A Kinetic Study of the Electron-Transfer Reactions of Nickel(III,II) Tripeptide Complexes with Cyano Complexes of Molybdenum, Tungsten, and Iron.

Experimentally measured rate constants, , for the reductions of [Ni(III)tripeptides(HO)] with Fe(CN), Mo(CN), and W(CN) are 10 to 10 times faster than the calculated rate constants with the Marcus theory for outer-sphere electron-transfer processes, , even when work terms are considered. This gives rise to a kinetic advantage of / = 10-10, which is consistent with an inner-sphere electron-transfer mechanism via a bridged intermediate. In addition, values are nearly independent of the electrochemical driving force of the reactions.

Chlorine dioxide oxidation of dihydronicotinamide adenine dinucleotide (NADH).

The oxidation of dihydronicotinamide adenine dinucleotide (NADH) by chlorine dioxide in phosphate buffered solutions (pH 6-8) is very rapid with a second-order rate constant of 3.9 x 10(6) M(-1) s(-1) at 24.6 degrees C.

Kinetics and mechanisms of chlorine dioxide oxidation of tryptophan.

The reactions of aqueous ClO2 (*) and tryptophan (Trp) are investigated by stopped-flow kinetics, and the products are identified by high-performance liquid chromatography (HPLC) coupled with electrospray ionization mass spectrometry and by ion chromatography. The rates of ClO2 (*) loss increase from pH 3 to 5, are essentially constant from pH 5 to 7, and increase from pH 7 to 10. The reactions are first-order in Trp with variable order in ClO2 (*).

Chlorine dioxide oxidation of guanosine 5'-monophosphate.

The reactions between aqueous ClO2 and guanosine 5'-monophosphate (5'-GMP) are investigated from pH 5.96 to 8.30.

Kinetics and mechanisms of chlorine dioxide and chlorite oxidations of cysteine and glutathione.

Chlorine dioxide oxidation of cysteine (CSH) is investigated under pseudo-first-order conditions (with excess CSH) in buffered aqueous solutions, p[H+] 2.7-9.5 at 25.

Chlorine dioxide oxidations of tyrosine, N-acetyltyrosine, and dopa.

The reactions of aqueous ClO2 with tyrosine, N-acetyltyrosine, and dopa (3,4-dihydroxyphenylalanine) are investigated from pH 4 to 7. The reaction rates increase greatly with pH to give a series of oxidized products. Tyrosine and N-acetyltyrosine have similar reactivities with second-order rate constants (25.

Chlorine dioxide reduction by aqueous iron(II) through outer-sphere and inner-sphere electron-transfer pathways.

The reduction of ClO(2) to ClO(2)(-) by aqueous iron(II) in 0.5 M HClO(4) proceeds by both outer-sphere (86%) and inner-sphere (14%) electron-transfer pathways. The second-order rate constant for the outer-sphere reaction is 1.

Kinetics and mechanisms of bromine chloride reactions with bromite and chlorite ions.

Chloride ion catalyzes the reactions of HOBr with bromite and chlorite ions in phosphate buffer (p[H(+)] 5 to 7). Bromine chloride is generated in situ in small equilibrium concentrations by the addition of excess Cl(-) to HOBr. In the BrCl/ClO(2)(-) reaction, where ClO(2)(-) is in excess, a first-order rate of formation of ClO(2) is observed that depends on the HOBr concentration.

Nickel(III) oxidation of its glycylglycylhistamine complex.

The doubly-deprotonated Ni(III) complex of Gly(2)Ha (where Ha is histamine) undergoes base-assisted oxidative self-decomposition of the peptide. At View Article and Find Full Text PDF

Decomposition kinetics of Ni(III)-peptide complexes with histidine and histamine as the third residue.

The decomposition kinetics of the Ni(III) complexes of Gly(2)HisGly and Gly(2)Ha are studied from p[H(+)] 3.5 to 10, where His is l-histidine and Ha is histamine. In these redox reactions, at least two Ni(III) complexes are reduced to Ni(II) while oxidizing a single peptide ligand.

Oxidative self-decomposition of the nickel(III) complex of glycylglycyl-L-histidylglycine.

Self-decomposition of the nickel(III) doubly deprotonated peptide complex of Gly2HisGly occurs by base-assisted oxidation of the peptide. At < or =p[H+] 7.0, the major pathway is a four-electron oxidation (via 4 Ni(III) complexes) at the alpha carbon of the N-terminal glycyl residue.

Nucleophile assistance of electron-transfer reactions between nitrogen dioxide and chlorine dioxide concurrent with the nitrogen dioxide disproportionation.

The reaction of chlorine dioxide with excess NO(2)(-) to form ClO(2)(-) and NO(3)(-) in the presence of a large concentration of ClO(2)(-) is followed via stopped-flow spectroscopy. Concentrations are set to establish a preequilibrium among ClO(2), NO(2)(-), ClO(2)(-), and an intermediate, NO(2). Studies are conducted at pH 12.

Kinetics and mechanisms of the reactions of hypochlorous acid, chlorine, and chlorine monoxide with bromite ion.

The reaction between BrO2(-) and excess HOCl (p[H+] 6-7, 25.0 degrees C) proceeds through several pathways. The primary path is a multistep oxidation of HOCl by BrO(2)(-) to form ClO(3)(-) and HOBr (85% of the initial 0.

Cu(II)Gly2HisGly oxidation by H2O2/ascorbic acid to the CuIII complex and its subsequent decay to alkene peptides.

Protonation and stability constants for Gly2HisGly and its Cu(II) complexes (beta(mhl)), determined at 25.0 degrees C and mu = 0.10 M (NaClO(4)), have values of log beta(011) = 7.

Kinetics and mechanisms of S(IV) reductions of bromite and chlorite ions.

The reaction of bromite with aqueous S(IV) is first order in both reactants and is general-acid catalyzed. The reaction half-lives vary from 5 ms (p[H+] 5.9) to 210 s (p[H+] 13.

New pathways for chlorine dioxide decomposition in basic solution.

The product distribution from the decay of chlorine dioxide in basic solution changes as the ClO(2) concentration decreases. While disproportionation reactions that give equal amounts of ClO(2)(-) and ClO(3)(-) dominate the stoichiometry at millimolar or higher levels of ClO(2), the ratio of ClO(2)(-) to ClO(3)(-) formed increases significantly at micromolar ClO(2) levels. Kinetic evidence shows three concurrent pathways that all exhibit a first-order dependence in [OH(-)] but have variable order in [ClO(2)].

Hypohalite ion catalysis of the disproportionation of chlorine dioxide.

The disproportionation of chlorine dioxide in basic solution to give ClO2- and ClO3- is catalyzed by OBr- and OCl-. The reactions have a first-order dependence in both [ClO2] and [OX-] (X = Br, Cl) when the ClO2- concentrations are low. However, the reactions become second-order in [ClO2] with the addition of excess ClO2-, and the observed rates become inversely proportional to [ClO2-].

Kinetics and mechanisms of the ozone/bromite and ozone/chlorite reactions.

Ozone reactions with XO(2)(-) (X = Cl or Br) are studied by stopped-flow spectroscopy under pseudo-first-order conditions with excess XO(2)(-). The O(3)/XO(2)(-) reactions are first-order in [O(3)] and [XO(2)(-)], with rate constants k(1)(Cl) = 8.2(4) x 10(6) M(-1) s(-1) and k(1)(Br) = 8.

Role of halogen(I) cation-transfer mechanisms in water chlorination in the presence of bromide ion.

Bromide ion is rapidly converted to HOBr via BrCl by reaction with HOCl. The subsequent slow reactions of (HOCl, OCl-)/(HOBr, OBr-) mixtures are monitored directly by multiwavelength UV-vis absorbance methods and simultaneously by ion chromatographic measurement of ClO2-, ClO3-, and BrO3- (p[H+] 5.6-7.

Kinetics and mechanisms of aqueous chlorine reactions with chlorite ion in the presence of chloride ion and acetic acid/acetate buffer.

The kinetics and mechanism of the reaction between Cl(2) and ClO(2)(-) are studied in acetate buffer by stopped-flow spectrometric observation of ClO(2) formation. The reaction is first-order in [Cl(2)] and [ClO(2)(-)], with a rate constant of k(1) = (5.7 +/- 0.

Bromite ion catalysis of the disproportionation of chlorine dioxide with nucleophile assistance of electron-transfer reactions between ClO(2) and BrO(2) in basic solution.

The rate of ClO(2) conversion to ClO(2)(-) and ClO(3)(-) is accelerated by BrO(2)(-), repressed by ClO(2)(-), and greatly assisted by many nucleophiles (Br(-) > PO(4)(3-) > HPO(4)(2-) > CO(3)(2-) > Cl(-) approximately OH(-) > CH(3)COO(-) approximately SO(4)(2-) approximately C(5)H(5)N >> H(2)O). The kinetics (at p[H(+)] = 9.3-12.

Mechanism of Chlorine Dioxide and Chlorate Ion Formation from the Reaction of Hypobromous Acid and Chlorite Ion.

The rate of oxidation of ClO(2)(-) by HOBr is first-order in each reactant and is general-acid-assisted in the presence of phosphate or carbonate buffers. The products are ClO(2) and ClO(3)(-), where the relative yield depends on the concentration ratio of ClO(2)(-)/OH(-). The kinetic dependence indicates the presence of a steady-state intermediate, HOBrOClO(-) (or HOBrClO(2)(-)), that undergoes general-acid-assisted reactions to generate a metastable intermediate, BrOClO (or BrClO(2)).

Kinetics of Hypobromous Acid Disproportionation.

The kinetics of aqueous hypobromous acid disproportionation are measured at 25.0 degrees C from p[H(+)] 0.2 to 10.

Characterization of Copper(III)-Tetrapeptide Complexes with Histidine as the Third Residue.

Copper(III) complexes of Gly(2)HisGly and Aib(2)HisGly are characterized, where Gly is glycine, His is L-histidine, and Aib is alpha-aminoisobutyric acid. Their respective reduction potentials (V vs NHE) are 0.978 and 0.

Disproportionation Kinetics of Hypoiodous Acid As Catalyzed and Suppressed by Acetic Acid-Acetate Buffer.

The kinetics of the disproportionation of hypoiodous acid to give iodine and iodate ion (5HOI right harpoon over left harpoon 2I(2) + IO(3)(-) + H(+) + 2H(2)O) are investigated in aqueous acetic acid-sodium acetate buffer. The rate of iodine formation is followed photometrically at -log [H(+)] = 3.50, 4.