FT-IR study of pectate and pectinate gels formed by divalent cations

Abstract The interaction of divalent cations with potassium pectate and three potassium pectinate samples with degrees of esterification E of 23.8, 59.1 and 93.4% were studied by FT-IR spectroscopy. Characteristic shifts occurred in C–O and ring vibrations in the 1200–900 cm −1 region as well as in the ν as and ν 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 pectate and K + and Mg 2+ even when no gels were formed. Ca 2+ and Sr 2+ interacted strongly with pectate and low methoxyl pectinates. Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ , and Pb 2+ also showed complex formation with the pectinates at E =59.1%, and Pb 2+ and Cu 2+ to some extent even with very highly esterified pectinate ( E =93.4%).

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