M. Saladini et al., Sugar complexes with metal(2+) ions: thermodynamic parameters of associations of Ca2+, Mg2+ and Zn2+ with galactaric acid, CARBOHY RES, 336(1), 2001, pp. 55-61
A solution study on the complex ability of galactaric acid (GalaH(2)) for c
omplexation with Ca2+, Mg2+ and Zn2+ ions is reported. The stability consta
nts of the complex species are determined by means of potentiometric measur
ements. From the dependence of stability constants on temperature, the Delt
aH degrees and DeltaS degrees values are also determined. The formation of
the complex species is an endothermic process and DeltaH degrees and DeltaS
degrees values suggest a chelate coordination mode of galactaric acid invo
lving carboxylic oxygen and a-hydroxylic group. The prevailing species at a
cidic or neutral pH is [MGala] (M = Ca2+, Mg2+, Zn2+) which is also isolate
d in the solid state and characterised by means of IR spectroscopy. On incr
easing pH, the [MGalaH -(1)](-) species is also formed, where the coordinat
ed OH group undergoes deprotonation. (C) 2001 Elsevier Science Ltd. All rig
hts reserved.