The structure of gellan in dilute aqueous solution

• Published in: Biopolymers Vol. 54; no. 2; pp. 115 - 126
• Main Authors: Bosco, M., Miertus, S., Dentini, M., Segre, A.L.
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 01-08-2000
• Subjects: Carbohydrate Conformation - drug effects; Carbohydrate Sequence; gellan; Magnetic Resonance Spectroscopy; Models, Chemical; Molecular Sequence Data; Molecular Structure; nmr; Nonlinear Dynamics; Polysaccharides, Bacterial - chemistry; Solubility; Solvents - pharmacology; structure; Temperature; Water - pharmacology
• ISSN: 0006-3525; 1097-0282
• DOI: 10.1002/1097-0282(200008)54:2<115::AID-BIP4>3.0.CO;2-W

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°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. © 2000 John Wiley & Sons, Inc. Biopoly 54: 115–126, 2000