title: An ab initio quantum chemical investigation of 43Ca NMR interaction parameters for the Ca2+ sites in organic complexes and in metalloproteins.
abstract: We have carried out an extensive ab initio quantum chemical (QC)43Ca NMR study on a series of Ca-O organic compounds and three different Ca-bound proteins and found that the HF/6-31G* level of function can reliably predict 43Ca NMR interaction parameters (delta(iso) and chi(q)), especially for organic solids. This QC study finds correlations between Ca-O bond environment (mean distance and coordination number) and delta(iso)(43Ca). Although relatively small values of chi(q)(43Ca) are found for Ca-O organic compounds with a coordination number between 6 and 10, the QC shows that chi(q)(43Ca) is sensitive to the Ca-O coordination geometry of the Ca2+ sites in metalloproteins--a potentially important observation. An application of such ab initio QC 43Ca NMR studies is in characterizing the Ca-O bonding environment around target Ca2+ sites. As an example, we propose a new potential analytical approach using the absolute (43)Ca chemical shielding constant to investigate the hydration shell of Ca2+ in a dilute CaCl2 aqueous solution. Furthermore, by adopting a NMR methodology similar to that reported in Wong et al. Chem. Phys. Lett. 2006, 427, 201, natural abundance 43Ca MAS NMR spectra of Ca(L-glutamate)(2) x 4H2O were recorded, and delta(iso)(43Ca) and the quadrupolar parameter (Pq) were estimated to be 6.6 ppm and 0.8 MHz, respectively.
authors.affiliation: Department of Physics, University of Warwick, Coventry CV47AL, UK.
authors.forename: Alan
authors.initials: A
authors.lastname: Wong
authors.forename: Danielle
authors.initials: D
authors.lastname: Laurencin
authors.forename: Gang
authors.initials: G
authors.lastname: Wu
authors.forename: Ray
authors.initials: R
authors.lastname: Dupree
authors.forename: Mark E
authors.initials: ME
authors.lastname: Smith
mesh_terms: D002118:Calcium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008667:Metalloproteins / Q000737:chemistry*; D009930:Organic Chemicals / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D011789:Quantum Theory; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D008667:Metalloproteins; D009930:Organic Chemicals; D010100:Oxygen; D002118:Calcium