Kinetic and Equilibrium Comparison of the Complexation Reaction of Cis- and Trans- Forms of Cr(ox)2(H2O)2.xH2O with Alanin

The kinetics and equilibrium studies of the complexation reaction of cis-Cr(ox)2(H2O)2 with Alanine has been performed. Equilibrium studies were performed at different temperatures. Log Keq for the complexation reaction was found to be ( 5.137, 5.15, 5.234 and 5.398 ) at ( 25, 30, 40 and 50oC) respectively and ΔGo= 4.61 kcal/mol. The results were compared with the complexation reaction of trans-Cr(ox)2(H2O)2 with Alanine. The kinetic studies show trans-effect on the kinetic lability of the complexation reaction. The observed pseudo first order rate constants are found at different temperatures (kobs = 0.0032, 0.0063, 0.0074, 0.0142 and 0.0254 at 26, 32, 37, 44 and 50oC respectively). The activation parameters are found to be (Ea=36.635 kCal /mol, ΔH*=35.213 kCal/mol, ΔS*= -43.246 Cal/mol). All kinetic and equilibrium studies are compared with those of complexation of transCr(ox)2(H2O)2 with alanine. The lability of the Trans-form of the complex was related to a first hydrolysis step of the complex to a monohydroxy form in the trans position of the complex and the effect of the OH- group on the opposite H2O group on the other side of the complex to be more loosely bonded to the central chromium atom and be more easy to be substituted.