The structure of gellan in dilute aqueous solution.
A full assignment of high-field nmr spectra of gellan was obtained in dilute aqueous solution by performing a series of selective one-dimensional nmr experiments. The observed nuclear Overhauser effects (NOEs) cannot be interpreted assuming that each sugar residue is intrinsically rigid and in a chair conformation. In fact, the rhamnose residue gives strong NOE contacts coherent only with an equilibrium involving both a chair as well as a boat (or a hemiboat) conformation. Molecular dynamic calculations performed on a heptamer with a central rhamnose support the above finding, and show a structure based on a very stiff single chain in which it is present a flipping of the rhamnose residue. At low temperatures (5-20 degrees C) in very dilute solutions (0.018 mg/mL) nmr spectra show a splitting of the resonance due to the methyl group of rhamnose residue, thus confirming the presence of a slow equilibrium among different conformers.
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Polytech, SCaRL AREA Science Park, Padriciano 99, I-34012 Trieste, Italy.
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D002236:Carbohydrate Conformation / Q000187:drug effects; D002240:Carbohydrate Sequence; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008969:Molecular Sequence Data; D015394:Molecular Structure; D017711:Nonlinear Dynamics; D011135:Polysaccharides, Bacterial / Q000737:chemistry*; D012995:Solubility; D012997:Solvents / Q000494:pharmacology; D013696:Temperature; D014867:Water / Q000494:pharmacology
D011135:Polysaccharides, Bacterial; D012997:Solvents; D014867:Water; C048288:gellan gum