J. T. Gerig, Phirtu Singh, L. Levy
Oct 1, 1987
Citations
0
Influential Citations
31
Citations
Journal
Journal of Inorganic Biochemistry
Abstract
Abstract The structure of the complex of calcium ions with 5,5'-difluoro-1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (FBAPTA) has been determined. The calcium complex, with stoichiometry Ca(CaFBAPTA) · 5H2O crystallizes in a monoclinic space group P21/c with 4 formula units/unit cell with a(A) = 9.767, b(A) = 26.309,c(A) = 11.769; β (deg) = 111.57. The structure may be considered as the calcium salt of a CaFBAPTA2- complex in which the octacoordinate calcium ion is complexed with the two ether oxygen atoms, the two nitrogens, and coordinated in a unidentate manner with the four acetate carboxyl groups. The geometry of the nitrogen atoms is nearly tetrahedral and provides a basis for the interpretation of the optical perturbations which result from calcium complexation with BAPTA type ligands. In addition, it is clear from the distance and relative orientation of the aromatic rings that ring current contributions to the fluorine chemical shifts are of negligible importance, so that such effects cannot be used in the design of NMR active indictators. Although BAPTA and analogs such as PBAPTA and quin2 have found extensive physiological applications as a consequence of the high degree of selectivity for calcium ions over magnesium ions which they exhibit, this is the first reported structural data for any of these complexes.