The effect of pH and complexation of amino acid functionality on the redox chemistry of methionine and X-Ray structure of [Co(en) 2(L-Met)](ClO 4) 2.H 2O

Abstract

Anodic oxidation of methionine under different pH conditions is reported. The results are compared with the oxidation process when the glycinic terminus of methionine is coordinated with Co(III). Synthesis of [Co(en) 2(L-Met)](ClO 4) 2, [Co(trien)(L-Met)](CF 3SO 3) 2, and [Co(trien)(OSO 2CF 3) 2]CF 3SO 3 is reported where L-Met = L-methionine, en = ethylenediamine, trien = triethylenetetraamine. The triflato complex ([Co(trien)(OSO 2CF 3) 2]CF 3SO 3) can serve as a starting material for synthesizing a variety of complexes. The x-ray structure of [Co(en) 2(L-Met)](ClO 4) 2.H 2O is also presented The complex crystallizes in space group P2 1 of the mono-clinic system with two independent molecules in the crystallographic asymmetric unit. The unit cell dimensions are a = 9.582 (2) Å, b = 11.554 (2) Å, c = 19.988 (6) Å, and f = 98.85 (2)°. The two molecular units are related by a pseudo-center of symmetry. The electrochemical data presented here suggest a major role of the neighboring group and pH in defining the ease of oxidation of methionine.