Sugar complexes with calcium ion: Infrared spectra of crystalline d-glucuronic acid and its calcium complexes
1983; Elsevier BV; Volume: 122; Issue: 2 Linguagem: Inglês
10.1016/0008-6215(83)88335-9
ISSN1873-426X
Autores Tópico(s)Carbohydrate Chemistry and Synthesis
ResumoThe Fourier-transform infrared spectra of d-glucuronic acid and three of its Ca2+ complexes have been recorded. These complexes are of the type Ca(d-glucuronate)X · 3H2O and Ca(d-glucuronate)2 · 4H2O, where X = Cl− or Br−. The structurally identified Ca(d-glucuronate)Br · 3H2O shows that the octacoordination of each Ca2+ ion is completed by three d-glucuronate residues and two water molecules. The d-glucuronate anion binds calcium cations through three chelation sites: one that involves a carboxyl-oxygen atom combined with O-5; one that includes the second carboxyl-oxygen atom acting in concert with O-4; and one involving the O-1–O-2 pair of hydroxyl groups. Spectroscopic evidence shows that the calcium halide complexes of d-glucuronic acid are structurally related in terms of 8-coordination and the common coordination-sites involved, whereas Ca(d-glucuronate)2 · 4H2O shows 8-coordination but in different structural arrangements. The strong, intermolecular hydrogen-bonding network of the free sugar is preserved upon metalation, whereas the intramolecular hydrogen-bonding system breaks down upon acid ionization. It is also evident that the d-glucuronate crystallizes as the α anomer in this series of metal complexes.
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