Coordination chemistry of polyhydroxy acids: Role of the hydroxy groups

T. Gajda, B. Gyurcsik, T. Jakusch, K. Burger, B. Henry, J. J. Delpuech

Research output: Contribution to journalArticle

34 Citations (Scopus)

Abstract

The coordination properties of five aldonic acids (D-gluconic, D- and L-gulonic, D-galactonic and D-ribonic acids) and of 2-amino-2-deoxy-D-gluconic acid towards copper (II) were studied in aqueous media by combined pH-metric, circular dichroism (CD) and electron paramagnetic resonance (EPR) spectroscopic and 13C NMR relaxation measurements. The equilibrium study (298 K, I = 0.1 M (NaClO4)) revealed the formation of several monomeric and dimeric complexes deprotonated to an extent depending on the pH and the metal-to-ligand ratio. The EPR spectra confirmed the formation of binuclear complexes involving strong antiferromagnetic coupling between the metal centres. For the dimeric species Cu2L2H-4 of different aldonic acids, the shape of the CD spectrum was determined by the configurations of C(2), C(3) and C(4), suggesting the involvement in the coordination of the hydroxy groups on these carbons. At low metal-to-ligand ratios, exclusively the monomeric complex CuL2H-2 was formed. The EPR study of this species indicated the existence of cis and trans isomers. This was also proved by 13C NMR relaxation measurements. The 13C relaxation enhancements induced by the paramagnetic metal centre allowed us to extract carbon-to-metal distances. The results also provided evidence of metal-promoted deprotonation and coordination of the C(2)-OH group besides the carboxylate oxygen. In this way, the C(4)-OH hydroxy group is at an appropriate distance for hydrogen bonding to an axially bound water molecule, which is in fact shown by the temperature dependence of the NMR parameters. Concerning the copper(II) complexes of 2-amino-2-deoxy-D-ghiconic acid, the bis amino acid type coordination diminishes significantly the coordination ability (possibility) of the hydroxy groups compared with that in the aldonic acids, but it is still higher than that in the copper(II)-serine complexes.

Original languageEnglish
Pages (from-to)130-140
Number of pages11
JournalInorganica Chimica Acta
Volume275-276
Publication statusPublished - Jul 1 1998

    Fingerprint

Keywords

  • Copper complexes
  • Polyhydroxy acid complexes
  • cis and trans isomers

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

Cite this