Implementation of high resolution (43)Ca solid state NMR spectroscopy: toward the elucidation of calcium sites in biological materials

Laurencin, Danielle and Gervais, Christel and Wong, Alan and Coelho, Cristina and Mauri, Francesco and Massiot, Dominique and Smith, Mark E. and Bonhomme, Christian (2009) Implementation of high resolution (43)Ca solid state NMR spectroscopy: toward the elucidation of calcium sites in biological materials. Journal of the American Chemical Society, 131 (37). pp. 13430-13440. ISSN 1520-5126

Abstract

Calcium is one of the most abundant cations in living organisms. It is found in the mineral phase of bone and in proteins like calmodulin. However, its exact environment beyond the first coordination sphere is often unknown, thus hampering the understanding of many biological processes. Here, calcium benzoate trihydrate (Ca(C6H5COO)(2)center dot 3H(2)O) was used as a model for the NMR analysis of calcium sites in biological materials, because of the similarity of its calcium coordination, to water and carboxylate ligands, to that in several calcium-proteins. First, calcium-43 magic angle spinning (MAS) and static NMR spectra of a Ca-43 enriched sample were recorded at different magnetic fields, to investigate the electronic environment of calcium. Complex static lineshapes were obtained because of the presence of anisotropic NMR interactions of similar magnitude (chemical shift anisotropy and quadrupolar interaction), and the full interpretation of the spectra required simulations and gauge-including projector augmented wave (GIPAW) DFT calculations. An NMR investigation of the coordination environment of Ca2? was carried out, using high resolution C-13-Ca-43 MAS NMR experiments such as TRAPDOR (transfer of population double resonance) and heteronuclear J-spin-echoes. It was shown that despite the weakness of C-13-Ca-43 interactions, it is possible to discriminate carbon atoms according to their calcium environment. Long-range calcium-carbon correlations were even evidenced by TRAPDOR, reaching distances >5.6 angstrom. This work demonstrates that by combining solid state NMR experiments, DFT calculations, and simulations, it will be possible to elucidate the electronic and coordination environment of calcium in many important and complex materials.