Abstract:

The interaction between EPS and bivalent cations was investigated by conductometry, circular dichroism spectroscopy, viscosimetry and nmr-spectroscopy. It is shown that the polysaccharide chains bind various bivalent cations (...) at pH 6 in aqueous solutions. Hyaluronate deriving from Streptococcus equi and xanthan deriving from Xanthomonas campestris was studied in comparison with dextran from Leuconostoc mesenteroides which was shown to develop no specific interactions with the bivalent cations. Circular dichroism spectra of the hyaluronate exhibit a cation-induced change n the n-Pi* transition, indicating that the acetamide group of the aminoglucane unit is involved during the complexation. The molar relation between the bivalent cations and the units of the resulting complex was studied with the result that onebivalentcation is bound by approximately five disaccharide units (hyaluronat)and two pentasaccharide units (xanthan). Heavy metal ions (CD, Pb) seem to bind stronger to the negative charged polyelectrolytes than their light counterparts (Ca, Mg).