Polyhedron p. 135 - 145 (2019)
Update date:2022-08-25
Topics:
Karuppasamy, Periyakaruppan
Thiruppathi, Dharmaraj
Ganesan, Muniyandi
Rajendran, Thangamuthu
Rajagopal, Seenivasan
Sivasubramanian, Veluchamy Kamaraj
The H2O2 oxidation of L-cysteine and s-alkyl-L-cysteines (s-met-L-cys, s-et-L-cys & s-pro-L-cys) catalyzed by iron(III)–salen (salen = N,N′-bis(salicylidene)ethylenediaminato) complexes in aqueous CH3CN proceeds through Michaelis–Menten kinetics. The rate constant (k) values correlate well with Hammett σ constants, which gives the positive reaction constant (ρ = 1.5–1.9) value. The CV of oxoiron(IV)-salen ion shows a clear oxidation peak at 1.28 V in 0.1 M phosphate buffer (PB) solution using 0.1 M tertiary butyl ammonium perchlorate (TBAP) as supporting electrolyte at 266 K. The rate of the reaction is highly sensitive to the length of the alkyl chains present in the L-cysteines, pH and solvent composition of the medium. The calculated binding constant values (Kf) in the range of 117–613 M?1, indicate that iron(III)–salen complexes carrying electron donating substituents in the salen ligand have higher binding constant values compared to those carrying electron withdrawing substituents. Product analysis shows the conversion of L-cys to its disulfide and s-alkyl-L-cys to the corresponding sulfoxides. Based on the spectral and kinetic data the plausible mechanism has been proposed.
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