ANHYDRO SUGAR AND LINKAGE CONTRIBUTIONS TO CIRCULAR-DICHROISM OF AGAROSE AND CARRAGEENAN, WITH CONFORMATIONAL IMPLICATIONS

The geometry-dependent linkage contributions to the circular dichroism (CD) of agarose and carrageenan were determined by subtracting the mo nomeric CD from the CD of the polymers. For this purpose, the CD of me thyl 3,6-anhydro-alpha-D-galactopyranoside, and of other anhydro sugar s, was measured. Application of empirical quadrant rules indicates the observed CD to be that expected for the helical conformations of agar ose and carrageenan as derived from diffraction data and modeling calc ulations. The difference in CD sign in the two polymers arises from a translocation of the beta-D-galactose O-2 atom from one quadrant to th e neighboring quadrant of the C-5-O-5-C-1 ether chromophore of the pre ceding anhydro sugar residue, demonstrating the unusually high spatial resolution of conformational analysis that can be achieved with CD un der favorable circumstances. (C) 1997 Elsevier Science Ltd.