Hybrid materials obtained through the synthesis of gold nanoparticles in the branched structure of a natural biopolymer, the polysaccharide glucuronoxylomannan (GXM), spontaneously form and demonstrate the highest stability in an alkaline environment. This is due to the fact that under these conditions, the ionisation of carboxyl groups leads to electrostatic repulsion of equally charged GXM fragments and the biomolecule ‘tends’ to form flexible, partially unfolded structures. In addition, polysaccharides undergo hydrolysis in an alkaline environment with gradual cleavage of monosaccharide links, starting from the reducing end of the polysaccharide (the so-called basic degradation of polysaccharides).
As a result of alkaline cleavage of heteroglycan, a shortened polysaccharide backbone is formed in the reaction mixture, and methasaccharide acids and unsaturated sugars are formed from the side chains, in the oligosaccharide residues of which acetyl groups are deacylated under the action of alkali. Alkali-induced hydrolysis leads to the growth of hydroxyl groups on small fragments, which in themselves can stabilise nanostructures, preventing their further growth, coalescence and dissolution. The presence of small and mobile polysaccharide fragments leads to a more rigid stabilisation of open fragments of spherical metal particles, on the one hand, and the formation of nanoparticles with triangular or quadrangular geometry, as we have shown for the case of monosaccharides . As a result, such hybrids have a dense and well-organised organic shell. A sufficiently large distance between metal nanoparticles and a solid layer of organic stabiliser makes the hybrid less prone to degradation over time. The report describes in detail the main mechanism of shortening the polysaccharide backbone due to alkaline degradation of polysaccharides and deacylation of the end fragments of the side chains. It also provides a brief overview of the results obtained by the authors for similar structures and suggests the most promising ways to use them.
