Mixed complexes of cobalt(III) with phenanthroline and galactose or arabinose

Mixed complexes of bis-phenanthroline cobalt(III) and a-D-galactose or beta -D- or L-arabinose are identified in aqueous solution from their H-1 NMR and circular dichroism (CD) spectra. Galactose forms only the Delta -complex, but D-arabinose gives preferentially Delta-, and L-arabinose preferentially Delta -complexes, consistent with structural optimization with PM3 (tm) parameters. The Lambda -complex is formed initially from beta -D-arabinose, but the Delta -complex is preferred thermodynamically. Examination of the absorption and CD spectra gives information on configuration at cobalt(III) and allows assignments of electronic transitions in Co(III) and the phenanthroline residues. (C) 2001 Elsevier Science Ltd. All rights reserved.