FORCE-FIELD AND VIBRATIONAL-SPECTRA OF OLIGOSACCHARIDES WITH DIFFERENT GLYCOSIDIC LINKAGES .2. MALTOSE MONOHYDRATE, CELLOBIOSE AND GENTIOBIOSE

Complete Raman and IR spectra of maltose monohydrate, cellobiose and gentiobiose have been recorded in the crystalline state. These three disaccharides present the same monosaccharide composition of the glucose molecule and the remaining studied position (1-4 and 1-6) of the glycosidic linkage. Moreover, maltose and cellobiose present the different configurations of the glycosidic linkage alpha, 1-4 and beta, 1-4, respectively. These data will constitute the support for theoretical calculations of normal modes of vibration. The assignments of the calculated bands of vibration will be made on the basis of the potential energy distributions using a modified Urey-Bradley-Shimanouchi intramolecular potential energy combined with a specific intermolecular potential energy function. The calculations show that using a correct initial force field, it is possible to reproduce correctly the density of observed vibrational states for large molecules such as disaccharides. The standard deviation between calculated and observed frequencies, below 1500 cm-1, leads to values of 4.7, 4.2 and 4.6 cm-1 for maltose monohydrate, cellobiose and gentiobiose, respectively. Our previous investigations on trehalose dihydrate, sophorose monohydrate and laminaribiose are confirmed in this study and complete the previous assignments for the whole set of disaccharides.