Kinetics and mechanism of periodate oxidation of two ternary nitrilotriacetatochromium(III) complexes involving histidine and aspartate co-ligands

Abstract

The oxidation of [Cr III (HNTA)(Hist)(H 2 O)] -and [Cr III (HNTA)(Asp)(H 2 O)] -(NTA = nitrilotriacetate, Hist = L-histidinate and Asp = DL-aspartate) by periodate in aqueous medium has been studied spectrophotometrically between 15.0 and 35.0°C under pseudo-first-order conditions, [IO 4 -] ) [complex]. The rate increases over the pH range 3.40-4.45 in both cases, but the two complexes give different rate laws. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO 4 -to chromium(III). A common mechanism for the oxidation of some chromium(III) complexes by periodate is proposed, and this is supported by an excellent isokinetic relationship between DH* and DS* values for these reactions.

Inner-sphere oxidation of a ternary dipicolinatochromium(III) complex involving a malonic acid co-ligand

“…This observation is attributed to a reaction between similarly charged species. Overall, this oxidation reaction can be assigned an innersphere mechanism, which is consistent with the reported behavior of IO 4 as a ligand binding to copper(III) [19] and nickel(IV) [20], such that coordinated H 2 O is substituted by IO 4 - [8][9][10][11][12]. Also, it may be concluded that from the reported equilibrium constants of aqueous IO 4 solutions …”

“…Enthalpies and entropies of activation for the oxidation of chromium(III) complexes by periodate are collected in Table 5. Values of DH* and DS* for the oxidation of these complexes were calculated related to the intramolecular electron transfer steps, except for [Cr III (HIDA) 2 [12]. DH* and DS* for these complexes are composite values including the enthalpy of formation of the precursor complexes and the intramolecular electron transfer steps.…”

“…In each case, electron transfer proceeds through an inner-sphere mechanism involving IO À 4 -coordination to chromium(III). The acidic periodate oxidation of binary and ternary chromium(III) nitrilotriacetate complexes with histidine and aspartate as secondary ligands [3,12] was studied, in order to understand the effect of the secondary ligands on the stability of the complexes. Trace amounts of metal ions can be used to catalyze periodate oxidations [6,7] e.g., manganese(II) catalyzes the periodate oxidation of chromium(III) dipicolinic acid and iminodiacetate complex in acetate buffer via oxidation to Mn(III), which acts as the oxidizing agent [6].…”

Silver(I) and Copper(II) Catalysis for Oxidation of Histidine by Cerium(IV) in Acid Medium: A Comparative Kinetic Study

“…It also forms complexes with some transition metal ions in aqueous media [13,14]. The oxidation of histidine by different oxidants has been previously studied in different media [13][14][15][16][17][18][19], and in most cases the main oxidation product of histidine was 2-imidazole acetaldehyde.…”

Concurrent two one‐electron transfer in the oxidation of chromium(III) complexes with trans‐1,2‐diaminocyclohexane‐N,N,N′,N′‐tetraacetate and diethylenetriaminepentaacetate ligands by periodate ion

“…These reactions are often assigned an inner sphere mechanism based on the form of the rate law. The rate laws for the oxidation of [Cr III (hedta)(HO)], [Cr III (ox) 2 (H 2 O) 2 ] − (ox = oxalate), [Cr III G 2 (H 2 O) 2 ] + (G = l ‐glutamate), [Cr III Gs(H 2 O) 4 ] 3+ (Gs = guanosine 5‐monophosphate), [Cr III (nta)(H 2 O)], [Cr III (Hnta)(hist)(H 2 O)] − and [Cr III (Hnta)(asp)(H 2 O)] − (nta = 2,2′,2″‐nitrilotriacetic, hist = histidine, asp = aspartate) by IO − 4 displayed saturation kinetics 5–11. The kinetics, in each case, is interpreted in terms of formation of a precursor complex followed by a slower intramolecular electron transfer step.…”