Stereoselective reduction of cobalt(III) complexes by bacteria

Abstract

A strain of Enterobacter cloacae, isolated from soil, reduces racemic abdtriglycinatocobalt(III), triglycinatocobalt(III), stereoselectively under anaerobic conditions. Washed suspensions of cells, grown anaerobically in the absence of triglycinatocobalt(III) initially reduce the L-enantiomer stereospecifically under argon yielding a labile Co(II) chelate. An approximately 5-fold increase in the rate of reduction of the complex occurs using cells disrupted by 2-phenylethanol; decomposition now proceeds with a slight preference for the D-enantiomer. Reduction of triglycinatocobalt(III) under argon by cell-free extracts, prepared by sonication, exhibits similar stereoselectivities to cells disrupted by 2-phenylethanol. However, extracts contain a factor capable of reducing D-triglycinatocobalt(III) with high stereoselectivity under molecular hydrogen. The behaviour of Enterobacter cloacae is compared with that of Aerobacter aerogenes, Proteus vulgaris, Escherichia anaerogenes and Serratia marcescens. Stereoselective effects are also observed in the bacterial reduction of other cobalt(III) complexes.