Water dynamics about selected monosaccharides in solution

Master Thesis


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University of Cape Town

The solubility of molecules in water is governed, amongst other things, by the inherent properties of the solute molecules and water molecules. Water molecules are able to simultaneously form hydrogen bonds as donors and acceptors and thus have unique properties as solvent molecules. These properties influence how water interacts with solute molecules. The mechanism of hydrogen bond exchange plays a role in the hydration of solute molecules. A key to understanding some of the biological processes lies in understanding how solutes interact with water. In this thesis, the hydration of monosaccharides has been studied using computational methods. The hydration structure is elucidated by pair distribution functions and spatial distribution functions. Hydrogen bond exchange dynamics were investigated on the basis of the molecular jump mechanism. Evaluation of the hydrogen bond exchange dynamics reveals two possible pathways. The first pathway corresponds to the molecular jump mechanism reported in literature. The second pathway is described. This pathway provides details on the water-hydroxyl interactions taking place around the monosaccharides. It is shown that the presence of a primary alcohol on pyranose based molecules induces a configuration that allows favourable interactions between water molecules and hydroxyl groups on the sugar molecules. A region of high water density is formed between the primary alcohol, ring oxygen and the hydroxyl on the anomeric carbon. This is due to rotations by water molecules from one hydroxyl, to the adjacent hydroxyl on the sugar molecule. It is not only the presence of the primary alcohol that plays a role in the hydration of the monosaccharides. The relative position of the hydroxyl on the anomeric carbon is shown to create a topology conducive of hydroxyl to hydroxyl hydrogen bond exchanges. The hydration of monosaccharides is rationalised by these effects.

Includes bibliographical references.