Determination of the linkages of disaccharides cotaining a 2-acetamido-2-deoxy sugar unit by solvent effects in circular dichroism

Circular dichroism and the conformation of sugars having vicinal diacylamino substituents

“…The maxima and minima of this curve occur at values of x = X - XO satisfying In ( ( x / A + l)/(x/A -1)) = 4Ax/a2 (2) Since solutions for this equation (2) exists only for x/A > 1, the experimentally observed extrema in the C D must always be at a separation greater than the calculated exciton splitting. A is the exciton splitting; K is proportional to the exciton rotational strength and 4 is the half bandwidth of the monomer absorption at 1 /e of the maximum.…”

“…The rotational strength arises mainly from a one-electron mechanism in which the asymmetric field of the atoms near the amide induces optical activity in the chromophore.1 Since the major electrostatic perturber is the 0002-7863/78/1500-4987S01.00/0 hydroxyl at C-3, changes in the solvent which modify the orientation of this group have a striking solvent effect on the CD spectrum. 2 In addition to the band near 209 nm, methyl glycosides of compounds such as GlcNAc and GalNAc show CD bands in the 185-192-nm region which are due to the -* transition of the amide chromophore which has a strong absorption band at 189 nm. The magnitude and position of these shorter wavelength bands depends in a regular way on the configuration of the glycosidic linkage.3 Similar results are found for oligosaccharides composed of 7V-acetylamino sugars such as the chitin oligosaccharides.3•4…”

Preparation and circular dichroism analysis of sodium hyaluronate oligosaccharides and chondroitin

“…The acetamido group orientation, as affected by the carboxylate group presence, may nonetheless be an indirect influence on the CD properties. Bush and co-workers (Yeh & Bush, 1974; Coduti et al, 1977;Dickinson et al, 1977) have presented evidence that the CD of free acetamido sugars is strongly affected by changes in the dihedral angle about the C-0 bond at C3 of the hexosamine. In the case of nonsulfated glycosaminoglycans, this dihedral angle may be influenced by both the acetamido group orientation at C2 and the hydroxyl group configuration at C4.…”

“…This band reflects the n-x* transitions of two chromophoric groups in NaHA: the acetamido and carboxylate moieties. Studies on the CD properties of uronic acids and acetamido sugars indicate a sensitivity to the orientation of neighboring substituents relative to the chromophoric group (Kabat et al, 1969;Listowsky et al, 1969; Yeh & Bush, 1974; Morris et al, 1975;Aubert et al, 1976;Coduti et al, 1977; Dickinson et al, 1977). These data suggest a possible dependence of NaHA CD on the conformational angles about the glycosidic bonds linking the sugars and therefore on hyaluronate conformation.…”