Oxidation-reduction electron transfer of tetra-sulphonated phthalocyanine cobalt(II)-apomyoglobin and tetra-sulphonated phthalocyanine iron(II)-apomyoglobin

Abstract

Studies on electron transfer in (tspc)Co(II)-apoMb and (tspc)Fe(II)-apoMb were carried out as a function of PH by using optically transparent thin layer electrodes. (tspc)Co(II)-apoMb goes to two-stage oxidation-reduction equilibria, whereas, (tspc)Fe(II)-apoMb is stabilized by the protein itself. The mechanism proposed for stabilization of (tspc)Fe(II)-apoMb is the ligand-metal charge transfer from the imidazole of the histidine residue of protein to the central Fe ion of (tspc)Fe(III)-apoMb. The formation of a super-oxide is proposed for the oxygenation of (tspc)Co(II)-apoMb. The reduction potential of (tspc)Co(II)-apoMb⇌(tspc)Co(III)-apoMb, using ferrocene mono carboxylic acid as mediator, is reported, as also the reduction potential for (tspc)Co(II)-apoMb⇌(tspc)Co(I)-apoMb, using Ru(NH3)6Cl3 as mediator. The dependence ofE 1/2 obs on pH indicates the presence of the ionizable functional groups on the protein, which undergo ionization when the protein changes from the reduced to the oxidised form. TheK ox andK red parameters were calculated and are reported here.