Disaccharides hydrogen bonding

Fig. 27.—Schematic drawing of a hyaluronan segment. Each disaccharide repeat has the potential to participate in four hydrogen bonds, 1 and 2 across the (1— 4). an< 3 and 4 across the (1— 3)-linkage.

A computer-built model, having an axial rise per disaccharide of 0.84 nm and possible stabilization by an 0-3-H 0-5, intramolecular hydrogen-bond from a hexosamine to a uronic acid residue, is a rather extended, two-fold helix (see Fig. 8),346 with each fold approximately corresponding341,346 to the disaccharide repeat in Fig. 7a. A substantially similar model was obtained by use of calculations also taking into consid-... 

The molecules are helices having a twofold screw-axis, with an axial rise per disaccharide residue of 9.45 A (945 pm). The axes of the chains are parallel, and about equally spaced, but are not further organized into crystalline arrays. A hydrogen bond was proposed between the OH-3 group of the 2-acetamido-2-deoxy-D-glucose residues and 0-5 of the D-galactose 6-sulfate residues. 

The hydroxyproline residues stabilize the triple helix by forming hydrogen bonds between the a-chains, while the hydroxyl groups of hydroxylysine are partly glycosylated with a disaccharide (-Glc-Gal). 

Even isolated mono- and disaccharides are capable of extensive hydrogen bonding, which results in extremely low vapor pressures. Attempts at vaporization of these materials results in decomposition. Volatile derivatives must be prepared and the approaches are similar to those described for amino acids. The most common derivatives are methyl or trimethylsilyl ethers and acetyl or trifluoroacetyl esters. A highly detailed review of applications of GLC to carbohydrates including over 1000 references concerning derivatization and types of columns used has been written by Dutton (69,70). 

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