Estimation of dimethylsulphoxide with chloramine-T

A rapid and accurate method for the estimation of dimethyl-sulphoxide has been developed based on its oxidation to dimethyl-sulphone at room temperature by chloramine-T at pH 4-4.5. The effect of variables such as the pH, the mode of addition of reagents and the concentration of chloride ion on the extent and nature of oxidation has been studied and optimal conditons for analytical determination of dimethylsulphoxide derived.     

Low-temperature heterogeneous oxidation of sulfide ions on a higher Co oxide system in aqueous medium

Low-temperature heterogenous oxidation of sulfide ions on a higher Co oxide system in aqueous medium has been studied. The effects of pH, temperature and catalyst amount on the kinetic parameters as well as on the selectivity of the oxidation process were investigated. An oxidation mechanism has been proposed based on the results of kinetic investigations and on the data obtained by IR and XPS spectroscopic studies of Co oxide before and after sulfide ion oxidation.     

Electrochemical behavior of mesidine in aqueous solutions

The electrochemical oxidation of mesidine has been investigated in the pH range 0.7–11 at a platinum electrode with periodical renewal of the diffusion layer and at a stationary carbon paste electrode. A E_1/2/pH relation for the platinum electrode has been derived in the pH range 0–7. It has been indicated that the only oxidation products of mesidine are 2,6-dimethylbenzoquinone-4-(2′,4′,6′-trimethyl)-anil at pH <8 and 2,4,6,2′,4′,6′-hexamethylazoxybenzene at pH>8. Oxidation mechanisms consistent with the kinetic parameters and the oxidation products are discussed.     

The Effect of Crown Ethers on the Oxidation of Triethylamine by Ferricyanide Ion in Aqueous Solutions at Different pH Values

The effect of benzo-15-crown-5,15-crown-5 and 12-crown-4 on the oxidation of triethylamine by aqueous ferricyanide ion has been studied at pH 4, 7 and 11. The crown ethers retard the normal oxidation process at all pH values, the effect depending on the crown ether concentration. The three crown ethers show the same retardation effect at pH 4 and 7, while at pH 11 the retardation decreases in the order B15C5 > 12C4 > 15C5.     

Environmental Effect of Macrocyclic Molecules on the Oxidation of Triethylamine by Ferricyanide Ion in Aqueous Solution

The effect of 18-crown-6 and kryptofix (2,2,1) on the oxidation of triethylamine byaqueous ferricyanide ion has been studied at pH 4, 7, and 9.The macrocycle retarded the normal oxidation process at all pH values,the effect depending on the macrocyclic ligand concentration Kryptofix (2,2,1) had a greater effect than 18-crown-6 at all pHvalues in this study. For 18-crown-6, retardation decreases in the order pH 9 > 4 > 7 while forkryptofix it follows the order pH 9 > 7 > 4.     

Influence of luminol on the chemiluminescence intensity in Fenton’s reaction

The kinetics of Fe⁺² oxidation and buildup of luminol oxidation products during Fenton’s reaction at pH 2 have been calculated. The characteristics of the process in neutral (pH 6) and alkaline (pH 12) media have been evaluated. The calculation results have been compared with experimental data on the yield of chemiluminescence induced by Fenton’s reagent and luminol. It has been shown that trivalent iron ions suppress the luminol emission. The presence of iron or another transition metal in the sample can significantly reduce the chemiluminescence quantum yield after luminol introduction if.     

Electrochemical oxidation of 2-thiouracil at pyrolytic graphite electrode

2-Thiouracil has been studied in phosphate buffers of pH 1.95-11.08 using linear and cyclic sweep voltammetry, coulometry, controlled potential electrolysis and spectral studies. One well-defined oxidation peak I(a) in the pH range 1.95-11.08 was noticed. The number of electrons involved in peak I(a) was found to be four in a thin layer cell whereas under exhaustive electrolysis condition oxidation was found to involve six electrons. A reduction peak II(c) (2e, 2H(+)) is noticed in the reverse sweep. Spectral studies during oxidation were carried out at different pH. Kinetic studies indicated that the decay of the UV-absorbing intermediate is a first order reaction. The products of the electrooxidation have been characterized and a tentative EC mechanism has been suggested for the oxidation of 2-thiouracil.     

Study on catalytic oxidation of planar binuclear copper phthalocyanine on 2-mercaptoethanol

Mononuclear copper phthalocyanine (CuPc) and binuclear copper phthalocyanine (Cu2Pc2) were synthesized by the phenylanhydride-urea route, and their catalytic oxidation activity on 2-mercaptoethanol was studied. Based on the experimental results, a catalytic mechanism of Cu2Pc2 on 2-mercaptoethanol has been proposed. Furthermore, the effects of pH, Cu2Pc2 concentration, and temperature on the catalytic oxidation activity were evaluated. The results showed that CuPc has no catalytic activity, while Cu2Pc2 has high catalytic oxidation activity towards 2-mercaptoethanol with the optimal activity at pH 11. The reaction can further be enhanced by increasing Cu2Pc2 concentration and temperature, due to its endothermic characteristics.     

磷酰化与非磷酰化蛋氨酸水溶液的脉冲辐解研究

蛋氨酸能快速清除导致辐射损伤的·OH自由基，在放射生物学上是一类很重要的辐射保护剂，因此，引起了人们的广泛关注［l一到．生物大分子的磷酸化作用亦越来越受到重视，特别是近年来基因调控研究发现，许多蛋白质和生物酶只有被磷酸化氧化才具有生理活性，文献［4－6］报导蛋     

In Process Citation

The electrochemical oxidation of khelline and amikhelline (chromone derivatives) has been performed by cyclic voltammetry at carbon-paste and polymeric carbon electrodes. The mechanism of oxidation of the two compounds at various pH values has been deduced. The detection limit is 8 x 10(-7)M. A constant-current coulometrie procedure is also described, based on the oxidation of the two chromones with vanadium(V) and backtitration of the excess of oxidant with iron(II).     

磷酰化与非磷酰化蛋氨酸水溶液的脉冲辅解研究

•OH radical induced oxidation of methionine and N-phosphoryl methionine in aqueous solutions has been investigated using optical pulse radiolytical technique, the influence of N-phosphoryl group on the radiolytical processes of methionine has been explained by molecular structure and the rate constants of oxidation of N-phosphoryl methionine (NDM) by the •OH radicals at different pH values have been determined. This research result suggests that the phosphonate ester has a coordinating effect on the radioprotection of methionine to the biological systems.     

Oxidation chemistry of 2'-deoxyadenosine at pyrolytic graphite electrode

The electrochemical oxidation of 2'-deoxyadenosine has been investigated in phosphate containing supporting electrolytes in pH range 2-10 at a pyrolytic graphite electrode by cyclic sweep voltammetry, spectral studies, controlled potential electrolysis and related techniques. The oxidation of 2'-deoxyadenosine occurred in a single well-defined oxidation peak (I(a)), over the entire pH range. The electrooxidation occurred by the loss of 6.0+/-0.5 e(-) per mole over the entire pH range. The kinetics of the decay of the UV-absorbing intermediates has been studied and found to follow pseudo first order kinetics having rate constant (k) in the range (5.7-7.7)x10(-4) s(-1). The major products of electrooxidation were separated by HPLC and characterized by GC-MS/MS, (1)H NMR and a tentative mechanism for electrooxidation of 2'-deoxyadenosine has been suggested.     

Solid State Electrochemical Oxidation Mechanisms Of Morin in Aqueous Media

The mechanism of electrochemical oxidation of morin has been studied using cyclic, differential pulse and square‐wave voltammetry techniques in aqueous electrolyte with solid, insoluble morin hydrate mechanically transferred to a glassy carbon electrode surface, over a wide pH range. The oxidation mechanism proceeds in sequential steps, related with the hydroxyl groups in the three aromatic rings and the oxidation is pH dependent over part of the pH range the oxidation potentials are shifted to lower values with increasing pH. Oxidation of the 2′,4′dihydroxy moiety at the B ring of morin occurs first, at very low positive potentials, and is a one electron one proton reversible reaction. The hydroxyl groups oxidized at more positive potentials were shown to undergo an irreversible oxidation reaction.     

Effect of anions and pH on the adsorption and oxidation of methanol on a platinum electrode

The influence of various anions and pH on methanol oxidation as well as its products of chemisorption on platinum has been studied by voltammetric and radiometric methods. It was found that the rate of methanol oxidation from the bulk solution was lowest for Na₂CO₃ and highest for NaOH solutions. The influence of anions on the chemisorbed species of methanol on a platinum electrode has also been investigated.     

Further electrochemical investigations of the oxidation of 1-phenylpyrazolidin-3-ones at high pH

The oxidation mechanism at pH 14 for a number of 1-phenylpyrazolidin-3-ones substituted in the 4 position of the heterocyclic ring has been investigated with electrochemical techniques. A general oxidation mechanism, resulting in the formation of a radical species and short-lived pyrazolinone tautomers has been postulated.     

Electrochemical Oxidation of Quercetin

The mechanism of electrochemical oxidation of quercetin on a glassy carbon electrode has been studied using cyclic, differential pulse and square‐wave voltammetry at different pH. It proceeds in a cascade mechanism, related with the two catechol hydroxyl groups and the other three hydroxyl groups which all present electroactivity, and the oxidation is pH dependent. Quercetin also adsorbs strongly on the electrode surface; and the final oxidation product is not electroactive and blocks the electrode surface. The oxidation of the catechol 3′,4′‐dihydroxyl electron‐donating groups, occurs first, at very low positive potentials, and is a two electron two proton reversible reaction. The hydroxyl group oxidized next was shown to undergo an irreversible oxidation reaction, and this hydroxyl group can form a intermolecular hydrogen bond with the neighboring oxygen. The other two hydroxyl groups also have an electron donating effect and their oxidation is reversible.     

Effect of inclusion complex on nitrous acid reaction with flavonoids

The kinetic of the nitrous acid reactions with quercetin and catechin has been studied using spectrophotometric method in aqueous solution. The results show that these antioxidants participate in oxidation reactions with nitrous acid which is derived from protonation of nitrite ion in mild acidic conditions. Corresponding o-quinones as relatively stable products were detected by spectrophotometric techniques. pH dependence of the reactions has been examined and the rate constants of reactions were obtained by non-linear fitting of kinetic profiles. The effect of β-cyclodextrin on the oxidation pathway was another object of this study. It is shown that β-cyclodextrin has an inhibitory effect on the oxidation reaction. The rate constants of oxidation reactions for complexed forms and their stability constants were obtained based on changes in the reaction rates as a function of β-cyclodextrin concentration.     

Observations on the determination of osmium by inductively-coupled plasma atomic emission spectroscopy

Osmium tetroxide gives rise to very characteristic atomic emission properties. In acidic samples it gives much higher sensitivity than that given by the lower oxidation states (IV, III, II). However, in alkaline medium (pH 10.5) its atomic emission sharply decreases, and the sensitivity is the same as that for the other oxidation states. It has been shown that there is a direct relation between these characteristics of OsO(4) solutions and pH. With increasing pH the intensity of its atomic emission decreases, the electrode potential of its solutions drops sharply and the molecular absorption of radiation at 193 nm undergoes a hyperchromic and bathochromic shift. The volatility of OsO(4) has also been studied, and found to be minimum at around pH 9.5. This favours its determination at this pH.     

Kinetics of Pindolol Oxidation by Peroxodisulfate

The kinetics of oxidation of pindolol by peroxodisulfate (PDS) in sulfuric acid and 40%(v/v) methanol + water solvent has been investigated. The pH profile of the rate constant was also investigated. It has been found that the reaction proceeds only in the pH range 0 to 4. A mechanism was proposed for the oxidation reaction; the reaction starts by the attack of peroxodisulfate (PDS) to form an indoleninic species that can rearrange into an indoxyl species. Once the indoxyl intermediate is formed, it can follow different paths leading to different products, depending on the acidity and PDS concentration. At low acid concentration, oxipindolol is formed whereas at high acid concentration dioxipindolol forms instead. Dioxipindolol can dimerize to form the indigo form of pindolol. A polar mechanism was proposed for the oxidation reaction, and the thermodynamic parameters were determined.     

A Vinylanthracene and Vinylferrocene‐Containing Copolymer: A New Dual pH/Sulfide Sensor

A single electroactive copolymer containing both anthracene and ferrocene units has been synthesized to form a dual pH/sulfide sensor. Under cyclic voltammetric conditions the oxidation of the ferrocene moiety undergoes an electrocatalytic reaction with sulfide, producing a linear increase in the oxidative peak current over the range 0.2–2.0 mM. Furthermore, square wave voltammetry was utilized to determine the pH of the solution by measuring the variation in the anthracene oxidation potential with respect to the ferrocene oxidation wave.