Amphiphilic properties of some sugar chains

Abstract

The idea that sugars and saccharide chains may display hydrophobic properties appears counter-intuitive at first sight; however, there are several instances where nonpolar interactions between saccharides and other molecules have been documented. Examination of molecular models of maltose and cellobiose ( a-1 ,4 newlinelinked and ~-1 ,4 linked dimers of D-glucose respectively) reveals that maltose folds newlineinto a L-shaped conformation with the inner face largely containing the methine newlinehydrogens and the outer face dotted with all the hydroxyl groups. Such a fold newlineappeared less likely or favourable in the case of the B-1 ,4 linked cellobiose. In the newlineabsence of any alkyl or aryl substitution, the only hydrophobic character here is newlinederived from the methine CH groups and hence negligibly weak in the monomer itself. newlineBut in the dimer maltose and higher oligomers, as monomers are linked in a newlinerow, an increasing and regular array of these nonpolar faces can develop, thus newlineincreasing the hydrophobic character. Regular repetition and consolidation of the newlinehydrophobic faces into a strip or a ribbon-like surface would be dependent on the newlinetype of the glycosidic linkage. The a-1 ,4 linkage in D-glucose reinforces the newlinehydrophobic surface while ~-1 ,4 linkage breaks this order. Primarily, this is a result newlineof the 4C1 ring conformation that the hexoses adopt, as well as the stereochemical newlineand anomeric constraints that are imposed on the saccharide chain. newlineIn general, four different conformational types are found in polysaccharides, newlinenamely Type A (extended ribbon), Type B (flexible helix), Type C (crumpled newlineribbon) and Type D (flexible coil). Of these the Type B conformation appears most newlinesuited to display amphiphilic properties. A good example is that of the a-(1 ,4)glucoside, newlinedextrin. These are linear analogs of the cyclodextrins, which are cyclic newlineoligoamyloses shaped like a basket whose interior is apolar, while the exterior is newlinehydrophilic and thereby are amphiphilic in nature.