Sergei V. Makarov's research while affiliated with Ivanovo State University of Chemistry and Technology and other places
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Publications (130)
Besides its use in medicine, vitamin B12 (cobalamin) and its derivatives have found in numerous applications as catalysts. However, studies related to the activation of oxidants via cobalamin are scant. In this work, we showed how the addition of aquacobalamin (H2OCbl) accelerates the destruction of azo-dye Orange II by peroxymonosulfate (HSO5−) in...
Nutritional deficiency and genetic errors that impair the transport, absorption and utilization of vitamin B12 (B12) lead to hematological and neurological manifestations. The cblC disease (cobalamin complementation type C) is an autosomal recessive disorder caused by mutations and epi-mutations in the MMACHC gene and the most common inborn error o...
Nitrosylcobinamide (NOCbi) is a tight complex between Co(II)-form of cobinamide, a nucleotide-free analog of cobalamin (vitamin B12), and nitric oxide (NO). Here, we report that NOCbi exhibits high resistance toward aerobic oxidation in comparison with nitrosylcobalamin. NOCbi slowly degrades in the presence of hydrogen peroxide and undergoes a mor...
Here, we report results of spectrophotometric, spectrofluorimetric, and ultrafiltration studies on the reaction between cobinamides (viz. aquahydroxo-, nitro-, aquacyano- and dicyanocobinamides; Cbi) and bovine serum albumin (BSA), and reactivity of formed complexes toward cyanide. (H2O)(HO−)Cbi binds BSA at almost equimolar ratio predominantly via...
The influence of proteins – bovine serum albumin (BSA) and trypsin from porcine pan-creas – on the interaction between sodium selenite and sodium hydroxymethanesulfinate (HMS) and thiourea dioxide (TDO) in aqueous solutions has been studied. It is shown that in the presence of trypsin and especially BSA the quantity of small-sized particles of nano...
A study on the kinetics of the reaction between cyanocobalamin (vitamin B12, CNCbl) and the reduced form of flavin mononucleotide (FMNH2) in weakly acidic, neutral, and slightly alkaline media is performed. It is shown that FMNH2 can reduce CNCbl to cobalamin(II) (Cbl(II)). It is established that protonated, mono-deprotonated, and di-deprotonated f...
Aquacobalamin binds hydrogen peroxide reversibly to form a cobalt(III) hydroperoxo adduct with a 0.25 mM dissociation constant, as evidenced by UV-vis absorption spectroscopy and corroborated by NMR, Raman spectroscopy, stopped-flow UV-vis measurements, and density functional theory calculations.
Hydrogen sulfide (H2S) is a gasotransmitter and the smallest signaling thiol metabolite with important roles in human health. The turnover of H2S in humans is mainly governed by enzymes of sulfur amino acid metabolism and also by the microbiome. As is the case with other small signaling molecules, disease-promoting effects of H2S largely depend on...
In this work, we showed that aquacobalamin (H2OCbl) undergoes decomposition in the presence of glucose oxidase and glucose under aerobic conditions at pH 6.3. This process is contributed by two reactions performed by glucose oxidase, i.e. (i) H2OCbl transformation to cob(II)alamin in the course of the reaction with reduced form of glucose oxidase,...
Hypochlorous acid (HOCl) is a strong oxidant produced by myeloperoxidase. Previous work suggested that HOCl modifies the corrin ring of cobalamins to yield chlorinated species via mechanisms that are incompletely understood. Herein, we report a mechanistic study on the reaction between cyanocobalamin (CNCbl, vitamin B12) and HOCl. Under weakly acid...
The present study examined generation of hydroxyl radical (HO•) in aqueous aerobic solutions (pH 7.1) containing selenite (SeO3²⁻) and glutathione (GSH) using terephthalic acid (TA) scavenging HO• to give highly fluorescent 2-hydroxyterephthalic acid (TA-OH). The highest reaction rate and yield of TA-OH were observed in a micromolar concentration r...
Thiourea dioxide (TDO, aminoiminomethanesulfinic acid, formamidinesulfinic acid) was used for the chemical modification of chitosan. The interaction of TDO with chitosan in the presence of alkali results in the guanidinylated chitosan, the substitution degree is 0.25-0.27 and does not depend largely on molar ratio of thiourea dioxide to chitosan. T...
Here, we report the results of kinetic and mechanistic studies of the first step of reaction between thiols (viz., cysteine, N-acetylcysteine, mercaptoethanol, thioglycolic acid and 5-thio-2-nitrobenzoic acid (TNB)) and selenite producing thiol-S-Selenites (RS-SeO2−) in aqueous solutions of various acidity. In this set of aliphatic thiols, their re...
Comparative studies on the reactions of reduced cobalamin (Cbl(II)), the complexes of reduced cobalamin with the SO2⁻˙ radical anion (B12rs, SO2⁻Cbl(II)), and super reduced cobalamin (B12s, Cbl(I)) with hydrogen peroxide (H2O2) and tert-butyl hydroperoxide (tBuOOH) were carried out in aqueous solution under anaerobic conditions. Analyses of the rea...
Thiolatocobalamins are a class of cobalamins comprised of naturally occurring and synthetic ligands. Glutathionylcobalamin (GSCbl) occurs naturally in mammalian cells, and also as an intermediate in the glutathione-dependent dealkylation of methylcobalamin (MeCbl) to form cob(I)alamin by pure recombinant CblC from C. elegans. Glutathione-driven deg...
The influence of L-cysteine and N-acetyl-L-cysteine on the stability and reducing activity of thiourea dioxide (NH2)2CSO2 (TDO) in the reaction with azo dye Orange II has been studied. The addition of L-cysteine and N-acetyl-L-cysteine leads to the increase in reducing activity of TDO in weakly acidic, neutral and weakly alkaline solutions, but doe...
Selenocysteine (Sec) is a crucial component of mammalian thioredoxin reductase (TrxR) where it serves as a nucleophile for disulfide bond rupture in thioredoxin (Trx). Generation of the reduced state of Sec in TrxR requires consecutive two electron transfer steps, namely: (i) from NADPH to flavin adenine dinucleotide, (ii) from reduced flavin to th...
Reduction of cobalamin by non-dedicated cellular reductases has been reported in earlier work, however, the sources of reducing power and the mechanisms are unknown. This study reports results of kinetic and mechanistic investigation of the reaction between aquacobalamin, H2OCbl, and reduced β-nicotinamide adenine dinucleotide, NADH. This interacti...
A new method for producing oxidized starches using hydrogen peroxide and thiourea dioxide is proposed. It is shown that this method makes it possible to broadly control the number of functional groups arising in modified starch as well as the viscosity of the paste made from modified starch. This is achieved by changing the molar ratio of thiourea...
Reduction of dietary selenite (SeO3H⁻, SeO3H2) is an important process in vivo, which predominantly involves glutathione (GSH). Although the reaction between selenite and thiols has been studied extensively, its mechanism and the identification of products remain controversial. Herein, we present kinetic, spectroscopic and in silico data on the fir...
This works reports that tetrasulfonated cobalt(II) phthalocyanine (Co(II)TSPc) catalyzes reduction of selenite (SeO32−), the one of the most toxic form of selenium, to slightly toxic Se(0) by dithionite (S2O42−) in neutral aqueous solutions. The overall reaction mechanism involves rapid reduction of Co(II)TSPc to Co(I)TSPc by dithionite followed by...
![Scheme 5. Previously proposed catalytic cycle [100] for sulfite...](publication/334779197/figure/fig1/AS:786555052490753@1564540746052/Scheme-5-Previously-proposed-catalytic-cycle-100-for-sulfite-reductase-based-on_Q320.jpg)
Oxidation of sulfide to sulfate is known to consist of several steps. Key intermediates in this process are the so-called small oxoacids of sulfur (SOS)—sulfenic HSOH (hydrogen thioperoxide, oxadisulfane, or sulfur hydride hydroxide) and sulfoxylic S(OH)2 acids. Sulfur monoxide can be considered as a dehydrated form of sulfoxylic acid. Although all...
In this paper, the decomposition mechanism of Thiourea dioxide (TDO) aqueous solution in 25–95 °C temperature range were studied in detail by electrode potential method, time-of-flight mass spectrometry (TOF-MS), Raman spectroscopy and quantum chemistry calculations. Oxidation-Reduction Potential (ORP) were used to reveal the effect of temperature...
The reaction of cyanocobalamin (CNCbl) with potassium hydroxide was studied in isopropyl alcohol (iPrOH) and dimethyl sulfoxide (DMSO) under anaerobic conditions. The reaction occurs in a few steps. At the first step, the deprotonation of the CNCbl by KOH proceeds to form the cyanocobalamin carbanion (CNCbl-) and water (H2O). The rate of this step...
Time of flight-mass spectroscopy (TOF-MS), ultraviolet (UV) absorption and Raman spectroscopy, and quantum chemistry calculations were used to investigate the thiourea dioxide (TDO) structure in aqueous solution. TOF-MS with the direct injection sample method was used to get molecular weight information of TDO in solution. The two structural models...
The kinetics and mechanism of the reaction of diaquacobinamide (Cbi(III)) with isoniazid (iso-nicotinoyl hydrazide (INH)) are studied. It is determined that the composition of the products depends on the ratio between the concentrations of the reactants. Adding excess INH to cobinamide results in the rapid formation of a stable complex of Cbi(III)...
The reaction between glutathionylcobalamin (GSCbl), a complex of Co(III)-cobalamin with glutathione, and selenocysteine (Sec) was investigated using ultraviolet-visible (UV–vis) spectroscopy. The interaction results in the formation of cob(II)alamin and proceeds via two pathways: (i) a rapid formation of complex between GSCbl and Sec followed by th...
The reaction of cyanocobalamin (CNCbl) with sodium hydroxymethanesulfinate (HMS) was studied over a wide range of pH (4-11) under aerobic conditions. CNCbl is destroyed in the presence of HMS in aqueous solution to form uncolored substances. The accumulation of stable yellow corrinoids (SYCs) preceded these changes at pH ≥ 8. The major stable yello...
The reaction between a reduced form of cobalamin (cobalamin(II), Cbl(II)) and periodate in alkaline medium is studied. It is shown that there is no destruction of cobalamin at the ratio of [Cbl(II)] : [IO\(_{4}^{ - }\)] = 2 : 1. The reaction mechanism includes interactions between Cbl(II) and H4IO\(_{6}^{ - }\) and H3IO\(_{6}^{{2 - }}\) leading to...
This study reports results of kinetic and mechanistic studies on the reactions of aquacobalamin (H2OCbl⁺) with oxo-derivatives of cysteine, i.e. cysteinesulfinic and cysteic acids, hypotaurine and taurine. The reactions with cysteinesulfinic acid and hypotaurine result in formation of S-bound complexes, whereas cysteic acid and taurine are coordina...
The system thiourea dioxide–hydrogen peroxide is found to effectively hydroxylate coumarin in aqueous solutions. The hydroxyl radical reacting with coumarin is shown to result from decomposition of the complex thiourea dioxide–H2O2. The obtained data are compared to the results of investigation of the reactions occurring in the system thiourea diox...
This study reports that aquahydroxocobinamide ((H₂O)(HO¯)Cbi(III)), a nucleotide‐free analogue of cobalamin (vitamin B₁₂; Cbl), is capable of catalyzing reduction of two‐electron oxidized form of vitamin C, dehydroascorbic acid (DHA), to ascorbic acid by glutathione (GSH), whereas catalytic quantities of aquacobalamin do not accelerate the reaction...
Serum albumin binds to a variety of endogenous ligands and drugs. Human serum albumin (HSA) binds to heme via hydrophobic interactions and axial coordination of the iron center by protein residue Tyr161. Human serum albumin binds to another tetrapyrrole, cobalamin (Cbl), but the structural and functional properties of this complex are poorly unders...
The interaction of aqua- and thiocyanatocobalamin with sodium hydroxymethanesulfinate in neutral aqueous solution has been studied, and the kinetic as well as activation parameters of the reactions have been determined. The reduction of the aqua complex is faster in comparison with the thiocyanato one. In contrast to the earlier studied reaction of...
The effect of glycine and monoethanolamine on the stability and reductive activity of thiourea dioxide in the reaction with acid orange II dye was studied. It was found that, in contrast to glycine, introduction of additives of monoethanolamine into aqueous solution of thiourea dioxide substantially increases its reductive activity in alkaline solu...
The kinetics of the reaction between the two-electron reduced form of cobalamin (super-reduced cobalamin, cob(I)alamin, or Cbl(I)) and sodium selenite in an alkaline medium is studied spectrophotometrically. It is shown that the selenite rapidly oxidizes Cbl(I) to cob(II)alamin (Cbl(II)). It is established that the active form of the oxidant is the...
We studied the reaction between aquacobalamin (H2OCbl) and selenocysteine (Sec), a selenium-containing analogue of cysteine, using conventional ultraviolet-visible (UV-Vis) spectroscopy. This reaction leads to the formation of cob(II)alamin (Cbl(II)) without any detectable intermediate complexation of Cbl(III) with selenocysteine, whereas the inter...
Glutathionylcobalamin (GSCbl), a tight complex of glutathione (GSH) with cobalamin(III), is readily oxidized to aquacobalamin by hypochlorite. Corrin macrocycle remains unmodified in the presence of threefold excess of hypochlorite, whereas aqua- and cyanocobalamins are partially transformed to chlorinated species under the same conditions. The sug...
Kinetics of the reaction of aquacobalamin (H2OCbl) with isoniazid (isonicotinic acid hydrazide, INH) in weakly alkaline, neutral, and weakly acidic media was studied using UV–Vis spectroscopy. It is shown that the reversible formation of a complex more stable than those of cobalamin(III) with pyridine and hydrazine occurs during the reaction. A mec...
The kinetics of reactions of cobalamin (II) and cobinamide (II) with sulfur dioxide was studied by UV-visible (UV-vis) spectroscopy. Reaction results in oxidation of Co(II) center and involves two aquated SO2 moieties. The final product is suggested to be complex Co(III)-S2O 4(•-) . The absence of corrin ring modifications during the reactions was...
The reaction between tetramethylthiourea (TMTU) and hydrogen peroxide was studied by UV–VIS spectroscopy, ESI mass spectrometry, ¹H NMR, cyclic voltammetry and surface-enhanced Raman scattering. We found that the reaction includes two consecutive steps, that is, (i) an oxidation of TMTU to TMTU monoxide (TMTMO) and (ii) further oxidation of TMTU mo...
The kinetics of aquacobalamin reaction with aspartic and glutamic acids, and with their amides in water solutions, is studied via spectrophotometry. The kinetic and activation parameters of the process are determined. It is shown that the reaction product is cobalamin–amino acid complex. The data are compared to results on the reaction between aqua...
The suitability of thiourea and its oxides for the hydroxylation of terephthalic acid in aqueous solutions was explored. Allsulfur-containing compounds tested were found to favor the formation of hydroxyterephthalic acid. It was shown that thiourea and its di- and trioxides can act as both traps and promoters of hydroxyl radicals in aqueous solutio...
The thiourea dioxide (TDO)-iodine reaction was investigated spectrophotometrically monitoring the consumption of total amount of iodine at 468 nm, at T = 25.0 ± 0.1 °C, and at 0.5 M ionic strength in buffered slightly acidic medium. The nitrogen- and carbon-containing products were found to be ammonium ion and dissolved carbon dioxide, respectively...
Reactions of aquacobalamin (H2O-Cbl(III)) and its one-electron reduced form (cob(II)alamin, Cbl(II)) with chlorite (ClO2(-)) and chlorine dioxide (ClO 2(•) ) were studied by conventional and stopped-flow UV-Vis spectroscopies and matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). ClO2(-) does not react with H2O-Cbl(III), but...
A comprehensive review on redox reactions of Co(III), Co(II) and Co(I) forms of cobalamins (vitamin B12) and their derivatives (cobinamide, cobyrinates) is presented. An influence of coordination environment of cobalt ion on reactivity of corresponding species is discussed. Mechanisms of reduction of Co(III) and Co(II) species as well as oxidation...
Sodium Dithionite, Rongalite and Thiurea Oxides provides an in depth overview of historical and newly developed fields of application for important sulfur-containing reductants. It begins with an introduction into the structure and general properties of sodium dithionite, sodium hydroxymethanesulfinate (rongalite) and thiourea oxides. Following thi...
The iron phthalocyaninate μ-nitrido dimer radical cation, as well as the μ-nitrido dimer complexes of iron phthalocyaninate, was found to have high catalytic activity in the oxidation of organic compounds. It was concluded that this compound is of interest as a model of active intermediates—catalase and oxidase enzymes.
The kinetics of the reaction between one-electron-reduced cobalamin (cobalamin(II), Cb(II)) and the two-electron-oxidized form of vitamin C (dehydroascorbic acid, DHA) with amino acids in an acidic medium is studied by conventional UV–Vis spectroscopy. It is shown that the oxidation of Cbl(II) by dehydroascorbic acid proceeds only in the presence o...
Reported here is the synthesis of aluminum-, zinc- and titanium-containing metal-organic frameworks based on terephthalic acid and an investigation on the possibility of using these compounds as adsorbents for the purification of unrefined vegetable oils. It is found that aluminum-, zinc- and titanium-containing metal-organic frameworks improve the...
Problem of negative impact on the environment over time does not lose its relevance, indicating that the lack of effective existing instruments of environmental monitoring and control. There is obvious need for simple tools not instrumental integrated methods for monitoring and control of impact on the environment and environmental change as a resu...
A comprehensive review on redox reactions of Co(III), Co(II) and Co(I) forms of cobalamins (vitamin B12) and their derivatives (cobinamide, cobyrinates) is presented. An influence of coordination environment of cobalt ion on reactivity of corresponding species is discussed. Mechanisms of reduction of Co(III) and Co(II) species as well as oxidation...
The kinetics of the chlorine dioxide–thiourea dioxide reaction was investigated by monitoring absorbance–time profiles at λ = 360 nm. Under acidic conditions, the primary carbon-containing product is cyanamide, not urea as considered previously for many oxidation reactions of thiourea dioxide. Increase of the rate of the reaction by an increase of...
A convenient method has been proposed for the synthesis of aluminum- and zinc-containing terephthalic acid-based metal-organic frameworks. The method offers high productivity and high product yield. Materials produced by this method have been characterized by physicochemical techniques, and their sorption capacity has been assessed.
The interactions of H2S with FeIVO porphyrin radical-cation structures and of peroxide-like H2OS systems with ferric heme have been investigated by DFT. The data are relevant for the formation of sulfheme in globins and for the catalytic cycle of sulfite reductases. Heme FeOS systems (and their protonated versions) feature relatively accessible pot...
![Table 1 . Selected bond lengths [] of some thiourea dioxides and...](profile/Qingyu-Gao-2/publication/266206660/figure/tbl1/AS:667063794294813@1536051810985/Selected-bond-lengths-of-some-thiourea-dioxides-and-trioxides_Q320.jpg)
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 f...
Being potent reductants, sulfoxylic acid S(OH)2 and its salts (sulfoxylates) are intermediates in many reactions of important industrial chemicals, such as sodium hydroxymethanesulfinate (rongalite) and thiourea dioxide. Sulfoxylates contain the -O-S-O- moiety, which is isoelectronic to trioxides, -O-O-O-. However, the apparent structural and valen...
We conducted a detailed kinetic study of the reaction of the vitamin B12 analog diaquacobinamide [(H2O)2Cbi(III)] with hydrogen sulfide in water from pH 3 to 11. The reaction proceeds in three steps: (1) the formation of three different complexes between cobinamide and hydrogen sulfide, viz., (HO-)(HS-)Cbi(III), (H2O)(HS-)Cbi(III), and (HS-)2Cbi(II...
EPR, optical, electrochemical and stoped-flow methods were used to demonstrate that Fe(NO)2 fragments in paramagnetic mononuclear and diamagnetic binuclear forms of dinitrosyl iron complexes with glutathione are reversibly reduced by a two-electron mechanism to be further transformed from the initial state with d7 configuration into states with the...
Graphical abstract
Spin densities on the base-on Co(II)–O2 and Co(II)–NO+ models.
Sorption of dyes Acid Orange and Rhodamine G with alumino- and titanium-containing frameworks based on terephthalic acid was investigated. It has been established that these compounds are of a higher absorbing capacity in comparison with the best examples of the compounds used for these purposes.
Dinitrosyl iron complexes have earned attention due to their applications as nitric oxide donors as well as their interesting electronic structures. Typical Fe-NO electromerism issues are complicated in this case by the presence of a second nitrosyl ligand. Each of the formal oxidation states of iron in such complexes - from Fe(III) to Fe(0) - have...
A study of catalytic activity of μ-nitrido- and μ-oxo-dimeric iron tetrasulfophthalocyanines in the oxidation of Orange II by tert- butylhydroperoxide in aqueous solutions has been performed. It is shown that though in one catalytic cycle activity of μ-oxo-dimer is higher, stability of this complex in oxidative conditions is poor. μ-nitrido-dimer c...
Indirect experimental evidence of the existence of a sluggish tautomerism of thiourea dioxide in acidic aqueous solution was discovered while studying its oxidation by chlorine dioxide. Thiourea dioxide slowly rearranges into aminoiminomethanesulfinic acid, but the reactivity of these two species towards chlorine dioxide marginally differs. It was...
A detailed kinetic study of the reaction of aquacobalamin [H2OCbl(III)] with hydrogen sulfide in water at pH 1 to 10 was carried out using conventional spectrophotometric, stopped-flow, and high-pressure stopped-flow techniques. The reaction proceeds in three steps: formation of the complex between aquacobalamin and hydrogen sulfide, inner-sphere e...
A comparative study of reactivity of μ-nitrido- and μ-oxo-dimers of iron tetrasulfophthalocyanine has been performed in aqueous solutions of various acidity. The substantially higher stability of the nitrido-bridged structure under both strongly acidic and strongly alkaline environments was demonstrated.
The reactions of the complexes with sulfur-c...
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 oxidati...
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.
Cobalt corrin complexes (cobalamins) are of great interest for coordination chemistry, biochemistry and medicine. Serving as cofactors of some enzymes, they take part in many processes, which occur in human body, for example, in methionine synthesis from homocysteine. Cobalamins and their reduced forms interact with many biologically active substan...
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...
Sulfur monoxide, SO, is a relatively unstable molecule whose metal-coordinating properties have received little attention in bioinorganic chemistry. Reported here is a density functional theory (DFT) examination of the four possible oxidation states for a heme-SO/OS adduct previously proposed to be a part of the catalytic cycle of sulfite reductase...
Different ways for utilization of by-products from the production of sunflower, soybean, linseed, and rapeseed oil in Russia are reviewed. Different options of using sunflower press cakes as sorbents, in the production of feedstuffs for animals, in the construction industry, and energy industry are described. Examples of application of oil meal in...
![Fig. 5-Dependence of k obs.2 on [Sulf] for the accumulation of Cbl(I)...](profile/Radu-Silaghi-Dumitrescu/publication/281925844/figure/fig2/AS:668934885896202@1536497913335/Dependence-of-k-obs2-on-Sulf-for-the-accumulation-of-CblI-during-the-reaction_Q320.jpg)
The kinetics of individual stages of reductive interaction of hydroxocobalamin with sulfoxylate in aqueous solutions, (Co(III)→Co(II) and Co(II)→Co(I)), have been investigated spectrophotometrically. The rate-limiting step in both reactions is the formation of intermediate complexes of sulfoxylate with Cbl(III) and Cbl(II), respectively. It is show...
Copper porphyrinates are generally known to display a less diverse reactivity compared to their iron counterparts. Here, we examine a water-soluble copper porphyrinate for its ability to engage in reactions involving axial ligation to the copper or possible redox cycling. Although UV–vis spectra indicate an expected lack of reactivity, electron par...
Siroheme‐containing sulfite reductases (SiR) catalyze the six‐electron reduction of sulfite to sulfide via a mechanism involving sulfite binding at the heme iron. The exact sequence in which the required electrons and protons are delivered to the heme‐bound sulfite has received little attention to date. Here, a detailed account is given of these st...
The kinetics and mechanism of cyanocobalamin reduction by sodium hydroxymethanesulfinate and dithionite in alkaline media are studied. It is established that the character of the rate-determining step depends on the concentration of the reducing agents: when they are in excess, it is a step of elimination of cyanocobalamin, at lower concentrations...
Kinetics of cobinamide (Cbi) reduction by glucose and fructose was studied at alkaline solutions. It was shown that the reaction of cobinamide with monosaccharides leads to the formation of Co(I) complex in contrast to the reduction of aquacobalamin (H(2)OCbl) resulting in the formation of Cbl(II).
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.
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 m-...
The kinetics of reaction between monosaccharides and cobalt tetrasulfophthalocyanine was studied spectrophotometrically. The reaction is shown to proceed with measurable rates only in strongly alkaline solutions. A product of reaction is determined to be Co-I phthalocyanine (Co-I(TSPc)(5-)). The reducing ability of monosaccharides decreases in foll...
The nitro/nitrito linkage isomerism in metal-nitrite complexes has been shown to be at work in heme proteins and related inorganic catalytic systems such as phthalocyanines. Here, a systematic examination of the nitro/nitrito isomerism is undertaken with computational methods aiming to identify factors controlling it. The systems addressed include...
The electronic structures of formally Fe(I) centers in thiolate- and imidazole-ligated hemoproteins are examined with density functional theory. The S = 1/2 spin state of the imidazole-ligated model apparently features a net total of one unpaired electron on the porphyrin, suggestive of a macrocycle-centered reductive process; however, this spin de...
A comparative study of the spectral properties and association of cobalt tetrasulfophthalocyanine and octasulfophenyltetrapyrazinoporphyrazine
was performed. The data obtained were compared with the results of a kinetic study of the interaction of the complexes with
a biologically important compound, ascorbic acid.
Cobalt octasulfophenyltetrapyrazinoporphyrazine was shown to be an effective catalyst of nitrite reduction by thiourea dioxide.
The intermediate product of nitrite reduction was nitrogen(II) oxide, and the final product was ammonia. The kinetic and activation
parameters of catalytic process stages were determined.
Metal nitrite adducts can, under certain conditions, insert one of their oxygen atoms into hydrocarbons. This reaction is to some extent reminiscent of the process whereby high-valent ferryl (formally FeIV=O) species such as compound I in hemoproteins also insert an oxygen atom into hydrocarbons. Density functional theory (DFT) data are shown here,...
EPR spectroscopy is employed to demonstrate chemical production of formally Fe(i) and Fe(0) states of phthalocyanines in water at room temperature, and physiologically-relevant pH.