CHARACTERIZATION OF A [4FE-4S]-FERREDOXIN MODEL-BASED ON A CONCAVE TETRADENTATE THIOL LIGAND SYSTEM

NMR and Mossbauer spectroscopy show that a novel tetrathiol ligand, ba sed on the cavitand diphenylglycoluril, encapsulates a 4Fe-4S cluster and induces asymmetry in it. The cluster gives a weak electrochemical current response in DME with a half-wave potential for the 2(-)/3(-) r eduction vs. Fc(+)/Fc of -1.7 V. Ba2+ ions are adsorbed, according to X-ray analysis of the SEM image of the electrode, and act as modulator and promoter of the electrochemical response. On the basis of cyclic voltammograms it is proposed that this adsorption creates electroactiv e sites, changing the type of diffusion controlling the mass transport to the electrode from radial to linear, and that it helps the negativ ely charged complex, which contains a dipole, to approach the negative electrode in an orientation favourable for electron exchange. This fe ature makes the complex an important model for ferredoxins; in spite o f a difference in redox potential.