Natural abundance 43Ca NMR study of calcium-containing organic solids: A model study for Ca-binding biomaterials

As a first step for probing Ca sites in biomolecules using solid-state 43Ca NMR spectroscopy, natural abundance 43Ca NMR data of calcium-containing organic solids is reported. The 43Ca NMR interaction parameters indicate small electric field gradients and a relatively small chemical shift range for the calcium sites in these bio-related model compounds. A correlation of the 43Ca isotropic chemical shift with Ca–O distance is found: the 43Ca shift increases as the mean Ca–O distance decreases, with a strong deshielding being observed for calcium with strong Ca–O bonds (distance <2.4 Å) in both organic and inorganic materials.