Inner-sphere oxidation of ternary iminodiacetatochromium(III) complexes involving DL-valine and L-arginine as secondary ligands. Isokinetic relationship for the oxidation of ternary iminodiacetato-chromium(III) complexes by periodate

The results have shown that the reaction is first order with respect to both [IO4-] and the complex concentration, and the rate increases over the pH range 2.62 – 3.68 in both cases. The experimental rate law is consistent with a mechanism in which both the deprotonated forms of the complexes [CrIII(IDA)(Val)(H2O)2] and [CrIII(IDA)(Arg)(H2O)2] are significantly more reactive than the conjugate acids. The value of the intramolecular electron transfer rate constant for the oxidation of [CrIII(HIDA)(Arg)(H2O)2]+, k3 (1.82 × 10-3 s-1), is greater than the value of k1 (1.22 × 10-3 s-1) for the oxidation of [CrIII(HIDA)(Val)(H2O)2]+ at 45.0°C and I = 0.20 mol dm-3. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO4- to chromium(III).The oxidation of [CrIII(HIDA)(Val)(H2O)2]+ and [CrIII(HIDA)(Arg)(H2O)2]+ by periodate may proceed through an inner-sphere mechanism via two electron transfer giving chromium(VI). The value of the intramolecular electron transfer rate constant for the oxidation of [CrIII(HIDA)(Arg)(H2O)2]+, k3, is greater than the value of k1 for the oxidation of [CrIII(HIDA)(Val)(H2O)2]+. A common mechanism for the oxidation of ternary iminodiacetatochromium(III) complexes by periodate is proposed, and this is supported by an excellent isokinetic relationship between ΔH* and ΔS* values for these reactions.Periodate oxidations have been reported to play an important role in biochemical studies [1,2]. They are used in the spectrophotometric determination of glucose and fructose in invert sugar syrups [1]. Alpha-amino acids in proteins can be determined by measuring the ammonia produced through oxidation with periodate in carbonate medium [2]. Periodate oxidation exerts a number of biological effects including the enhancement of lymphocyte activation and increased frequency of effecter to target cell binding [3]. Also, periodate has been used in the modification of human serum transferrin by conjugation to an