The ultracentrifuge is a useful tool for probing the effects of chemical or other types of substitution/mutation in macromolecules, although very few studies have been performed on polysaccharides. In this study we demonstrate that the substitution of hydroxyl groups on the polysaccharide xylan by p-carboxy-benzyl (CB) bromide groups has little observed effect on molecular weight and little apparent effect on conformation (as monitored by sedimentation velocity and intrinsic viscosity). Corn-cob arabino-(4-O-methylglucurono)xylan (AGX) and its chemically modified derivative CB-AGX were found to have intrinsic viscosities of (82.8 ± 0.4) ml/g and (77.6 ± 0.5) ml/g, respectively. Sedimentation coefficients, s20,w
0, were calculated to be (1.72 ± 0.06) S and (1.77 ± 0.06) S and (weight-average) molecular weights, Mw, from sedimentation equilibrium were found to be (37000 ± 1500) g/mol and (40000 ± 3000) g/mol. From these results we concluded that the UV tagging of arabinoxylan AGX does not significantly change the structural integrity of the xylan molecule; however, the decrease in intrinsic viscosity may indicate a very slight conformational change.