Abstrakt

Polysaccharide chain conformation and mechanical properties are governed by local conformational degrees of freedom, in particular the torsional states of glycosidic linkages. Understanding how local torsional energetics propagate into global chain stiffness is essential for interpreting experimental data and for the development and validation of carbohydrate-specific force fields. In this study, we systematically investigated the relationship between the energetic stability of anti-type glycosidic conformers and the global conformational properties of polysaccharide chains. Monte Carlo simulations based on a reduced coarse-grained model were performed for three glucans – amylose (containing α(1 → 4) linkages), curdlan (β(1 → 3)), and cellulose (β(1 → 4)) – by progressively penalizing anti-Φ and anti-Ψ torsional states over a wide energetic range. In addition, the heterogeneous polysaccharide hyaluronan was analyzed by selectively blocking specific torsional freedoms at its β(1 → 3) and β(1 → 4) linkages. The results reveal qualitatively different mechanical regimes depending on linkage topology. Amylose behaves as an entropy-dominated semiflexible coil, with stiffness controlled mainly by Ψ energetics and showing only modest, gradual stiffening. Curdlan is geometry-dominated and highly sensitive to Φ energetics, rapidly reaching a rigidity plateau. Cellulose exhibits a critical, highly nonlinear response, where suppression of Ψ conformers drives a transition to near rod-like behavior with persistence lengths increasing by orders of magnitude. Importantly, the experimentally observed stiffness ordering of glucans (amylose < curdlan < cellulose) is preserved for nearly all combinations of anti-conformer energy levels, indicating that qualitative mechanical trends are largely insensitive to the specific energetic parameterization. Comparison with experimental persistence lengths further suggests that the free-energy penalties of anti-Ψ conformers lie below 5 kJ/mol for amylose, at ca. 5 kJ/mol for anti-Φ in curdlan, and in the range of 5–10 kJ/mol for anti-Ψ in cellulose. Hyaluronan shows intermediate stiffness, with Ψ rotations at β(1 → 4) linkages acting as dominant mechanical control points. Overall, the study demonstrates that specific local torsional transitions play distinct mechanical roles, and that linkage geometry fundamentally determines how local conformational energetics translate into global polysaccharide stiffness.