ELECTRON-TRANSFER REACTION OF POLYETHYLENE OXIDE-MODIFIED MYOGLOBIN IN POLYETHYLENE OXIDE OLIGOMERS

Electron transfer from an indium tin oxide (ITO) electrode to myoglobin (Mb) in polyethylene oxide (PEO) oligomer was studied. The native Mb was chemically modified with activated PEO (molar mass of 5000 g) to solubilize in the PEO oligomer. PEO-modified Mb (PEO-Mb) was dissolved without denaturation in PEO200 (molar mass of 200 g) containing 0.50 M KCl as a supporting electrolyte. The ITO electrode, Pt wire and Ag wire were used as the working electrode, the counter-electrode and the reference electrode respectively. PEO-Mb was reduced in PEO200 under a nitrogen atmosphere when a negative potential (-1.0 V/Ag) was applied to the working ITO electrode. There are only two species concerned in the reaction, i.e. oxidized PEO-Mb and reduced PEO-Mb which was confirmed by the presence of some isosbestic points in the visible spectra during the electrolysis. This suggested strongly that PEO-Mb received an electron directly from the electrode. The reduction of PEO-Mb was analyzed as a pseudo-first-order reaction. The reduction rate constant of PEO-Mb depended on both the temperature and the degree of PEO modification. PEO-Mb, containing 10.3 PEO5000 chains on average, showed the highest reduction rate constant (7.6 x 10(-4)s-1 at 25-degrees-C). Reduced PEO-Mb was re-oxidized by applying a positive potential (+1.0 V/Ag). The reversible redox reaction of PEO-Mb in PEO200 was confirmed using potentioabsorptometry by applying -1.0 V/Ag and +1.0 V/Ag alternately.