Boric acid complexes with thiamine (vitamin B1) and pyridoxine (vitamin B6)

Complexation of boric acid with vitamins B1 (thiamine) and B6 (pyridoxine) was investigated. The products were isolated from aqueous solutions and characterized by elemental analysis, FT-IR, 13C MAS NMR and thermal methods. The results of chemical and spectral analyses suggested that the reaction between thiaminechloride hydrochloride and H3BO3 in water yielded a salt-like productwith no direct bonding of the thiamine cation to boron while mono- and bis-chelate complexes were obtained with pyridoxine. The bis-chelate pyridoxine complex containing two equivalent pyridoxine ligands was obtained in crystal form. X-ray crystallography verified that complexation with boric acid occurs through the deprotonated phenolic and deprotonated adjacent alcoholic oxygen atoms forming six membered chelate rings. The negative charge on tetrahedral boron is balanced by the sodium ion. The crystal structure contains discernible tunnels parallel to the [0 1 0] direction constructed by hydrogen bonded complex molecules.