NMR and ESR studies of interactions among divalent cations, phytic acid, and N-acetyl-amino acids

Abstract

Ion-selective electrode potentiometry, 13C and 31P nuclear magnetic resonance (NMR) and electron spin resonance (ESR) techniques have been utilized to study the independent and mutual interactions of divalent cations (zinc, copper, and calcium ions), phytic acid, and N-acetylhistidine or N-acetylglutamate. In pH 7.00 copper phytate and calcium phytate solutions (1 mM divalent cation, 10 mM phytate), the preferential phytate binding sites for calcium and copper(II) ions appear to be the P5 phosphate group, or between the P5 phosphate group and the P4 or P6 phosphate groups, with the phytate molecule in the 5 equatorial/1 axial conformation. An insoluble zinc phytate complex with a 4:1 zinc ion:phytate molar ratio slowly precipitated from the pH 7.00 zinc phytate solution (1 mM zinc ions, 10 mM phytate). Soluble ternary complexes involving phytate, N-acetylhistidine, and calcium, copper(II), or zinc ions may exist at pH 7.00. There was no evidence of ternary phytate-divalent cation-N-acetylglutamate complexes existing at pH 7.00.