The catalytic effect of copper(II) ions toward the oxidation of L-asparagine (Asn) by an anticancer platinum(IV) complex in the form of hexachloroplatinate(IV) (HCP) has been investigated in aqueous acid medium at the constant ionic strength and temperature. The progress of both uncatalyzed and copper(II)-catalyzed oxidation reactions has been monitored spectrophotometrically. The stoichiometry in both cases is [Asn]/[HCP] = 1:1. The kinetics of both redox reactions is first order with respect to [oxidant] and less than the unit order in [acid]. The order with respect to [Asn]T decreases from unity in the uncatalyzed path to less than unity in the catalyzed one. The catalyzed path is first order in [CuII]T. Increasing ionic strength and dielectric constant decreases the oxidation rates. The final oxidation products of L-asparagine are identified as the corresponding aldehyde (α-formyl acetamide), ammonium ion, and carbon dioxide. Tentative mechanisms of both reactions have been suggested.

The kinetics of oxidation of L-histidine (His) by platinum(IV) in the absence and presence of copper(II) catalyst was studied using spectrophotometry in alkaline medium at a constant ionic strength of 0.1 mol dm-3 and at 25 C. In both cases, the reactions exhibit a 1:1 stoichiometry ([His]:[PtIV]). The rate of the uncatalyzed reaction is dependent on the first power of each of the concentrations of oxidant, substrate and alkali. The catalyzed path shows a first-order dependence on both [PtIV] and [CuII], but the order with respect to both [His] and [OH-] is less than unity. The rate constants increase with increasing ionic strength and dielectric constant of the medium. The catalyzed reaction has been shown to proceed via formation of a copper(II)_ histidine intermediate complex, which reacts with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step. Platinum(IV) is reduced to platinum(II) by the substrate in a one-step two-electron transfer process. This is followed by other fast steps, giving rise to the oxidation products which were identified as 2-imidazole acetaldehyde, ammonia and carbon dioxide. A tentative reaction mechanism is suggested, and the associated rate laws are deduced. The activation parameters with respect to the slow step of the mechanism are reported and discussed.

: The reaction kinetics for the oxidation of L-histidine by permanganate ions have been investigated spectrophotometrically in sulfuric acid medium at constant ionic strength and temperature. The order with respect to permanganate ions was found to be unity and second in acid concentration, whereas a fractional order is observed with respect to histidine. The reaction was observed to proceed through formation of a 1:1 intermediate complex between oxidant and substrate. The effect of the acid concentration suggests that the reaction is acid catalyzed. Increasing the ionic strength has no significant effect on the rate. The influence of temperature on the rate of reaction was studied. The presence of metal ion catalysts was found to accelerate the oxidation rate, and the order of effectiveness of the ions was Cu2+ > Ni2+ > Zn2+. The final oxidation products were identified as aldehyde (2-imidazole acetaldehyde), ammonium ion, manganese(II), and carbon dioxide. Based on the kinetic results, a plausible reaction mechanism is proposed. The activation parameters were determined and discussed with respect to a slow reaction step. C 2014 Wiley Periodicals, Inc. Int J Chem Kinet 46: 370–381, 2014

The kinetics and mechanism of oxidation of silver (I) by permanganate ion in aqueous perchlorate solutions at a constant ionic strength of 1.0 mol dm-3 have been studied spectrophotometrically. The reaction time curves of the pseudo first-order plots were found to be of sigmoidal shape throughout the entire course of reaction. The initial rates were found to be relatively fast in the early stages, followed by a more slow reaction over longer time periods. The experimental results indicated a first-order dependence in [MnO4 - ] and fractional first-order kinetics with respect to [Ag+ ] for both stages. The results showed that the oxidation reaction was acid-catalyzed in which the reaction rates were increased with increasing the [H+ ]. Kinetic and spectrophotometric evidences for formation of 1:1 binuclear intermediate complex have been revealed in both two -stages. The activation parameters have been evaluated and a tentative reaction mechanism consistent with the kinetic results was discussed.

The synergistic effect between 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol (AMTT) and halides on the corrosion of mild steel in 0.5 M H2SO4 solution at 20 oC is investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Experimental results revealed the significant synergistic action of halides on the protective effect of AMTT. Both protection efficiency (%P) and degree of surface coverage (θ) increase with increasing AMTT concentration, and the effect of halides on the protection efficiency follow the trend: Cl- < Br- < Iindicating that the radii and electronegativity of the halide play a prominent role in the adsorption process. In contrary the synergism followed the reverse order due to the effective inhibition efficiency of iodide. The adsorption of the AMTT accords with the Temkin adsorption isotherm. Some thermodynamic and kinetic parameters have been calculated and discussed.

The synergistic inhibition effect between Cu2+ and 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol (AMTT) on the corrosion behavior of mild steel in 0.5 M H2SO4, both in the absence and presence of chloride ions, has been investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The ptentiodynamic polarization and EIS results consistently revealed that Cu2+ and AMTT mixture had a synergistic inhibitive effect on the corrosion of mild steel in 0.5 M H2SO4 as a result of the cooperative adsorption of the two species on mild steel. AMTT alone and in combination with Cu2+ and/or chloride were found to obey Temkin adsorption isotherm. Chemical adsorption is proposed based on obtained values of G o ads.

The effect of Nthiazolyl2cyanoacetamide derivatives on the corrosion of aluminum in 0.01N sodium hydroxide has been studied using weightloss and glvanostatic polarization techniques.The inhibition efficiency was found to increase with increasing the concentration of inhibitor and with decreasing tempera ture. The inhibition process was explained in terms of its adsorption on the aluminum surface The adsorption is obeyed Frumkin isotherm. The addition of Ba2+, Sr2+, Ca2+ and Mg2+ ions to Nthiazolyl2cyanoaceta mide derivatives enhanced the inhibition efficiency due to synergistic effect. Polarization data suggested that the additives used as mixed type inhibitors. Some activated thermodynamic parameters were calculated and explained

Kinetic studies on the oxidation of two substituted azinyl formamidines (Azn-Fs), namely N,N-dimethylN’-(pyrimidin-2-yl) formamidine (Pym-F) and N,N-dimethyl-N’-(pyridin-2-yl) formamidine (Py-F), by alkaline permanganate have been performed by spectrophotometry. The spectroscopic and kinetic evidence reveals the formation of 1:1 intermediate complexes between the oxidant and substrates. The influence of pH on the oxidation rates indicated that the reactions are base-catalyzed. The reactions show identical kinetics, being first order each in [MnO4 -]0 and [Azn-F]0, but with a fractional first-order dependence on [OH-]. The effect of temperature on the reaction rate has been studied. Increasing ionic strength has no significant effect on the rate. The final oxidation products of Pym-F and Py-F were identified as 2-aminopyrimidine and 2-aminopyridine, respectively, in addition to dimethyl amine and carbon dioxide. Under comparable experimental conditions, the oxidation rate of Py-F is higher than that of Pym-F. A reaction mechanism adequately describing the observed kinetic behavior is proposed, and the reaction constants involved in the different steps of the mechanism have been evaluated. The activation parameters with respect to the rate-limiting step of the reactions, along with thermodynamic quantities, are presented and discussed.

Kinetic investigations on the oxidation of L-asparagine (Asn) by alkaline permanganate have been carried out spectrophotometrically at a constant ionic strength and temperature. The reaction is first order with respect to [MnO4 -] and less than unit order with respect to both [Asn] and [alkali]. The influence of pH indicated that the oxidation is base catalyzed. The reaction rate was found to increase with increasing ionic strength and temperature. The addition of alkali metal ion catalysts accelerates the oxidation rate. The proposed reaction mechanism involves the formation of a 1:1 intermediate complex between L-asparagine and an alkali-permanganate species in a pre-equilibrium step, which was confirmed by both spectral and kinetic evidence. The complex decomposes slowly in a rate determining step, resulting in the formation of a free radical. The latter reacts again with another alkali-permanganate species in a subsequent fast step to yield the final reaction products which were identified as aldehyde (a-formyl acetamide), ammonia, manganate(VI) and carbon dioxide. The appropriate rate laws are deduced. The reaction constants involved in the mechanism were evaluated. The activation and thermodynamic parameters were determined and discussed.

The behavior of some biopolymeric metal-alginate hydrogel spheres of ionotropic nature in aqueous solutions has been investigated. Cross-linked ionotropic biopolymeric hydrogels such as MnII , CoII , NiII , CaII, SrII and SeIV-alginate showed an appreciable tendency for swelling in water, whereas that of CuII-, SnII-, BaII, PbII, AlIII, CrIII and FeIII-alginates showed a remarkable tendency for shrinking. The swelling processes were accompanied by an increase in volume and transparency; while a decrease in the pore size with a simultaneous increase in hardness was followed the shrinking processes. Drying of these metal-alginate ionotropic hydrogel spheres indicated that the water content exceeds 90% of the gel weights. The kinetics of swelling and shrinking processes have been studied. The factors which affect that behavior were examined and discussed in terms of the mechanical stability and the changes in some rheological properties of these ionotropic hydrogel spheres.