butenyl ester, benzyl, phenethyl) and metoxycinnamic acid cinnamyl esters. Both samples also contained average signals of flavonoids (mainly pinocembrin and pinostrobin chalcone). It is essential to point out that these samples did not contain pinobanksin 3-acetate (the main flavonoid of other investigated samples) and had only traces of non-esterified pinobanksin when another sample (also classified as P. nigra) contained these flavanols at high concentrations. In the literature, both flavonoids are frequently reported in P. nigra buds [17]. P.N.1 and P.N.2 were introduced to Arboretum from an old tree stand (Dęblin, on-Vistula river, Poland) and were previously evaluated as genetically pure P. nigra. As already mentioned in the Introduction, P. nigra easily crosses with available poplar species [1,4]. Therefore, we hypothesize pinobanksin and pinobanksin 3-acetate presence in the so-called P. nigra bud sample is a result of P. nigra hybridization, unnoticeable by morphological examination methods. Another possibility is that the P.N.3 sample originates from a specific phenotype (chemotype) of P. nigra.
The fourth group was hydroxycinnamic acid glycerides, mainly represented by P. lasiocarpa (P.LAS), P. wilsonii (P.WIL), and P. × wilsocarpa (P. wilsonii × P. lasiocarpa, P.×WCA). The main components in this group included 2-acetyl-1,3-di-caffeoylglycerol, 2-acetyl-1-caffeoyl-3-p-coumaroylglycerol, and 2-acetyl-1,3-di-p-coumaroylglycerol. In this group, P.LAS exhibited the strongest relative abundance of these compounds. Moreover, EtOH extracts in this group contained relatively low amounts of flavonoids, while hydroxycinnamic acid monoesters were absent. Hydroxycinnamic acid glycerides are specific markers of P. lasiocarpa from Asian great leaf poplar buds (section Leucoides) [34] as well as aspen poplars (Eurasian P. tremula [16,23] and American P. tremuloides [35]). Apart from P.LAS, P.WIL, and P.×WCA, the rest of the bud extracts contained only trace signals of these compounds (mainly monocaffeoylglycerol and rarely other glycerol esters).
The last group was a (five) mixed type, including five EtOH extracts (P.M×P.TRI.—P. maximowiczii × P. trichocarpa; P.RO—P. trichocarpa clone ‘Rochester’; P.TA×P.TRI.1, P.TA×P.TRI.2—P. tacamahaca × P. trichocarpa, sample 1 and 2; P.TRI—P. trichocarpa). It is worth pointing out that all samples in this group were P. trichocarpa and its crossbreed specimens with P. maximowiczii and P. tacamahaca. The lack of parent species—P.MAX, P.TA.1, and P.TA.2 in the (five) mixed group—led to a hypothesis that the impact of P. trichocarpa on secondary metabolites production in its hybrids is more substantial than the impact of other parent species. P.M×P.TRI, P.RO, P.TRI, and P.TA×P.TRI.2 revealed average and strong signals of p-coumaric acids, 2′,6′-dihydroxy-4′-methoxy dihydrochalcone and p-coumaric acid cinnamyl ester. Moreover, EtOH extracts also exhibited the presence of substances tentatively identified as balsacones (dihydrochalcones with additional phenylpropyl units). These components were previously isolated from P. balsamifera [36] but were absent in P.BA.EtOH extract. Readers need to remember that P. trichocarpa is sometimes classified as a subspecies of P. balsamifera [2]. The rest of the components in the mixed type were more varied. P.RO had strong signals of pinocembrin, pinocembrin dihydrochalcone, and pinobanksin 3-acetate, while the rest of the five samples had no more eye-catching components.
In summary, batch negative mode LC-MS analysis of poplar bud extracts revealed the dominance of polyphenols’ peaks with patterns specific enough to distinguish six groups. This method can be considered a promising strategy for poplar bud fingerprinting. Moreover, all EtOH extracts had stronger signals of polyphenols (from one to three relative levels of difference between considerable components; see Supplementary Table S1) than W/E, which can be practical information for further studies.
It is worth adding that buds of P.BA, P.KOM, P.MAX, P.M × P.TRI, P.N.3, P × PE.2, P.RO, P × RA, P.RO, P.TA.1, P.TA × P.TRI.1, P.TA × P.TRI.2, and P.TRI were relatively big (up to 4 cm), contained a lot of resins (organoleptic tests), and provided high extraction yield (>39% per dry mass of buds for EtOH extracts; see Supplementary Table S1. Finally, their extracts revealed strong signals of polyphenols. Therefore, they may be utilized as a source of specific components or extracts rich in polyphenols.

2.2. Antimicrobial Properties of Extracts

The antimicrobial properties of extracts are presented in Table 2 (Comparison of antimicrobial effect of ethanol and water/ethanol extracts of Populus buds). Performed research included determination of MIC (minimal inhibitory concentration) and MBC or MFC (minimal bactericidal/fungicidal concentration) as well as MBC/MIC or MFC/MIC ratio. Both extract types (EtOH and W/E) revealed relatively higher activity against Gram-positive bacteria and fungi than against most Gram-negative ones. Only Helicobacter pylori violated this rule; therefore, it was described separately below. Similar profiles of activity were already reported for poplar propolis [19,20,33] as well as buds of P. nigra [19,20], P. balsamifera [11,37], P. tremula [19,20], and P. tremuloides [35].

2.2.1. Activity against Gram-Negative Strains

Most lyophilized poplar bud extracts (50/52) exhibited MIC (minimal inhibitory concentration) 1000 and >1000 µg/mL against Escherichia coli, Salmonella Typhimurium, Proteus mirabilis, and Klebsiella pneumoniae. MICs determination performed for EtOH extracts showed MIC values from 500 (only P.M × P.B vs. P. mirabilis) to >1000 µg/mL values. For this reason, the screening method was modified for W/E, and if MIC was >1000 µg/mL, MBC was not tested due to the expected unattractive high value and low activity. In the literature, ethyl acetate extracts exhibited MIC = 250 µg/mL (P. nigra) and 500 µg/mL (P. tremula) against P. aeruginosa and >5000 µg/mL (P. nigra and P. tremula) against E. coli [19]. In the case of methanol extracts of P. nigra, P. alba, and P. tremula, MIC > 4000 µg/mL were observed against E. coli, K. pneumoniae, P. mirabilis, P. aeruginosa, and S. enterica serovar Typhimurium [21]. In the case of P. balsamifera, weak activity against Gram-negative strains was exhibited in the disc-diffusion test [11].
Low activity against Gram-negative species may be a general rule for Populus bud extracts. It may result from components non-specifically eliminated via efflux pumps in many Gram-negative species [38], as well as differences in the structure of Gram-positive and Gram-negative cell barriers [39].

2.2.2. Activity against Gram-Positive Strains

The tested Gram-positive bacteria strains included Staphylococcus aureus, S. epidermidis, Micrococcus luteus, Bacillus subtilis, B. cereus, and Enterococcus faecalis. Comparison of MIC with MBC in pairs of EtOH and W/E extracts exhibited that the MBC/MIC ratio was usually equal to or lower than four for most strains and samples. These results showed that EtOH and W/E exhibit rather bactericidal than bacteriostatic effects. The bactericidal effect may result from a multifactorial mechanism of action. Antibacterial agents of poplar buds’ resins, propolis, and flavonoids are known for disrupting cytoplasmic membrane function, inhibiting nucleic acid synthesis, and inhibiting the energy metabolism of bacterial strains [40]. Similar effects on bacterial cell membranes were also caused by caffeic acid monoesters, especially CAPE (caffeic acid phenethyl ester), which is the most investigated [41]. Potentially, ingredients that disrupt cell barrier function and stability may facilitate the penetration of active ingredients across the cell barrier. Active components may cause damage to bacterial cells in different ways, e.g., by increasing oxidative stress [42]. Finally, a bacterial cell cannot be repaired and undergoes lysis.
There were noted differences between the activity of EtOH and W/E extracts in most cases. Moreover, EtOH extracts usually showed a stronger antibacterial activity than W/E. Among all extracts, the weakest activity was exhibited by extracts belonging to the hydroxycinnamic acid glycerides group (P.LAS, P.WIL, and P. × WCA; MICs from 250 to ≥1000 µg/mL against all Gram-positive strains). The remaining extracts exhibited varied MICs (from 31.3 to ≥1000 µg/mL) against different strains. In the case of propolis, previous research showed that the presence of hydroxycinnamic acid glycerides may be connected with weaker antimicrobial activity for 70% aqueous ethanol extracts [20,43]. On the other hand, Isidorov et al. [19] showed that ethyl acetate extracts of P. tremula buds, rich in hydroxycinnamic acid glycerides, had better MIC against Gram-positive bacteria (Staphylococcus schleiferi, S. aureus, B. cereus, and B. thuringiensis). In another research, better activity of P. tremula methanolic extracts was exhibited against S. aureus and B. cereus [21]. It seems important to point out that both reports revealed only a twofold difference between the MIC of P. tremula and P. nigra. In the case of disc-diffusion studies of P. tremula and P. nigra buds’ antibacterial activity, it was shown that the more potent activity of P. tremula extracts was not a rule, and sometimes P. nigra was a better antibacterial agent [20]. In summary, the impact of hydroxycinnamic acids glycerides on whole extracts’ activity against Gram-positive bacteria is somewhat complex and probably depends on the presence and concentration of other components and their interactions.
Among all poplar bud extracts, the most potent antibacterial agent against Gram-positive bacteria was EtOH extract from P.TA×P.TRI.2 (MIC = 7.8 µg/mL vs. S. epidermidis and M. luteus, 15.6 µg/mL vs. E. faecalis and 31.3 µg/mL S. aureus, B. cereus and B. subtillis). Among others, only the EtOH extract of P.TA×P.TRI.2 exhibited stronger activity against B. cereus (MIC = 15.6 µg/mL). Other strong antibacterial agents included EtOH extracts of P.M × P.TRI, P.TA × P.TRI.1, P.TRI, and P.RO, as well as the W/E extract of P.TA × P.TRI.2, possessing significant activity against all tested Gram-positive strains (MIC ≤ 62.5 µg/mL). The potent extracts contained p-coumaric acid (P.TA × P.TRI.2, P.TRI, P.RO), pinocembrin (P.RO), isosakuranetin dihydrochalcone (P.TA × P.TRI.2), pinocembrin dihydrochalcone (P.TA × P.TRI.2), 2′,6′-dihydroxy-4′-methoxydihydrochalcone (P.TA × P.TRI.1, P.TA × P.TRI.2, P.TRI, P.RO), p-coumaric acid cinnamyl ester (P.TA × P.TRI.2, P.TRI, P.RO), and different components, tentatively identified as balsacones (P.TA × P.TRI.1, P.TA × P.TRI.2, P.TRI, P.RO). So far, it has been reported that balsacones exhibit activity against S. aureus strains [44]. Therefore, the presence of balsacones was the main difference between the mixed group and the rest of the phytochemical groups; these components may play an important role in the antibacterial effect. The structures of balsacones and other compounds hypothetically responsible for high anti-Gram-positive bacteria activity are presented in Figure 2. In summary, Populus buds classified in a mixed group exhibited the most potent activity against Gram-positive bacterial strains (see Table S1). Moreover, all of them were clones of P. trichocarpa and its crossbreed species.
Research on propolis showed that significant amounts of p-coumaric acid are connected with lower antimicrobial activity [20,45]. p-Coumaric acid alone showed antimicrobial activity but was an inferior antimicrobial agent to propolis flavonoids [46]. Moreover, the high amounts of p-coumaric acid were correlated with a low abundance of flavonoids. As a result, it was suggested that the weaker activity of propolis with a high concentration of p-coumaric acid was caused by the lower amounts of flavonoids [20]. In the literature, antibacterial effects against Gram-positive bacteria of propolis extracts were usually connected to the presence of some caffeic acid esters, such as CAPE [45], and flavonoids (pinobanksin 5-methyl ether, pinobanksin, chrysin, galangin, and pinobanksin 3-acetate) [43]. Most of these components were present in P.TA × P.TRI.2 and the other most potent antibacterial agents (P.M × P.TRI, P.TA × P.TRI.1, P.TRI, P.RO). However, their signals were weaker than in samples with lower activity (flavonoid, hydroxycinnamic monoesters, and flavonoid + hydroxycinnamic monoester types). For this reason, it may be suspected that these components do not play a decisive role in the antibacterial effect of Populus bud extracts. In our opinion, the final activity against Gram-positive strains results from different interactions between specific components.

2.2.3. Activity against Candida spp.

Determination of antifungal activity included a screening of MIC and MFC against three Candida species (C. albicans, C. glabrata, and C. parapsilosis). Most extracts (EtOH and W/E) exhibited moderate activity (MIC ≥ 125 µg/mL and ≤500 µg/mL). Weak activity (MIC ≥ 1000 µg/mL) was observed for EtOH extracts of P.LAS, P.LAU, P.WIL, and P. × WCA, as well as for W/E extracts of P.WIL and P. × WCA. Good activity (MIC = 62.5 µg/mL) was only presented by EtOH extracts of P.CA, P. × PE.1, P.TRI (vs. C. parapsilosis), P.N.3 (vs. C. glabrata), and P.RO (vs. C. glabrata and C. parapsilosis) as well as W/E of P.N.3 (vs. C. glabrata) and P.TRI (vs. C. glabrata and C. parapsilosis). Observed MICs against Candida strains were generally higher than against Gram-positives. Moreover, most samples had a fungicidal rather than a fungistatic effect. In the literature, P. nigra bud extracts exhibited MICs = from 62.5 µg/mL (ethyl acetate extract) [19] to 1000 µg/mL (methanol extract) against C. albicans, while P. tremula buds were inactive (ethyl acetate extract) [19] or exhibited mild activity (methanol extract) (MIC = 500–1000 µg/mL) [19]. Research on propolis from these two species (P. tremula and P. nigra) demonstrated similar results [43]. A comparison of the experimental data with the literature allows us to suspect that apolar extracts of Populus buds should exhibit better activity against fungi polar extracts. However, data on the antifungal activity of propolis and Populus buds are not as widely available as for antibacterial activity. For these reasons and promising activity, further research is required (especially regarding the mechanism of action).

2.2.4. Activity against Helicobacter pylori

Most of the EtOH extracts exhibited good activity (MIC ≤ 62.5 µg/mL) against H. pylori; only the activities of EtOH extracts from P.LAS, P.WIL, and P. × WCA were moderate (MIC from 250 to >1000 µg/mL). This suggests that a higher concentration of apolar flavonoids and phenolic acid monoesters increases the anti-Helicobacter activity of extracts. For propolis, it was proven that multiple polyphenolic substances can be connected with notable activity against H. pylori [46]. As listed previously, they are pinobanksin, pinobanksin 5-methyl ether, pinobanksin 3-acetate, chrysin, pinocembrin, and galangin, as well as p-methoxycinnamic acid cinnamyl ester [46]. Except for pinobanksin 5-methyl ether, these components were abundant in active extracts of Populus buds, and their presence correlated with anti-Helicobacter activity. Antibacterial agents of poplar buds may attack the cell barrier, disrupt metabolism, inhibit energy production, and cause oxidative stress in bacterial cells. The anti-Helicobacter effect of flavonoids was documented [47]. Krzyżek et al. [48] proved that myricetin slows the process of transformation into coccoid forms, reduces biofilm formation of H. pylori, and exhibits additive effects with clarithromycin and metronidazole. Other anti-Helicobacter properties were recorded by González et al. [49]. In their research, flavonoids such as chrysin inhibited the function of HsrA (one of the transcriptional regulators essential for cell viability) [49]. Moreover, it was proven that flavonoid-rich propolis extracts [46] and single flavonoids isolated from propolis [49] inhibit the urease of H. pylori. Urease increases the low pH of gastric juice, which allows the survival of H. pylori. This effect may be potentially used in anti-Helicobacter therapies. From the clinical point of view, it is also important that Korean propolis exhibits an anti-inflammatory effect on gastric mucous membranes (infected gastric mucosal injury mice model) [50]. In summary, all earlier propolis research suggests that poplar bud extracts may be used in anti-Helicobacter therapy in the future. Herewith, we report the observations in this field systematically.

3. Materials and Methods

3.1. Populus Buds and Chemicals

Poplar buds samples were collected in Spring 2015 from Szczodre, Poland (P. nigra, sample code: P.N.3) and Botanical Garden of the Adam Mickiewicz University in Poznań (P. suaveolens sample code: P.SU) as well as from Arboretum of Institute of Dendrology, Polish Academy of Sciences in Spring 2021 (P. balsamifera, P. cathayana, P. deltoides, P. deltoides × P. nigra, P. ‘Eridano’ (P. deltoides × maximowiczii clone Eridano), P. komarowii, P. laurifolia, P. lasiocarpa, P. maximowiczii, P. maximowiczii × P. berolinensis, P. maximowiczii × P. trichocarpa, P. nigra, sample 1; P. nigra, sample 2; P. petrowskiana, sample 1; P. × petrowskiana (P. laurifolia × P. deltoides), sample 2; P. × rasumoskowiana, P. trichocarpa ‘Rochester’, P. simonii, P. tacamahaca sample 2, P. tacamahaca sample 2, P. tacamahaca × P. trichocarpa sample 1, P. tacamahaca × P. trichocarpa sample 2, P. trichocarpa, P. wilsoni and P. × wilsocarpa, samples codes: P.BA, P.CA, P.DE, P.DE × P.N, P.ERI, P.KOM, P.LAU, P.LAS, P.MAX, P.M × P.B, P.M × P.TRI, P.N.1, P.N.2, P. × PE.1, P. × PE.2, P. × RA., P.RO, P.SI, P.TA.1, P.TA.2, P.TA × P.TRI.1., P.TA.2 × TRI, P.TRI, P.WIL P. × WCA, respectively). Samples P.N.1, P.LAS, P.SU, P.WIL, and P. × WCA were collected from mature specimens while the rest were obtained from coppices. Samples from natural environment (Szczodre) were identified by author (P.O.) and originated from former Populus plantation in Szczodre (part of forest now). Plants originating from Botanical Garden of the Adam Mickiewicz University in Poznań and Arboretum of Institute of Dendrology, Polish Academy of Sciences originated from long-time collection and were marked according to the latest tree and shrub internal catalogues of these institutions. After collection, fresh plant material was dried at in room temperature in a dry, shady room with free airflow. The initial drying process took three weeks. Next, initially, dried buds were ground in a mill and again dried for a week at room temperature and free airflow in a dry, shady room. Due to the very sticky form of plant material, it was not sifted thought sieves. Full drying took four weeks. Before extraction, dried, ground plant material was stored in sealed containers under −20 °C.
LiChrosolv® hypergrade eluents for UHPLC-MS/MS and UHPLC-DAD analysis (acetonitrile, water, and methanol) were purchased from Merck company (Darmstadt, Germany). Mueller–Hinton agar and Sabouraud agar were obtained from Oxoid (Hampshire, UK).
Standards of acacetin, apigenin, chrysin, kaempferol, kaempferide isorhamnetin, isosakuranetin, luteolin, genkwanin, pinocembrin, pinocembrin chalcone, pinocembrin dihydrochalcone, pinobanksin, pinostrobin, quercetin, rhamnetin, sakuranetin, tectochrysin were purchased from Extrasynthese (Genay, France) while caffeic acid, caffeic acid phenethyl ester (CAPE), ferulic acid were obtained from Sigma-Aldrich (Saint Louis, MO, USA).

3.2. Preparation of Populus Bud Extracts

The extraction process was based on our previous research on propolis and poplar buds [16,20]. Ground plant material was extracted with ethanol (96%, V/V) or with 50/50 ethanol in water (V/V) at the ratio of 1:10 (1.0 g of buds per 10.0 mL of solution). The extraction yield was provided in Supplementary Table S1. Extraction was performed in an ultrasonic bath (Sonorex, Bandelin, Berlin, Germany). Extraction conditions were set to 20 °C (initial temperature) for 15 min and 756 W (90% of ultrasonic bath power). The process was repeated thrice (total extraction time was 45 min). The temperature during all the process did not exceed 45 °C. Obtained extracts were stored at room temperature for 12 h for stabilization purposes (precipitation of potentially co-extracted wax). Next, extracts were filtered through the Whatman No. 10 paper (Cytiva, Marlborough, MA, USA), and ethanol was evaporated under reduced pressure. Next, extracts were frozen and lyophilized in Alpha 2-4 LD Plus lyophilizer (Christ, Osterode am Harz, Germany). Extraction yield was evaluated as a gram of lyophilized extract per gram of dried buds (see Supplementary Table S1).

3.3. UHPLC-DAD-MS/MS Profiling of Populus Bud Extracts

UHPLC analyses were performed as previously described [33] with a Thermo Scientific UltiMate 3000 system (Thermo Scientific™ Dionex™, Sunnyvale, CA, USA), coupled with an autosampler and DAD detector recording spectral data in the 200–600 nm range and monitoring at 280, 320, and 360 nm. UHPLC-MS/MS was carried out using a Compact ESI-qTOF MS/MS detector (Bruker Daltonics, Bremen, Germany). MS detector was used in electrospray negative mode. Conditions of analysis were ion source temperature was set to 210 °C, nebulizer gas pressure to 2.0 bar, and dry gas (nitrogen) flow to 8.01 L/min. The capillary voltage was 4.5 kV. The collision energy was set to 8.0 eV. Internal calibration was obtained run by run with a 10 mM sodium formate solution. For ESI-MS/MS experiments, collision energy was set at 35.0 eV, and nitrogen was used as collision gas. The scan range was set between 30 and 1300 m/z.
Identification of components was based on several parameters, such as retention times of chromatographic peaks and UV spectra, calculated formulas of deprotonated molecular ions, and MS/MS fragmentation spectra of deprotonated molecular ions. These values were compared with previous research (the same LC-ESI-UV-qTOF-MS/MS methods were used) [33], standards, and literature. The standards were used directly in current investigations (see list in Section 3.1) or in our previous research on propolis, a poplar resin mixed with beeswax [33]. For this reason, propolis may be partially used as a plant reference standard for poplar bud extracts. Literature about propolis LC-MS research is significantly more abundant than about poplar buds. For this reason, it is a valuable resource for comparisons.
Due to information collected from the literature, four levels of identification confidence were obtained: A (comparison of UV and MS/MS spectra with standards; the highest level of confidence), B (comparison of MS/MS and/or UV spectrum with literature; good level of confidence), C (component was identified according to deprotonated molecular ion formula and prediction from MS/MS spectra detected in Populus genus in literature, but there are no sufficient MS and UV data; average/weak level of confidence), and D (component was identified according to deprotonated molecular ion and prediction from MS spectra, but there are no sufficient MS/MS and UV data and substances were not reported in Populus genus literature; the weakest level of confidence). In the case of high-resolution mass spectrometry and calculations of the formulas, those with errors higher than 5 ppm were disqualified.
Semi-quantitative analysis was based on the relative abundance of components in the UV chromatogram (280 nm) and MS chromatogram. Relative abundance of most constituents was obtained due to deprotonated molecular ion intensity in a single chromatographic peak (IDMI). Due to received intensity, eight levels of relative abundance were created: tr (IDMI < 5 × 104); + (5 × 104 < IDMI > 1.5 × 105); ++ (1.5 × 105 < IDMI > 3 × 105); +++ (3 × 105 < IDMI > 4.5 × 105); ++++ (4.5 × 105 < IDMI > 6.0 × 105); +++++ (6.0 × 105 < IDMI > 7.5 × 105); ++++++ (7.5 × 105 < IDMI > 1.0 × 106); +++++++ (1.0 × 106 < IDMI). Only pinostrobin and tectochrysin relative amounts were based on UV peak intensity due to their weak ionization in negative mode.

3.4. Determination of Antimicrobial Activity

The propolis extracts dissolved in dimethylsulfoxide (DMSO) were screened for antibacterial and antifungal activities by microdilution broth method according to both the European Committee on Antimicrobial Susceptibility Testing (EUCAST) (www.eucast.org accessed on 3 January 2023) using Mueller–Hinton broth or RPMI with MOPS for growth of fungi, as we described elsewhere [51]. Minimal inhibitory concentrations (MICs) of the tested extracts were evaluated for the wide panel of the reference microorganisms, including Gram-negative bacteria (Salmonella Typhimurium ATCC 14028, Escherichia coli ATCC 25922, Proteus mirabilis ATCC 12453, Klebsiella pneumoniae ATCC 13883, Pseudomonas aeruginosa ATCC 9027 and Helicobacter pylori), Gram-positive bacteria (Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis ATCC 12228, Micrococcus luteus ATCC 10240, Bacillus subtilis ATCC 6633, Bacillus cereus ATCC 10876, and Enterococcus. faecalis ATCC 29212), and fungi (Candida glabrata ATCC 90030, Candida albicans ATCC 102231, Candida parapsilosis ATCC 22019). The sterile 96-well polystyrene microtitration plates (Nunc, Roskilde, Denmark) were prepared by dispensing 100 μL of appropriate dilution of the tested extracts in broth medium per well by serial twofold dilutions to obtain final concentrations of the tested extracts ranging from 1000 to 1.95 mg/L The inocula were prepared with fresh microbial cultures in sterile 0.85% NaCl to match the turbidity of 0.5 McFarland standard and were added to wells to obtain final density of 5 × 105 CFU/mL for bacteria and 5 × 104 CFU/mL for yeasts (CFU, colony forming units). After incubation (35 °C for 24 h), the MICs were assessed visually as the lowest concentration of the extracts that shows complete growth inhibition of the reference microbial strains. Appropriate DMSO control (at a final concentration of 10%), a strain growth control (inoculum without the tested extracts), and medium sterility control (the tested extracts without inoculum) were included on each microplate. The MIC for H. pylori ATCC 43504 was determined using a twofold microdilution method in MH broth with 7% of lysed horse blood at extract concentration ranging from 1000 to 1.95 mg/L with bacterial inocula of 3 McFarland standard. After incubation at 35 °C for 72 h under microaerophilic conditions (5% O2, 15% CO2, and 80% N2), the growth of H. pylori was visualized with the addition of 10 μL of 0.04% resazurin to each well. The MIC endpoint was recorded after 4 h incubation as the lowest concentration of extract that completely inhibits growth [52].
Minimal bactericidal concentration (MBC) or minimal fungicidal concentration (MFC) was obtained by a culture of 5 mL from each well that showed through growth inhibition, from the last positive one, and from the growth control onto recommended agar plates. The plates were incubated at 35 °C for 24 h for all microorganisms except H. pylori, which was incubated for 72 h in microaerophilic conditions. The MBC/MFC was defined as the lowest extract concentration without the growth of microorganisms. The MBC/MIC ratios were calculated to determine the bactericidal or bacteriostatic effect of the assayed extract. Vancomycin, ciprofloxacin, metronidazole, and nystatin were the reference drugs for Gram-positives, Gram-negatives, H. pylori, and yeasts, respectively. The experiments were repeated in triplicate. Representative data are presented.

4. Conclusions

Most of the 54 analyzed bud extracts from various poplar taxons were potent antibacterial agents against Gram-positive bacterial strains and Helicobacter pylori. Moderate activity was exhibited against Candida species while nonsignificant activity was demonstrated against most Gram-negative bacterial strains. The main identified or tentatively identified constituents of active extracts were flavonoid aglycones, hydroxycinnamic acid monoesters, and specific glycerides.
The good activity against Gram-positive bacterial strains and H. pylori makes poplar bud extracts an excellent candidate for the treatment of external infections caused by Gram-positive cocci and Candida spp., as well as for the treatment of stomach mucous membrane infection caused by H. pylori. Moreover, poplar buds may also serve as a source of specific components and extracts rich in bioactive polyphenols.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules29020437/s1, Table S1. Relative abundance of extract components and bud extraction yield.

Author Contributions

Conceptualization, P.O., J.W., K.N., S.R., M.W., P.M.K. and I.K.-G.; methodology, P.O., J.W., K.N., S.R., M.W., P.M.K., K.S. and I.K.-G.; software, P.O., K.S. and I.K.-G.; validation, P.O., K.S. and I.K.-G.; formal analysis, P.O., K.S. and I.K.-G.; investigation, P.O., J.W., S.R., K.S. and I.K.-G.; resources, P.O., J.W., K.N., P.M.K. and I.K.-G.; data curation, P.O. and I.K.-G.; writing—original draft preparation, P.O.; writing—review and editing, J.W., K.N., S.R., M.W. and I.K.-G.; visualization, P.O.; supervision, P.O. and I.K.-G.; project administration, P.O. and I.K-G.; funding acquisition, P.O., J.W., K.N., P.M.K. and I.K.-G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Wroclaw Medical University, Poland (grant number SUBK.D110.22.020) and the Medical University of Lublin, Poland (DS 29). The Institute of Dendrology (Polish Academy of Sciences, Kórnik, Poland) supported the investigation by maintaining the Populus genus collection.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

UHPLC-DAD and UHPLC-MS/MS analyses were carried out in the Laboratory of Elemental Analysis and Structural Research, Faculty of Pharmacy, Wroclaw Medical University. We thank Hanna Czapor-Irzabek from the Laboratory for Elemental Analysis and Structural Research for assistance with UHPLC-MS/MS analyses. We also thank Justyna Wiland-Szymańska and employees of The Botanical Garden of the Adam Mickiewicz University in Poznań, as well as the employees of the Institute of Dendrology (Kórnik, Poland), and Łukasz Janik and Antoni Bujwid from Lasy Państwowe (State Forests of Poland) for access to botanical collections and their help with the collection of Populus bud samples.

Conflicts of Interest

The authors declare no conflicts of interest.

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Molecules 29 00437 g001
Figure 1. LC-MS chromatograms of Populus buds EtOH extracts representing five chemical groups (negative mode, base peak chromatograms). Figure legend: Lanes: orange—P.N.3—P. nigra, sample 3 (flavonoid type); blue—P.N.1—P. nigra, sample 1 (hydroxycinnamic monoesters type); green—P.BA—P. balsamifera (hydroxycinnamic monoesters + flavonoid type); black—P.TA × P.TRI.2—P. tacamahaca × P.trichocarpa, sample 2 (mixed type); red—P.LAS—P. lasiocarpa (hydrocinnamic acids glycerides type). Component abbreviations: A-CA-p-COG—2-Acetyl-1-caffeoyl-3-p-coumaroylglycerol; A-d-CAG—2-Acetyl-1,3-di-caffeoylglycerol; A-d-p-COG—2-Acetyl-1,3-di-p-coumaroylglycerol; API—apigenin; BA-A-F.1—Balsacone A/B/E/F isomer I; BA-A-F.2—Balsacone A/B/E/F isomer II; BA-C/B—Balsacone C or D; CA.A—Caffeic acid; CA-2M-2BE—Caffeic acid 2-methyl-2-butenyl ester; CA-3M-2BE—Caffeic acid 3-methyl-2-butenyl ester; CA-3M-3BE—Caffeic acid 3-methyl-3-butenyl ester; CA-B/I.1—Caffeic acid butyl or isobutyl ester isomer I; CA-B/I.2—Caffeic acid butyl or isobutyl ester isomer II; CABE—Caffeic acid benzyl ester; CAL—2′,6′-Dihydroxy-4′,4-dimethoxydihydrochalcone (calomelanone); CA-pCOG—Caffeoyl-p-coumaroylglycerol; CAPE—Caffeic acid benzyl ester; CHR—Chrysin; d-CAG—di-Caffeoylglycerol; DHMC—2′,6′-Dihydroxy-4′-methoxydihydrochalcone; DHMPPh—2′,6′-Dihydroxy-4′-methoxypentanophenone; DISOC—Isosakuranetin dihydrochalcone; d-p-COG—1,3-di-p-Coumaroylglycerol; GAL—Galangin; ISA—Isosakuranetin; KAE—Kaempferol; LUT-5-ME—Luteolin 5-methyl ether; M-CA.CE—Metoxycinnamic acid cinnamyl ester; M-CHR—Methoxychrysin; P.C—Pinocembrin chalcone; p-CO.A—p-Coumaric acid; p-CO-3M-3BE—p-Coumaric acid 3-methyl-3-butenyl ester; p-CO-BE—p-Coumaric acid benzyl ester; p-CO-CE—p-Coumaric acid cinnamyl ester; p-CO-MB.I—p-Coumaric acid 3-methyl-2-butenyl or 2-methyl-2-butenyl ester isomer I; p-CO-MB.II—p-Coumaric acid 3-methyl-2-butenyl or 2-methyl-2-butenyl isomer II; p-CO-PE—p-Coumaric acid phenethyl ester; PIN—Pinobanksin; PIN-3-A—Pinobanksin 3-acetate; PIN-3-P—Pinobanksin 3-propanoate; PIN-3-B/I—Pinobanksin 3-butanoate or -isobutanoate; PIN-3-P/I.1—Pinobanksin 3-pentanoate or -isopentanoate isomer I; PIN-3-P/I.2—Pinobanksin 3-pentanoate or -isopentanoate isomer II; PIN-5-ME—Pinobanksin 5-methyl ether; PM.DC—Pinocembrin dihydrochalcone; PNM—Pinocembrin; PS.CH—Pinostrobin chalcone.
Figure 1. LC-MS chromatograms of Populus buds EtOH extracts representing five chemical groups (negative mode, base peak chromatograms). Figure legend: Lanes: orange—P.N.3—P. nigra, sample 3 (flavonoid type); blue—P.N.1—P. nigra, sample 1 (hydroxycinnamic monoesters type); green—P.BA—P. balsamifera (hydroxycinnamic monoesters + flavonoid type); black—P.TA × P.TRI.2—P. tacamahaca × P.trichocarpa, sample 2 (mixed type); red—P.LAS—P. lasiocarpa (hydrocinnamic acids glycerides type). Component abbreviations: A-CA-p-COG—2-Acetyl-1-caffeoyl-3-p-coumaroylglycerol; A-d-CAG—2-Acetyl-1,3-di-caffeoylglycerol; A-d-p-COG—2-Acetyl-1,3-di-p-coumaroylglycerol; API—apigenin; BA-A-F.1—Balsacone A/B/E/F isomer I; BA-A-F.2—Balsacone A/B/E/F isomer II; BA-C/B—Balsacone C or D; CA.A—Caffeic acid; CA-2M-2BE—Caffeic acid 2-methyl-2-butenyl ester; CA-3M-2BE—Caffeic acid 3-methyl-2-butenyl ester; CA-3M-3BE—Caffeic acid 3-methyl-3-butenyl ester; CA-B/I.1—Caffeic acid butyl or isobutyl ester isomer I; CA-B/I.2—Caffeic acid butyl or isobutyl ester isomer II; CABE—Caffeic acid benzyl ester; CAL—2′,6′-Dihydroxy-4′,4-dimethoxydihydrochalcone (calomelanone); CA-pCOG—Caffeoyl-p-coumaroylglycerol; CAPE—Caffeic acid benzyl ester; CHR—Chrysin; d-CAG—di-Caffeoylglycerol; DHMC—2′,6′-Dihydroxy-4′-methoxydihydrochalcone; DHMPPh—2′,6′-Dihydroxy-4′-methoxypentanophenone; DISOC—Isosakuranetin dihydrochalcone; d-p-COG—1,3-di-p-Coumaroylglycerol; GAL—Galangin; ISA—Isosakuranetin; KAE—Kaempferol; LUT-5-ME—Luteolin 5-methyl ether; M-CA.CE—Metoxycinnamic acid cinnamyl ester; M-CHR—Methoxychrysin; P.C—Pinocembrin chalcone; p-CO.A—p-Coumaric acid; p-CO-3M-3BE—p-Coumaric acid 3-methyl-3-butenyl ester; p-CO-BE—p-Coumaric acid benzyl ester; p-CO-CE—p-Coumaric acid cinnamyl ester; p-CO-MB.I—p-Coumaric acid 3-methyl-2-butenyl or 2-methyl-2-butenyl ester isomer I; p-CO-MB.II—p-Coumaric acid 3-methyl-2-butenyl or 2-methyl-2-butenyl isomer II; p-CO-PE—p-Coumaric acid phenethyl ester; PIN—Pinobanksin; PIN-3-A—Pinobanksin 3-acetate; PIN-3-P—Pinobanksin 3-propanoate; PIN-3-B/I—Pinobanksin 3-butanoate or -isobutanoate; PIN-3-P/I.1—Pinobanksin 3-pentanoate or -isopentanoate isomer I; PIN-3-P/I.2—Pinobanksin 3-pentanoate or -isopentanoate isomer II; PIN-5-ME—Pinobanksin 5-methyl ether; PM.DC—Pinocembrin dihydrochalcone; PNM—Pinocembrin; PS.CH—Pinostrobin chalcone.
Molecules 29 00437 g001
Molecules 29 00437 g002
Figure 2. Antimicrobial agents of Populus buds.
Figure 2. Antimicrobial agents of Populus buds.
Molecules 29 00437 g002
Table 1. Identification of components in Populus bud extracts by LC-UV-ESI-qTOF-MS/MS.
Table 1. Identification of components in Populus bud extracts by LC-UV-ESI-qTOF-MS/MS.
No.ComponentRT
(min)		UVmax
(nm)		[M−H]−Base MS/MS PeakSecondary
MS/MS Peaks
m/z (A (%))		[M−H]−
(Formula)		Error
(mDa)		Error
(ppm)		RDB
1Unidentified0.84ND/-181.0721--C6H13O6−0.3−1.80.0
2Unidentified0.87ND/-195.0515--C6H11O7−0.4−2.31.0
3Unidentified0.89ND/-341.1090113.1273-C12H21O11−0.1−0.22.0
4Unidentified1.22290191.0201111.1597-C6H7O7−0.4−2.03.0
5C Leonuriside A4.31268331.1029123.1365-C14H19O90.51.511.0
6A Chlorogenic acid6.55*324353.0876191.1526135.1 (62.42), 179.2 (50.00)C16H17O90.20.58.0
7B Caffeoylglucose isomer I8.24328341.0884161.1265133.1 (20.50), 135.1 (6.55), 179.1 (4.77)C15H17O9−0.6−1.67.0
8B Caffeoylglucose isomer II9.19326341.0889161.0962179.1 (56.51), 135.1 (55.31), 177.2 (32.50), 221.2 (31.58)C15H17O9−1.1−3.17.0
9A Vanilline9.36273, 304sh151.0397108.1554-C8H7O30.32.15.0
10C Salicyl alcohol dihexoside10.02265447.1508269.2836-C19H27O120.00.06.0
11B Caffeoylglucose isomer III10.24321341.0880135.1517179.2 (91.78), 161.1 (62.10), 221.2 (28.24), 177.1 (23.94)C15H17O9−0.2−0.57.0
12Cp-Coumaric acid hexoside isomer I10.54314325.0936145.1268117.1 (22.35)C15H17O8−0.7−2.37.0
13B Catechin or Epicatechin10.87279289.0724123.1394109.1 (87.26), 221.3 (35.68), 137.3 (36.96), 203.2 (30.66)C15H13O6−0.6−2.29.0
14A Caffeic acid11.46323179.0346135.0449107.0 (8)C9H7O40.42.06.0
15B di-Caffeoylglycerol11.91323415.1240161.1272415.4 (15.58), 179.1 (6.67), 133.2 (6.42)C18H23O110.61.57.0
16D Feruloyl or isoferuloyl hexoside isomer I12.14328355.1041175.1718160.1 (90.68)C16H19O9−0.7−1.87.0
17B Methoxybenzaldehyde12.64*279135.045192.3923-C8H7O20.00.05.0
18B Caffeoylglycerol13.06*320253.0711161.0743133.2 (92.59), 135.1 (40.05)C12H13O60.62.56.0
19C p-Coumaric acid hexoside isomer II13.11*314325.0931145.1625119.2 (72.18), 163.1 (50.79), 205.1 (33.66)C15H17O8−0.2−0.77.0
20D Feruloyl or isoferuloyl hexoside isomer II13.36*325355.1037134.1126160.2 (95.34), 193.2 (87.81), 191.1 (66.31), 235.2 (62.90)C16H19O9−0.3−0.87.0
21A p-Coumaric acid14.42309163.0401119.166893.1 (10.59)C9H7O30.0−0.16.0
22C 3,4,5-Trimethoxy-cinnamic acid14.42ND/-237.0777117.1037145.1 (84.14)C12H13O5−0.8−3.46.0
23B Salicortin14.93273423.1303123.1625155.2 (61.54), 121.2 (49.91), 111.3 (45.59)C20H23O10−0.6−1.49.0
24C 7-O-caffeoylsalirepin15.18324463.1247179.1438161.2 (42.81), 135.2 (24.90)C22H23O11−0.1−0.211.0
25A Ferulic acid15.20321193.0509134.1322-C10H9O4−0.3−1.56.0
26B Caffeic acid dihydroxypentyl or isopentyl ester isomer I15.22ND/-281.1031161.1330135.1 (48.99), 133.3 (56.95), 179.2 (8.42)C14H17O6−0.1−0.26.0
27A Isoferulic acid15.71322193.0504134.1696-C10H9O40.31.46.0
28C Taxifolin (Dihydroquercetin) isomer I16.00289303.0517125.0824153.2 (21.31)C15H11O7−0.7−2.310.0
29D Caffeic acid derivate16.01326439.1613161.1313439.4 (17.06), 179.1 (11.23), 133.2 (5.41), 135.1 (3.72)C21H27O10−0.3−0.78.0
30D Caffeic acid derivate16.23326439.1612161.1249439.4 (19.80), 179.15 (10.97), 135.2 (5.13), 133.2 (4.22)C21H27O10−0.3−0.68.0
31D Caffeic acid derivate16.46326439.1612161.1236439.5 (28.26), 179.2 (11.69), 133.2 (3.78)C21H27O10−0.2−0.68.0
32D Caffeic acid derivate16.65326439.1601161.1282439.5 (41.10), 179.1 (6.95), 133.2 (3.52)C21H27O100.90.28.0
33Unidentified16.67ND295.0828161.1384133.3 (55.74), 135.1 (37.87), 159.3 (11.28), 137.1 (8.71), 179.2 (6.48)C14H15O7−0.4−1.57.0
34B Populoside isomer I16.68326447.1297161.1201323.3 (29.72), 179.1 (16.49), 123.1 (9.47), 135.1 (6.61), 203.2 (3.00)C22H23O10−0.1−0.211.0
35C Azelaic acid (Nonanedioic acid)17.07ND/-187.0976--C9H15O4−0.1−0.32.0
36D p-Coumaric derivate17.13311425.1459145.1490163.1 (45.05), 307.3 (31.45), 117.1 (21.30), 265.2 (19.12), 205.2 (18.31), 119.1 (15.12), 161.1 (6.99), 235.2 (5.94)C20H25O10−0.6−1.38.0
37B Populoside isomer II17.33*326447.1295161.1565179.1 (11.93), 123.1 (7.17), 121.1 (6.73), 135.1 (6.01), 133.3 (7.23), 323.3 (6.06), 447.3 (2.49)C22H23O100.10.311.0
38C Eriodictyol (Dihydroluteolin) isomer17.37288287.0560139.2901137.2 (24.06)C15H11O60.10.510.0
39Unidentified17.40*293451.1249121.1191283.2 (46.50), 163.1 (12.29), 175.1 (4.64), 193.1 (3.37), 135.1 (3.40), 145.1 (2.41), 181.1 (2.31)C21H23O11−0.3−0.710.0
40C Pinobanksin- or Naringenin 7-O-hexoside17.57286433.1145271.2293165.1 (73.88), 433.4 (42.77), 253.2 (16.18), 243.2 (14.45), 225.2 (10.81), 313.3 (6.69), 227.2 (3.49), 197.2 (2.75), 151.2 (3.19), 241.2 (2.87)C21H21O10−0.5−1.211.0
41Unidentified17.69*283451.1247138.2292121.1 (5.43), 413.1 (4.41), 163.1 (4.39), 151.1 (4.07), 181.2 (3.36), 405.3 (2.60), 193.2 (2.04)C21H23O11−0.1−0.310.0
42C Vanilloyl-methyl-ketone17.79*286193.0504133.1891-C10H9O40.21.06.0
43C Taxifolin (Dihydroquercetin) isomer II17.84289303.0519151.1068303.1 (17.51)C15H11O7−0.9−2.810.0
44B Salireposide18.27ND/-405.1192242.2316151.1 (78.89), 107.1 (27.34)C20H21O9−0.1−0.310.0
45Unidentified18.42ND/-193.0872--C11H13O3−0.2−1.05.0
46Unidentified18.46ND/-465.1397123.1096155.2 (46.57)C22H25O110.51.210.0
47Unidentified18.48ND/-511.1463155.1086123.1 (98.45), 111.1 (94.09), 137.1 (46.54), 109.1 (22.50), 405.4 (21.74), 121.1 (14.37)C23H27O13−0.5−1.110.0
48B Eriodictyol (Dihydroluteolin)18.83291287.0564125.1152177.2 (56.00), 152.4 (32.51), 107.4 (12.25), 259.3 (11.25), 213.2 (9.01)C15H11O6−0.2−0.810.0
49B Isograndidentatin A18.88314423.1651145.1113163.1 (12.51), 119.1 (6.64), 117.2 (5.33), 423.4 (6.05)C21H27O91.02.38.0
50B Grandidentatin19.30312431.1349145.1447163.1 (13.99), 123.1 (12.54), 307.4 (10.10), 119.1 (5.65), 121.1 (4.50), 187.1 (3.86)C22H23O9−0.1−0.311.0
51B Caffeic acid dimethyl ether19.48324207.0664--C11H11O4−0.1−0.56.0
52D Caffeic acid derivate19.72321481.1716161.1269179.2 (38.23), 481.4 (14.79), 135.1 (6.74), 421.5 (6.68), 439.6 (5.39)C23H29O11−0.1−0.19.0
53C Taxifolin 3′-methyl ether (Dihydroisorhamnetin)20.29ND/-317.0673152.1004125.1 (38.44), 179.2 (16.01), 192.2 (11.21)C16H13O7−0.6−2.010.0
54B Populoside isomer III20.91325447.1301179.1367135.1 (26.66), 161.1 (24.41)C22H23O10−0.4−0.911.0
55B Apigenin 7-O-glucoside (Apigetrin)21.10264, 309sh431.0983268.2682431.3 (23.37), 240.1 (9.85), 211.2 (9.64)C21H19O100.00.112.0
56B Diosmetin 7-O-rutinoside (Diosmin)21.21ND/-607.1675111.1002155.2 (88.44), 123.1 (57.43), 161.1 (28.94), 137.1 (28.43), 109.1 (20.03), 423.5 (18.42), 405.4 (15.17), 299.3 (12.25), 113.1 (7.23), 561.5 (8.28), 101.3 (6.73), 143.1 (4.42), 93.2 (3.19), 317.5 (4.12), 165.2 (2.96), 449.3 (2.56), 159.2 (2.39)C28H31O15−0.6−1.013.0
57Unidentified22.15ND/-385.1508223.2634208.2 (10.07), 152.1 (6.81), 205.2 (2.06)C18H25O9−0.4−1.16.0
58D Caffeic acid derivate22.22328489.1407161.1159179.2 (15.01), 123.1 (12.65), 133.2 (8.52), 135.1 (6.63), 489.3 (4.33)C24H25O11−0.5−0.912.0
59B Caffeic ethyl ester22.65322207.0664133.3012135.1162 (48.30), 161.0890 (16.11)C11H11O4−0.1−0.56.0
60C Aromadendrin (Dihydrokaempferol)23.08288287.0566135.1329151.1078 (15.43)C15H11O6−0.5−1.810.0
61B Pinobanksin 5-methyl ether23.40287285.0777252.0429224.0 (55.83), 138.0 (38.07), 241.0 (31.50), 165.0 (14.95), 239.1 (12.13), 195.0 (12.02), 151.0 (11.81), 213.1 (11.34), 267.1 (11.02), 285.1 (9.31), 136.0 (8.53), 107.0 (6.81)C16H13O5−0.8−2.910.0
62C Kaempferol 3-methyl ether (Isokaempferide)23.66288299.0553227.1837255.2 (69.84), 284.2 (9.97), 299.1 (7.83)C16H11O60.82.612.0
63Unidentified23.83ND/-589.1563122.2014139.1 (89.97), 155.1 (75.54), 111.1 (52.83), 387.4 (44.27), 137.2 (32.78), 109.1 (26.60), 233.3 (22.16), 215.3 (20.13), 135.1 (16.17), 205.2 (6.94), 543.5 (8.81), 165.1 (4.14), 163.2 (3.15), 405.3 (2.79), 265.3 (2.13)C28H29O140.0−0.114.0
64B di-Caffeoylglycerol24.58320415.1033253.2248161.1 (84.50), 179.1 (65.63), 135.1 (55.89)C21H19O90.10.312.0
65A Quercetin25.10364, 270sh, 265301.0353151.0034121.0 (29.41), 107.0 (22.18), 149.0 (14.01), 178.9 (13.92), 301.0 (7.58), 245.0 (6.32), 273.0 (5.48), 163.0 (4.87), 211.0 (3.84)C15H9O70.10.311.0
66D Caffeic acid derivate25.33ND/-445.1510161.1296445.5 (18.12), 179.2 (7.44), 135.2 (4.83)C23H25O9−0.6−1.311.0
67A Luteolin25.40370285.0412133.1356285.2 (83.77), 151.0 (33.21), 199.1 (15.09), 107.1 (12.83)C15H9O6−0.8−2.711.0
68B Quercetin 3-methyl ether26.85255, 355315.0497271.0253300.0 (71.14), 255.0 (42.89), 243.0 (22.59), 227.0 (2.55)C16H11O70.20.511.0
69A Pinobanksin (Dihydrogalangin)27.25291271.0615197.0617253.0 (89.28), 161.1 (67.51), 271.1 (56.26), 125.02 (53.39), 151.0 (30.14), 225.1 (24.71), 107.0 (23.97), 209.1 (16.07), 185.1 (15.86), 115.1 (15.08), 157.1 (14.43), 181.1 (14.14), 215.1 (11.83)C15H11O5−0.3−1.110.0
70C Boropinic acid (Caffeic acid 3-methyl, 4-(3-methyl−2-buten−1-yl) ether)28.52ND/-261.1133145.1340117.2 (48.10), 119.1 (14.84), 115.1 (3.56), 113.1 (3.07)C15H17O4−0.1−0.27.0
71A Naringenin (Dihydroapigenin)28.60290271.0612119.1344151.0 (43.37), 107.1 (21.94), 187.2 (10.00)C15H11O50.00.110.0
72B Chrysin 5-methyl ether28.80ND/-267.0662224.1747180.2 (92.97), 252.2 (26.27), 195.2 (15.00)C16H11O40.10.311.0
73B Eriodictyol 3’-methyl ether (Homoeriodictyol)
or Eriodictyol 4’-methyl ether (Hesperetin)		28.83292301.0723152.0994176.1 (55.71), 283.2 (57.41), 125.1 (50.48), 301.2 (51.90), 227.4 (33.57), 268.2 (25.56), 107.2 (17.38)C16H13O6−0.6−1.910.0
74B 1-Caffeoyl−3-p-coumaroylglycerol28.96312399.1085163.1721161.1 (48.44), 119.1 (48.96), 253.2 (46.08), 179.2 (25.62), 145.2 (24.73), 235.1 (20.40), 161.2 (10.73), 237.2 (8.31), 399.2 (5.30)C21H19O80.00.112.0
75C Flavonoid29.55286269.0822150.0692184.2 (88.87), 165.1 (80.74), 122.1 (55.22), 254.2 (50.90), 227.2 (38.24), 269.3 (20.13)C16H13O4−0.3−1.010.0
76D Caffeic acid derivate29.63326277.1084135.1237179.1 (11.92)C15H17O5−0.3−0.97.0
77B Caffeic acid propyl or isopropyl ester
29.88323221.0824133.7267161.1 (22.49)C12H13O4−0.5−2.26.0
78C Aromadendrin 7-methyl ether30.36287301.0722164.1585151.1 (72.31), 136.1 (49.48), 134.3 (49.49), 108.1 (29.20), 242.2 (17.13), 286.2 (15.52), 214.6 (17.83)C16H13O6−0.5−1.510.0
79C Naringenin chalcone30.45290271.0617125.1004145.1 (23.55), 117.4 (8.59), 151.1 (6.04), 107.1 (3.82)C15H11O5−0.5−1.710.0
80A Apigenin30.51267, 336269.0457117.0349269.0 (52.06), 151.0 (39.01), 149.0 (25.91), 227.0 (12.66), 107.0 (11.48), 225.0 (10.59), 201.1 (7.44), 183.0 (6.40), 181.1 (5.14), 121.0 (4.92), 197.1 (2.28)C15H9O5−0.2−0.711.0
81A Kaempferol31.19264, 365285.0405285.0400239.0 (8.81), 187.0 (8.20), 185.0 (8.14), 229.0 (7.99), 159.0 (6.63)C15H9O6−0.1−0.311.0
82B Caffeic acid hydroxyphenylethyl ester31.47*324299.0922135.1402179.2 (24.97), 161.1 (5.41)C17H15O50.31.010.0
83A Quercetin 3’-methyl ether (Isorhamnetin)31.77*253, 357315.0509300.1989151.1 (26.66), 271.4 (11.37), 164.1 (7.61), 283.1 (6.12), 148.1 (5.64), 315.2 (5.60), 255.2 (4.65), 216.2 (3.38), 108.2 (2.95), 244.2 (2.60), 136.2 (2.55)C16H11O70.10.311.0
84B Quercetin methyl ether isomer I32.28254, 367315.0511300.1857151.1 (26.12), 271.3 (11.15), 164.1 (7.58), 283.1 (5.81), 216.3 (4.63)C16H11O70.0−0.111.0
85B Luteolin 5-methyl ether33.03265, 349299.0549255.0300227.03 (59.96), 284.0 (15.07), 211.0 (6.11)C16H11O6−0.2−0.711.0
86C Syringenin (sinapyl alcohol)33.24*296209.0826165.1925125.1 (95.68), 123.2 (53.31), 124.3 (23.62)C11H13O4−0.7−3.25.0
87B Caffeic acid butenyl or isobutenyl ester33.73ND/-233.0818133.3938-C13H13O40.10.57.0
88B Quercetin dimethyl ether isomer I33.74256, 354329.0669271.1688299.2 (99.34), 243.2 (90.63), 285.4 (51.12), 257.2 (31.51), 314.2 (29.44), 227.2 (5.23), 215.2 (3.74), 199.2 (3.06), 255.1 (2.88)C17H13O7−0.2−0.611.0
89D p-Coumaric acid derivate33.81ND311.0923119.1298163.2 (30.72), 135.1 (7.31), 145.1 (3.83)C18H15O50.20.711.0
90B 1,3-di-p-Coumaroylglycerol33.98312383.1143163.1491119.1 (69.49), 145.1 (61.09), 117.2 (8.68), 219.2 (7.20), 237.2 (6.59), 383.4 (2.42)C21H19O7−0.7−1.812.0
91B Galangin 5-methyl ether34.41*260, 350283.0612211.1796239.2 (58.94), 283.3 (5.07), 268.2 (4.79)C16H11O50.0−0.111.0
92B 1,2-di-p-Coumaroylglycerol II34.46315383.1137163.1447119.1 (78.80), 145.1 (70.92)C21H19O7−0.1−0.212.0
93B Pinobanksin 5-methyl ether 3-acetate34.69288327.0878224.1781267.2 (67.46), 252.2 (62.85), 285.2 (45.11), 239.5 (36.67)C18H15O6−0.4−1.111.0
94Bm-Coumaric acid (3-Hydroxycinnamic acid)35.01311163.0400119.1298163.2 (30.72), 135.1 (7.31), 145.1 (3.83)C9H7O30.10.46.0
95B Pinobanksin 3-hydroxybutanoate isomer I35.14*292357.0977253.2321271.2 (7.29), 197.2 (4.96), 209.3 (3.60)C19H17O70.30.811.0
96B 2-Acetyl−1,3-di-caffeoylglycerol35.23326457.1143179.1554161.1 (75.83), 235.2 (53.60), 135.1 (48.32), 295.3 (40.83), 457.3 (5.85), 397.3 (5.27)C23H21O10−0.3−0.713.0
97B 1-Acetyl−2,3-di-caffeoylglycerol35.73325457.1135
98D Caffeic acid derivate35.81*326291.1248135.1307179.1 (21.22), 269.1 (4.90)C16H19O5−1.0−3.37.0
99B Quercetin methyl ether isomer II36.15ND/-315.0883164.0962136.1 (51.83), 285.2 (39.16), 315.2 (22.41), 300.3 (14.01), 271.3 (12.30), 273.2 (10.71), 258.2 (7.41)C17H15O6−0.8−2.710.0
100A Quercetin 7-methyl ether (Rhamnetin)36.53256, 353315.0509165.1079121.1 (39.04), 300.2 (27.72), 151.1 (9.49), 272.2119 (6.69), 244.2 (4.72), 256.3 (3.45)C16H11O70.10.411.0
101B Kaempferol methyl ether isomer I36.68ND/-299.0563284.1907299.2 (7.35), 256.1 (5.21), 133.2 (5.23), 151.1 (2.37), 227.3 (2.53)C16H11O6−0.2−0.711.0
102B Caffeic acid butyl or isobutyl ester isomer I37.33325235.0978133.5359161.1 (41.79)C13H15O4−0.2−1.06.0
103B Pinobanksin 3-hydroxybutanoate isomer II37.55293357.0983253.223197.2 (4.80), 271.2 (4.93), 209.4 (2.89), 225.2 (2.52)C19H17O7−0.3−0.811.0
104Unidentified37.74288, 308sh205.0877117.388145.2 (23.35)C12H13O3−0.7−3.36.0
105B Caffeic acid butyl or isobutyl ester isomer II37.96325235.0976161.1424135.1 (93.59)C13H15O4−0.1−0.26.0
106C 2’,4’,6’-Trihydroxypentanophenone38.89286209.0827152.0951124.1 (84.90), 194.2 (11.41), 148.1 (9.02), 111.1 (8.47), 96.2 (6.71), 179.1 (4.46)C11H13O4−0.73.45.0
107B Quercetin dimethyl ether isomer II39.00261, 357329.0669299.1970271.2 (30.28), 314.2 (21.06), 285.2 (2.46)C17H13O7−0.3−0.811.0
108B Caffeic acid 2-methyl−2-butenyl ester39.19325247.0979135.1258161.1 (36.02), 179.1 (11.25)C14H15O4−0.4−1.57.0
109B Quercetin dimethyl ether isomer III39.41ND329.0670299.1828271.2 (39.73), 314.2 (27.41), 285.2 (12.61), 329.3 (2.26)C17H13O7−0.3−0.911.0
110B Caffeic acid 3-methyl−2-butenyl ester (basic prenyl ester)40.68324247.0979134.2235106.1 (6.32)C14H15O4−0.4−1.77.0
111B Caffeic acid 3-methyl−3-butenyl ester (prenyl ester isomer I)41.16325247.0977134.2234106.2 (5.64)C14H15O4−0.1−0.47.0
112B Sakuranetin dihydrochalcone41.56285287.0921166.1295181.2 (73.27), 152.1 (44.21), 124.1 (30.43), 226.2 (11.95), 193.1 (10.26), 254.2 (9.25), 178.2 (8.01), 139.1 (7.01), 93.1 (6.92), 189.2 (6.18), 150.2 (3.68), 269.3 (3.49)C16H15O50.41.59.0
113Unidentified41.66286251.1648--C15H23O30.51.84.0
114B 2-Acetyl−1-caffeoyl−3-p-coumaroylglycerol41.79315441.1197163.1479179.1 (85.75), 161.1 (42.10), 135.1 (40.85), 145.2 (39.56), 119.1 (35.73), 235.2 (27.59), 295.3 (14.64), 219.2 (7.31), 173.2 (6.88), 381.4 (7.79), 217.2 (4.50), 441.3 (4.75), 189.2 (3.80), 277.3 (2.86)C23H21O9−0.6−1.313.0
115A Chrysin42.12267, 312sh253.0505253.0507143.0 (41.53), 145.0 (21.10), 209.1 (14.10), 107.0 (13.33), 181.1 (8.16), 185.1 (6.19)C15H9O4−0.7−2.811.0
116B Caffeic acid benzyl ester42.55324269.0818134.1302161.0 (22.96), 137.0 (4.03)C16H13O4−0.3−1.110.0
117B 2-Acetyl−3-caffeoyl−2-feruloylglycerol42.59314471.1290193.1743179.1 (91.94), 135.1 (38.51), 161.1 (37.37), 175.1 (35.75), 235.2 (23.96), 295.2 (15.68), 149.1 (9.17), 411.3 (9.38), 173.2 (7.01), 249.2 (6.57), 471.5 (7.85), 217.1 (5.91), 367.2 (4.13), 189.2 (3.32), 117.2 (3.04), 277.3 (2.88)C24H23O100.71.513.0
118D Flavonoid42.60ND/-285.0772119.1332165.28 (29.97), 150.4 (14.74), 121.1 (5.58), 122.1 (5.43), 269.3 (5.59), 97.1 (3.07), 136.2 (2.95), 177.2 (2.52)C16H13O5−0.3−1.110.0
119Unidentified42.71313217.0869117.1863145.2 (2.80)C13H13O30.10.47.0
120A Pinocembrin43.07289255.0666171.0464151.0 (80.69), 255.1 (75.17), 213.1 (74.89), 145.1 (70.09), 107.0 (52.59), 185.1 (34.69), 169.1 (24.91), 211.1 (23.68), 164.0 (17.93), 187.1 (16.78), 136.0 (16.34)C15H11O4−0.2−0.810.0
121A Pinocembrin chalcone43.30342255.0668171.2600151.1 (61.32), 107.3 (40.48), 145.1 (29.50), 255.2 (25.04), 169.2 (23.80), 213.1 (21.71), 211.2 (14.01), 164.1 (9.13), 136.3 (7.29), 187.2 (6.32), 143.2 (4.35), 193.3 (3.34)C15H11O4−0.5−2.010.0
122A Naringenin 7-methyl ether (Sakuranetin)43.32289285.0768119.1265165.1 (18.08)C16H13O50.30.710.0
123Unidentified43.88ND223.0985179.2917139.1 (70.78), 137.1 (40.96), 115.2 (8.88)C12H15O4−0.9−3.95.0
124A Naringenin 4’-methyl ether (Isosakuranetin)44.31290285.0773124.1060139.1 (64.17), 145.1 (42.28), 148.1 (8.73), 165.1 (4.71)C16H13O5−0.4−1.610.0
125A Galangin44.82265, 357269.0454269.0454169.1 (12.64), 171.0 (10.87), 213.0 (10.73), 143.0 (8.90), 223.0 (8.03,) 195.0 (7.34)C15H9O5−0.2−0.811.0
126B Isosakuranetin dihydrochalcone44.91291287.0925243.2789166.1 (70.19), 152.1 (32.79), 119.1 (27.87), 188.2 (24.60), 203.2 (23.97), 186.2 (20.81), 122.1 (18.36), 228.2 (16.99), 125.1 (14.66), 287.2 (14.92), 254.2 (13.89), 201.21 (11.46), 135.1 (8.29), 269.2 (7.27), 107.2 (6.87), 213.2 (6.61), 161.2 (5.14), 138.2 (4.19), 146.2 (3.57)C16H15O50.00.19.0
127A Pinocembrin dihydrochalcone45.45287257.0820213.2040173.2 (66.35), 151.1 (33.34), 171.2 (31.95), 156.2 (24.29), 122.1 (19.76), 257.2 (12.86), 169.3 (13.48), 239.3 (11.24)C15H13O4−0.1−0.49.0
128A Apigenin 3’-methyl ether (Acacetin)
or A Apigenin 7-methyl ether (Genkwanin)		45.45267, 338283.0619268.2004240.2 (6.84), 151.1 (4.25)C16H11O5−0.7−2.311.0
129B Caffeic acid pentyl or isopentyl ester46.52324249.1138161.1050-C14H17O4−0.6−2.36.0
130A Caffeic acid phenethyl ester (CAPE)46.82326283.0981135.1231161.1 (46.24), 179.1 (20.40)C17H15O4−0.6−2.010.0
131A Kaempferol 3’-methyl ether (Kaempferide)46.89267, 364299.0564165.1098163.1 (76.38), 256.2 (73.45), 243.2 (69.45), 284.2 (70.50), 271.2 (64.61), 151.0 (53.68), 228.2 (49.64), 178.1 (39.93), 212.2 (32.76), 240.2 (23.93)C16H11O6−0.3−0.911.0
132B Pinobanksin 3-acetate47.27295313.0725253.051197.1 (5.86), 271.1 (5.36), 209.1 (4.75), 143.0 (3.17)C17H13O6−0.7−2.316.0
133B Kaempferol methyl ether isomer II47.52264, 360299.0561284.2051151.1 (32.52), 164.1 (9.83), 107.2 (6.51), 132.1 (5.38), 299.2 (3.39), 228.2 (3.31)C16H11O60.10.211.0
134B Tetramethyl flavonoid47.84ND/-329.0669299.1782271.2 (41.49), 314.2 (14.48)C17H13O7−0.2−0.611.0
135B Methoxychrysin47.87265283.0614211.0405239.0 (65.55), 268.0 (8.80)C16H11O5−0.2−0.611.0
136C 2’,6’-Dihydroxy−4’-methoxypentanophenone48.00287223.0983152.0864124.1 (77.51), 193.1 (13.04), 125.1 (11.95), 175.1 (6.65), 208.2 (5.84), 96.2 (6.22), 223.2 (3.86), 191.2 (3.24), 205.3 (2.47), 162.2 (2.47)C12H15O4−0.7−3.05.0
137Unidentified48.12310219.1033117.1531145.1 (48.72), 119.1 (7.85)C13H15O3−0.7−3.16.0
138Unidentified48.93310219.1028117.3711145.1 (32.70)C13H15O3−0.2−0.86.0
139B Kaempferol 3,4’-dimethyl ether (Ermanin)49.93350, 267313.0719283.2122255.2 (24.32), 253.2 (17.11), 298.2 (10.64)C17H13O6−0.1−0.311.0
140Bp-Coumaric acid 3-methyl−3-butenyl ester50.27310231.1028117.1725119.1 (90.59), 145.1 (49.02), 163.1 (4.99)C14H15O3−0.1−0.47.0
141B 2-Acetyl−1,3-di-p-coumaroylglycerol50.51312425.1242163.0403145.0 (53.67), 119.0 (49.02), 219.1 (11.88), 215.1 (6.36), 237.1 (5.21), 171.1 (5.05), 117.0 (4.31)C23H21O80.00.113.0
142B 1-Acetyl−2-p-coumaroyl−3-feruloylglycerol51.48315455.1347163.1173193.2 (78.06), 134.2 (46.98), 145.1 (41.86), 175.1 (42.27), 119.1 (40.73)C24H23O90.10.213.0
143B 1-Acetyl−2,3-di-p-coumaroylglycerol51.68311425.1244163.1361145.1 (64.46), 119.1 (57.20), 219.2 (13.02), 171.3 (7.70)C23H21O8−0.2−0.413.0
144Bp-Coumaric acid 3-methyl−2-butenyl or 2-methyl−2-butenyl51.75311231.1027117.2347-C14H15O30.00.07.0
145Bp-Coumaric acid 3-methyl−2-butenyl or 2-methyl−2-butenyl52.43311231.1029117.2403-C14H15O3−0.2−0.97.0
146Unidentified53.16ND/-311.2237157.1924153.3 (41.78), 187.2 (5.50), 135.3 (5.35), 113.3 (4.75)C18H31O4−0.9−3.03.0
147Bp-Coumaric acid benzyl ester53.48316253.0869117.2666145.1 (12.89), 121.3 (3.15)C16H13O30.10.310.0
148Unidentified54.60299, 329433.0921243.2264271.2 (41.07), 415.4 (26.05), 161.1 (19.62), 253.3 (11.06), 125.1 (7.62), 135.1 (6.88), 152.1 (5.62), 180.1 (4.85), 165.1 (4.69), 227.3 (4.97), 199.2 (3.56), 371.4 (3.43), 225.3 (3.13), 280.2 (2.54)C24H17O80.81.716.0
149B Ferulic acid benzyl ester54.92 283.0979133.1788147.3 (16.46), 119.2 (8.42)C17H15O4−0.3−1.010.0
150B Caffeic acid phenylpropenyl ester55.71325295.0978134.1210-C18H15O4−0.2−0.711.0
151B Caffeic acid phenylpropyl ester55.85326297.1139161.1417135.1 (44.14), 297.3 (15.52), 179.2 (11.00), 137.2 (4.01)C18H17O4−0.7−2.210.0
152B Pinobanksin 3-propanoate57.82294327.0878253.2179197.2 (5.41), 209.2 (3.72), 271.3 (2.71), 143.2 (2.09)C18H15O6−0.4−1.211.0
153B Caffeic acid hexyl or isohexyl ester isomer I57.99ND/-263.1298134.5851161.1 (73.06), 135.1 (51.49), 179.1 (10.43), 263.3 (10.02)C15H19O4−0.9−3.36.0
154Bp-Coumaric acid phenethyl ester58.08310267.1031119.1235145.1 (76.86), 117.2 (81.82), 163.1 (11.95)C17H15O3−0.5−1.810.0
155Unidentified58.78ND/-233.1192152.0855124.1 (81.75)C14H17O3−0.8−3.66.0
156B Caffeic acid hexyl or isohexyl ester isomer II59.51ND/-263.1294161.1533135.1 (70.52), 263.3 (14.21)C15H19O4−0.5−1.96.0
157Unidentified59.68ND/-403.1187293.2895109.1 (43.64), 171.2 (26.99), 189.1 (17.54), 255.3 (19.17), 189.2 (16.73), 385.4 (16.30), 403.4 (14.83), 265.4 (10.04), 187.2 (7.72), 211.2 (7.08), 213.2 (6.59), 251.2 (5.91), 145.2 (5.09), 317.3 (4.94), 249.3 (4.31), 231.2 (3.90), 359.4 (4.00), 202.2 (3.44), 299.6 (3.66)C24H19O60.10.115.0
158B Pinostrobin chalcone60.28343269.0827122.0703165.1 (83.49), 253.4 (86.88), 177.2 (49.29), 226.2 (47.58), 171.1 (35.51), 150.1 (31.31), 163.1 (21.30), 269.2 (16.42), 136.1 (13.47), 198.2 (14.25)C16H13O4−0.3−0.810.0
159Unidentified61.08ND/-403.1194281.2707135.1 (32.65), 255.3 (34.47), 237.2 (29.91), 267.3 (26.49), 109.1 (17.43), 171.3 (14.49), 177.1 (12.64), 211.2 (12.58), 403.5 (10.85), 293.3 (7.11), 163.2 (4.33), 239.2 (3.69), 295.2 (3.70), 151.1 (3.50), 213.3 (3.82), 169.1 (2.89), 187.2 (2.60), 195.2 (2.49), 145.2 (2.40), 190.1 (2.25), 299.2 (2.19)C24H19O6−0.1−1.715.0
160C 2’,6’-Dihydroxy−4’,4-dimethoxy dihydrochalcone (Calomelanone)61.32285301.1091152.1075124.1 (55.29), 253.2 (54.38), 165.4 (23.22), 268.3 (20.76), 301.3 (12.14), 180.1 (8.43), 119.1 (7.49), 283.2 (8.06), 188.1 (6.14), 193.2 (6.40), 203.3 (3.19)C17H17O5−0.9−3.19.0
161B 2’,6’-Dihydroxy−4’-methoxy dihydrochalcone61.90286271.0979152.0937124.1 (60.13), 210.2 (27.77), 238.3 (25.34), 173.2 (13.05), 165.1 (10.13), 271.2 (7.97), 253.2 (6.31)C16H15O4−0.3−1.19.0
162A Tectochrysin (Chrysin 7-methyl ether) [M+H]!62.70267, 310sh269.0815269.2764226.2 (59.49), 254.2 (23.65), 167.1 (8.30), 270.5 (6.16), 186.3 (4.73), 129.1 (2.37), 209.2 (2.14)C16H13O4−0.7−2.511.0
163B Pinobanksin 3-butenoate or isobutenoate62.91ND/-339.0880253.2128197.2 (5.11), 209.1 (3.28)C19H15O6−0.5−1.612.0
164A Pinostrobin (Pinocembrin 7-methyl ether) [M+H]!63.20289271.0969167.1288131.1 (33.29), 103.2 (24.27), 269.3 (11.76), 226.3 (8.78), 271.2 (4.49), 270.5 (3.31), 254.3 (2.97), 186.3 (2.31), 165.2 (2.29)C16H15O4−0.4−1.510.0
165Unidentified63.92*351551.1708267.2518283.2 (46.28), 255.3 (28.92), 551.6 (5.49), 281.2 (3.07), 135.1 (2.44), 429.5 (2.48)C33H27O80.40.620.0
166Bp-Coumaric acid cinnamyl ester63.94313279.1029117.3253-C18H15O3−0.3−1.011.0
167Unidentified64.26*310281.1193117.5723145.2 (61.96), 121.1 (2.83), 281.3 (2.54)C18H17O3−0.1−3.610.0
168B Caffeic acid heptyl or isoheptyl ester64.41ND/-277.1453161.1393135.1 (62.26), 277.3 (19.86), 179.2 (12.63)C16H21O4−0.7−2.66.0
169B Pinobanksin 3-butanoate or isobutanoate64.74293341.1037253.2173197.2 (4.89), 209.2 (3.17)C19H17O6−0.6−1.811.0
170Unidentified64.81ND/-387.1239387.4150171.2 (61.15), 173.1 (47.69), 283.2 (42.97), 197.2 (32.37), 343.8 (33.65), 215.2 (14.04), 255.2 (12.57), 301.4 (13.69), 211.3 (10.84), 169.2 (9.51), 239.4 (7.86), 145.2 (6.57), 156.2 (5.92), 281.2 (4.77), 359.4 (5.34), 183.3 (3.92), 147.2 (3.44), 226.3 (3.24), 213.2 (2.60), 259.3 (2.47)C24H19O5−0.2−0.415.0
171C Balsacone A/B/E/F isomer I65.06266,289419.1510419.4067375.4 (53.98), 283.3 (28.14), 257.2 (17.67), 173.2 (13.80), 389.4 (12.76), 203.5 (13.11), 213.2 (8.97), 298.3 (8.44), 401.3 (7.43), 152.1 (5.63), 254.2 (5.53), 311.3 (5.42), 171.2 (4.79), 333.4 (5.16)C25H23O6−1.0−2.414.0
172Unidentified65.21262, 347387.1240387.4117281.2 (97.94), 267.2 (78.24), 171.2 (60.37), 119.1 (46.94), 283.3 (43.02), 237.2 (36.62), 173.2 (27.63), 197.3 (28.18), 177.1 (23.64), 343.4 (27.07), 293.4 (21.25), 252.4 (17.83), 163.1 (12.94), 255.2 (12.36), 145.2 (11.09), 169.2 (10.43), 156.2 (10.70), 148.3 (11.59), 211.2 (9.84), 239.2 (9.08), 301.4 (9.81)C24H19O5−0.2−0.615.0
173C Balsacone A/B/E/F isomer II65.37266,289419.1502299.3067313.3 (99.88), 419.5 (60.65), 119.1 (37.21), 375.4 (37.37), 178.2 (23.02), 269.4 (15.55), 325.4 (12.80), 203.2 (10.30), 152.1 (8.19), 192.2 (7.87), 137.1 (6.24), 213.6 (7.04), 254.4 (5.10), 285.4 (5.04), 257.3 (4.35), 93.1 (3.44), 145.2 (3.48), 265.3 (3.48), 173.2 (3.50), 287.3 (3.31), 243.2 (2.63), 295.3 (2.53), 163.2 (2.29)C25H23O6−0.2−0.514.0
174Unidentified65.39ND469.1875341.4908469.5 (96.13), 257.2 (38.88), 357.4 (25.58), 383.8 (26.07), 311.3 (19.05), 438.4 (18.53), 328.3 (14.76), 339.3 (13.56), 327.8 (24.60), 125.1 (7.25), 297.3 (7.74), 215.2 (7.16), 242.2 (5.92), 223.3 (5.67), 353.3 (3.21)C26H29O8−0.7−1.512.0
175B Pinobanksin 3-pentenoate or isopentenoate isomer I65.40292353.1039253.2231197.2305 (4.88), 209.1898 (2.96)C20H17O6−0.9−2.512.0
176C Balsacone C or Balsacone D65.72266,289389.1402283.3324269.3 (90.93), 119.1 (47.02), 345.4 (58.63), 389.5 (54.23), 173.1 (25.16), 239.4 (23.64), 178.1 (17.40), 213.2 (13.48), 295.2 (12.39), 257.2 (9.36), 171.2 (9.05), 152.1 (9.06), 281.4 (11.13), 267.2 (7.85), 235.2 (7.28), 265.2 (7.13), 145.1 (6.59), 191.3 (6.98)C24H21O5−0.7−1.914.0
177Unidentified65.74290469.1877469.4952437.5 (32.16), 343.3 (24.07), 353.4 (16.39), 341.3 (15.58), 223.3 (11.52), 385.4 (11.04), 325.4 (10.76), 393.5 (9.40), 257.3 (8.54), 297.4 (7.75), 215.3 (7.33), 357.4 (7.13), 311.6 (8.16), 125.1 (4.21), 280.6 (5.98), 189.2 (3.63), 367.4 (4.22)C26H29O8−0.9−1.912.0
178B Pinobanksin 3-pentenoate or isopentenoate isomer II65.74282353.1035253.2266271.2 (26.83), 197.3 (5.55), 209.6 (3.51), 225.3 (2.59)C20H17O6−0.5−1.912.0
179Unidentified65.76ND/-387.1238267.3253119.1 (58.67), 281.2 (57.66), 177.2 (26.82), 387.8 (34.42), 163.1 (16.67), 293.2 (14.40), 283.2 (9.40), 239.2 (7.44), 345.3 (6.47), 237.3 (6.12), 173.2 (4.93), 225.2 (4.67), 255.7 (5.16), 197.2 (3.28)C24H19O50.0−0.115.0
180Unidentified66.01ND/-417.1336297.2710119.1 (73.94), 311.3 (69.24), 417.3 (40.26), 163.1 (20.53), 177.1 (20.29), 323.3 (12.23), 293.3 (8.90), 283.2 (7.45), 267.3 (6.89), 282.7 (12.85), 285.3 (2.95)C25H21O60.81.915.0
181Unidentified66.10ND/-413.1972134.2314161.1 (98.90), 179.1 (23.69), 137.1 (11.08), 395.3 (6.95), 251.3 (7.21), 325.7 (4.12)C24H29O6−0.2−0.510.0
182Unidentified66.24ND/-399.2180134.1583178.4 (38.54), 399.5 (21.28), 161.2 (4.22)C24H31O5−0.3−0.79.0
183Unidentified66.57ND/-417.1349135.1393295.3 (28.85), 109.1 (20.68), 281.3 (13.63), 269.2 (11.44), 252.9 (5.46), 307.3 (2.47), 267.2 (2.40), 238.3 (2.36)C25H21O6−0.5−1.215.0
184Unidentified66.60ND/-399.2176134.2299179.1 (15.44), 399.5 (14.91), 137.1 (10.24), 139.1 (2.82), 121.1 (2.64)C24H31O50.10.39.0
185B Pinobanksin 3-benzoate66.8064.81375.0878253.2202197.1 (4.84), 225.2 (3.56), 121.2 (3.04), 209.2 (2.85)C22H15O6−0.4−1.015.0
186Unidentified67.12ND/-377.1396258.2083377.4 (78.69), 344.4 (17.20), 271.4 (13.77), 359.5 (12.78), 230.3 (12.47), 165.1 (8.77), 316.4 (9.27), 362.4 (8.55), 138.1 (4.54), 245.3 (5.43), 269.2 (3.55), 173.3 (2.37), 243.2 (2.03)C23H21O5−0.2−0.513.0
187B Pinobanksin derivate67.49291389.1037253.2235271.2 (48.46), 197.2 (5.15), 225.2 (3.00)C23H17O6−0.7−1.715.0
188Unidentified67.63ND295.2290277.4654171.2 (70.40), 295.5 (10.03)C18H31O3−1.2−4.03.0
189B Pinobanksin 3-pentanoate or isopentenoate isomer I67.76293355.1192253.2167197.2 (4.62), 271.2 (3.55), 209.2 (2.17)C20H19O6−0.5−1.511.0
190B Pinobanksin 3-pentanoate or isopentenoate isomer II67.91293355.1194 197.2 (4.47), 209.2 (2.52)C20H19O6−0.6−1.811.0
191C Caffeic acid monoterpene (geranyl) ester68.07326315.1604134.2007137.1 (5.27), 179.2 (2.20), 106.1 (1.86)C19H23O4−0.2−0.88.0
192Unidentified68.20ND/-401.1403371.3482401.4 (51.83), 297.2 (18.94), 267.2 (11.76), 385.6 (7.59), 254.3 (6.17), 171.2 (4.55), 295.2 (4.52), 282.3 (4.10), 197.2 (2.99), 226.4 (3.29), 343.2 (2.32)C25H21O5−0.8−2.015.0
193Unidentified68.49ND/-403.1557373.3656403.4 (80.28), 269.2 (13.96), 385.9 (18.04), 297.4 (10.90), 370.5 (9.85), 355.3 (7.55), 342.4 (5.91), 271.3 (5.43), 173.2 (3.54), 309.3 (3.05), 241.2 (2.33)C25H23O5−0.6−1.614.0
194B Pinobanksin 3-hexenoate or isohexenoate68.54ND/-367.1189253.2181271.2 (31.89), 197.3 (5.77), 209.5 (3.20), 225.3 (2.91)C21H19O6−0.2−0.412.0
195Unidentified68.70ND/-397.2018145.1398118.4 (56.33), 163.2 (26.66), 251.4 (16.67), 121.1 (4.44)C24H29O50.20.610.0
196C Ricinoleic acid or 8-(3-octyloxiran−2-yl)octanoic acid68.84ND/-297.2435297.4100171.2 (28.17)C18H33O30.00.02.0
197C Balsacone L68.86*264, 344519.1804267.2076269.2 (30.61), 519.8 (15.48), 399.5 (11.70), 251.3 (8.02), 471.7 (7.67), 413.3 (4.76), 119.1 (3.28), 279.2 (3.01), 293.6 (3.09)C33H27O60.91.820.0
198B Pinobanksin 3-cinnamate68.89278401.1033253.2046197.1602 (4.77), 225.2060 (2.94)C24H17O6−0.2−0.616.0
199Unidentified69.01ND/-401.1390119.1599279.2 (73.08), 281.4 (29.74), 254.2 (23.23), 295.2 (21.52), 401.4 (22.55), 93.1 (8.97), 175.3 (9.77), 297.3 (9.24), 267.3 (8.38), 358.3 (7.40), 386.3 (7.06), 307.2 (5.82), 238.2 (4.23), 171.2 (3.75), 269.3 (3.18), 161.12 (2.92), 163.3 (3.07)C25H21O50.41.115.0
200B Pinobanksin 3-hydroxycinnamate69.16285403.1197253.2276271.2 (4.98), 197.2 (4.05), 225.3 (2.92), 149.1 (2.44)C24H19O6−1.0−2.515.0
201C Balsacone J or Balsacone P69.16ND/-521.1971401.4243521.6 (62.86), 415.4 (54.23), 119.1 (40.59), 295.3 (40.43), 281.2 (23.40), 307.3 (12.76), 309.3 (11.57), 269.2 (9.67), 389.4 (9.17), 399.4 (8.49), 283.2 (5.57), 427.5 (6.46), 519.5 (5.15), 321.4 (4.44), 477.4 (3.18), 345.3 (2.93), 267.4 (3.17)C33H29O6−0.1−0.319.0
202B Metoxycinnamic acid cinnamyl ester isomer I69.27282293.2125293.4701185.2 (57.87), 125.2 (49.45), 141.2 (18.74), 197.3 (15.90), 97.2 (11.61)C18H29O3−0.3−0.94.0
203Unidentified69.29*272403.1557119.1396281.3 (83.80), 283.3 (38.72), 297.3 (35.80), 403.5 (18.39), 93.1 (12.52), 309.3 (11.57), 269.2 (8.11), 178.1 (7.02), 279.3 (6.06), 164.3 (6.49), 263.6 (6.04), 173.2 (3.81), 271.3 (2.39), 295.3 (2.31) −0.6−1.414.0
204B Pinobanksin 3-hexanoate or isohexanoate isomer I69.57294369.1347253.2138271.2 (4.95), 197.2 (3.43), 225.1 (2.37), 115.2 (1.95)C21H21O6−0.3−0.811.0
205B Pinobanksin 3-heptenoate or isoheptenoate isomer I69.72ND/-381.1351253.2257197.2 (4.11), 271.3 (4.03), 225.2 (1.96)C22H21O6−0.7−1.912.0
206B Metoxycinnamic acid cinnamyl ester isomer II69.82282293.2120293.3632185.2 (59.65), 125.2 (51.93)C18H29O30.30.94.0
207B Pinobanksin 3-hexanoate or isohexanoate isomer II69.87ND/-369.1347253.2245197.2 (4.52), 271.2 (3.90), 225.3 (2.22), 209.2 (1.98), 115.2 (1.93)C21H21O6−0.3−0.811.0
208C Iryantherin D or Balsacone K70.20ND/-551.2078299.2895251.3 (21.30), 551.6 (22.85), 445.4 (7.98), 287.2 (5.17), 419.5 (4.72), 311.3 (4.26), 257.2 (2.60)C34H31O70.20.319.0
209Unidentified70.26ND/-343.2855283.3972211.3 (96.37), 197.3 (72.36), 253.4 (30.83), 279. 5 (19.71)C20H39O4−0.1−0.31.0
210Unidentified70.64ND/-295.2286295.4295141.2 (39.76), 125.2 (19.27)C18H31O3−0.7−2.53.0
211Unidentified70.78ND/-489.3585489.6854427.6 (28.38), 445.6 (8.05), 471.6 (2.35)C30H49O50.10.16.0
212B Pinobanksin 3-phenylpentenoate or phenylisopentenoate ester70.97*291429.1344253.2249271.2 (57.79), 197.2 (3.17), 225.4 (3.81)C26H21O60.0−0.116.0
213Unidentified71.37ND/-505.3391283.4780-C26H49O9−0.9−1.84.0
214C 2-Hydroxyethyl palmitate or 12-Hydroxystearic acid71.52ND/-299.2595299.4604253.6 (14.77), 281.3 (7.78), 113.2 (6.13)C18H35O3−0.3−1.01.0
215Unidentified71.84ND/-491.3590311.5273-C26H51O8−0.1−0.11.0
216Unidentified72.43ND/-473.2337473.5999229.1 (15.75), 320.4 (17.64), 216.2 (8.35), 280.2 (5.94), 267.3 (3.38), 292.3 (2.68), 188.2 (2.50)C30H33O5−0.3−0.614.0
217Unidentified72.48ND/-477.2644255.2330477.6 (4.09), 475.5 (3.45), 211.6 (3.10), 151.1 (1.97)C30H37O50.20.512.0
218Unidentified73.07ND/-519.3542297.4605-C27H51O9−0.3−0.62.0
219Unidentified73.85ND/-371.3171311.4860225.4 (63.83), 239.4 (61.36)C22H43O4−0.5−1.31.0
220Unidentified74.37ND/-533.3707311.5549-C28H53O9−1.2−2.22.0
221Unidentified74.70ND/-533.3703311.3955-C28H53O9−0.8−1.52.0
222Unidentified76.33ND/-447.3329--C24H47O7−0.2−0.31.0
223Unidentified77.88ND/-561.4021339.6137211.3 (30.50)C30H57O9−1.3−2.42.0
Abbreviations: A(%)—relative abundance; RT—retention time; A—identification by comparison of UV and MS/MS spectra with standards (the highest level of confidence); B—identification by comparison of MS/MS and/or UV spectrum with literature (good level of confidence); C—component was identified according to deprotonated molecular ion formula and prediction from MS/MS spectra detected in Populus genus in literature, but there are no sufficient MS and/or UV data (average/weak level of confidence); D—component was identified according to deprotonated molecular ion and prediction from MS spectra, but there are no sufficient MS/MS, and UV data and components have not been reported in poplars in literature (the weakest level of confidence); [M + H]!—components does not produce ions in ESI-negative mode; therefore, positive fragmentation was presented; ND/-—UV maximum was not determined due to low concentration, overlapping peaks or lack of UV absorption by components; *—UV maximum was evaluated approximately due to low concentration or overlapping peaks.
Table 2. Comparison of antimicrobial effect (MIC and MBC (μg/mL)) of ethanolic and ethanolic-water extracts of Populus buds.
Table 2. Comparison of antimicrobial effect (MIC and MBC (μg/mL)) of ethanolic and ethanolic-water extracts of Populus buds.
ExtractB. cereusB. subtilisE. faecalisM. luteusS. aureusS. epidermidisE. coliK. pneumoniaeP. mirabilisP. aeruginosaS. TyphimuriumH. pyloriC. glabrataC. albicansC. parapsilosis
P.BA.EtOH62.5/1000 S125/250 C500/500 C31.3/31.3 C125/125 C125/250 C>1000/>1000>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/125 C125/250 C125/500 C
P.BA.W/E>1000/Nd N125/125 C125/>1000 N62.5/62.5 C125/125 C125/500 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/N.d>1000/Nd N125/>1000 N125/125 C125/125 C125/125 C
P.CA.EtOH125/>1000 N125/500 C250/1000 C125/125 C125/500 C125/500 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/250 C250/500 C62.5/250 C
P.CA.W/E1000/1000 C250/500 C500/1000 C125/250 C125/250 C250/250 C>1000/N.d N>1000/Nd N>1000/Nd N>1000/Nd>1000/N.d N500/>1000 N250/250 C250/250 C250/500 C
P.DE.EtOH500/>1000 N125/125 C500/>1000 N125/125 C125/250 C250/1000 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/250 C250/250 C250/500 C
P.DE.W/E>1000/Nd N125/125 C500/1000 C62.5/250 C125/250 C500/500 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N62.5/62.5 C250/250 C250/500 C250/500 C
P.DE × P.N.EtOH125/>1000 N125/500 C500/500 C125/125 C125/250 C250/500 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/500 C250/250 C125/250 C
P.DE × P.N.W/E>1000/Nd N125/125 C500/1000 C62.5/250 C125/250 C500/500 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N500/>1000 N250/250 C250/500 C250/500 C
P.ER.EtOH31.3/>1000 N62.5/125 C250/500 C62.5/125 C125/125 C125/125 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/250 C250/250 C250/500 C
P.ER.W/E>1000/Nd N62.5/125 C250/>1000 N62.5/125 C125/125 C125/500 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N250/>1000 N125/125 C250/250 C250/250 C
P. × KOM.EtOH62.5/>1000 N62.5/125 C125/250 C62.5/62.5 C62.5/125 C125/125 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/125 C125/250 C125/500 C
P. × KOM.W/E125/>1000 N125/125 C250/250 C62.5/62.5 C62.5/125 C125/250 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N250/250 C C125/250 C250/250 C125/250 C
P.LAU.EtOH62.5/>1000 N125/125 C500/>1000 N125/125 C125/250 C250/>1000 S>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C250/250 C250/1000 C250/1000 C
P.LAU.W/E>1000/Nd N500/1000 C1000/>1000 N250/500 C500/1000 C1000/>1000 N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N250/1000 C>1000/Nd N>1000/Nd N>1000/Nd N
P.LAS.EtOH500/>1000 N250/1000 C1000/>1000 N250/250 C250/1000 C500/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N250/500 C>1000/>1000 N>1000/>1000 N>1000/>1000 N
P.LAS.W/E>1000/Nd N500/1000 C1000/>1000 N250/500 C500/1000 C1000>1000 N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N
P.M.HB.ETOH31.3/>1000 N62.5/125 C125/250 C31.3/31.3 C62.5/125 C125/250 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N31.3/31.3 C125/125 C125/125 C125/250 C
P.M.HB.W/E62.5/1000 S62.5/62.5 C250/250 C62.5/62.5 C62.5/250 C125/125 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N250/250 C250/250 C250/250 C125/250 C
P.M × P.B.ETOH125/>1000 N62.5/250 C250/500 C62.5/62.5 C125/250 C125/250 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N31.3/31.3 C125/125 C125/125 C125/250 C
P.M × P.B.W/E1000/>1000 N125/125 C250/1000 C62.5/250 C62.5/125 C125/250 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N250/1000 C125/125 C125/125 C125/125 C
P.M × P.TRI.ETOH62.5/1000 S62.5/125 C31.3/250 S15.6/15.6 C62.5/62.5 C15.6/62.5 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/500 C125/1000 S125/500 C
P.M × P.TRI.W/E31.3/>1000 N62.5/125 C62.5/125 C15.6/15.6 C62.5/62.5 C62.5/62.5 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N62.5/125 C125/125 C125/125 C125/250 C
P.N.1.ETOH62.5/250 C125/125 C125/250 C31.3/31.3 C125/250 C125/125 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/125 C125/250 C125/500 C
P.N.1.W/E>1000/Nd N250/500 C500/>1000 N125/500 C250/500 C500/1000 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N125/250 C250/250 C500/500 C250/500 C
P.N.2.ETOH125/>1000 N125/125 C250/500 C62.5/125 C125/250 C250/500 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/125 C125/125 C125/250 C62.5/500 S
P.N.2.W/E>1000/Nd N125/125 C125/250 C62.5/62.5 C125/125 C250/250 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N125/250 C125/125 C125/250 C125/250 C
P.N.3.EtOH31.3/62.5 C31.3/62.5 C125/250 C31.3/62.5 C62.5/62.5 C62.5/125 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N31.3/31.3 C62.5/125 C125/125 C125/250 C
P.N.3.W/E>1000/Nd N62.5/62.5 C250/250 C62.5/62.5 C62.5/62.5 C62.5/125 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N250/250 C62.5/125 C125/125 C125/125 C
P. × PE1.EtOH62.5/>1000 N62.5/250 C125/250 C31.3/62.5 C62.5/125 C125/125 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/125 C125/125 C62.5/250 C
P. × PE1.W/E>1000/Nd N125/125 C250/250 C31.3/62.5 C62.5/125 C125/250 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N250/250 C125/125 C125/125 C125/250 C
P. × PE2.EtOH125/>1000 N125/125 C500/1000 C125/125 C125/250 C250/1000 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/250 C250/500 C250/500 C
P. × PE2.W/E>1000/Nd N500/>1000 N1000/>1000 N125/500 C250/1000 C250/500 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N1000/>1000 N500/500 C500/1000 C500/1000 C
P. × RA.EtOH62.5/>1000 N125/125 C500/500 C31.3/62.5 C125/250 C125/250 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/500 C250/500 C125/125 C
P. × RA.W/E125/>1000 N125/125 C500/500 C62.5/62.5 C125/125 C250/250 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N500/500 C250/250 C250/250 C125/250 C
P.RO.EtOH62.5/>1000 N31.3/62.5 C62.5/250 C15.6/31.3 C62.5/62.5 C15.6/31.3 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N31.3/31.3 C62.5/62.5 C125/125 C62.5/250 C
P.RO.W/E>1000/Nd N31.3/62.5 C62.5/125 C15.6/31.3 C31.3/62.5 C31.3/31.3 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N62.5/125 C62.5/250 C125/125 C62.5/125 C
P.SI.EtOH62.5/>1000 N125/250 C250/500 C62.5/125 C125/250 C125/125 C>1000/>1000 N>1000/>1000 N1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/125 C125/250 C125/250 C
P.SI.W/E125/>1000 N125/125 C250/500 C62.5/250 C125/250 C125/500 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N250/500 C125/250 C250/250 C250/250 C
P.SU.EtOH62.5/>1000 N62.5/125 C250/250 C31.3/62.5 C62.5/125 C125/125 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N31.3/62.5 C125/125 C125/250 C125/250 C
P.SU.W/E125/>1000 N125/125 C250/500 C62.5/62.5 C125/125 C125/250 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N62.5/62.5 C125/125 C125/125 C125/250 C
P.TA.1.EtOH62.5/500 S125/125 C500/500 C31.3/62.5 C125/125 C125/250 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/125 C125/250 C125/500 C
P.TA.1.W/E>1000/Nd N125/125 C250/>1000 N62.5/62.5 C125/250 C125/500 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N250/>1000 N125/250 C125/250 C125/250 C
P.TA.2.EtOH250/>1000 N125/125 C62.5/500 S31.3/62.5 C125/250 C125/250 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/125 C125/250 C125/250 C
P.TA.2.W/E>1000/Nd N250/250 C500/>1000 N125/500 C250/500 C250/500 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N500/>1000 N250/250 C250/500 C500/500 C
P.TA1 × PTRI.EtOH15.6/1000 S62.5/62.5 C125/250 C15.6/15.6 C62.5/125 C31.3/62.5 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N62.5/62.5 C125/125 C125/500 C125/1000 S
P.TA1 × PTRI.W/E>1000/Nd N62.5/125 C125/250 C15.6/31.3 C125/125 C62.5/62.5 C>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N125/250 C125/250 C250/250 C250/250 C
P.TA.2 × P.TRI.EtOH31.3/500 S31.3/31.3 C15.6/500 S7.8/7.8 C31.3/31.3 C7.8/15.6>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N31.3/31.3 C125/125 C125/500 C1000/1000 C
P.TA.2 × P.TRI.W/E31.3/500 S62.5/62.5 C62.5/125 C31.3/31.3 C62.5/62.5 C31.3/125>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd>1000/Nd N62.5/125 C125/500 C125/500 C125/500 C
P.TRI.EtOH31.3/>1000 N62.5/62.5 C62.5/125 C15.6/15.6 C62.5/62.5 C31.3/31.3 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000>1000/>1000 N31.3/31.3 C62.5/125 C125/250 C125/500 C
P.TRI.W/E>1000/Nd N62.5/62.5 C62.5/125 C15.6/31.3 C62.5/62.5 C31.3/500>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N62.5/125 C62.5/62.5 C125/250 C62.5/250 C
P. × WCA.EtOH>1000/>1000 N>1000/>1000 N>1000/>1000 N1000/1000 C1000/1000 C1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000 N250/250 C>1000/>1000 N>1000/>1000 N>1000/>1000 N
P. × WCA.W/E>1000/Nd N>1000/Nd N>1000/Nd N1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N500/1000 C>1000/Nd N>1000/Nd N>1000/Nd N
P.WIL.EtOH>1000/>1000 N1000/>1000 N>1000/>1000 N500/1000 C1000/1000 C250/1000 C>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000 N>1000/>1000 N250/250 C>1000/>1000 N>1000/>1000 N>1000/>1000 N
P.WIL.W/E>1000/>1000 N1000/>1000 N1000/>1000 N500/>1000 N1000/>1000 N1000/>1000 N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N>1000/Nd N1000/>1000 N>1000/Nd N1000/Nd N>1000/Nd N
Reference drugs0.98 VAN0.24 VAN1.95 VAN0.12 VAN0.98 VAN0.98 VAN0.015 CIP0.12 CIP0.03 CIP0.49 CIP0.06 CIP31.3 MET0.24 NYS0.48 NYS0.24 NYS
Activity abbreviations: S—bacteriostatic or fungistatic effect; C—bactericidal or fungicidal effect; N—MBC/MIC or MFC/MIC ratio was not determined; Nd—MBC or MFC was not determined. Highly active samples as well as the lowest MICs are highlighted in bold (average, ≤62.5 μg/mL) or frame (high, ≤15.6 μg/mL). Poplar taxons acronyms: P.BA—P. balsamifera; P.CA—P. cathayana; P.DE—P. deltoides; P.DE × P.N—P. deltoides × P. nigra; P.ER—P. ‘Eridano’; P. × KOM—P. × komarowii; P.LAU—P. laurifolia; P.LAS—P. lasiocarpa; P.MAX—P. maximowiczii; P.M × P.B—P. maximowiczii × P. berolinensis; P.M × P.TRI—P. maximowiczii × P. trichocarpa; P.N—P. nigra (samples 1–3); P. × PE—P. × petrowskiana (samples 1–2); P. × RA—P. × rasumoskowiana; P.RO—P. trichocarpa ‘Rochester’; P.SI—P. simonii; P.SU—P. suaveolens; P.TA—P. tacamahaca (samples 1–2); P.TA × P.TRI—P. tacamahaca × P. trichocarpa (samples 1–2); P.TRI—P. trichocarpa, P.WIL—P. wilsonii, P. × WCA—P. × wilsocarpa. Reference drugs: CIP—ciprofloxacin; MET—metronidazole; NYS—nystatin; VAN—vancomycin.
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Okińczyc, P.; Widelski, J.; Nowak, K.; Radwan, S.; Włodarczyk, M.; Kuś, P.M.; Susniak, K.; Korona-Głowniak, I. Phytochemical Profiles and Antimicrobial Activity of Selected Populus spp. Bud Extracts. Molecules 2024, 29, 437. https://doi.org/10.3390/molecules29020437

AMA Style

Okińczyc P, Widelski J, Nowak K, Radwan S, Włodarczyk M, Kuś PM, Susniak K, Korona-Głowniak I. Phytochemical Profiles and Antimicrobial Activity of Selected Populus spp. Bud Extracts. Molecules. 2024; 29(2):437. https://doi.org/10.3390/molecules29020437

Chicago/Turabian Style

Okińczyc, Piotr, Jarosław Widelski, Kinga Nowak, Sylwia Radwan, Maciej Włodarczyk, Piotr Marek Kuś, Katarzyna Susniak, and Izabela Korona-Głowniak. 2024. "Phytochemical Profiles and Antimicrobial Activity of Selected Populus spp. Bud Extracts" Molecules 29, no. 2: 437. https://doi.org/10.3390/molecules29020437

APA Style

Okińczyc, P., Widelski, J., Nowak, K., Radwan, S., Włodarczyk, M., Kuś, P. M., Susniak, K., & Korona-Głowniak, I. (2024). Phytochemical Profiles and Antimicrobial Activity of Selected Populus spp. Bud Extracts. Molecules, 29(2), 437. https://doi.org/10.3390/molecules29020437

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