¹H NMR investigations of the molecular nature of low-molecular-mass calcium ions in biofluids

Abstract.

High-resolution ¹H NMR spectroscopy was employed to explore the complexation of Ca²⁺ by low-molecular-mass biomolecules in human saliva. The results acquired revealed that the organic acid anion (OAA) citrate acts as a powerful oxygen-donor chelator for salivary Ca²⁺, and accurate determination of its resonances' frequencies and spin-system pattern could be successfully utilized to determine its degree of saturation with this metal ion. Computer modelling studies demonstrated that the OAA lactate is the only competing salivary Ca²⁺ complexant available. Moreover, the Ca²⁺-complexation status of salivary citrate is substantially modified by dentifrice-mediated elevations in its concentration. ¹H NMR analysis was also applied to determinations of the Ca²⁺ saturation status of citrate in a variety of alternative biofluids and the biochemical significance of these results is discussed.