CONFORMATIONAL PROPERTIES OF BETA-(1-]4)-D-GALACTAN DETERMINED FROM CHIROPTICAL MEASUREMENTS

A chiroptical method of conformational analysis is applied to the neutral pectic polysaccharide beta-(1-->4)-D-galactan. The method is based on experimental measurements of Na(D) optical rotation and vacuum-UV CD and a recently developed calculational model for saccharide optical activity. We conclude that the solution conformation is well described by the linkage geometry (phi,psi) = (60-degrees,40-degrees), in agreement with calculated potential energy contours; fluctuations about this conformation are relatively limited. The solid-state conformation is determined to within a specific range of (phi,psi) values, including a conformation only slightly different from the solution conformation. A second possibility for the solid-state conformation is (phi,psi) = (160-degrees,20-degrees), also not energetically unfavorable.