Hassan A. Ewais

KINETICS AND MECHANISM OF OXIDATION OF CHROMIUM (III)-L-ARGININE COMPLEX BY PERIODATE

Oxidation of the chromium(III)-l-arginine complex [CrIII(L)2(H2O)2]+ by periodate has been investigated. In aqueous solutions, [CrIII(L)2(H2O)2]+ is oxidized by IO−4 according to the rate law: d[CrVI]/dt=k2K5[CrIII]T [IVII]T/1 +([H+]/K1)+K5[IVII]T where k2 is the rate constant for the electron transfer process, K1 the equilibrium constant for the dissociation of [CrIII(L)2- (H2O)2]+ to [CrIII(L)2(H2O)(OH)]+H+, and K5 the pre-equilibrium formation constant. Values of k2= 4.02×10−3s−1, K1=5.60×10−4m and K5=171m−1 were obtained at 30°C and I=0.2m. Thermodynamic activation parameters were calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO−4 to chromium(III).

Kinetics and mechanism of oxidation of the chromium(III)-dl-valine complex/periodate reaction. Evidence for iron(II) catalysis

Oxidation of the chromium(III)-dl-valine complex [CrIII(L)2(H2O)2]+ by periodate has been investigated in aqueous medium. The kinetics of the reaction in aqueous medium in the presence of iron(II) as catalyst obeyed the rate law:Catalysis by iron(II) is believed to be due to the oxidation of iron(II) to iron(III), which acts as the oxidizing agent. The thermodynamic activation parameters were calculated and we propose that electron transfer proceeds through an inner-sphere mechanism via coordination of IO4− to chromium(III).

Inner-sphere Oxidation of a Ternary Complex Involving Iminodiacetatochromium(III) and DL-Aspartic acid by Periodate

The oxidation of chromium from the trivalent to hexavalent states is an important environmental process because of the high mobility and toxicity of chromium(VI) [1]. Chromium(VI) compounds are well known to be potent toxic and carcinogenic agents. Because chromium(VI) is easily taken up by cells and is subsequently reduced to the trivalent form, the formation of chromium(III) or other Inorganic Reaction Mechanisims, Vol. 6, pp. 31-38

Kinetics and Mechanism of Oxidation of Iminodiacetatochromium(III) by Periodate

The oxidation of chromium from the trivalent to hexavalent states is an important environmental process because of the high mobility and toxicity of chromium(VI) [1]. Periodate oxidations have been reported to play an important role in biological determinants [2, 3]. They are used to degrade carbohydrate determinants in proteins without altering protein or lipid epitopes [2, 3]. The oxidation of hexacyanoferrate(II) by periodate has been investigated previously in weakly alkaline and neutral phosphate buffer solution and the kinetic were observed to be simple [4]. The oxidation kinetics of hexacyanoferrate(II) by periodate in acetate buffer was also studied [5]. It was reported that the mechanism of oxidation greatly differed on going from alkaline to acidic solution, whereas in acidic solutions the reaction rate was not only independent of periodate, but also inhibited by its increasing concentration. Symons [6] reported that the oxidation of iron(II) by periodate proceeds via a series of one electron-transfer steps. The polymerization of added acrylonitrile was taken as a criterion for the formation Inorganic Reaction Mechanisims, Vol. 6, pp.39-47

Kinetics and Mechanism of Oxidation of Chromium(III)-Guanosine Complex By Periodate

The oxidation kinetics of the chromium(III)-guanosine complex, [Cr(G)(H2O)4] (G = guanosine) with periodate in aqueous solution were studied and found to obey the rate law: Rate = [Cr]T[IO4 ] {k1K5 + ( k2K1K6 /[H+])} / {1 + (K1/[H]) + K5[IO4-] + (K1K6[IO4-]/ [H+])} where K1, K5 and K6 are the deprotonation of [Cr(G)(H2O)4] and pre-equilibrium formation constants [Cr(G)(H2O)3-OIO3] and[Cr(G)(H2O)2(OH)OIO3] precursor complexes respectively. Thermodynamic activation parameters have been calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO4to chromium(III).

Kinetics and Mechanistic Studies of Oxidation of a Ternary Nitrilotri-Acetatocobalt(II) Complexes Involving DL-valine and DL-aspartic Acid as a Secondary Ligands by Periodate

Oxidation of ternary complexes, [CoII (NTA)(L)(H2O)X]-n by periodate in aqueous medium has been studied spectrophotometrically over the (25.0 – 45.0) ± 0.1°C range. The reaction show first order kinetics with respect to both [IO4-] and the complexes, and the rate of the reaction increases over the [H+] range (1.05 – 28.20) x 10-5 mol dm-3 in both cases. Preparation and characterization of [CoII (NTA)(Asp)(H2O)2]-3 and [CoII (NTA)Val(H2O)2]2- is performed. Conformation of the formation of the ternary complexes has been done using IR spectrum, TGA, UV‐visible spectroscopic and cyclic voltammetry measurements. The thermodynamic activation parameters have been calculated. It is assumed that electron transfer takes place via an inner-sphere mechanism.