Recognition Processes with Amphiphilic Carbohydrates in Water

Abstract

The article deals with carbohydrate interactions in aqueous media.Carbohydrate head groups of glycolipids not only form the hydrated surface of micelles and vesicles. They also stick together in hydrogen-bonded cycles and attach to each other via stereoselective hydrophobic interactions.Even in water supramolecular structures are thus formed, e.g., quadruple helices or chiral boron ester fibers. Such structures collapse on addition of the enantiomers to form planar bilayer or monolayer crystals (“chiral bilayer effect”). Furthermore, the length of a carbohydrate head groups often determines the curvature of molecular assemblies in water and may drastically change the relative surface areas. In water-amphiphile interfaces hydrogen bonds are found experimentally to be more stable by several orders of magnitude as compared to bulk solution. A theoretical model, which implies a change of “electrostatic potential”, gives only about a factor of four. Boronate groups on the surface of hydrophobic liquid crystals or porphyrin macrocycles also interact strongly with monosaccharides. Most surprisingly and possibly important is the recent finding, that pyranoses and model compounds stick to hydrophobic nanometer gaps and do not equilibrate with bulk water over periods of days. Some new results on water-carbohydrate interactions in glycoprotein and cyclodextrin cavities are also briefly discussed for a comparison.