MOLECULAR MODELING OF SUBSTITUTED POLYSACCHARIDES

X-ray diffraction patterns of gellan, high acyl native gellan and bran ched polymer welan correspond to polycrystalline and well oriented spe cimens. Their molecular structures are strikingly similar, but their p acking arrangements are not. The benzyl ester of gellan diffracts like gellan implying that a gellan-like double helix can sustain this subs titution. Likewise, the benzyl ester of hyaluronan can adopt any of th e reported single- and double-helical forms of hyaluronan itself. Carb oxymethylhydroxypropyl guaran (CMHPG) diffracts similarly to guaran. T he hydroxypropyl and carboxymethyl groups can cause favorable associat ion of a pair of CMHPG chains which can further be stabilized by dival ent cations, one for two carboxymethyl groups belonging to different c hains. X-ray data combined with modeling calculations have revealed th e details of the molecular architectures in each case to varying exten ts.