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.

:The inhibitive effects of some antibacterial cephalosporin (cefotaxime, cefalexin, cefradine and cefazolin) on the corrosion of iron in 0.5 M H2SO4 solution was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Results showed that the inhibition efficiency increased with an increase in concentration of inhibitor. Potentiodynamic studies proved that the inhibitors act as mixed type .The inhibitors are adsorbed on the iron surface according to Langmuir isotherm equation. All impedance spectra in EIS tests exhibit one capacitive loop which indicates that the corrosion reaction is controlled by charge transfer process. Inhibition efficiencies obtained from Tafel polarization, charge transfer resistance (Rct) is consistent.

The change in rheological and mechanical properties for some ionotropic cross-linked metal-alginate hydrogel complexes in particularly copper-alginate membranes in the presence of some organic solvents (benzene, toluene, xylene, carbon tetrachloride, acetone, chloroform, dichloroethane, isobutyl alcohol and ethyl alcohol) or buffer solutions (acetates, borates and universal buffers) have been investigated. The experimental results showed a remarkable tendency of the studied hydrogels for shrinking in polar solvents, whereas no influence was observed for the hydrogels in non-polar solvents. On the other hand, the gels were found to swell or shrink in the buffer solutions depending on the pH of the buffer used. The swelling extent for hydrogel spheres was found to decrease in the order Cu > Ba ≈ Ca > Zn > Pb-alginates in universal buffers of pH = 5.33. The factors affected this behavior have been examined and discussed.

The kinetics of oxidation of kappa-carrageenan (KCAR) as a sulfated polysaccharide by cerium(IV) in aqueous perchlorate solutions at a constant ionic strength of 2.0 mol dm−3 have been investigated, spectrophotometically. The results showed a first-order dependence in [CeIV] and fractional-first-order kinetics in carrageenan concentration. A kinetic evidence for the formation of 1:1 complex has been revealed. The hydrogen ion dependence of the reaction rate indicated that the oxidation process is acid catalyzed. The oxidation product was identified by the spectral data and elemental analysis. The activation and thermodynamic parameters have been evaluated and a relevant reaction mechanism is suggested and discussed.

The kinetics of oxidation of kappa-carrageenan polysaccharide as natural polymer by permanganate ion in aqueous perchlorate solutions at a constant ionic strength of 2.0 mol dm−3 have been investigated spectrophotometrically. The experimental observations showed that the pseudo-first-order plots were of inverted S-shape throughout the entire course of reaction. The initial rates were found to be relatively slow in the early stages, followed by an increase in the oxidation rates over longer time periods. A first-order dependence in permanganate and fractional-order kinetics with respect to carrageenan concentration for both the induction and autoacceleration periods were revealed. The results obtained at various hydrogen ion concentrations showed that the oxidation is acid-catalyzed throughout the two stages of reaction. The added salts lead to the prediction that MnIII and/or MnIV are the reactive species throughout the autoacceleration period. Kinetic evidences for the formation of 1:1 intermediate complexes are presented. The kinetic parameters have been evaluated and a tentative reaction mechanism consistent with the kinetic results is discussed.

Spectrophotometric detection of the formation of short-lived hypomanganate(V), ½KCAR–MnVO4 3, and manganate(VI), ½KCAR–MnVIO4 2, intermediates has been confirmed through the oxidation of K-carrageenan (KCAR) by potassium permanganate in alkaline solutions of pH’s P12 using a conventional spectrophotometer. The short-lived transient species were characterized and a mechanism consistent with experimental observations is suggested.

The catalytic effect of copper(II) catalyst on the oxidation of L-tryptophan (Trp) by hexacyanoferrate(III) (HCF), has been investigated spectrophotometrically in an aqueous alkaline medium at a constant ionic strength of 0.5 mol dm
3 and at 25
C. The stoichiometry for both the uncatalyzed and catalyzed reactions was 1:2 (Trp:HCF). The reactions exhibited first order kinetics with respect to [HCF] and less than unit orders with respect to [Trp] and [OH
]. The catalyzed reaction exhibited fractional-first order kinetics with respect to [CuII]. The reaction rates were found to increase as the ionic strength and dielectric constant of the reaction medium increase. The effect of temperature on the rates of reactions has also been studied, and the activation parameters associated with the rate-determining steps of the reactions have been evaluated and discussed. Addition of the reaction product HCF(II) to the reaction mixture did not affect the rates. Plausible mechanistic schemes for uncatalyzed and catalyzed reactions explaining all of the observed kinetic results have been proposed. In both cases, the final oxidation products are identified as indole-3- acetaldehyde, ammonia, and carbon dioxide. The rate laws associated with the reactions’ mechanisms are derived. The rate constants of the slow steps of the reactions along with the equilibrium constants are also calculated.