FT-IR STUDY OF PECTATE AND PECTINATE GELS FORMED BY DIVALENT-CATIONS

The interaction of divalent cations with potassium pectate and three p otassium pectinate samples with degrees of esterification E of 23.8, 5 9.1 and 93.4% were studied by FT-IR spectroscopy. Characteristic shift s occurred in C-O and ring vibrations in the 1200-900 cm(-1) region as well as in the nu(as) and nu(s) carboxylate bands at around 1617 and 1420 cm(-1), indicating a metal coordination by the pectate chains in accordance with the 'egg-box' hypothesis [Grant et al. FEBS Lett., 32 (1973) 195-198]. The FT-IR spectra showed some interaction between pec tate and K+ and Mg2+ even when no gels were formed. Ca2+ and Sr2+ inte racted strongly with pectate and low methoxyl pectinates. Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ also showed complex formation with the pectinates at E=59.1%, and Pb2+ and Cu2+ to some extent even with very highly es terified pectinate (E=93.4%). (C) 1998 Elsevier Science Ltd. All right s reserved.