Abstract
The oxidation of [Cr(III)(Try)(2)(H2O)(2)](+) (Try = DL-tryptophan) by periodate in aqueous solution to Cr(VI) has been studied kinetically under pseudo-first order conditions at different pH, ionic strength and temperatures. The kinetics of oxidation obeyed the following rate law:
rate = k(1)K(2)[Cr(III)](T) [I(VII)](T)/1 + [H+]/K-1 + K-2[I(VII)](T)
where k(1) is the rate constant for the electron transfer process; K-1 - the equilibrium constant for dissociation of [Cr(III)(Try)(2)(H2O)(2)](+) to [Cr(III)(Try)(2)(H2O)(2)](+) + H+; K-2 - the pre-equilibrium formation constant. Values of k(1) = 4.67 x 10(-3) s(-1), K-1 = 7.99 x 10(-4) mol dm(-3) and K-2 = 122 dm(-3) mol(-1) have been obtained at 30 degrees C and I = 0.2 mol dm(-3). The rate oxidation increases with increasing of pH, temperatures and independent on ionic strength. Thermodynamic activation parameters have been calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO4- to chromium(III).