The determination of the stoichiometry of complex formation and the mechanism of fluorescence quenching of telmisartan (TMST) with Y(III) and Nd(III) was carried out in great detail by a fluorometric method. The quenching was interpreted in terms of chelation-enhanced quenching. The experimental results showed that both Y(III) and Nd(III) quench the intrinsic fluorescence of TMST without inducing any conformational change in it. The quenching of fluorescence was found to be static and due to the formation of a nonfluorescent complex in the ground state. Linear Stern−Volmer plots were obtained for both complexes. The pH of the solution was found to have a profound effect on quenching, and effective quenching was obtained at pH 7. The stoichiometry of metal−TMST complexes was found to be 1:2 through the Benesi−Hildebrand method. The quenching constant K sv and association constant were determined together with their thermodynamic parameters at (25, 35, and 45) °C. The negative ΔG values indicate that the complexation process is spontaneous. A decrease in log K with an increase in temperature and the negative values of ΔH for the complexation show that all the complexation reactions are exothermic and the metal−ligand binding process is enthalpy driven.

The binding interaction of captopril (CPL) bimolecular quenching constant K q , binding constant K and the binding sites "n" were determined together with their thermodynamic parameters at 27 and 37 ℃. The positive entropy change indicated the gain in configurational entropy as a result of chelation. The process of interaction was spontaneous and mainly ∆S-driven.

No abstract

The kinetics and mechanism of oxidation of levofloxacin (LF) by manganese(VII) in alkaline medium at constant ionic strength was studied spectrophotometrically. The reaction exhibits 2:1 Mn:LF stoichiometry and is first order in permanganate but fractional order in both LF and alkali. Decrease in the dielectric constant of the medium results in a decrease in the rate of reaction. The effects of added products and ionic strength have also been investigated. The main products identified were hydroxylated LF and Mn(VI). A mechanism involving free radicals is proposed. In a composite equilibrium step, levofloxacin binds to MnO 4 -to form a complex that subsequently decomposes to the products. Investigations of the reaction at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism.

Kinetic data for the oxidation of 2-aminopentanedioic acid/L-glutamic acid (Glu-e) by quinolinium dichromate (QDC) in perchloric acid medium are reported. The results of the reactions studied spectrophotometrically over a wide range of experimental conditions show that the rate of the reaction is increased by increases in perchloric acid, the ionic strength, and the concentration of Glu-e. The reactions are first order with respect to both QDC and Glu-e. Added products are found to have an insignificant effect on the reaction rate. The activation parameters and thermodynamics have been evaluated and lend further support to the proposed mechanism.