Range Of Reduction Potentials Research Articles

Electronic reduction of haloaromatic compounds. A theoretical study

A series of haloaromatic molecules with a wide range of standard reduction potentials (E°) and bond-cleavage rate constants (k) has been studied using the MNDO semiempirical procedure. It has been found that the standard potential correlates better with the difference in energy between the radical anion and the neutral geometry when the geometry of the former is kept unchanged, in agreement with the Franck–Condon principle. A reaction co-ordinate study of the bond cleavage of the radical anion for the chloro derivatives shows the existence of two radical anions (π and σ) that differ in the orbital occupied by the unpaired electron. Whereas the π-radical anion is the most stable, the bond-breaking process takes place through the σ-structure. The study of the energies as well as of different molecular parameters related to the C–Cl bond cleavage allows us to explain qualitatively the experimental ordering of rate constants when different substituent groups are considered. However, the theoretical predictions do not account for the kinetic differences when only small structural changes are present. The significance of the solvent effect in these cases is pointed out.

The electrochemical characteristics of cathodic processes involving aromatic hydrocarbons and CO 2: Part I. General mechanistic considerations

The cathodic reactions involving CO 2 and nine aromatic hydrocarbons covering a large range of reduction potentials were studied in N, N-dimethylformamide solutions by cyclic voltammetry at a Hg electrode. It was shown that the experimental response of the system depends on whether the aromatic hydrocarbon reduction potential is lower, similar or higher than that of CO 2. In the last case, which includes naphthalene, phenanthrene and p-terphenyl, it was concluded that the reaction mechanism involves a coupling between CO 2 radical anions and the aromatic species. In the intermediate case, including chrysene and picene, the proximity of the peak potentials does not allow an unambiguous interpretation of the process. Finally, for the cases where the aromatic hydrocarbon reduces well before CO 2, as for anthracene, 9,10-diphenylanthracene, benzo(a)pyrene and perylene, it was concluded that the reactions can be represented better by an ECE/DISP mechanism starting with a coupling reaction involving an aromatic radical anion and CO 2.

Reduction and Release of Ferritin Iron By Plant Phenolics

The reductive release of ferritin iron by several naturally occurring o-diphenols was studied. The initial rate of iron release was quantified by spectrophotometric measurement of the Fe(ferrozine) 3 2+ complex, which absorbs maximally at 562 nm. The initial rate of iron release was dependent upon o-diphenol concentration, but not on the concentration of the chromophoric chelating agent, ferrozine Stoichiometric measurements resulted in a ratio of 2Fe(II) released per molecule of o-diphenol. The series of o-diphenols studied included, caffeic acid, chlorogenic acid, dihydrocaffeic acid, 3,4-dihydroxybenzoic acid, and several analogs. These reductants represent an oxidation reduction potential range of 0.38 volts. A direct correlation between reducing power of the o-diphenols and rate of ferntin iron release was observed. Superoxide dismutase, catalase, mannitol, or general radical traps had no effect on the rate of iron removal, however, EDTA and oxalate inhibited iron release. A mechanism for ferritin iron reduction and release by o-diphenols consistent with the experimental observations is discussed.

Determination of Codeine, Dionin and Thebaine by Differential Pulse Polarography

Abstract The method proposed for determining codeine, dionin and thebaine by differential pulse polarography is based on the reduction (in ammoniacal medium) of the nitroderivatives obtained by dissolving the substances in concentrated nitric acid. The values of the reduction potentials range between -0.45 and -0.69 V. Morphine and heroine do not interfere in the determination of the mentioned alkaloids.

ChemInform Abstract: HETEROPOLYTUNGSTATES AS CATALYSTS FOR THE PHOTOCHEMICAL REDUCTION OF OXYGEN AND WATER

AbstractEine Reihe von Polywolframatanionen [XW,204"]"′ (X: P, Si, Fe, Co oder H2; n: 3 ‐ 6) werden in Gegenwart von organischen Elektronendonatoren, wie Alkoholen, photoreduziert.

Charge transfer and oxy radicals in antimalarial action. Quinones, dapsone metabolites, metal complexes, imunium ions, and peroxides

A mechanism of action is proposed that encompasses almost all of the main categories of antimalarial agents: quinones and precursors, dapsone metabolites, metal complexes of thisemicarbazones and biguanides, imunium-type ions from acridines and quinolines, and peroxides. The toxic effect of the drugs is believed to result from the generation of reactive oxygen oxygen radicals that usually arise via charge transfer. Electrochemical studies (reduction potential and reversibility) were performed on a number of these agents. Reduction potentials range from −0.23 to −1.52 V. It is likely that the in vivo values are aprreciably more positive in certain cases.

Charge transfer and oxy radicals in antimalarial action. Quinones, dapsone metabolites, metal complexes, imunium ions, and peroxides

A mechanism of action is proposed that encompasses almost all of the main categories of antimalarial agents: quinones and precursors, dapsone metabolites, metal complexes of thisemicarbazones and biguanides, imunium-type ions from acridines and quinolines, and peroxides. The toxic effect of the drugs is believed to result from the generation of reactive oxygen oxygen radicals that usually arise via charge transfer. Electrochemical studies (reduction potential and reversibility) were performed on a number of these agents. Reduction potentials range from −0.23 to −1.52 V. It is likely that the in vivo values are aprreciably more positive in certain cases.

Heteropolytungstates as catalysts for the photochemical reduction of oxygen and water

A series of polytungstate anions [XW12O40]n–(X = P, Si, Fe, Co, or H2; n= 3,4,5,6, and 6 respectively), spanning a range of reduction potentials, have been studied as sensitizers for the photoreduction of water and O2. [SiW12O40]4– was the most efficient sensitizer for H2 evolution in the presence of colloidal platinum. Saturation kinetics were found with respect to the concentrations of Pt,[SiW12O40]4–, and CH3OH as predicted by a simple kinetic scheme. The maximum rate depended on competition between the natural decay of the excited polyanion and quenching by alcohol. Electron transfer from photoreduced polyanions to O2 was also investigated by flash photolysis. Rate constants depended on the reduction potential of the polyanion and increased by a factor of 3 700 on going from [PW12O40]3– to [FeW12O40]5–, in line with the Marcus equation for adiabatic electron-transfer reactions.

A STRUCTURAL APPROACH TO THE COPPER SITES OF THE BLUE ELECTRON TRANSFER PROTEINS

Abstract The copper-binding regions of plastocyanins and azurins are examined by the Chou-Fasman method. Similar structural features are found in the proposed copper-binding site for stellacyanin. These structural features are related to the copper-ligand bond lengths and to the reduction potentials of the blue copper proteins. The range of reduction potentials observed in these proteins is considered to be a function of the chelating peptide loop sizes and of the nature of the amino acid side chains in the loop region. A copper core of two histidines, a cysteine and a methionine is proposed for rusticyanin with a tighter chelate loop structure in the C-terminal region than is found in plastocyanin and azurin.