Cobalt(III)-Binding of Gluconate and 2-Amino-2-Deoxy-Gluconate

Abstract

Two isomers of the [Co(tren)(D-Glc1A1,2H-2-K2O1,2)]+ (1) chelate are formed in equal parts in the reaction of [Co(tren)Cl2]Cl and sodium gluconate. In contrast, the gluconate’s 2-amino-2-deoxy derivative glucosaminate formed a single isomer of [Co(tren)(D-Glc1A2N1H-1-k2N,O2)]2+ (2). Crystals of the OC-6-34 isomer of 1, [1a]PF6 H2O, showed the support of the metal-binding site by intramolecular hydrogen bonds. Due to the inertness of the cobalt(III) chelates, spectroscopy on redissolved crystals of [1a]PF6 H2O allowed the separation of the two 13C NMR signal sets of the isomeric mixture. In a DFT approach, a small energy difference explained the formation of two isomers in the case of the gluconate. A larger difference was obtained for the glucosaminate, in line with the known rules for the stereospecific amino acid-Co(tren) chelation