The study of spatial structure of calcium gluconate in aqueous solutions

Conformation transformations of calcium gluconate molecules, which are the consequence of the formation of intermolecular hydrogen bonds at the increase in the concentration of the aqueous solution were found by the 1Н NMR method. The observed concentration behavior of the conformation of calcium gluconate indicates the presence of the intramolecular hydrogen bond -О(С4)Н$\cdot \cdot$О(С2) found earlier for molecules of gluconic acid. It was established that gluconate molecules exist in the form of two conformations: zigzag 1-Р and cyclic 3G+. The main cross peaks on homonuclear 2D 1Н NMR spectra indicate the preferably zigzag conformation, and the relatively weak cross peak Н3-Н6' indicates the formation of the cyclic conformation. The possible cyclization is due to the interaction of oxygen of the hydroxyl group at the end carbon atom O(С6) with the calcium atom, i.e., to the formation of the polydentate center.