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In this study, we developed a novel colorimetric chemosensor for selective and sensitive recognition of Glutathione (GSH) using a simple binary mixture of commercially accessible and inexpensive metal receptors with names, Bromo Pyrogallol Red (BPR) and Xylenol Orange (XO). This procedure is based on the synergistic coordination of BPR and XO with cerium ion (Ce3+) for the recognition of GSH over other available competitive amino acids (AAs) especially thiol species in aqueous media. Generally, cysteine (Cys) and homocysteine (hCys) can seriously interfere with the detection of GSH among common biological species because they possess similar chemical behavior. Using all the information from 1HNMR and FT-IR studies, the proposed interaction is presented in which GSH acts as a tri-dentate ligand with three N donor atoms in conjunction with BPR and XO as mono and bi-dentate ligands respectively. This approach opens a path for selective detection of other AAs by argumentatively selecting the ensemble of mixed organic ligands from commercially available reagents, thereby eliminating the need for developing synthetic receptors, sample preparation, organic solvent mixtures, and expensive equipment. Evaluating the feasibility of the existing method was led to the determination of GSH in human plasma samples., (Copyright © 2021. Published by Elsevier Inc.)

Biomass-derived phenols have recently arisen as an attractive alternative for building blocks to be used in synthetic applications, due to their widespread availability as an abundant renewable resource. In the present paper, commercial laccase from the thermophilic fungus Myceliophthora thermophila was used to bioconvert phenol monomers, namely catechol, pyrogallol and gallic acid in water. The resulting products from catechol and gallic acid were polymers that were partially characterized in respect to their optical and thermal properties, and their average molecular weight was estimated via solution viscosity measurements and GPC. FT-IR and ¹H-NMR data suggest that phenol monomers are connected with ether or C-C bonds depending on the starting monomer, while the achieved molecular weight of polycatechol is found higher than the corresponding poly(gallic acid). On the other hand, under the same condition, pyrogallol was dimerized in a pure red crystalline compound and its structure was confirmed by ¹H-NMR as purpurogallin. The herein studied green synthesis of enzymatically synthesized phenol polymers or biological active compounds could be exploited as an alternative synthetic route targeting a variety of applications.

Cocrystals are molecular solids composed of at least two types of neutral chemical species held together by noncovalent forces. Crystallization of thymine [systematic name: 5-methylpyrimidine-2,4(1H,3H)-dione] with four phenolic coformers resulted in cocrystal formation, viz. catechol (benzene-1,2-diol) giving thymine-catechol (1/1), C5H6N2O2·C6H6O2, (I), resorcinol (benzene-1,3-diol) giving thymine-resorcinol (2/1), 2C5H6N2O2·C6H6O2, (II), hydroquinone (benzene-1,4-diol) giving thymine-hydroquinone (2/1), 2C5H6N2O2·C6H6O2, (III), and pyrogallol (benzene-1,2,3-triol) giving thymine-pyrogallol (1/2), C5H6N2O2·2C6H6O3, (IV). The resorcinol molecule in (II) occupies a twofold axis, while the hydroquinone molecule in (III) is situated on a centre of inversion. Thymine-thymine base pairing is common across all four structures, albeit with different patterns. In (I)-(III), the base pair is propagated into an infinite one-dimensional ribbon, whereas it exists as a discrete dimeric unit in (IV). In (I)-(III), the two donor N atoms and one carbonyl acceptor O atom of thymine are involved in thymine-thymine base pairing and the remaining carbonyl O atom is hydrogen bonded to the coformer. In contrast, in (IV), just one donor N atom and one acceptor O atom are involved in base pairing, and the remaining donor N atom and acceptor O atom of thymine form hydrogen bonds to the coformer molecules. Thus, the utilization of the donor and acceptor atoms of thymine in the hydrogen bonding is influenced by the coformers.

We reported a new application of silver nanoparticles (NPs) for the visual sensing of aromatic polyphenols, such as gallic acid, pyrogallol and tannic acid, which is based on the intensified plasmon absorbance signals and visual changes from yellow to orange due to hydrogen-bonding recognition and subsequent catalytic oxidation of the target phenols by chitosan-capped Ag NPs (Ch-Ag NPs). The Ch-Ag NPs are generated by the well-known reaction of AgNO3 with NaBH4 and stabilized with chitosan which is a polysaccharide biopolymer with excellent dispersive properties and stability in aqueous media. After optimizing some experimental conditions, a very simple and facile sensing system has been developed for the detection of gallic acid, pyrogallol and tannic acid in water samples. The proposed system promises high selectivity toward gallic acid, pyrogallol and tannic acid, and other phenolic compounds including p-aminobenzoic acid, pentachlorophenol, 2,4,6-trinitrophenol, 2,4-dinitrophenol, p-nitrophenol, 1-naphthol, β-naphthol, p-aminophenol, catechol, hydroquinone, m-dihydroxybenzene, phloroglucin and phenol could not induce a color change even at 0.1 mM. The outstanding selectivity property of the proposed method for gallic acid, pyrogallol and tannic acid resulted from the Ch-Ag NPs-mediated reduction of Ag(+) by the target phenols. Also, a wide linear response range was obtained for the three targets. The linear response ranges for gallic acid, pyrogallol, and tannic acid were from 1 × 10(-5) to 1 × 10(-3) M, 1 × 10(-5) to 1 × 10(-2) M and 1 × 10(-6) to 1 × 10(-4) M with a respective detection limit (DL) of 1 × 10(-5), 1 × 10(-5), and 1 × 10(-6) M. The proposed method was successfully applied to detect target phenols in environmental water samples. Furthermore, because the color change from yellow to orange is observable by the naked eye, it is easy to realize visual detection of the target phenols without any instrumentation or complicated design. The experimental results reported here open up an innovative application of the catalytic reactivity of Ag NPs.

A novel spectrofluorometric method, using 2-(2-pyridyliminomethyl)phenol as a fluorescent probe, was developed for the determination of superoxide anion radical (O(2) (*-)) and superoxide dismutase activity (SOD). The new fluorescent probe was synthesized and characterized with elemental analysis and IR spectra. It was oxidized by O(2) (*-) to form a less fluorescence product. Based on this reaction, a spectrofluorometric method was proposed and successfully used to determine superoxide anion radicals and SOD activity. The effects of interferences were studied. The reaction was simple, precise and sensitive. It was applied to determine SOD activity in garlic, papaya and spinach successfully.

The suicide inactivation mechanism of tyrosinase acting on its substrates has been studied. The kinetic analysis of the proposed mechanism during the transition phase provides explicit analytical expressions for the concentrations of o-quinone against time. The electronic, steric and hydrophobic effects of the substrates influence the enzymatic reaction, increasing the catalytic speed by three orders of magnitude and the inactivation by one order of magnitude. To explain the suicide inactivation, we propose a mechanism in which the enzymatic form E(ox) (oxy-tyrosinase) is responsible for such inactivation. A key step might be the transfer of the C-1 hydroxyl group proton to the peroxide, which would act as a general base. Another essential step might be the axial attack of the o-diphenol on the copper atom. The rate constant of this reaction would be directly related to the strength of the nucleophilic attack of the C-1 hydroxyl group, which depends on the chemical shift of the carbon C-1 (delta(1)) obtained by (13)C-NMR. Protonation of the peroxide would bring the copper atoms together and encourage the diaxial nucleophilic attack of the C-2 hydroxyl group, facilitating the co-planarity with the ring of the copper atoms and the concerted oxidation/reduction reaction, and giving rise to an o-quinone. The suicide inactivation would occur if the C-2 hydroxyl group transferred the proton to the protonated peroxide, which would again act as a general base. In this case, the co-planarity between the copper atom, the oxygen of the C-1 and the ring would only permit the oxidation/reduction reaction on one copper atom, giving rise to copper(0), hydrogen peroxide and an o-quinone, which would be released, thus inactivating the enzyme.

The synthesis and characterization of a new radical and its use for testing the antioxidant activity of polyphenols by electron transfer are reported. This new and stable species of magnetic nature, tris(2,3,5,6-tetrachloro-4-nitrophenyl)methyl (TNPTM) radical, has been characterized by electron paramagnetic resonance and its molecular structure determined by X-ray analysis. This new radical of the PTM (perchlorotriphenylmethyl) series, unlike 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, is stable in conditions of hydrogen abstraction reactions. TNPTM radical is able to discriminate between the antioxidant activities of catechol and pyrogallol in hydroxylated solvent mixtures such as chloroform/methanol (2:1). These features determine the antioxidant/pro-oxidant character and the biological activities of natural and synthetic flavonoids.

The relationship between the structure and antibacterial activity of 22 polyphenols was analyzed by using minimum inhibitory concentration (MIC) as a criterion against 26 species of bacteria which can grow in Mueller-Hinton medium. There was no clear correlation between Gram-staining and bacterial susceptibility to polyphenols, and the extent of the susceptibility was approximately dependent on the species of bacteria. In the same Gram-negative bacteria, the antibacterial activity of the polyphenols against Aeromonas hydrophila, Vibrio parahaemolyticus and Vibrio vulnificus was comparatively strong. On the other hand, the activity against 11 species of the Enterobacteriaceae was comparatively weak, and the activity against six species of aerobic bacteria causing plant disease was moderate. Polyphenols having pyrogallol groups showed strong antibacterial activity, and those with catechol and resorcinol rings showed lower activity. The structure-activity relationship was extended to 26 polyphenol-rich plant extracts which could have potent antibacterial activity suitable for commercial use.

The uptake coefficients of NO2 on aqueous solutions containing guaiacol, syringol and catechol were determined over the pH range from 1 to 13 using the wetted wall flowtube technique. The measured uptake coefficients were used to determine the rate coefficients for the reaction of the physically dissolved NO2 with the neutral and deprotonated forms of phenolic compounds listed above. These organic compounds are ubiquitous not only in biomass burning plumes but also in soils, where they form part of the building blocks of humic acids. The NO2 uptake kinetics on solutions containing guaiacol, syringol or catechol were observed to be strongly pH dependent with uptake coefficients increasing from below 10(-7), under acidic conditions, to more than 10(-5) at pH values above 10. This behaviour illustrates the difference of reactivity between the neutral phenolic species and the phenoxide ions. The corresponding second order rate coefficients were typically observed to increase from 10(5) M(-1) s(-1) for the neutral compounds to a minimum of 10(8) M(-1) s(-1) for the phenoxide ions.

Tea polyphenols (PP) are known as potent antioxidants. At the same time, PP have been repeatedly reported to oxidize by molecular oxygen with the formation of active forms of oxygen. In this work, the Clark electrode technique was applied to study the kinetics of the autoxidation of tea extracts and individual tea PP as well as model PP, catechol, gallic acid, and pyrogallol. Aqueous extracts of both green and black teas were found to undergo extensive autoxidation under physiological conditions. The addition of superoxide dismutase (SOD) and milk resulted in a significant decrease in the rate of oxidation. Studied individually, PP were found to autoxidize at a rate, which increased with pH, proportional to PP concentration and nearly proportional to oxygen concentration. The collected data were used for the extrapolation/interpolation of the starting rates of oxidation to the standard conditions (at pH 7.40, 100 microM PP, 200 microM O2). PP oxidizability is basically determined by that of the key PP fragment (pyrogallol > gallate > catechol). Meta-OH groups do not contribute to the oxidation even at pH 13.0. Similar to tea brew, the oxidation of individual PP was inhibited by milk and SOD addition, with catechol being the only exception (the oxidation of catechol was accelerated when SOD was added). Comparison of the autoxidation of PP (o-hydroquinones) with that of p-hydroquinones (Roginsky, V.; Barsukova, T. K. J. Chem. Soc., Perkin Trans. 2 2000, 1575-1582) displays the dramatic difference both in the oxidizability and in the kinetic regularities. The difference in the kinetics has been suggested to be due to the difference in the initiation of the chain process. Whereas for p-hydroquinones the oxidation is initiated by the reaction between hydroquinone and a corresponding quinone, the oxidation of o-hydroquinones is likely started by direct interaction between substrate and molecular oxygen. As the second process is much slower, this may explain the relatively low oxidizability of PP as compared to p-hydroquinones.