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The occurrence of a.2~3 and a.2~6 linkages in different complex carbohydrates has raised the question of glycosidic linkage specificity of the sialidases [1]. Sialyloligosaccharide moieties of cell-surface glycoproteins and glycolipids exhibit significant structural diversity, and ability of sialic acid to serve as a receptor detenninant of viruses depends on the carbohydrate structure of sialylglycoprotein, ganglioside, or sialyloligosaccharide. Particulary, it was shown that the ability of influenza viruses to binding with cell-surface glycans is differentiated between the Neu5Aca.2~3Gal-and Neu5Aca.2~6Gal-tenninated sequences, while role of more distant carbohydrate parts of the receptor is poorly defined [2]. The increased expression of a.2~3-linked sialic acid which occurs for acute-phase protein transferrin in cancer and for a.1-acid glycoprotein in liver cirrhosis was also found [3].In the present study, we used Raman scattering spectroscopy for the detennination of the type of linkage (a.2~3 or a.2~6) of sialic acid residues to cabohydrate units of glycoconjugates. Raman spectra of aqua solution of tri-saccharides (Fig. 1 ) Neu5Aca.2~3Galf3I-44Glc and Neu5Aca.2~6Galf3I-44Glc were analyzed. Significant differences in the regions 400-800 cm-I of Raman spectra of these tri-saccharides were observed. There are some additional lines, such as at 572, 620, 707 and 754 cm-I , in the Raman spectrum of Neu5Aca.2~6Galf3I~4Glc. The intensity of line at 440 em-I is increased in the spectrum of Neu5Aca.2~3Galf3I-44Glc in comparison with the spectrum ofNeu5Aca.2~6Galf3I-44Glc.Normal coordinate calculations for the Neu5Aca.2~6Gal and Neu5Aca.2~6Gal fragments show that the line at 440 cm-I is arisen from COC symmetric deformation of the a.2~3 glycoside bond. In the case of a.2~6 glycoside bond, the eoe vibration mixes with CCC and oce deformations and to some extent with ee stretching. In particular, the eoe symmetric deformation contributes only 11-12% of the potential energy of vibrations 572, 620 and 754 cm-I ; the CO stretching gives 28% in 620 em-I and 7% in 707 em-I vibrations; the ee stretching of a.2~6 glycoside chain -6% in 572 and 620 cm-I , and 11 % of potential energy in 754 cm-I vibrations. The carbon and oxygen atoms nearest to glycosidic bond between the sialic and galactose moieties give significant contribution to potential energy of these vibrations.

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