Résumé
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
1
H,
31
P and
13
C 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 P
2
phosphate group in strongly acidic media.