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15 pages, 3979 KiB

Open AccessArticle

Development of a Ratiometric Fluorescent Cu(II) Indicator Based on Poly(N-isopropylacrylamide) Thermal Phase Transition and an Aminopyridyl Cu(II) Ligand

by Lea Nyiranshuti, Emily R. Andrews, Leonid I. Povolotskiy, Frances M. Gomez, Nathan R. Bartlett, Arun Timothy Royappa, Arnold L. Rheingold, William Rudolf Seitz and Roy P. Planalp

Molecules 2023, 28(20), 7097; https://doi.org/10.3390/molecules28207097 - 15 Oct 2023

Cited by 1 | Viewed by 1235

Abstract

An aqueous Cu²⁺ and Zn²⁺ indicator is reported based on copolymerizing aminopyridine ligands and the environment-sensitive dansyl fluorophore into the responsive polymer poly(N-isopropylacrylamide) (PNIPAm). The metal ion binding creates charge and solvation that triggers PNIPAm’s thermal phase transition from hydrophobic globule [...] Read more.

An aqueous Cu²⁺ and Zn²⁺ indicator is reported based on copolymerizing aminopyridine ligands and the environment-sensitive dansyl fluorophore into the responsive polymer poly(N-isopropylacrylamide) (PNIPAm). The metal ion binding creates charge and solvation that triggers PNIPAm’s thermal phase transition from hydrophobic globule to hydrophilic open coil. As a basis for sensing the metal-binding, the dansyl fluorescence emission spectra provide a signal at ca. 530 nm and a signal at 500 nm for the hydrophobic and hydrophilic environment, respectively, that are ratiometrically interpreted. The synthesis of the title pyridylethyl-pyridylmethyl-amine ligand (acronym PEPMA) with a 3-carbon linker to the copolymerizable group, aminopropylacrylamide (PEPMA-C3-acrylamide), is reported, along with a nonpolymerizable model ligand derivative. The response of the polymer is validated by increasing temperature from 25 °C to 49 °C, which causes a shift in maximum emission wavelength from 536 nm to 505 nm, along with an increase in the ratio of emission intensity of 505 nm/536 nm from 0.77 to 1.22 (λ_ex = 330 nm) as the polymer releases water. The addition of divalent Cu or Zn to the indicator resulted in a dansyl emission shift of 10 nm to a longer wavelength, accompanied by fluorescence quenching in the case of Cu²⁺. The addition of EDTA to the Cu²⁺-loaded indicator reversed the fluorescence shift at 25 °C to 35 °C. The affinities of Cu²⁺ and Zn²⁺ for the PEPMA derivatives are log K_f = 11.85 and log K_f = 5.67, respectively, as determined by potentiometric titration. The single-crystal X-ray structure of the Cu²⁺-PEPMA derivative is five-coordinate, of-geometry intermediate between square-pyramidal and trigonal-bipyramidal, and is comparable to that of Cu²⁺ complexes with similar formation constants. Full article

(This article belongs to the Special Issue Fluorescence Chemosensors: Design, Synthesis, and Application)

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22 pages, 8792 KiB

Open AccessArticle

Naphthalimide-Piperazine Derivatives as Multifunctional “On” and “Off” Fluorescent Switches for pH, Hg²⁺ and Cu²⁺ Ions

by Kristina Pršir, Mislav Matić, Marlena Grbić, Gerhard J. Mohr, Svjetlana Krištafor and Ivana Murković Steinberg

Molecules 2023, 28(3), 1275; https://doi.org/10.3390/molecules28031275 - 28 Jan 2023

Cited by 7 | Viewed by 2673

Abstract

Novel 1,8-naphthalimide-based fluorescent probes NI-1 and NI-2 were designed and screened for use as chemosensors for detection of heavy metal ions. Two moieties, methylpyridine (NI-1) and hydroxyphenyl (NI-2), were attached via piperazine at the C-4 position of the napthalimide [...] Read more.

Novel 1,8-naphthalimide-based fluorescent probes NI-1 and NI-2 were designed and screened for use as chemosensors for detection of heavy metal ions. Two moieties, methylpyridine (NI-1) and hydroxyphenyl (NI-2), were attached via piperazine at the C-4 position of the napthalimide core resulting in a notable effect on their spectroscopic properties. NI-1 and NI-2 are pH sensitive and show an increase in fluorescence intensity at around 525 nm (switch “on”) in the acidic environment, with pK_a values at 4.98 and 2.91, respectively. Amongst heavy metal ions only Cu²⁺ and Hg²⁺ had a significant effect on the spectroscopic properties. The fluorescence of NI-1 is quenched in the presence of either Cu²⁺ or Hg²⁺ which is attributed to the formation of 1:1 metal-ligand complexes with binding constants of 3.6 × 10⁵ and 3.9 × 10⁴, respectively. The NI-1 chemosensor can be used for the quantification of Cu²⁺ ions in sub-micromolar quantities, with a linear range from 250 nM to 4.0 μM and a detection limit of 1.5 × 10⁻⁸ M. The linear range for the determination of Hg²⁺ is from 2 μM to 10 μM, with a detection limit of 8.8 × 10⁻⁸ M. Conversely, NI-2 behaves like a typical photoinduced electron transfer (PET) sensor for Hg²⁺ ions. Here, the formation of a complex with Hg²⁺ (binding constant 8.3 × 10³) turns the green fluorescence of NI-2 into the “on” state. NI-2 showed remarkable selectivity towards Hg²⁺ ions, allowing for determination of Hg²⁺ concentration over a linear range of 1.3 μM to 25 μM and a limit of detection of 4.1 × 10⁻⁷ M. Full article

(This article belongs to the Special Issue Fluorescence Chemosensors: Design, Synthesis, and Application)

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12 pages, 28595 KiB

Open AccessArticle

A Ratiometric Fluorescent Sensor Based on Dye/Tb (III) Functionalized UiO-66 for Highly Sensitive Detection of TDGA

by Yangchun Fan, Xin Jiang, Jie Che, Mingfeng Li, Xuejuan Zhang, Daojiang Gao, Jian Bi and Zhanglei Ning

Molecules 2022, 27(19), 6543; https://doi.org/10.3390/molecules27196543 - 3 Oct 2022

Cited by 5 | Viewed by 1939

Abstract

Thiodiglycolic acid (TDGA) is a biomarker for monitoring vinyl chloride exposure. Exploring a facile, rapid and precise analysis technology to quantify TDGA is of great significance. In this research, we demonstrate a fluorescent sensor based on dual-emissive UiO-66 for TDGA detection. This ratiometric [...] Read more.

Thiodiglycolic acid (TDGA) is a biomarker for monitoring vinyl chloride exposure. Exploring a facile, rapid and precise analysis technology to quantify TDGA is of great significance. In this research, we demonstrate a fluorescent sensor based on dual-emissive UiO-66 for TDGA detection. This ratiometric fluorescent material named C460@Tb-UiO-66-(COOH)₂ was designed and synthesized by introducing organic dye 7-diethylamino-4-methylcoumarin (C460) and Tb³⁺ into UiO-66-(COOH)₂. The as-obtained C460@Tb-UiO-66-(COOH)₂ samples showed highly selective recognition, excellent anti-interference and rapid response characteristics for the recognition of TDGA. The detection limit is 0.518 mg·mL⁻¹, which is much lower than the threshold of 20 mg·mL⁻¹ for a healthy person. In addition, the mechanism of TDGA-induced fluorescence quenching is discussed in detail. This sensor is expected to detect TDGA content in human urine. Full article

(This article belongs to the Special Issue Fluorescence Chemosensors: Design, Synthesis, and Application)

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13 pages, 3916 KiB

Open AccessArticle

A Novel Turn-On Fluorescence Probe Based on Cu(II) Functionalized Metal–Organic Frameworks for Visual Detection of Uric Acid

by Jie Yang, Jie Che, Xin Jiang, Yangchun Fan, Daojiang Gao, Jian Bi and Zhanglei Ning

Molecules 2022, 27(15), 4803; https://doi.org/10.3390/molecules27154803 - 27 Jul 2022

Cited by 24 | Viewed by 2501

Abstract

As an important biomarker in urine, the level of uric acid is of importance for human health. In this work, a Cu(II) functionalized metal–organic framework (Cu²⁺@Tb-MOFs) is designed and developed as a novel fluorescence probe for wide-range uric acid detection in [...] Read more.

As an important biomarker in urine, the level of uric acid is of importance for human health. In this work, a Cu(II) functionalized metal–organic framework (Cu²⁺@Tb-MOFs) is designed and developed as a novel fluorescence probe for wide-range uric acid detection in human urine. The study shows that this fluorescence platform demonstrated excellent pH-independent stability, high water tolerance, and good thermal stability. Based on the strong interaction between metal ions and uric acid, the designed Cu²⁺@Tb-MOFs can be employed as efficient turn-on fluorescent probes for the detection of uric acid with wide detection range (0~10⁴ µM) and high sensitivity (LOD = 0.65 µM). This probe also demonstrates an anti-interference property, as other species coexisted, and the possibility for recycling. The sensing mechanisms are further discussed at length. More importantly, we experimentally constructed a molecular logic gate operation based on this fluorescence probe for intelligent detection of uric acid. These results suggest the Cu(II) functionalized metal–organic framework can act as a prominent candidate for personalized monitoring of the concentration of uric acid in the human urine system. Full article

(This article belongs to the Special Issue Fluorescence Chemosensors: Design, Synthesis, and Application)

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8 pages, 2842 KiB

Open AccessCommunication

A Novel NIR Fluorescent Probe for Highly Selective Detection of Nitroreductase and Hypoxic-Tumor-Cell Imaging

by Feng Liu, Hong Zhang, Kun Li, Yongmei Xie and Zhihui Li

Molecules 2021, 26(15), 4425; https://doi.org/10.3390/molecules26154425 - 22 Jul 2021

Cited by 12 | Viewed by 2804

Abstract

Nitroreductase as a potential biomarker for aggressive tumors has received extensive attention. In this work, a novel NIR fluorescent probe for nitroreductase detection was synthesized. The probe Py-SiRh-NTR displayed excellent sensitivity and selectivity. Most importantly, the confocal fluorescence imaging demonstrated that HepG-2 cells [...] Read more.

Nitroreductase as a potential biomarker for aggressive tumors has received extensive attention. In this work, a novel NIR fluorescent probe for nitroreductase detection was synthesized. The probe Py-SiRh-NTR displayed excellent sensitivity and selectivity. Most importantly, the confocal fluorescence imaging demonstrated that HepG-2 cells treated with Py-SiRh-NTR under hypoxic conditions showed obvious enhanced fluorescence, which means that the NTR was overexpressed under hypoxic conditions. Moreover, the probe showed great promise that could help us to study related anticancer mechanisms research. Full article

(This article belongs to the Special Issue Fluorescence Chemosensors: Design, Synthesis, and Application)

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12 pages, 1571 KiB

Open AccessArticle

A Fluorogenic Assay: Analysis of Chemical Modification of Lysine and Arginine to Control Proteolytic Activity of Trypsin

by Kunal N. More, Tae-Hwan Lim, Julie Kang and Dong-Jo Chang

Molecules 2021, 26(7), 1975; https://doi.org/10.3390/molecules26071975 - 31 Mar 2021

Cited by 3 | Viewed by 3179

Abstract

The chemical modification of amino acids plays an important role in the modulation of proteins or peptides and has useful applications in the activation and stabilization of enzymes, chemical biology, shotgun proteomics, and the production of peptide-based drugs. Although chemoselective modification of amino [...] Read more.

The chemical modification of amino acids plays an important role in the modulation of proteins or peptides and has useful applications in the activation and stabilization of enzymes, chemical biology, shotgun proteomics, and the production of peptide-based drugs. Although chemoselective modification of amino acids such as lysine and arginine via the insertion of respective chemical moieties as citraconic anhydride and phenyl glyoxal is important for achieving desired application objectives and has been extensively reported, the extent and chemoselectivity of the chemical modification of specific amino acids using specific chemical agents (blocking or modifying agents) has yet to be sufficiently clarified owing to a lack of suitable assay methodologies. In this study, we examined the utility of a fluorogenic assay method, based on a fluorogenic tripeptide substrate (FP-AA1-AA2-AA3) and the proteolytic enzyme trypsin, in determinations of the extent and chemoselectivity of the chemical modification of lysine or arginine. As substrates, we used two fluorogenic tripeptide probes, MeRho-Lys-Gly-Leu(Ac) (lysine-specific substrate) and MeRho-Arg-Gly-Leu(Ac) (arginine-specific substrate), which were designed, synthesized, and evaluated for chemoselective modification of specific amino acids (lysine and arginine) using the fluorogenic assay. The results are summarized in terms of half-maximal inhibitory concentrations (IC₅₀) for the extent of modification and ratios of IC₅₀ values (IC₅₀arginine/IC₅₀lysine and IC₅₀lysine/IC₅₀arginine) as a measure of the chemoselectivity of chemical modification for amino acids lysine and arginine. This novel fluorogenic assay was found to be rapid, precise, and reproducible for determinations of the extent and chemoselectivity of chemical modification. Full article

(This article belongs to the Special Issue Fluorescence Chemosensors: Design, Synthesis, and Application)

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18 pages, 1650 KiB

Open AccessArticle

New Coumarin Dipicolinate Europium Complexes with a Rich Chemical Speciation and Tunable Luminescence

by Sebastiano Di Pietro, Dalila Iacopini, Aldo Moscardini, Ranieri Bizzarri, Mauro Pineschi, Valeria Di Bussolo and Giovanni Signore

Molecules 2021, 26(5), 1265; https://doi.org/10.3390/molecules26051265 - 26 Feb 2021

Cited by 6 | Viewed by 2772

Abstract

Europium (III) luminescent chelates possess intrinsic photophysical properties that are extremely useful in a wide range of applications. The lack of examples of coumarin-based lanthanide complexes is mainly due to poor photo-sensitization attempts. However, with the appeal of using such a versatile scaffold [...] Read more.

Europium (III) luminescent chelates possess intrinsic photophysical properties that are extremely useful in a wide range of applications. The lack of examples of coumarin-based lanthanide complexes is mainly due to poor photo-sensitization attempts. However, with the appeal of using such a versatile scaffold as antenna, especially in the development of responsive molecular probes, it is worth the effort to research new structural motifs. In this work, we present a series of two new tris coumarin-dipicolinate europium (III) complexes, specifically tailored to be either a mono or a dual emitter, tuning their properties with a simple chemical modification. We also encountered a rich chemical speciation in solution, studied in detail by means of paramagnetic NMR and emission spectroscopy. Full article

(This article belongs to the Special Issue Fluorescence Chemosensors: Design, Synthesis, and Application)

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Review

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19 pages, 5395 KiB

Open AccessReview

Research Update of Emergent Sulfur Quantum Dots in Synthesis and Sensing/Bioimaging Applications

by Keke Ning, Yujie Sun, Jiaxin Liu, Yao Fu, Kang Ye, Jiangong Liang and Yuan Wu

Molecules 2022, 27(9), 2822; https://doi.org/10.3390/molecules27092822 - 28 Apr 2022

Cited by 14 | Viewed by 3326

Abstract

Due to their unique optical property, low toxicity, high hydrophilicity, and low cost, sulfur quantum dots (SQDs), an emerging luminescent nanomaterial, have shown great potential in various application fields, such as sensing, bioimaging, light emitting diode, catalysis, and anti-bacteria. This minireview updates the [...] Read more.

Due to their unique optical property, low toxicity, high hydrophilicity, and low cost, sulfur quantum dots (SQDs), an emerging luminescent nanomaterial, have shown great potential in various application fields, such as sensing, bioimaging, light emitting diode, catalysis, and anti-bacteria. This minireview updates the synthetic methods and sensing/bioimaging applications of SQDs in the last few years, followed by discussion of the potential challenges and prospects in their synthesis and sensing/bioimaging applications, with the purpose to provide some useful information for researchers in this field. Full article

(This article belongs to the Special Issue Fluorescence Chemosensors: Design, Synthesis, and Application)

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