Synthesis, spectral properties, and photodynamic activity of water-soluble amino acid fullerene C-60 derivatives (AFD) and four original AFD-PPa dyads, obtained by covalent addition of dye pyropheophorbide (PPa) to AFD, were studied. In aqueous solution, these AFD-PPa dyads form nanoassociates as a result of self-assembly. In this case, a significant change in the absorption spectra and strong quenching of the dye fluorescence in the structure of the dyads were observed. A comparison of superoxide or singlet oxygen generation efficiency of the studied compounds in an aqueous solution showed the photodynamic mechanism switching from type II (singlet oxygen generation of the native dye) to I type (superoxide generation of dyads). All dyads have pronounced phototoxicity on cells Hela with IC50 9.2 mu M, 9.2 mu M, 12.2 mu M for dyads Val-C-60-PPa, Ala-C-60-PPa and Pro-C-60-PPa, respectively. Such facilitation of type I photodynamic mechanism could be perspective against hypoxic tumors. (C) 2021 Published by Elsevier B.V.

Oxidation of methane with a hydrogen-air mixture at 70 °C and a partial pressure of methane of 30 atm was studied. Water-soluble glutathione-stabilized nanoclusters Aun (n = 18–25) were used as catalysts for this process. Methanol, methyl hydroperoxide (MeOOH), formaldehyde, and a small amount of CO2 were identified as the reaction products. Formation of H2O2 was also revealed; its maximum concentration was 0.5 mmol L−1, and it decreased fivefold in the presence of methane. The study of the reaction kinetics showed that the ratio of initial rates of formation of MeOH, MeOOH, and CH2O was 1: 1: 2. The reaction terminated after 9 h, MeOOH almost completely disappeared, whereas the concentrations of methanol and formaldehyde reached the stationary values of 0.6 and 0.4 mmol L−1, respectively. This phenomenon was observed despite the presence of both the oxidizing agent and the substrate in the reaction zone. Possibly, blockage of active sites by the reaction products took place at a certain time because once the volatile products were removed from the system and the gas phase was renewed, the catalyst showed a stable activity over several cycles. When H2 was excluded from the reaction system, the MeOH yield decreased sixfold, whereas the MeOOH yield tripled after 6 h of reaction. When NADH was used as a hydrogen source, the selectivity with respect to methanol decreased. With the use of quantum chemical calculations, a mechanism for the methane oxidation has been developed. It assumes the existence of the same intermediate as a precursor of all main reaction products.

The ability of the 2-nitroxysuccinate 3-hydroxy-6-methyl-2-ethylpyridine (I) compound to generate nitrite ions (NO2) and nitrogen monoxide (NO) in model systems with cysteine (Cys) and deoxyhemoglobin (Hb) has been studied. It has been established that there is a more efficient release NO2 and NO from compound I than from Nicorandil. The accumulation rate is 1.5 times higher in the system of Cys with I than with Nitroglycerin. It is shown that, unlike Nitroglycerin, compound I is not reduced by Hb.

The antioxidant and antiradical properties of the tetra nitrosyl iron complex with thiosulfate ligands (TNIC) were studied in vitro in mouse brain homogenates. It was found for the first time that TNIC is an effective antioxidant. The effect of TNIC on the catalytic activity of mitochondrial enzymes cytochrome c oxidase and monoamine oxidase A was studied. It was shown for the first time that TNIC is an inhibitor of the catalytic activity of cytochrome c oxidase and monoamine oxidase A in animal brain mitochondria in vitro.

The processes of deep oxidation during the reaction of rutin and quercetin with HAuCl 4 under anaerobic conditions at temperatures of 30, 60, and 100 °C were studied. The formation of CO and CO 2 was revealed by mass spectrometric analysis to occur at temperatures ≥30 °C. Since the processes of oxidation of quercetin and rutin are similar, it was concluded that, on the one hand, the sugar residue of rutin is not mainly subjected to deep oxidation and, on the other hand, the hydrolysis of the primary product of rutin oxidation occurs to form the primary product of quercetin oxidation. The analysis of the optical absorption spectra of the systems studied shows that gold nanoparticles are formed at the reduction of Au III to Au 0 . In a large excess of Au III ions, some portion of them remains non-consumed and the IR spectrum of an Au: rutin (40: 1) system after water sublimation mainly exhibits vibrations of the sugar residue. A possible mechanism for CO formation due to the decomposition of the hydrated isomer of the product of two-electron oxidation of quercetin containing three consecutively bonded carbonyl groups was proposed on the basis of the PBE density functional quantum chemical calculations.

Protective properties of gold nanoparticles and gold-rutin complexes were studied. Aurophilic bacteria Micrococcus luteus and methanotrophic bacteria Methylococcus capsulatus were studied. Gold-rutin nanoparticles and complexes protect the respiratory activity of the bacteria against toxins. Pretreatment of the cells with gold is more efficient than the treatment after the action of toxin.

A new procedure for the preparation of biocompatible gold nanoparticles using bioflavonoids: rutin, quercetin, and luteolin as reducing agents and stabilizers was proposed. On varying the bioflavonoid concentration, nanoparticles of different size are formed. By the combined use of spectroscopy and atomic force microscopy, the nanoparticle size was estimated (40–50 nm). Uniform and highly dispersed gold nanoparticles were obtained at Au: rutin ratios of 1: 1, 2: 1, and 4: 1 and Au: quercetin ratios of 2: 1 and 4: 1. The nanoparticle yield remains almost constant as the Au: rutin ratio varies over a broad range from 1: 1 to 12: 1. It was suggested that complete reduction of AuIII to Au0 with a large excess of Au is accompanied by extensive oxidation of bioflavonoid involving an intermediate oxidant formed in the system due to the high oxidative capacity of AuIII. For elucidating the catalytic role of bioflavonoids in the formation of gold nanoparticles, quantum chemical modeling of the process was performed.

The standard redox potentials of the sequential oxidation of lysodektose to the corresponding nitrone were estimated by quantum chemistry methods. It follows from these estimates that the experimentally observed accumulation of the intermediate nitroxyl radical in substantial amounts during the oxidation of lysodektose can be explained by high medium reorganization energy in the oxidation of the nitrosyl radical with simultaneous proton abstraction. The EPR spectra of the radical lysodektose form were modeled. Arguments in favor of the suggestion that one nonequivalent proton appeared in the formation of an intramolecular H-bond were presented. Quantum-chemical calculations of the hyperfine structure constants were in satisfactory agreement with experiment.

The Au(III)-luteolin system was studied by means of cyclic voltammetry, spectrometry, and quantum chemical simulation. The mutual effect of luteolin to Au(III) reduction and Au(III) to luteolin oxidation was studied by means of cyclic voltammetry on Pt and carbon glass electrodes in 0.05 M tris-buffer solution (pH 8) containing ethyl alcohol. The absorption spectra of luteolin were recorded with and without Au(III) in 0.05 M tris-buffer solution (pH 8) containing ethyl alcohol. The quantum chemical simulation of Au(III)-tris, Au(III)-luteolin, and Au(III)-tris-luteolin systems was carried out. On the basis of the collected data, formation of Au(III)-tris-luteolin complex in 0.05 M tris-buffer solution (pH 8) in the presence of ethanol was suggested.

Reduction of chloroauric acid on platinum and gold electrodes in a 0.1 M tris-HCl buffer of pH 8 containing riboflavin, rutin, 1,1-dipyridyl, or 1-naphthol is studied by cyclic voltammetry and in situ ESR methods. On the basis of the obtained data it is assumed that in the buffer there occurs the reduction of Au(III) to Au(I). In the presence of 1,1-dipyridyl, there occurs the reduction of complex [Au(III)-1,1-dipyridyl]. The reduction of Au(III) in the presence of 1-naphthol is realized in the composition of complex [Au(III)-tris-1-naphthol]. The hampering of the electrode process of the Au(III) reduction in the presence of 1-naphthol is caused by the adsorption of the [tris-1-naphthol] associates at the electrode surface. The presence of Au(III) does not exert any influence on the process of electroreduction of riboflavin. The obtained results make it possible to presume that the resistance of gold-accumulating cells Micrococcus luteus toward toxic compounds that are inhibitors of the respiratory chain, such as 1,1-dipyridyl and 1-naphthol, is caused by their binding in gold-containing complexes in the composition of Au-protein.

With the use of labeled methane-14C and by chromatographic analysis it was shown that gold-containing protein ("Au-protein"), isolated from goldphilic Micrococcus luteus bacteria, catalyzes the oxidation of methane to methanol in the system also containing NADH, air, K(3)Fe(CN)(6) and Tris-HCl buffer. Presumably Au-protein helps bacteria to survive when usual sources of carbon and energy are scarce.