Kinetics and Mechanism of the Interaction of Glycyl-L-Leucine with [(H₂O)(Tap)²Ruoru(Tap)²(H₂O)]²⁺ Ion at Physiological Ph

Abstract

The interaction of glycyl-L-leucine (L-L 0 H) with [(H 2 O) (tap) 2 RuORu(tap) 2 (H 2 O)] 2 þ (tap ¼ 2-(m-tolylazo) pyridine) has been studied spectrophotometrically in aqueous medium as a function of [(H 2 O) (tap) 2 RuORu(tap) 2 (H 2 O) 2 þ ], [glycyl-L-leucine], pH and temperature. The reaction was monitored at 600 nm where the spectral difference between the reactant and product is a maximum. At pH 7.4, the interaction with glycyl-L-leucine shows two parallel steps, i.e. it shows a non-linear dependence on the concentration of glycyl-L-leucine; both processes are ligand dependent. The rate constants for the processes are: k 1 *10 À3 s À 1 and k 2 *10 À5 s À 1 . The activation parameters calculated from Eyring plots are: DH = 1 ¼ 15:8+0:6 kJ mol À 1 , DS = 1 ¼ À232+2 J K À 1 mol À 1 , DH = 2 ¼ 31:7+3:5 kJ mol À 1 , DS = 2 ¼ À216+10 J K À 1 mol À 1 . Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. From the temperature dependence of the outer sphere association equilibrium constant, the thermodynamic parameters were also calculated, which gave a negative DG8 value for both the steps at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex. The product of the reaction has been characterized from IR and ESI-mass spectroscopic analysis.