The formation kinetics of ferroin is studied under varied acid conditions at 25 • C and fixed ionic strength (0.48 mol dm −3 ) under pseudo-first-order conditions with respect to Fe 2+ by using the stopped-flow technique. The reaction followed is first and third order with respect to Fe 2+ and 1,10-phenanthroline (phen) T , respectively. Increasing the acid concentration retarded the reaction, and the reaction rate showed a positive salt effect. The rate-limiting step involved the complexation of the phen or protonated phen with [Fe(phen) complex ion. Simulated curves for the acid variation experiments agreed well with the corresponding experimental curves and the estimated rate coefficients supporting the proposed mechanism. Relatively low energy of activation (26 kJ mol −1 ) and high negative entropy of activation (−159.8 J K −1 mol −1 ) agree with the proposed mechanism and the formation of compact octahedral complex ion. C 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 515-523, 2008

The kinetics of reaction between ferrocyanide and ferric ions under acidic conditions was studied at fixed ionic strength (0.1 M) and (25 ± 0.1) o C by using the stopped flow technique, under limiting conditions of [ferrocyanide] and with other reactants in excess. The reaction had first-order dependence on ferrocyanide, Fe(III) and H + ion concentrations and had negative salt effect. On the basis of the experimental findings, a plausible mechanism for the formation of soluble form of Prussian blue (KFe{Fe(CN)6}x H2O) and rate law are proposed. The activation parameters for the title reaction are estimated. A relatively low energy of activation (23 kJ mol-1) and high negative entropy of activation (-231 J K-1 mol-1) agree well with the proposed mechanism and configuration of complex ion leading to the formation of insoluble Prussian blue, Fe4{Fe(CN)6}3 y H2O.

Influence of tetrabutylammoniumbromide (TBAB) on the chemical speciation of binary complexes of copper (II) with biologically important ligands, L-glutamine, and succinic acid has been studied in varying concentrations (0.0-3.0 %, w/v) of TBAB-water mixtures using a Control Dynamics-APX 175E/C pH meter at an ionic strength of 0.16 mol dm-3 and temperature 303 K. The models for the species of these ligands are refined by using the computer programs SCPHD and MINIQUAD75. Copper(II) active forms are ML, ML2, and ML2H for succinic acid and ML2 and ML2H for L-glutamine. The variation of stability constants with % w/v TBAB is explained based on electrostatic and non-electrostatic forces. The formed species distribution with pH at different solvent compositions and equilibria of the species are reported in the present study. The plausible structures for refined species are also presented.

Effect of Tetrabutylammoniumbromide (TBAB) on the chemical speciation of binary complexes of Zinc(II) with L-glutamine and succinic acid has been studied pH metrically in varying concentrations (0.0-3.0 %, w/v) of TBAB-water mixtures. The temperature and the ionic strength maintained in the titrant are 0.16 mol dm-3 and 303 K, respectively. The possible models that represent the title systems are refined by using the computer programs SCPHD and MINIQUAD75. The models contain ML and MLH for succinic acid and ML2 and ML2H for L-glutamine complexes of Zinc(II). The variation of the stability constants with a dielectric constant is explained based on electrostatic and non-electrostatic forces. The species distribution with pH at different solvent compositions, corresponding chemical equilibria, and structures of the complex species are described.