CONFORMATIONAL PREFERENCES AND PROTONATION SEQUENCE OF MYOINOSITOL HEXAPHOSPHATE IN AQUEOUS-SOLUTION - POTENTIOMETRIC AND MULTINUCLEAR MAGNETIC-RESONANCE STUDIES

Potentiometric methods and multinuclear NMR spectroscopy have been used to determine the protonation sequence and conformational preferences of myo-inositol (cyclohexane-1,2,3,4,5,6-hexol) hexaphosphate over the range pH 0-12. The H-1, P-31 and C-13 resonances have been assigned from both homo- and hetero-nuclear coupling constants obtained by one- and two-dimensional NMR spectroscopy. The phosphate exists in aqueous solution in either of two conformations, axial and equatorial, as a result of intramolecular hydrogen-bond formation between phosphate groups which leads to stabilization of the equatorial form up to pH 10 and of the axial at pH > 10. Analysis of lanthanide-induced shift data shows unambiguously that the last protonation occurs on the P2 phosphate group in strongly acidic media.