Why sugar chains swell in a solvent that should make them shrink
12 Aug 2026 - Rosie de Laune
A multidisciplinary group of researchers from across the world, led by teams from the Technical University of Munich and University of Leeds, have used neutrons to explain why polysaccharide chains first swell and then collapse in water/glycerol mixtures; a behaviour which the classical descriptions of polymer chain contracting in a poorer solvent cannot account for. Their findings deepen our knowledge of biological processes and could inform industrial processing and the design of future foods, hydrogels, and bioelectronics.
Polysaccharides such as starch and cellulose are complex carbohydrates made of long chains of smaller sugar units. Together with nucleic acids, proteins, and lipids, they are one of the four fundamental building blocks of life. The shape, or conformation, they adopt dictates both their biological function and their flow properties, which are important for industrial processing.
While many polysaccharides adopt a flexible shape in water, several living organisms, including plants, fish, insects, and fungi, accumulate cosolvents such as glycerol in micromolar to molar concentrations. Glycerol is also widely used in industrial processes and so it’s important to understand polysaccharide behaviour when glycerol is present.
In this study, published in Carbohydrate Polymers, the group used quasi-elastic neutron scattering (QENS) on Iris at ISIS, and elastic scattering on IN13 at ILL, to study a polysaccharide called as pectin, extracted from okra fruits, in a series of water/glycerol mixtures. Their QENS measurements allowed them to directly observe the nanoscale water dynamics around the pectin chain.
As glycerol is a poorer solvent for polysaccharides like pectin, the expected result would be for the pectin to gradually be less soluble in the solution as the glycerol level was increased. Instead, they found that, at low glycerol levels, the pectin actually becomes more soluble. This is because glycerol, rather than water, preferentially gathers around the chain and displaces some of the water. As glycerol rises to 60 and then 80%, the pectin chains collapse, where the situation reverses, and it is water that preferentially gathers near the chain while glycerol is excluded.
The picture that emerges is of a chain that changes shape to conserve its total contact with water.
Pallab Kumar Borah, TU Munich
“The picture that emerges is of a chain that changes shape to conserve its total contact with water,” explains first author Pallab Kumar Borah, from TU Munich.
By calculating the entropy changes at each stage, they found that, at lower glycerol levels, the swelling is accompanied by an increase in conformational entropy. In contrast, at higher glycerol concentrations, the polysaccharide collapse is associated with a modest increase in the entropy of hydration water.
The framework proposed by the researchers accounts for shape shifting in other complex polysaccharides such as agar, alginate, carboxymethylcellulose, and dextran in water/glycerol mixtures, published independently by other groups, suggesting that the same physical principle may be at work, and provides a rich paradigm for future progress.
In a biological context, this raises the possibility that living organisms may exploit this mechanism by accumulating poorer cosolvents to modify the environment inside and out of their cells.
From an industrial perspective, this mechanism provides a foundation for novel strategies for controlling polysaccharide conformation. This could inform the design of responsive hydrogels, or the development of novel functionality in carbohydrate-based foods, bioelectronics, and pharmaceuticals.
The full paper can be found at DOI: 10.1016/j.carbpol.2026.125726
