On the nature of mutual inactivation between [Cp*Rh(bpy)(H 2O)] 2+ and enzymes – analysis and potential remedies

Abstract

Pentamethylcyclopentadienyl rhodium bipyridine ([Cp*Rh(bpy)(H 2O)] 2+) is a versatile catalyst to promote biocatalytic redox reactions. However, its major drawback lies in the mutual inactivation of [Cp*Rh(bpy)(H 2O)] 2+ and the biocatalyst. This interaction was investigated using the alcohol dehydrogenase from Thermus sp. ATN1 (TADH) as model enzyme. TADH binds 4 equiv. of [Cp*Rh(bpy)(H 2O)] 2+ without detectable decrease in catalytic activity and stability. Higher molar ratios lead to time-, temperature-, and concentration-dependent inactivation of the enzyme suggesting [Cp*Rh(bpy)(H 2O)] 2+ to function as an ‘unfolding catalyst’. This detrimental activity can be circumvented using strongly coordinating buffers (e.g. (NH 4) 2SO 4) while preserving its activity as NAD(P)H regeneration catalyst under electrochemical reaction conditions.