Metal-carboxylate interactions in metal-alginate complexes studied with FTIR spectroscopy

FTIR spectroscopy was used in order to obtain information about metal-carboxylate interactions in metal-alginate complexes of alginic acid and sodium alginate from the brown algae Laminaria digitata after crosslinking with Ca²⁺, Cu²⁺, Cd²⁺, Zn²⁺, Ni²⁺ and Pb²⁺. From the frequencies of the characteristic peaks for asymmetric COO stretching vibration (ν_asym(COO⁻) and symmetric COO stretching vibration (ν_sym(COO⁻)) a ‘pseudo bridged’ unidentate coordination with intermolecular hydrogen bonds is proposed for the metal-carboxylate complexes in polyguluronic regions while for the polymannuronic regions the bidentate bridging coordination was proposed. The PIB factor introduced previously as a relationship between metal sorption and frequencies of the asymmetric vibrations was found not to correlate with sorption capacity or any other physical property of the metal-alginate complexes studied.