Formation and structure of a complex of sucrose with cobalt(III)bis(phenanthroline)

Sucrose forms a dicationic complex with cobalt(III)bis(phenanthroline) whic h can be isolated as the sparingly water-soluble triiodide salt or the wate r-soluble chloride. The circular dichroism (CD) spectrum demonstrates the D elta configuration at Co(III) and the presence of two phenanthroline and on e sucrose residues in the complex. The 0-2(g)-O-1(f) distance in crystallin e sucrose permits strain-free coordination of these centers with Co(III) an d in the complex the H-1,1 ' (f) singlet of sucrose separates into a pair o f doublets. The H-1 NMR spectrum in DMSO-d(6) shows that OH-2(g) is deproto nated and the signal of OH-1(f) is shifted strongly downfield by complexati on with Co(III). Coordination involving glucose and fructose residues is co nsistent with neither a-methyl glucoside nor fructofuranose forming mixed c omplexes with phenanthroline. Structure simulation with the semi-empirical PM3(tm) basis set indicates that complexation by O-2(g) and OH-1(f) can giv e a Delta -complex with little structural distortion, whereas in hypothetic al Delta -complexes there is distortion of the sucrose residue. Observation of an NOE involving the sucrose and phenanthroline residues supports the p ostulated structure of the Delta -complex. (C) 2001 Elsevier Science Ltd. A ll rights reserved.