Electrochemical regeneration of NADH using conductive vanadia-silica xerogels.

Electrically conductive sol-gel matrices have been first introduced in order to enhance the efficiency of electrochemical NADH regeneration systems for biocatalysis. Vanadia-silica mixed gels as conductive sol-gels were synthesized using vanadium (V) oxytripropoxide (VOTP) and tetramethyl orthosilicate (TMOS) as precursors. Direct electrochemical reductions of NAD+ were carried out in the presence of vanadia-silica xerogels using unmodified platinum electrodes. Vanadia-silica gels from higher ratios of VOTP to TMOS could effectively improve electrochemical generations of NADH from NAD+. Direct electrochemical regenerations of NADH were coupled to the synthesis of l-glutamate from alpha-ketoglutarate catalyzed by glutamate dehydrogenases (GDH). In this case, vanadia-silica gels were used as matrices for enzyme encapsulation, as opposed to serving as additives. When GDH were entrapped in "nonconductive" silica gels, synthesized using only TMOS, in the control experiment, the initial supply of NADH exhausted quickly and a final conversion of 30% was obtained. However, the use of conductive vanadia-silica gels with encapsulated GDH resulted in complete conversion of alpha-ketoglutarate to l-glutamate. A turnover number of a cofactor was also enhanced 3-fold by the application of conductive vanadia-silica gels.