POLYSACCHARIDE VIBRATIONAL RAMAN OPTICAL-ACTIVITY - LAMINARIN AND PULLULAN

The backscattered Raman optical activity (ROA) spectra of the beta(1-3 )-linked polysaccharide laminarin, and its dimer repeating unit D-lami naribiose, together with those of the predominantly alpha(1-4)-linked polysaccharide pullulan, and its trimer repeating unit D-maltotriose, between 350 and 1500 cm(-1) in aqueous solution are reported and discu ssed Several differences are evident between the ROA spectra of lamina rin and D-laminaribiose which are ascribed to triple helix formation i n the polysaccharide. In particular, the signs of four ROA signals bet ween ca. 1050 and 1150 cm(-1) are reversed and two ROA signals assigne d to vibrations involving the glycosidic link observed at cu. 445 and 1431 cm(-1) change sign and increase in intensity, respectively, In co ntrast, pullulan, which adopts a random coil-type structure in aqueous solution, generates an ROA spectrum that closely resembles that of D- maltotriose.