Electrochemistry of [Fe₄S₄(SCH₂CH₂COO-)₄]⁶⁻ in liposomes and microemulsions

Abstract

[Fe₄S₄(SCH₂CH₂COO-)₄]⁶⁻, a structural analogue of active center of ferredoxin and P cluster of nitrogenase, shows two distinct reversible couples with redox potential values –643±5 mV and –972±5 mV vs. Ag-AgCl due to 3+/2+ and 2+/1+ couples of the core [Fe₄S₄] respectively in liposomes. Two redox linked protonation sites, with pKox at 3.2 with corresponding pKred at 4.3 due to carboxylate and another pKred at 5.8 due to thiopropionate S shift the redox potential of 3+/2+ couple by 200 mV. In microemulsion containing negative sds molecules (ME-sds) the redox potentials due to 3+/2+ and 2+/1+ couples are –670 mV and –920 mV (pH=4.6) while these values are –544 mV and –800 mV respectively (pH=5.5) versus Ag-AgCl in microemulsion containing positive ctab molecules (ME-ctab). The trend in diffusion co-efficient of the cluster in different medium is found to be: ME-sds>ME-ctab>lposomes.