Oxidation of Glycogen by Periodate to Functional “Molecular Nanoparticles”

Glycogen is a natural polymer having a very high molecular weight (Mw ~7 106 g/mol). It is made of macromolecules having mostly spherical shape with 21.3 nm diameter (from DLS). It is thus a sort of natural nanoparticle that can be used to prepared nanostructured functional materials. A possible strategy to provide glycogen with functional properties for optical or biological application relies on the insertion of specific functional groups on the surface of this nanoparticle by chemical modification. The oxidation of glycogen with periodate groups seems a promising strategy since this reaction occurs under mild conditions with the formation of aldehyde groups. These lasts are very reactive groups and can be converted easily in a variety of chemical and biological functionality by reactions suitable amines derivatives. Glycogen was oxidized with IO4- amount per glycosidic unit in the range 0.5-20 % mol/mol. Water, methanol, propanol and N,N-dimethylformamide (DMF) were used as reaction solvents. The reaction products were characterised by NMR spectroscopy and base titration after treatment with hydroxylamine chlorohydrate to obtaining the oxidation degree. The selective cleavage of the oxidized units of glycogen followed by SEC analysis provided information on the distance of the aldehyde groups from the glycogen chain-ends, that roughly corresponds to the distance from the surface of the nanoparticle. The experimental results showed that a good control over the aldehyde group amount can be obtained by controlling the periodate amount in the reaction feed while the distribution of the groups depends on the glycogen accessibility in the reaction solvent. In particular fictionalization only at the surface was obtained in DMF.