Theoretical study of hyaluronan oligosaccharides.

The structure and energetics of hyaluronan oligomers from di- to decasaccharides have been studied by density functional theory calculations at the B3LYP/6-31G** level. The study covered selected conformers of the sodium salt, anionic disaccharides, and neutral acids in the isolated state and in aqueous solution using the PCM model approach. We investigated the structural changes of the hyaluronan chain when the Na ion is removed or replaced by proton. These processes result in some characteristic changes in the glycosidic torsional angles and hydrogen bonding interactions. We evaluated the folding for the hyaluronan chains and obtained values between 2.2 and 3.2, somewhat smaller than reported for the crystals. We found a contraction of the hyaluronan chains upon enlargement in most derivatives attributed partly to the helical character of hyaluronan. The energy consequences of the enlargement have been modeled by isodesmic reactions. The enlargement processes proved to be exothermal and the energies consistent within the gradual enlargement. [ABSTRACT FROM AUTHOR]