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Article

Novel Copper(II) Complexes with N4,S-Diallylisothiosemicarbazones as Potential Antibacterial/Anticancer Drugs

by
Vasilii Graur
1,*,
Irina Usataia
1,
Ianina Graur
1,
Olga Garbuz
1,2,
Paulina Bourosh
3,
Victor Kravtsov
3,
Carolina Lozan-Tirsu
4,
Greta Balan
4,
Valeriu Fala
4 and
Aurelian Gulea
1,*
1
Laboratory of Advanced Materials in Biofarmaceutics and Technics, Moldova State University, 60 Mateevici Street, MD-2009 Chisinau, Moldova
2
Institute of Zoology, Moldova State University, 1 Academiei Street, MD-2028 Chisinau, Moldova
3
Institute of Applied Physics, Moldova State University, 5 Academiei Street, MD-2028 Chisinau, Moldova
4
Department of Preventive Medicine, State University of Medicine and Pharmacy “Nicolae Testemitanu”, 165 Stefan cel Mare si Sfant Bd., MD-2004 Chisinau, Moldova
*
Authors to whom correspondence should be addressed.
Inorganics 2023, 11(5), 195; https://doi.org/10.3390/inorganics11050195
Submission received: 6 April 2023 / Revised: 24 April 2023 / Accepted: 29 April 2023 / Published: 30 April 2023
(This article belongs to the Special Issue Editorial Board Members’ Collection Series in “Bioinorganic Chemistry of Copper”)
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Versions Notes

Abstract

:
The six new copper(II) coordination compounds [Cu(HL1)Cl2] (1), [Cu(HL1)Br2] (2), [Cu(H2O)(L1)(CH3COO)]·1.75H2O (3), [Cu(HL2)Cl2] (4), [Cu(HL2)Br2] (5), [Cu(H2O)(L2)(CH3COO)] (6) were synthesized with 2-formyl- and 2-acetylpyridine N4,S-diallylisothiosemicarbazones (HL1 and HL2). The new isothiosemicarbazones were characterized by NMR, FTIR spectroscopy, and X-ray crystallography ([H2L2]I). All copper(II) coordination compounds were characterized by elemental analysis, FTIR spectroscopy, and molar conductivity of their 1mM methanol solutions. Furthermore, the crystal structure of complex 3 was determined using single-crystal X-ray diffraction analysis. The studied complexes manifest antibacterial and antifungal activities, that in many cases are close to the activity of medical drugs used in this area, and in some cases even exceed them. The complexes 4 and 5 showed the highest indexes of selectivity (280 and 154) and high antiproliferative activity against BxPC-3 cell lines that surpass the activity of Doxorubicin. The complexes 1–3 also manifest antioxidant activities against cation radicals ABTS•+ that are close to that of trolox, the antioxidant agent used in medicine.

1. Introduction

Copper is one of the crucial micronutrients that is located in different amounts in all human body tissues. The highest amount of copper is in the liver [1]. Various metalloproteins depend on copper as their active site, which makes it essential in a range of biochemical processes: electron transfer, oxidation, and oxygen transport. Copper also participates in cellular respiration, antioxidant protection, neurotransmission, connective tissue biosynthesis, and cellular iron metabolism [2]. Over the past few years, copper compounds have been studied as potential therapeutic agents for application as cancer medicine and as diagnostic drugs [3,4]. Many Cu(II) coordination compounds rapidly interact with glutathione in cells to form adducts and as a result the Cu(I) coordination compound is formed. This compound can generate a superoxide anion, which can induce ROS formation in a Fenton-like reaction [5]. However, antiproliferative action is not the only one for copper coordination compounds such as therapeutic agents, because of their high redox activity. For example, the copper(II) coordination compound with indomethacin is widely used as an anti-inflammatory drug in veterinary practice [6].
Cu(II) complexes of thiosemicarbazone are widely described in the literature because they are able to form stable complexes with different metal ions, which are lipophilic, and can easily permeate cell membranes. These complexes exhibit various types of biological activity: anticancer [7,8,9,10,11,12], antibacterial and antifungal [13,14,15,16,17,18], and antioxidant [19]. The antioxidant activity of copper(II) complexes is less studied.
There are many reasons why oxidative stress occurs: pollution, smoking, alcohol consumption, obesity etc. Antioxidants can protect us from free radicals that are produced in our body due to oxidative stress. Such free radicals can cause different diseases such as diabetes, cardiac diseases, cancer, and atherosclerosis [20].
In isothiosemicarbazones, alkylation of the sulfur fragment occurs, and they usually coordinate to the central metal atom through azomethine and thioamide nitrogen atoms. Therefore, in contrast to NS donor atoms of thiosemicarbazones, the isothiosemicarbazones have NN donor atoms. Due to the difference in coordination, it becomes possible to obtain coordination compounds of isothiosemicarbazones with a different structure, which will affect their chemical and biological properties. In some cases isothiosemicarbazones and their copper(II) coordination compounds outperform in activity the complexes of corresponding thiosemicarbazones [21]. Copper(II) complexes with isothiosemicarbazones are less often described in the literature [22,23,24] and there are several references to their biological activity, such as antibacterial [25,26] and anticancer [27,28].
Recently, we have synthesized 2-formylpyridine and 2-acetylpyridine 4-allyl-S-methylisothiosemicarbazones and their copper(II) coordination compounds [29,30]. Their biological activities such as anticancer, antibacterial, antifungal, and antioxidant have also been researched. These compounds showed promising results. In this paper we have replaced the S-methyl radical with the S-allyl one in the structure of isothiosemicarbazone to study how this will affect biological activity.
The aim of the present investigation is the synthesis, characterization, and study of antibacterial, antifungal, anticancer, and antioxidant activities of Cu(II) coordination compounds with 2-formylpyridine and 2-acetylpyridine N4,S-diallylisothiosemicarbazones (HL1 and HL2, Figure 1).

2. Results and Discussion

In this work we have synthesized two new S-substituted isothiosemicarbazones, namely 2-formylpyridine N4,S-diallylisothiosemicarbazone (HL1) and 2-acetylpyridine N4,S-diallylisothiosemicarbazone (HL2), that were obtained by a three-step method starting with interaction between N4-allylthiosemicarbazide with allyl iodide, then condensation with 2-formyl-/2-acetil-pyridine, and, finally, neutralization with sodium carbonate (Scheme 1).
The structures of the HL1 and HL2 were confirmed using 1H and 13C NMR spectroscopy (Figures S1–S4). The NMR spectra of HL1 contain peaks of three tautomeric forms that according to the literature [31] presumably are imino form and cis(N1-N4)/trans(N1-N4) amino forms (Scheme 2). The NMR spectra of HL2 contain peaks of two tautomeric forms. Only cis(N1-N4) and trans(N1-N4) amino forms of HL2 can be observed in its spectra.
Furthermore, the single crystals of HL2·HI were obtained by its recrystallization from methanol and their structure has been determined using single-crystal X-ray diffraction analysis. As a result, it was determined that this organic compound crystallizes in the triclinic space group P¯1 and represents an ionic compound [H2L2]I (Table 1, Figure 2a). The organic cation [H2L2]+ forms upon the transfer of the proton from HI to HL2.
The NNCN torsion angle of the isothiosemicarbazide fragment in this cation is 0.1°, which indicates its cis(N1-N4) form (both terminal nitrogen atoms are on one side of the double C1=N2 bond). The C(1)–N(1) and C(1)–N(2) bonds equal 1.330(7) and 1.312(7) Å (Table 2). This indicates that the isothiosemicarbazide fragment is stabilized in the amino form [31]. The conformation of the [H2L2]+ cation is favorable for formation of two intermolecular hydrogen bonds with the iodide anion (Table 3, Figure 2a) and for a tridentate coordination to the transition metal atoms. The survey of the Cambridge Structural Database (CSD) [32] revealed that non-coordinated isothiosemicarbazones are mainly stabilized in the amino form [30,33,34,35,36], but in the case of {2-[(2-oxyphenyl)methylidene]hydrazinyl}(methylsulfanyl)-N-(prop-2-en-1-yl)methaniminium iodide [37] the imino form is realized. The cis(N1-N4) conformation similar to that in [H2L2]+ cation was found in [30,37] with corresponding torsion angles in the range 0.56–2.31°, while in [33,34,35,36] these angles are in the range of 175.01–178.97°. In the crystal of [H2L2]I two intermolecular hydrogen bonds N–H···I link the organic cation to the iodide anion (Table 3). Two weak hydrogen C–H···I bonds unite charged components into chains (Figure 2b).
Six new copper(II) complexes were obtained by the interaction of the corresponding copper(II) salts with isothiosemicarbazones HL1 and HL2 (Scheme 3). They have the following compositions: Cu(HL1)Cl2 (1), Cu(HL1)Br2 (2), Cu(L1)(CH3COO)·2.75H2O (3), Cu(HL2)Cl2 (4), Cu(HL2)Br2 (5), Cu(L2)(CH3COO)·H2O (6).
Molar conductivity values of the complexes 1–2 and 4–5 in methanol are in the range of 169–192 Ω−1∙cm2∙mol−1 which indicates that they behave like 1:2 electrolytes, while the molar conductivity values of complexes 3 and 6 are in the range of 82–85 Ω−1∙cm2∙mol−1 which corresponds to the 1:1 type of electrolyte. The fact that the synthesized complexes 1–6 behave like electrolytes means that the anions of acid residues (Cl−, Br−, CH3COO−) from the inner sphere are readily substituted with solvent molecules while having been dissolved. It means that complexes 1–2 and 4–5 contain two anions of acid residue (Cl−/Br−) in their composition and that in the process of dissolution complex cations and two anions of acid residue are formed. In the case of complexes 3 and 6 only one anion acid residue is present in their composition.
The FTIR spectra of complexes 1–6 were compared with the spectra of corresponding isothiosemicarbazones (HL1/HL2) in order to determine the changes that occur during their formation (Figures S5–S12). It was observed that three donor nitrogen atoms of the isothiosemicarbazones HL1 and HL2 are involved in the coordination to the copper(II) central atoms. In the spectra of complexes 1–2 and 4–5 the ν(NH) stretching vibration band is shifted by 63–86 cm−1 towards lower wavenumbers. Meanwhile, this band disappears in the spectra of complexes 3 and 6. It means that the NH group of isothiosemicarbazones is deprotonated in the process of coordination to the copper(II) ions in the presence of acetate ions that act like a weak base. The ν(C=N1) and ν(C=Npyr) bands that are observed in the range of 1601–1558 cm−1 are shifted by 10–30 cm−1 suggesting the coordination of isothiosemicarbazones using azomethine and pyridine nitrogen atoms. Absorption bands of C–S bonds practically are not displaced in the spectra of complexes. Consequently, the sulfur atom is not involved in the coordination to the metal ion in these compounds. Furthermore, the characteristic bands of acetate ions are present in the FTIR spectra of complexes 3 (1620 and 1324 cm−1) and 6 (1614 and 1312 cm−1). According to the literature [38] the difference (Δ) between these two characteristic bands (Δ = 296 cm−3 for 3 and Δ = 302 cm−3 for 6) corresponds to monodentate acetate ion in the inner sphere of the coordination compound.
Single crystals of complex 3 were obtained as a result of recrystallization from methanol and their structure was determined using single-crystal X-ray diffraction analysis. The complex 3 crystallizes in the triclinic space group P¯1 (Table 1). Structural study determined that the formula of 3 is [Cu(H2O)(L1)(CH3COO)]·1.75H2O. The asymmetric part of the unit cell contains one molecular complex [Cu(H2O)(L1)(CH3COO)] (Figure 3) and 1.75 solvate water molecules. The Cu(II) in 3 is five-coordinated and the coordination polyhedron represents a square pyramid. The tridentate isothiosemicarbazone ligand is coordinated to the central atom in the monodeprotonated form (L1)− using an N3-set of donor atoms (Figure 3a) and forms two fused metallacycles. Such a coordination mode of similar ligands was found in the complexes of various transition metals [27,30,36,37,39]. Nevertheless, the sulfur atom of isothiosemicarbazones can also participate in coordination [30,35,40].
The basal plane of the Cu(II) polyhedron is formed by three donor atoms of the ligand (L1)− and an oxygen atom of the acetate ion. The oxygen atom of the coordinated water molecule is at the apex of this polyhedron. The bond distances and angles in coordination surrounding are given in Table 4. The coordination of the (L1)− to the Cu(II) ion did not lead to a change in its conformation, but affected the redistribution of bond lengths in the isothiosemicarbazide fragment: C–N interatomic distances, namely C(1)–N(1) and C(1)–N(2) values of 1.305(4) and 1.361(4) Å (Table 2) indicate the stabilization of the imino form.
The components of the crystal are united in the chain by a system of hydrogen bonds in which two coordinated and four solvate water molecules from two formula units form a six-membered chair-like H-bonded cycle (Table 3, Figure 3b). These chains are associated in the layer parallel to (ab) crystallographic plane by intermolecular hydrogen bonds O(W)−H···O(acetate) and O(W)−H···N2.
In order to study the biological properties of the synthesized copper(II) complexes the antibacterial and antifungal properties of the complexes 1–6 were tested on Gram-positive (S. aureus, B. cereus) bacteria, Gram-negative (E. coli, A. baumannii) bacteria, and fungi (C. albicans). The obtained results in form of minimum inhibitory/bactericidal/fungicidal concentrations are shown in Table 5.
First of all, it is seen that copper(II) coordination compounds in most cases show higher activity than the corresponding N4,S-diallylisothiosemicarbazones HL1 and HL2. The copper(II) complexes manifest higher antibacterial activity towards Gram-positive microorganisms. Among all synthesized copper(II) complexes, the least active ones were the complexes obtained from copper acetate (3 and 6). Other complexes showed approximately the same values of activities. So, the dependence between the activity and acid residue can be seen in these results. The activity decreases in the following order: Cl− ≈ Br− > CH3COO−. The ligand also affects the activity: copper(II) complexes with 2-acetylpyridine N4,S-diallylisothiosemicarbazone (HL2) are more active towards Gram-positive microorganisms and A. baumanii than the complexes with 2-formylpyridine N4,S-diallylisothiosemicarbazone (HL1). A group of antibiotics (Furacillinum [37,41] and Tetracycline [42,43,44,45]) and a group of antifungals (Nystatine [37] and Fluconazole [46]) were used in order to compare the antibacterial and antifungal activities of synthesized complexes with the corresponding activities of medicines. The synthesized complexes 1, 2, and 5 manifest greater activity than Furacillinum towards Gram-positive microorganisms and E. coli. Complexes 4 and 5 surpass 2–5 times the activity of Furacillinum in the case of A. baumanii. Furthermore, complex 5 approximately coincides with the activity of Tetracycline towards Gram-negative microorganism E. coli. All the studied copper(II) complexes surpass 4–20 times the activity of standard antifungals (Nystatine and Fluconazole).
The antibacterial activity of the synthesized copper(II) complexes can be compared with compounds with similar structures that were previously described in other articles: copper(II) coordination compounds with 2-formylpyridine and 2-acetylpyridine N4-allyl-S-methylisothiosemicarbazones (S-MeT2FP and S-MeT2AP, correspondingly) [29,30]. Three types of microorganisms were taken for comparison: Gram-positive S. aureus, Gram-negative E. coli microorganisms, and fungus C. albicans. The copper(II) complexes with 2-formylpyridine N4,S-diallylisothiosemicarbazone (1, 2) showed more modest results towards S. aureus than their S-methyl substituted analogs (Figure 4a). While the copper(II) complexes with 2-acetylpyridine isothiosemicarbazone HL2 obtained in this work surpass the activity of Cu(S-MeT2AP)Cl2 and Cu(S-MeT2AP)Br2 described in the literature. In the case of Gram-negative microorganisms E. coli complexes 1 and 2 are 4 times more active than the recently described copper(II) complexes (Figure 4b). The complex 5 manifests higher activity than coordination compounds with S-MeT2AP.
For comparison of antifungal properties, the activity against C. albicans was analyzed (Figure 5). All the synthesized complexes 1, 2, 4, 5 exceed the activity of the corresponding coordination compounds with S-MeT2FP and S-MeT2AP.
Moreover, for the screening of the antiproliferative activity, HL2 and copper(II) complexes 4 and 5 have been tested towards a series of cancer cell lines (HeLa, BxPC-3, RD) and a normal cell line (MDCK). The obtained results, in the form of semimaximal inhibitory concentrations (IC50) and selectivity indexes (SI), are shown in Table 6 as well as the corresponding values of similar compounds, 2-acetylpyridine N4-allyl-S-methylisothiosemicarbazone and its copper(II) complexes, that are described in [30].
While 2-acetylpyridine N4,S-diallylisothiosemicarbazone (HL2) does not manifest anticancer activity (only tested on HeLa and BxPC-3 cell lines), copper(II) complexes manifest a strongly marked antiproliferative activity. The complexes 4 and 5 manifest about the same level of activity. They showed the highest selectivity indexes, 280 and 154, towards BxPC-3 which is one of the most aggressive forms of neoplastic diseases [47]. Recently described copper(II) coordination compounds surpass the antiproliferative activity of studied complexes 4 and 5 towards MDCK and RD cell lines. Doxorubicin (DOXO) is a chemotherapy medication used to treat cancer that was used as a standard. Both synthesized complexes showed higher activity and selectivity than DOXO for all of the studied series of cancer cell lines.
The antiradical activity against ABTS•+ cation radicals was studied for HL1, HL2, and copper(II) complexes 1–6. The obtained results in form of semimaximal inhibitory concentrations (IC50) are shown in Table 7. The HL1 and its copper(II) complexes 1–3 manifest the highest antiradical activity that is close to the activity of trolox, which is used in medicine as standard antioxidant agent. Complexes 4 and 5 are practically inactive towards ABTS•+ cation radicals.

3. Experimental Section

3.1. Materials and Instrumentation

All the reagents used were chemically pure. Copper(II) salts CuCl2·2H2O, CuBr2, Cu(CH3COO)2·H2O (Merck) were used as supplied. Allyl isothiocyanate, 50–60% (w/w) aqueous solution of hydrazine, allyl iodide, 2-formylpyridine, 2-acetylpyridine, and sodium carbonate were used as received (Sigma-Aldrich). N4-Allyl-3-thiosemicarbazide was synthesized by reaction of fourfold excess of 50–60% (w/w) aqueous solution of hydrazine and allyl isothiocyanate [48]. The solvents were purified and dried according to standard procedures [49].
Bruker DRX-400 was used to record the 1H and 13C NMR spectra. Acetone-d6 was used as a solvent to prepare probes for the NMR study. Bruker ALPHA FTIR spectrophotometer was used to record FTIR spectra of studied substances in the range of 4000–400 cm−1 at rt. The elemental analysis was performed similarly to the literature procedures [50] and on the automatic Perkin Elmer 2400 elemental analyzer. R-38 rheochord bridge was used to measure the resistance of 1 mM methanol solutions of complexes 1–6 at 20 °C.

3.2. Synthesis

3.2.1. Synthesis of N4,S-Diallylisothiosemicarbazones

2-Formylpyridine N4,S-Diallylisothiosemicarbazone (HL1)

At the first step, the allyl iodide (1.68 g, 10.0 mmol) has been added to the solution of N4-allylthiosemicarbazide (1.31 g, 10.0 mmol) in ethanol [51]. After 2 h of stirring at room temperature, 2-formylpyridine (1.07 g, 10.0 mmol) was added. The solution was stirred at 70 °C for 30 min. After cooling to room temperature, a yellow precipitate formed from the solution, which was filtered off, washed with ethanol, and dried in air. The obtained precipitate was dissolved in ethanol, and aqua solution of sodium carbonate was added dropwise to the obtained solution until the pH reached value 7–8. After that, the 2-formylpyridine N4,S-diallylisothiosemicarbazone was extracted by chloroform and dried in vacuo.
Pale yellow solid. Yield: 75%; mp 62–63 °C. FW: 260.36 g/mol; Anal Calc. for C13H16N4S: C, 59.97; H, 6.19; N, 21.52; S, 12.32; found: C, 60.28; H, 6.03; N, 21.48; S, 12.49%. FTIR data (cm−1): ν(N-H) 3219; ν (C=N) 1599, 1575, 1560; ν(CH2–S) 1096; ν (C–S) 766.
Form A (amino form, cis(N1-N4)). 1H NMR (acetone-d6): 8.59 (d, 1H, CH aromatic); 8.33 (s, 1H, CH=N); 8.04 (d, 1H, CH aromatic); 7.79 (t, 1H, CH aromatic); 7.33 (t, 1H, CH aromatic); 7.47 (br, 1H, NH); 6.12–5.88 (m, 2H, CH allyl); 5.44–4.96 (m, 4H, 2×CH2=C); 3.96 (t, 2H, CH2-N); 3.72 (d, 2H, CH2-S). 13C NMR (acetone-d6): 163.61 (C-S); 154.91, 152.51, 135.38, 123.35, 119.92 (C aromatic); 149.46 (CH=N); 136.04, 134.17 (CH allyl); 117.24, 115.37, (CH2=); 45.34 (CH2-N); 32.24 (CH2-S).
Form B (imino form). 1H NMR (acetone-d6): 8.57 (d, 1H, CH aromatic); 8.24 (s, 1H, CH=N); 8.13 (d, 1H, CH aromatic); 7.77 (t, 1H, CH aromatic); 7.31 (t, 1H, CH aromatic); 5.13 (br, 1H, NH); 6.12–5.88 (m, 2H, CH allyl); 5.44–4.96 (m, 4H, 2×CH2=C); 4.09 (d, 2H, CH2-N); 3.83 (d, 2H, CH2-S). 13C NMR (acetone-d6): 163.56 (C-S); 155.21, 151.73, 134.91, 123.62, 120.46 (C aromatic); 149.37 (CH=N); 136.05, 133.75 (CH allyl); 117.83, 115.26, (CH2=); 45.58 (CH2-N); 32.49 (CH2-S).
Form C (amino form, trans(N1-N4)). 1H NMR (acetone-d6): 8.69 (d, 1H, CH aromatic); 8.23 (s, 1H, CH=N); 8.24 (d, 1H, CH aromatic); 7.97 (t, 1H, CH aromatic); 7.48 (t, 1H, CH aromatic); 6.12–5.88 (m, 2H, CH allyl); 5.44–4.96 (m, 4H, 2×CH2=C); 3.95 (t, 2H, CH2-N); 3.93 (d, 2H, CH2-S). 13C NMR (acetone-d6): 163.13 (C-S); 154.49, 152.53, 133.42, 124.18, 122.77 (C aromatic); 148.96 (CH=N); 137.25, 133.01 (CH allyl); 118.01, 116.87 (CH2=); 47.50 (CH2-N); 35.78 (CH2-S).

2-Acetylpyridine N4,S-Diallylisothiosemicarbazone (HL2)

The isothiosemicarbazone HL2 was synthesized similarly to HL1 using 2-acetylpyridine (1.21 g, 10.0 mmol) instead of 2-formylpyridine.
Pale yellow solid. Yield: 80%; mp 96–97 °C. FW: 274.38 g/mol; Anal Calc. for C14H18N4S: C, 61.28; H, 6.61; N, 20.42; S, 11.69; found: C, 61.07; H, 6.48; N, 20.37; S, 11.48%. FTIR data (cm−1): ν(N-H) 3215; ν (C=N) 1601, 1583, 1558; ν(CH2–S) 1044; ν (C–S) 743.
Form A (amino form, cis(N1-N4)). 1H NMR (acetone-d6): 8.58 (d, 1H, CH aromatic); 8.26 (d, 1H, CH aromatic); 7.71 (t, 1H, CH aromatic); 7.29 (t, 1H, CH aromatic); 7.27 (br, 1H, NH); 5.99 (m, 2H, CH allyl); 5.20 (m, 4H, 2×CH2=C); 3.96 (t, 2H, CH2-N); 3.86 (d, 2H, CH2-S); 2.51 (s, 3H, CH3). 13C NMR (acetone-d6): 161.53 (C-S); 157.19, 156.99, 135.66, 123.00, 120.16 (C aromatic); 148.46 (C=N); 135.55, 134.41 (CH allyl); 116.98, 115.15, (CH2=); 45.31 (CH2-N); 32.35 (CH2-S); 12.30 (CH3).
Form B (amino form, trans(N1-N4)). 1H NMR (acetone-d6): 8.56 (d, 1H, CH aromatic); 8.20 (d, 1H, CH aromatic); 7.75 (т, 1H, CH aromatic); 7.31 (t, 1H, CH aromatic); 5.98 (m, 2H, CH allyl); 5.29 (m, 4H, 2×CH2=C); 5.10 (br, 1H, NH); 4.11 (t, 2H, CH2-N); 3.69 (d, 2H, CH2-S); 2.43 (s, 3H, CH3). 13C NMR (acetone-d6): 161.26 (C-S); 158.23, 156.79, 135.60, 123.25, 120.35 (C aromatic); 148.53 (C=N); 134.99, 133.99 (CH allyl); 117.67, 115.38 (CH2=); 45.88 (CH2-N); 32.28 (CH2-S); 12.02 (CH3).

3.2.2. Synthesis of Copper(II) Complexes

[Cu(HL1)Cl2] (1)

Copper(II) chloride dihydrate (CuCl2·2H2O) (0.170 g, 1 mmol) was added to a hot (55° C) ethanolic solution (25 mL) of 2-formylpyridine N4,S-diallylisothiosemicarbazone HL1 (0.260 g, 1 mmol). The mixture was stirred for 30 min at 55 °C. By cooling to room temperature, a green precipitate was obtained. It was filtered out, washed with cold ethanol, and dried in vacuo.
Green solid. Yield: 80%. Anal. Calc. for C13H16Cl2CuN4S (394.81 g mol−1): C, 39.55; H, 4.08; Cl, 17.96; Cu, 16.10; N, 14.19; S, 8.12. Found: C, 39.38; H, 4.05; Cl, 17.91; Cu, 15.89; N, 14.02; S, 7.95. Main FTIR peaks (cm−1): ν(NH) 3156, ν(C=N) 1591, 1567, 1534, ν(CH2–S) 1095, ν(C–S) 768. χ(CH3OH): 169 Ω−1 cm−2 mol−1.

[Cu(HL1)Br2] (2)

The coordination compound 2 was synthesized similarly to compound 1 using CuBr2 (0.223 g; 1 mmol) and HL1 (0.260 g; 1 mmol).
Green solid. Yield: 85%. Anal. Calc. for C13H16Br2CuN4S (483.71 g mol−1): C, 32.28; H, 3.33; Br, 33.04; Cu, 13.14; N, 11.58; S, 6.63. Found: C, 32.05; H, 3.20; Br, 33.17; Cu, 13.45; N, 11.71; S, 6.72. Main FTIR peaks (cm−1): ν(NH) 3139, ν(C=N) 1593, 1567, 1538, ν(CH2–S) 1098, ν(C–S) 765. χ(CH3OH): 178 Ω−1 cm−2 mol−1.

[Cu(H2O)(L1)(CH3COO)]·1.75H2O (3)

The coordination compound 3 was synthesized similarly to compound 1 using Cu(CH3COO)2·H2O (0.200 g; 1 mmol) and HL1 (0.260 g; 1 mmol).
Brown solid. Yield: 82%. Anal. Calc. for C15H23.5CuN4O4.75S (431.48 g mol−1): C, 41.75; H, 5.49; Cu, 14.73; N, 12.98; S, 7.43. Found: C, 41.62; H, 5.58; Cu, 14.79; N, 12.81; S, 7.29. Main FTIR peaks (cm−1): ν(C=O) 1620, ν(C=N) 1596, 1558, 1532, ν(C–O) 1324, ν(CH2–S) 1091, ν(C–S) 766. χ(CH3OH): 85 Ω−1 cm−2 mol−1.

[Cu(HL2)Cl2] (4)

The coordination compound 4 was synthesized similarly to compound 1 using CuCl2·2H2O (0.170 g; 1 mmol) and HL2 (0.274 g; 1 mmol).
Green solid. Yield: 78%. Anal. Calc. for C14H18Cl2CuN4S (408.84 g mol−1): C, 41.13; H, 4.44; Cl, 17.34; Cu, 15.54; N, 13.70; S, 7.84. Found: C, 41.23; H, 4.56; Cl, 17.51; Cu, 15.72; N, 13.57; S, 7.93. Main FTIR peaks (cm−1): ν(N–H) 3129, ν(C=N) 1591, 1571, 1544, ν(CH2–S) 1044, ν(C–S) 746. χ(CH3OH): 192 Ω−1 cm−2 mol−1.

[Cu(HL2)Br2] (5)

The coordination compound 5 was synthesized similarly to compound 1 using CuBr2 (0.223 g; 1 mmol) and HL2 (0.274 g; 1 mmol).
Green solid. Yield: 72%. Anal. Calc. for C14H18Br2CuN4S (497.74 g mol−1): C, 33.78; H, 3.65; Br, 32.11; Cu, 12.77; N, 11.26; S, 6.44. Found: C, 33.95; H, 3.82; Br, 32.29; Cu, 12.65; N, 11.10; S, 6.26. Main FTIR peaks (cm−1): ν(NH) 3143, ν(C=N) 1591, 1569, 1542, ν(CH2–S) 1043, ν(C–S) 747. χ(CH3OH): 178 Ω−1 cm−2 mol−1.

[Cu(H2O)(L2)(CH3COO)] (6)

The coordination compound 6 was synthesized similarly to compound 1 using Cu(CH3COO)2·H2O (0.200 g; 1 mmol) and HL2 (0.274 g; 1 mmol).
Brown solid. Yield: 81%. Anal. Calc. for C16H22CuN4O3S (413.98 g mol−1): C, 46.42; H, 5.36; Cu, 15.35; N, 13.53; S, 7.75. Found: C, 46.19; H, 5.42; Cu, 15.12; N, 13.59; S, 7.49. Main FTIR peaks (cm−1): ν(C=O) 1614, ν(C=N) 1595, 1561, 1543, ν(C–O) 1312, ν(CH2–S) 1041, ν(C–S) 741. χ(CH3OH): 82 Ω−1 cm−2 mol−1.

3.3. X-ray Crystallography

The single-crystal X-ray analysis of [H2L2]I and complex 3 were carried out at room temperature (293 K) on an Xcalibur E CCD diffractometer equipped with a CCD area detector and a graphite monochromator, MoKα radiation (0.71073 Å). CrysAlis PRO software was used for data collection and reduction, and unit cell determination. The structures were solved and refined using the SHELXS97 and SHELXL2014 software packages [52,53]. The non-hydrogen atoms were treated anisotropically (full-matrix least squares method on F2). The hydrogen atoms were placed in calculated positions and were treated using riding model approximations with Uiso(H) = 1.2Ueq(C), while the oxygen-bounded H atoms were found from differential Fourier maps at an intermediate stage of the structure refinement. These hydrogen atoms were refined with the isotropic displacement parameter Uiso(H) = 1.5Ueq(O).
The crystallographic data were deposited with the Cambridge Crystallographic Data Center, CCDC nos. 2253067 and 2253068 for [H2L2]I and 3, respectively. Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge CHB2 1EZ, UK (Fax: +44-1223-336033; e-mail: [email protected] or www.ccdc.cam.ac.uk (accessed on 26 April 2023)).

3.4. Antibacterial and Antifungal Activity

Antibacterial and antifungal activities of the isothiosemicarbazones HL1, HL2, and copper(II) coordination compounds 1–6 were studied on a series of standard strains: Bacillus cereus (ATCC 11778), Staphylococcus aureus (ATCC 25923), Acinetobacter baumannii (BAA-747), Escherichia coli (ATCC 25922), and Candida albicans (ATCC 10231). The minimum inhibitory concentrations (MICs, μg mL−1), minimum bactericidal concentrations (MBCs, μg mL−1), and minimum fungicidal concentrations (MFCs, μg mL−1) were determined using the method of serial dilutions in liquid broth. The solutions of the tested substances were prepared in DMSO with a 10 mg mL−1 concentration. Subsequent dilutions were prepared by incorporating 2% peptonate bullion.

3.5. Antiproliferative Activity

3.5.1. Cell Cultures

The BxPC-3 (ATCC CRL-1687) cells were grown as a monolayer in Roswell Park Memorial Institute 1640 medium to which penicillin–streptomycin (final concentration of penicillin 100 U mL−1; final concentration of streptomycin 100 μg mL−1) was added. Furthermore, fetal bovine serum (FBS) was added to the medium at a concentration of 10% v/v.
The HeLa (ATCC CCL-2), RD (ATCC CCL-136), and MDCK (ATCC CCL-34) cell lines were grown in Dulbecco’s modified essential medium. The medium contained glucose (4.5 g L−1), l-glutamine (4 mM), HEPES buffer (20 mM), bovine albumin fraction (0.2% v/v), and penicillin-streptomycin (final concentration of penicillin 100 U mL−1; final concentration of streptomycin 100 μg mL−1). Moreover, the medium was supplemented with FBS at a concentration of 10% v/v.
The cells were cultured in 75-cm2 dishes in a 5% humidified CO2 environment at 37 °C.

3.5.2. Resazurin Test

The viability of cancer cells (BxPC-3, HeLa, RD) and normal cells (MDCK) was determined by using resazurin as a reagent.
Stock solutions (1·10−2 M) of the tested compounds (HL1, HL2, and complexes 1–6) were prepared by dissolving 10−5 mol of each substance in 1 mL DMSO. These stock solutions were then used to prepare diluted solutions with final concentrations of 0.1, 1, 10, 100, and 1000 µM. Corresponding media were used for the dilution process.
To perform the assay, 90 µL of corresponding culture medium containing 1 × 104 cells were placed in the wells of a 96-well microtiter plate and incubated at 37 °C, 5% CO2 for a 2–3 h period to allow the attachment of cells. Next, 10 μL of diluted solutions (0.1–1000 µM) of the tested compounds were added to the wells with culture medium. The incubation continued for 24 h, after which resazurin indicator solution (20 μL) was added to each well. After 4 h of incubation in presence of resazurin, the absorbance was measured at two wavelengths (570 nm and 600 nm).

3.6. Antiradical Activity

The ABTS•+ method [54] with modifications was used to study the antiradical activity of HL1, HL2, and complexes 1–6.
The reaction of 2,20-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid (ABTS, 7 nM) and potassium persulfate (140 mM) gave the ABTS•+ radical cations. The reaction was performed in the dark at 25 °C for 12 h. The acetate-buffered saline (0.02 M, pH 6.5) was used for dilution of the obtained solution up to a concentration at which its absorbance at 734 nm was 0.70 ± 0.01 AU.
Stock solutions (1 × 10−2 M) of the tested compounds (HL1, HL2, and complexes 1–6) in DMSO were diluted to obtain final concentrations of 10, 100, and 1000 µM. After that, 180 μL of ABTS•+ working solution and 20 μL of each tested compound solution were mixed and homogenized in the wells of a 96-well microtiter plate. After 30 min of incubation at 25 °C, the absorbance of the solutions was measured at 734 nm. The experiment was conducted three times to ensure accuracy.

4. Conclusions

Two new N4,S-diallylisothiosemicarbazones and six new copper(II) coordination compounds have been synthesized. The structure of isothiosemicarbazones HL1 and HL2 was determined using NMR spectroscopy. Isothiosemicarabzones exist in different tautomeric forms in the solution. Crystal structures of [H2L2]I and complex 3 ([Cu(H2O)(L1)(CH3CO1O)]·1.75H2O) were proved using X-ray diffraction analysis. The studied isothiosemicarbazones behave as tridentate ligands with N3-set of donor atoms. All the studied complexes (1–6) are electrolytes, which indicates the process of substitution of acidic residues (Cl−, Br−, CH3COO−) by solvent molecules in the process of dissolution of these complexes.
Biological evaluation showed that the synthesized complexes manifest promising antibacterial, antifungal, and anticancer activity. Their antibacterial/antifungal activity in many cases is close to the activity of some drugs that are used in medicine for these purposes and, in some cases, surpass them. Complexes 4 and 5 selectively inhibit proliferation of BxPC-3 cancer cell line with IC50 values 5–8 nM. Thus, these complexes exceed 400–700 times the corresponding activity of doxorubicin and 2.5–18 times the activity of the corresponding copper(II) complexes with 2-acetylpyridine N4-allyl-S-methylisothiosemicarbazone. Moreover, their selectivity indexes are in the range of 150–280 which confirms their strongly marked selectivity.
In addition, HL1 and complexes 1–3 exhibit antiradical activity that exceeds that of trolox. Therefore, copper(II) complexes with S-substituted N4-allylisothiosemicarbazones manifest promising biological properties, which are also affected by the nature of S-substituent.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/inorganics11050195/s1, Figure S1: 1H NMR spectrum of 2-formylpyridine N4,S-diallylisothiosemicarbazone (HL1); Figure S2: 13C NMR spectrum of 2-formylpyridine N4,S-diallylisothiosemicarbazone (HL1); Figure S3: 1H NMR spectrum of 2-acetylpyridine N4,S-diallylisothiosemicarbazone (HL2); Figure S4: 13C NMR spectrum of 2-acetylpyridine N4,S-diallylisothiosemicarbazone (HL2); Figure S5: FTIR spectrum of HL1; Figure S6: FTIR spectrum of 1; Figure S7: FTIR spectrum of 2; Figure S8: FTIR spectrum of 3; Figure S9: FTIR spectrum of HL2; Figure S10: FTIR spectrum of 4; Figure S11: FTIR spectrum of 5; Figure S12: FTIR spectrum of 6.

Author Contributions

Conceptualization, A.G.; methodology, I.U. and O.G.; validation, V.G., O.G., V.K., G.B. and A.G.; formal analysis, O.G., P.B. and C.L.-T.; investigation, I.U., I.G., O.G., P.B., C.L.-T. and G.B.; resources, V.K., G.B., V.F. and A.G.; data curation, V.G., P.B., V.K. and A.G.; writing—original draft preparation, V.G., I.G., P.B.; writing—review and editing, V.G., V.K. and A.G.; visualization, V.G., P.B. and V.K.; supervision, A.G.; project administration, V.K. and A.G.; All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by ANCD, grant numbers 20.80009.5007.10 and 20.80009.5007.15.

Data Availability Statement

Data is contained within the article or supplementary material.

Acknowledgments

The authors are thankful to Olga Burduniuc, N. Testemitsanu State Medical and Pharmaceutical University for the assistance in conducting biological tests of synthesized substances.

Conflicts of Interest

The authors declare no conflict of interest.

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Inorganics 11 00195 g001 550
Figure 1. Structural formula of HL1 (R = H) and HL2 (R = CH3).
Figure 1. Structural formula of HL1 (R = H) and HL2 (R = CH3).
Inorganics 11 00195 g001
Inorganics 11 00195 sch001 550
Scheme 1. Synthesis of N4,S-diallylisothiosemicarbazones HL1 and HL2 (HL1: R = H; HL2: R = CH3).
Scheme 1. Synthesis of N4,S-diallylisothiosemicarbazones HL1 and HL2 (HL1: R = H; HL2: R = CH3).
Inorganics 11 00195 sch001
Inorganics 11 00195 sch002 550
Scheme 2. The equilibrium in the solutions of HL1 (R = H) and HL2 (R = CH3).
Scheme 2. The equilibrium in the solutions of HL1 (R = H) and HL2 (R = CH3).
Inorganics 11 00195 sch002
Inorganics 11 00195 g002 550
Figure 2. (a) Molecular structure of [H2L2]I. (b) The formation of chains in the crystal of [H2L2]I.
Figure 2. (a) Molecular structure of [H2L2]I. (b) The formation of chains in the crystal of [H2L2]I.
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Inorganics 11 00195 sch003 550
Scheme 3. Synthesis of complexes 1–6 (n = 1, 2.75).
Scheme 3. Synthesis of complexes 1–6 (n = 1, 2.75).
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Inorganics 11 00195 g003 550
Figure 3. (a) The structure of the molecular complex [Cu(H2O)(L1)(CH3COO)] in 3. (b) The six-membered water cluster unites complexes in the chain in 3.
Figure 3. (a) The structure of the molecular complex [Cu(H2O)(L1)(CH3COO)] in 3. (b) The six-membered water cluster unites complexes in the chain in 3.
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Inorganics 11 00195 g004 550
Figure 4. Comparison of the activity of studied complexes with their analogues against S. aureus (a) and E. coli (b).
Figure 4. Comparison of the activity of studied complexes with their analogues against S. aureus (a) and E. coli (b).
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Inorganics 11 00195 g005 550
Figure 5. Comparison of the activity of studied complexes with their analogues against C. albicans.
Figure 5. Comparison of the activity of studied complexes with their analogues against C. albicans.
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Table
Table 1. Crystal and Structure Refinement Data for [H2L2]I and 3.
Table 1. Crystal and Structure Refinement Data for [H2L2]I and 3.
Compound[H2L2]I3
Empirical formulaC14H19I1N4S1C15H23.5Cu1N4O4.75S1
Formula weight402.29431.48
Crystal system TriclinicTriclinic
Space groupP 1 ¯ P 1 ¯
Unit cell dimensions
a (Å)7.3553(8)8.6225(5)
b (Å)9.0535(9)10.9536(5)
c (Å)13.3945(18)11.3493(8)
α (°)103.136(10)89.140(4)
β (°)91.306(11)69.700(6)
γ (°)100.693(9)81.612(4)
V (Å3)851.56(18)993.85(11)
Z22
ρcalc (g cm−3)1.5691.442
μMo (mm−1)1.9991.234
F(000)400449
Crystal size (mm)0.60 × 0.12 × 0.080.48 × 0.40 × 0.21
θ Range (°)3.12–25.053.39–25.25
Index range−8 ≤ h ≤ 8,
−10 ≤ k ≤ 10,
−15 ≤ l ≤ 15 		−10 ≤ h ≤ 10,
−12 ≤ k ≤ 13,
−13 ≤ l ≤ 11
Reflections collected/unique6159/6159
(twin)		6114/3587
(Rint = 0.0238)
Completeness (%)99.8 (θ = 25.05°)99.6 (θ =25.25°)
Reflections with I > 2σ(I)45183037
Number of refined parameters184240
Goodness-of-fit (GOF)1.0021.001
R (for I > 2σ(I))R1 = 0.0437,
wR2 = 0.0954		R1 = 0.0403,
wR2 = 0.1226
R (for all reflections)R1 = 0.0608,
wR2 = 0.0992		R1 = 0.0496,
wR2 = 0.1296
Δρmax/Δρmin (e·Å−3)0.988/−0.5210.687/−0.279
Table
Table 2. Selected Bond Lengths (Å) and Angles (deg) in fragments of isothiosemicarbazones in [H2L2]I and 3.
Table 2. Selected Bond Lengths (Å) and Angles (deg) in fragments of isothiosemicarbazones in [H2L2]I and 3.
Bonds[H2L2]I3
(Å)
N(3)–C(2)1.292(7)1.286(4)
N(3)–N(2)1.374(6)1.362(3)
C(1)–N(1)1.330(7)1.305(4)
C(1)–N(2)1.312(7)1.361(4)
C(1)–S(1)1.760(6)1.768(3)
S(1)–C(11)1.821(6)1.796(4)
N(1)–C(8)1.463(7)1.474(4)
Angles(°)
C(2)–N(3)–N(2)112.8(5)123.1(2)
N(3)–N(2)–C(1)111.5(5)107.0(2)
N(2)–C(1)–N(1)127.1(6)122.9(3)
N(2)–C(1)–S(1)115.8(5)117.0(2)
N(1)–C(1)–S(1)117.1(5)120.1(2)
C(1)–S(1)–C(11)102.5(3)104.4(2)
C(1)–N(1)–C(8)126.6(5)122.1(3)
Table
Table 3. Hydrogen Bond Distances (Å) and Angles (deg) for [H2L2]I and 3.
Table 3. Hydrogen Bond Distances (Å) and Angles (deg) for [H2L2]I and 3.
D–H⋅⋅⋅Ad(H⋅⋅⋅A)d(D⋅⋅⋅A)∠(DHA)Symmetry Transformation for Acceptor
[H2L2]I
N(1)–H(1)⋅⋅⋅I(1)2.843.622(5)152x, y, z
N(4)–H(2)⋅⋅⋅I(1)2.753.490(5)146x, y, z
C(14)–H(2)⋅⋅⋅I(1)3.314.241(6)165−x + 2, −y + 1, −z + 1
C(14)–H(3)⋅⋅⋅I(1)3.164.121(7)175−x + 1, −y + 1, −z + 1
3
O(1W)–H(1)⋅⋅⋅O(3W)1.882.761(4)166−x, −y + 1, −z + 2
O(1W)–H(2)⋅⋅⋅N(2)1.942.835(3)176−x, −y, −z + 2
O(2W)–H(1)⋅⋅⋅O(1W)2.052.814(4)151x, y, z
O(2W)–H(2)⋅⋅⋅O(2)1.952.759(4)158x − 1, y, z
O(3W)–H(1)⋅⋅⋅O(2W)1.922.735(5)159x, y, z
O(3W)–H(2)⋅⋅⋅O(1)1.992.838(3)174x, y, z
Table
Table 4. Bond Lengths (Å) and Angles (deg) in Coordination Metal Environment in 3.
Table 4. Bond Lengths (Å) and Angles (deg) in Coordination Metal Environment in 3.
BondsÅ
Cu(1)–N(1)1.962(3)
Cu(1)–N(3)1.948(2)
Cu(1)–N(4)2.037(3)
Cu(1)–O(1)1.942(2)
Cu(1)–O(1W)2.353(2)
Angles°
N(1)–Cu(1)–N(3)78.61(10)
N(1)–Cu(1)–N(4)158.36(11)
N(1)–Cu(1)–O(1)99.28(10)
N(1)–Cu(1)–O(1W)98.61(10)
N(3)–Cu(1)–N(4)80.30(10)
N(3)–M(1)–O(1)172.76(10)
N(3)–M(1)–O(1W)99.94(9)
N(4)–M(1)–O(1)101.04(10)
N(4)–M(1)–O(1W)89.75(10)
O(1)–M(1)–O(1W)87.21(9)
Table
Table 5. Minimal inhibitory, bactericidal, and fungicidal concentrations (μg mL−1) of HL1, HL2, and copper(II) complexes 1–6.
Table 5. Minimal inhibitory, bactericidal, and fungicidal concentrations (μg mL−1) of HL1, HL2, and copper(II) complexes 1–6.
CompoundStaphylococcus aureus
ATCC 25923		Bacillus cereus
ATCC 11778		Escherichia coli
ATCC 25922		Acinetobacter baumannii
BAA-747		Candidaalbicans
ATCC 10231
MICMBCMICMBCMICMBCMICMBCMICMFC
HL112525031.362.5>1000>1000--15.631.3
10.9771.950.9771.9515.631.315.631.37.8115.6
20.9771.951.953.9115.631.315.631.33.917.81
331.362.531.362.5250500--31.362.5
HL231.362.562.562.5>1000>1000>1000>10007.8162.5
40.4880.4880.4880.48831.362.51.951.953.9115.6
50.4880.4880.4880.4881.953.911.951.953.9115.6
63.913.911.953.9162.562.531.331.33.9131.3
Furacillinum [37,41]9.39.34.74.718.537.54.79.4--
Tetracycline [42,43,44,45]0.251.960.06-0.983.910.5---
Nystatine [37]--------8080
Fluconazole [46]--------15.631.3
Note: MIC—minimum inhibitory concentration; MBC—minimum bactericidal concentration; MFC—minimum fungicidal concentration; «-»—data not available.
Table
Table 6. IC50 values of HL2 and complexes 4 and 5 towards non-cancerous cell line (MDCK), cancer cell lines (HeLa, BxPC-3, RD), and the corresponding selectivity indexes in comparison with doxorubicin and similar compounds described in [30].
Table 6. IC50 values of HL2 and complexes 4 and 5 towards non-cancerous cell line (MDCK), cancer cell lines (HeLa, BxPC-3, RD), and the corresponding selectivity indexes in comparison with doxorubicin and similar compounds described in [30].
CompoundMDCKHeLa BxPC-3RD
IC50, μM IC50, μM SIIC50, μM SIIC50, μM SI
DOXO7.1 ± 0.310.0 ± 0.40.713.7 ± 0.31.916.2 ± 0.60.44
HL2->100->100---
41.4 ± 0.10.5 ± 0.12.800.005 ± 0.0012800.2 ± 0.17.00
51.23 ± 0.010.39 ± 0.013.150.008 ± 0.0011541.3 ± 0.40.95
S-MeT2AP13.0 ± 1.347.6 ± 4.90.271.5 ± 0.58.7>100-
[Cu(S-MeT2AP)Cl2]1.00 ± 0.023.0 ± 1.20.330.09 ± 0.01110.16 ± 0.016.3
[Cu(S-MeT2AP)Br2]0.35 ± 0.010.6 ± 0.20.580.02 ± 0.01180.05 ± 0.017.0
Note: S-MeT2AP—2-acetylpyridine N4-allyl-S-methylisothiosemicarbazone [30]; SI = IC50(MDCK)/IC50(cancer cell line)—selectivity index.
Table
Table 7. Antiradical activity of complexes 1–6 against ABTS•+.
Table 7. Antiradical activity of complexes 1–6 against ABTS•+.
CompoundIC50, μM
HL128.5 ± 4.0
128.9 ± 6.1
232.7 ± 0.9
330.1 ± 1.3
HL280.8 ± 13.4
4>100
5>100
695.0 ± 7.3
Trolox33.3 ± 0.2
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Graur, V.; Usataia, I.; Graur, I.; Garbuz, O.; Bourosh, P.; Kravtsov, V.; Lozan-Tirsu, C.; Balan, G.; Fala, V.; Gulea, A. Novel Copper(II) Complexes with N4,S-Diallylisothiosemicarbazones as Potential Antibacterial/Anticancer Drugs. Inorganics 2023, 11, 195. https://doi.org/10.3390/inorganics11050195

AMA Style

Graur V, Usataia I, Graur I, Garbuz O, Bourosh P, Kravtsov V, Lozan-Tirsu C, Balan G, Fala V, Gulea A. Novel Copper(II) Complexes with N4,S-Diallylisothiosemicarbazones as Potential Antibacterial/Anticancer Drugs. Inorganics. 2023; 11(5):195. https://doi.org/10.3390/inorganics11050195

Chicago/Turabian Style

Graur, Vasilii, Irina Usataia, Ianina Graur, Olga Garbuz, Paulina Bourosh, Victor Kravtsov, Carolina Lozan-Tirsu, Greta Balan, Valeriu Fala, and Aurelian Gulea. 2023. "Novel Copper(II) Complexes with N4,S-Diallylisothiosemicarbazones as Potential Antibacterial/Anticancer Drugs" Inorganics 11, no. 5: 195. https://doi.org/10.3390/inorganics11050195

APA Style

Graur, V., Usataia, I., Graur, I., Garbuz, O., Bourosh, P., Kravtsov, V., Lozan-Tirsu, C., Balan, G., Fala, V., & Gulea, A. (2023). Novel Copper(II) Complexes with N4,S-Diallylisothiosemicarbazones as Potential Antibacterial/Anticancer Drugs. Inorganics, 11(5), 195. https://doi.org/10.3390/inorganics11050195

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