Cobalt(III)-binding of gluconate and 2-amino-2-deoxy-gluconate

摘要

Two isomers of the [Co(tren)(D-Glc1A1,2H_(-2)- κ~2O~(1,2))]~+ (1) chelate are formed in equal parts in the reaction of [Co(tren)Cl_2]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)-κ~2N,O ~2)]~(2+) (2). Crystals of the OC-6-34 isomer of 1, [1a]PF_6·H_2O, 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]PF _6·H_2O allowed the separation of the two ~(13)C 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.