BIPHENOL AS AN ELECTRON-TRANSFER MEDIATOR FOR GLUCOSE-OXIDASE

Biphenol (4,4'-dihydroxy-biphenyl) was found to be an electron transfer mediator for glucose oxidase (GOD) of Aspergillus niger. At a glassy carbon electrode, a 1.44x10(-4) M solution of biphenol in phosphate-buffered saline (PBS) at pH 7.4 gives an quasi-reversible, one-electron, pH-sensitive couple at 255mV (relative to the standard calomel electrode). The apparent second-order rate constant for electron transfer from reduced GOD to oxidized biphenol was determined to be 3x10(5) M(-1) s(-1). When biphenol and GOD are cophysiadsorbed on a graphite electrode immersed in PBS and held at 400mV, a glucose-dependent current response is noted. In addition to the predominant quasi-reversible biphenol redox couple, repetitive cyclic voltammetry at a graphite electrode gave rise to a polybiphenol polymer; this is most marked at a pH above the biphenol pK(a) of about 9.5. At pH 7.4, the polymerization is less significant. Polybiphenol formed either side of the pK(a) remains electrochemically active (E degrees(app). = 245mV) but no longer mediates GOD.