Evidence for Egg-Box-Compatible Interactions in Calcium−Alginate Gels from Fiber X-ray Diffraction
2007; American Chemical Society; Volume: 8; Issue: 7 Linguagem: Inglês
10.1021/bm0701503
ISSN1526-4602
AutoresPawel Sikorski, Frode Mo, Gudmund Skjåk‐Bræk, Bjørn T. Stokke,
Tópico(s)Seaweed-derived Bioactive Compounds
ResumoThe structures of guluronic-acid-rich alginate in the acid and calcium forms were investigated using fiber X-ray diffraction. Data recorded for alginate fibers in the acid form show a repeat along the chain axis of c = 0.87 nm, a value that is in agreement with the one measured by Atkins et al. (Biopolymers 1973, 12, 1865) and contradicts a repeat of 0.78 nm recently suggested by Li et al. (Biomacromolecules 2007, 8, 464). In the Ca2+ form, our observations indicate that the junction zone involves dimerization of polymer chains through Ca2+ coordination according to the egg-box model. For reasons that are not understood at present, coordination of the divalent cations reduces the ability for the lateral crystallographic packing of the dimers. A proposed model for the junction zone involves polymer chains packed on a hexagonal lattice with a lattice constant a = 0.66 nm. Random pairs of chains form dimers through coordination of Ca2+ cations. Further lateral interaction between dimers is mediated by disordered Na+ and Ca2+ cations, water molecules, and hydrogen bonding.
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