Sergei V. Makarov

Silver ion reduction with peat fulvic acids

Formation of silver nanoparticles in chemical reduction of AgNO3 with peat fulvic acids in an aqueous alkali solution was studied spectrophotometrically. The size of the resulting nanoparticles and their stability were examined in relation to the reaction temperature and time, and concentrations of fulvic acids and silver nitrate.

Cobalamin reduction by dithionite. Evidence for the formation of a six-coordinate cobalamin(II) complex.

Evidence for the formation of a unique, six-coordinate cobalamin(II) complex with the anion-radical SO(2)(-) during the reduction of aquacobalamin(III) by sodium dithionite, was obtained from spectrophotometric and EPR measurements. The pK(a) value of the weakly coordinated dimethylbenzimidazole group was found to be 4.8 ± 0.1 at 25 °C.

Comparative study of reaction of cobalamin and cobinamide with thiocyanate

The interaction of Co(III) and Co(II) cobalamin (Cbl) and cobinamide (Cbi) with thiocyanate was examined with UV-vis and EPR spectra. S/N-linkage isomerism was explored on Co(III) and Co(II) Cbl and Cbi models using density functional theory (DFT; BP86, B3LYP). Performed calculations suggest the prevalence of isothiocyanato isomers over thiocyanato complexes on both Co(III) and Co(II) centers. The formation of Cbl(II) complex with thiocyanate was observed at high ligand concentrations which was proposed to be hexacoordinated. DFT data maintain the possibility of hexacoordinated Co(II) complexes with thiocyanate in which one of extra-ligands is weakly coordinated. It is found that high thiocyanate concentrations could retard cyanide binding to cobalamin but not to cobinamide.

Recent Developments in the Chemistry of Thiourea Oxides

Thiourea dioxide is one of the best known, important, and stable products of thiourea oxidation. This compound has long been considered as an effective reducing agent for many years. Traditional areas of its application include the textile and paper industries. In recent years, however, thiourea dioxides and trioxides have been widely used in new fields including organocatalytic, polymerization, and phase-transfer reactions; reduction of graphene and graphite oxides; bitumen modifications; synthesis of guanidines and their derivatives; and studying nonlinear dynamical phenomena in chemical kinetics. The review gives a detailed survey of the latest developments and main trends in the chemistry and application of thiourea mon-, di-, and trioxides.

STRUCTURE AND STABILITY OF AMINOIMINOMETHANESULFONIC ACID

Abstract The crystal structure of aminoiminomethanesulfonic acid (AIMSOA), (NH 2 ) 2 CSO 3 , was determined by X-ray crystallography. The molecular geometry about the central C atom of this zwitterionic species was found to be strictly planar. The tetrahedral S atom was characterized by three nearly equivalent S–O bonds. The unusually high value for the calculated density of 1.948 g cm −3 indicated extremely efficient packing of the (NH 2 ) 2 CSO 3 molecules in the crystal lattice. Correlation was made between stability of (NH 2 ) 2 CSO 3 and aminoiminomethanesulfinic acid (AIMSA) (NH 2 ) 2 CSO 2 in aqueous solution. A number of unexpected differences were observed in their reactivities, stabilities and decomposition products.

Redox non-innocence of a nitrido bridge in a methane-activating dimer of iron phthalocyanine

A nitrido-bridged iron phthalocyanine has recently been shown to catalyze hydrocarbon activation, displaying in this respect distinctly different reactivity than the monomeric phthalocyanine or the oxo-bridged dimer. Here, DFT calculations are shown on models of this catalyst, indicating a distinct difference in electronic structures between the μ-oxo and μ-nitrido-bridged dimers, with the nitride acting as a remarkable charge reservoir and acquiring S = 1 N-character while the oxo bridge remains redox-inert; this difference in charge localization appears to be mirrored by a tendency towards higher symmetry in the Fe–N/O bonds with the nitrido bridge compared to the oxo one, and by a tendency of the nitride to favour lower-spin states more efficiently than the oxide.

Cobalt 4-octasulfophenyltetrapyrazinoporphyrazine as a catalyst for the oxidation of organic substrates with atmospheric oxygen

Cobalt 4-octasulfophenyltetrapyrazinoporphyrazine is an efficient catalyst for the oxidation of diethylamine and cysteine with atmospheric oxygen. This complex activates the substrate through its one-electron oxidation, not an oxygen molecule. The role of oxygen is the oxidation of the intermediate anionic complex (catalyst regeneration step).

Sodium dithionite and its relatives: past and present

In this paper, the implications of sodium dithionite and of some of its related compounds for the development of chemistry in the twentieth century, as well as their applications in newer fields of chemistry, are described.

Kinetics and mechanism of oxidation of super-reduced cobalamin and cobinamide species by thiosulfate, sulfite and dithionite

We studied the kinetics of reactions of cob(I)alamin and cob(I)inamide with thiosulfate, sulfite, and dithionite by UV-Visible (UV-Vis) and stopped-flow spectroscopy. We found that the two Co(I) species were oxidized by these sulfur-containing compounds to Co(II) forms: oxidation by excess thiosulfate leads to penta-coordinate complexes and oxidation by excess sulfite or dithionite leads to hexa-coordinate Co(II)-SO2(-) complexes. The net scheme involves transfer of three electrons in the case of oxidation by thiosulfate and one electron for oxidation by sulfite and dithionite. On the basis of kinetic data, the nature of the reactive oxidants was suggested, i.e., HS2O3(-) (for oxidation by thiosulfate), S2O5(2-), HSO3(-), and aquated SO2 (for oxidation by sulfite), and S2O4(2-) and SO2(-) (for oxidation by dithionite). No difference was observed in kinetics with cob(i)alamin or cob(i)inamide as reductants.

Acid-base properties and stability of sulfoxylic acid in aqueous solutions

A comparative study of decomposition of sulfoxylic acid S(OH) 2 and sulfoxylate anion and their reactions with formaldehyde in aqueous solutions with different acidity was carried out. Using the obtained results, the pK1 value of S(OH) 2 was determined for the first time.