Oxidation of Glycogen “Molecular Nanoparticles” by Periodate

Glycogen, a natural hyperbranched polymer of glucose characterized by a substantially spherical macromolecular structure, was oxidized by periodate to obtain reactive intermediates for the preparation of nanostructured materials. The reaction was carried out at room temperature in water, methanol, isopropanol or N,N-dimethylformamide as solvents. The oxidized glycogen was analyzed by H-1 NMR and the oxidation degree was determined by titration. The repartition of the aldehydes between the surface and the volume of the macromolecular nanoparticles was studied by selective cleavage of the oxidized monomeric units under Smith degradation conditions and SEC analysis. Tuning of the oxidation degree in the range of 1-40% (mole fraction of aldehyde per glucoside unit) was achieved by controlling the reagent feed ratio (periodate/glycogen), while the topology of the aldehyde group distribution was controlled by exploiting the kinetics of mass transport. When the reaction was carried out in water, at low oxidation degree values (0.5-3 mol% of oxidized monomeric units), the aldehyde groups were found to be mostly near the nanoparticle surface. A gradient of distribution of the aldehydes from the surface to the particle core was obtained at higher oxidation degrees (>5%). When the reaction was carried out in organic solvents the functionalization occurred mostly at the nanoparticle surface and also at a high oxidation degree. In particular, in N,N-dimethylformamide at 5% oxidation degree, the aldehyde groups were found to be near the macromolecular chain-ends, mostly located on the particle external shell.