Determination of the structure of dextran by 13C-nuclear magnetic resonance spectroscopy

The 13C-n.m.r. spectra have been recorded for a series of dextrans whose structures, in terms of degree and type of branching, had previously been determined by methylation analysis. The spectra established that all observable linkages in these dextrans are alpha-linked. Correlation of the spectra with methylation data indicated that the 75-85-p.p.m. spectral region is diagnostic for establishing the presence of alpha-D-(1 leads to 2)-, alpha-D-(1 leads to 3)-, or alpha-D-(1 leads to 4)-linkages. Each chemical shift has been found to be temperature-dependent (deltadelta/deltaT) when referenced to either the deuterium lock or an external standard (tetramethylsilane). All carbohydrate deltadelta values are positive, and range from 0.01 to 0.03 p.p.m./degrees C. These values are considerably larger than analogous deltadelta/deltaT values previously observed for smaller molecules. Larger than average deltadelta/deltaT values are associated with the non-anomeric, sugar-linking carbon atoms.