84895-58-9Relevant academic research and scientific papers
Calcium affinity of coordinated diphosphonate ligands. Single-crystal structure of [(en)2Co(O2P(OH)CH2P(OH)O2)]ClO 4·H2O. Implications for the chemistry of technetium-99m-diphosphonate skeletal imaging agents
Jurisson, Silvia S.,Benedict, James J.,Elder,Whittle,Deutsch, Edward
, p. 1332 - 1338 (2008/10/08)
A series of (diphosphonato)bis(ethylenediamine)cobalt(III) complexes, where the diphosphonate ligand has the formula HO3P-CR(R′)-PO3H2-, has been prepared. Members of the series include the following R/R′ combinations: H/H, H/CH3, CH3/CH3, H/OH, CH3/OH, phenyl/OH, tert-butyl/OH, H/NH2, CH3/NH2, H/N(CH3)2, H/Cl, and Cl/Cl. The complexes have been characterized in all cases by visible-UV, IR, 1H NMR, and 31P NMR spectra, in several cases by elemental analyses, and for the prototype title complex (R/R′ = H/H) by single-crystal X-ray structural analysis refined to a conventional R factor of 0.034. Equilibrium constants governing the one-to-one association with calcium(II) in dilute aqueous solution (pH 10, NH4OH/NH4Cl buffer, μ = 0.1 M (KCl), 25°C) have been determined potentiometrically for all diphosphonate complexes as well as for the analogous pyrophosphato and oxalato complexes. Values of the equilibrium constants for the H/OH, H/H, and CH3/OH complexes are 2.4 × 106,1.8 × 104, and 1.1 × 104 M-1, respectively, showing (a) that coordinated diphosphonate ligands have considerable affinity for calcium(II) and (b) that when R′ = OH the calcium affinity is enhanced, presumably via coordination of this OH group to calcium and formation of a bidentate-tridentate bridge from cobalt to calcium. This ordering of affinities exactly parallels the ordering of skeletal uptake of these three diphosphonate ligands when labeled with 99mTc, implying that binding of Tc-diphosphonate complexes to calcium at the surface of bone is an important step in the mechanism of in vivo action of 99mTc-diphosphonate skeletal imaging agents.
