: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.

The catalytic effect of silver(I) and copper(II) ions on the oxidation of histidine by cerium(IV) in aqueous sulfuric acid solutions was studied spectrophotometrically at a constant ionic strength of 3.0 mol dm−3 and at 25°C. In both uncatalyzed and metal ions-catalyzed paths, the reactions exhibited first-order kinetics with respect to [Ce(IV)] and [catalyst], and fractional first-order dependences with respect to [His] and [H+]. The oxidation rates increased as the ionic strength and dielectric constant of the reactions media increased. The catalytic efficiency of Ag(I) was higher than that of Cu(II). Plausible mechanistic schemes for both uncatalyzed and catalyzed reactions were proposed, and the rate laws associated with the suggested mechanisms were derived. In both cases, the final oxidation products of histidine were identified as 2-imidazole acetaldehyde, ammonium ion, and carbon dioxide. The activation parameters associated with the second-order rate constants were evaluated

The oxidation kinetics of isosorbide (S) by potassium permanganate in both perchloric and sulfuric acid solutions was investigated spectrophotometrically at a constant ionic strength of 2.0 moldm-3 and at 25 C. In both acids, the oxidation reactions showed a first-order dependence on ½MnO 4 , apparent a less than unit-order dependence with respect to [S] and a fractional-second-order dependence with respect to [H?]. Variation of either the ionic strength or dielectric constant of the reactions media did not significantly affect the oxidation rates. In both acids, the final oxidation product of isosorbide was identified by both spectroscopic and chemical tools as the corresponding monoketone derivative, namely (1S,4S,5R)-4-hydroxy-2,6-dioxabicyclo[3.3.0] octan-8-one. Under comparable experimental conditions, the oxidation rate of isosorbide in perchloric acid was lower than that in sulfuric acid. The oxidation mechanism describing the kinetic results was proposed and the rate law expression was derived. The activation parameters of the second-order rate constants were computed and are discussed

The inhibition of the corrosion of mild steel in 0.5 M H2SO4 by vanillin in the presence of various amino acids, typically valine, methionine, cysteine and methylcysteine hydrochloride, are studied using potentiodynamic technique aiming at the elucidation of the mechanism of the corrosion inhibition. The corrosion inhibition of vanillin and amino acids was evaluated, both in their individual presence and in their coexistence. The largest inhibition efficiency has been found in the presence of vanillin and cysteine mixture. To have an insight into the mechanism of the inhibition and probe the adsorption sites of the inhibitor, the inhibition efficiency of a Schiff base, synthesized from vanillin and a selected amino acid, typically cysteine, has been compared with the inhibition efficiency of the vanillin and cysteine mixture. Interestingly, it has been found that the inhibition efficiency of the vanillin and cysteine mixture is much larger than the relevant Schiff base, and that the inhibition efficiency of the latter is much smaller than the inhibition efficiency in the presence of the individual components, i.e., vanillin and cysteine. This points to the blocking of the probable adsorption sites, upon the formation of Schiff base, which is the amino group of cysteine and the aldehydic group of vanillin. The adsorption of the methylcysteine, as an example, in the presence of vanillin was found to follow Temkin isotherm and that the chemical adsorption mode is controlling as revealed from the free energy of adsorption (44.4 kJ/mol).