Glycans comprise perhaps the largest biomass in nature, and more and more
glycans are used in a number of applications, including those as pharmaceutical agents in the clinic. However, defining
glycan molecular weight distributions during and after their preparation is not always straightforward. Here, we use pulse field gradient (PFG) (1)H NMR self-diffusion measurements to assess molecular weight distributions in various
glycan preparations. Initially, we derived diffusion coefficients, D, on a series of
dextrans with reported weight-average molecular weights from about 5 kDa to 150 kDa. For each
dextran sample, we analyzed 15 diffusion decay curves, one from each of the 15 major (1)H resonance envelopes, to provide diffusion coefficients. By measuring D as a function of
dextran concentration, we determined
D at infinite dilution, D(inf), which allowed estimation of the hydrodynamic radius, R(h), using the Stokes-Einstein relationship. A plot of log D(inf) versus log R(h) was linear and provided a standard calibration curve from which R(h) is estimated for other
glycans. We then applied this methodology to investigate two other
glycans, an alpha-(1-->2)-L-rhamnosyl-alpha-(1-->4)-D-galacturonosyl with quasi-randomly distributed, mostly terminal beta(1-->4)-linked
galactose side-chains (GRG) and an alpha(1-->6)-D-galacto-beta(1-->4)-D-
mannan (
Davanat), which is presently being tested against
cancer in the clinic. Using the
dextran-derived calibration curve, we find that average R(h) values for GRG and
Davanat are 76+/-6 x 10(-10) m and 56+/-3 x 10(-10) m, with GRG being more polydispersed than
Davanat. Results from this study will be useful to investigators requiring knowledge of
polysaccharide dispersity, needing to study
polysaccharides under various
solution conditions, or wanting to follow degradation of
polysaccharides during production.