Structure and Dynamics of Hydrated Biopolymers
Time: Fri 2023-08-25 10.00
Subject area: Fibre and Polymer Science
Doctoral student: Poornima Ramamohan , Fiber- och polymerteknologi, Wallenberg Wood Science Center, Biocomposites
Opponent: Docent Fritjof Nilsson, Fiber- och polymerteknologi
Supervisor: Docent Jakob Wohlert, Fysik, Wallenberg Wood Science Center, Biokompositer; Professor Istvan Furo, Tillämpad fysikalisk kemi, Centrum för Industriell NMR-teknik, Wallenberg Wood Science Center
Hydrated polysaccharide systems primarily using xylans along with mutans and alternans were studied using long atomistic simulations over a few microseconds to analyse structure-function relationships and nanoscale interactions with moisture. The influence of various structural and chemical factors such as alignment, nature of glycosidic linkage, effect of moisture / chemical substitutions was explored with a focus on structure-dynamics correlations to aid in the effective functionalisation of biomaterials for the development of a green, circular bioeconomy. The effect of initial geometry in terms of alignment of the xylan chains was observed to affect xylan chain extension and water dynamics significantly. Xylan interaction with moisture studied at high and low moisture contents showed compression along with structural locking, and evolution into segregated water-rich and polymer-rich phases respectively. The effect of chemical heterogeneity in terms of substitutions appeared to improve xylan dispersion in water resulting in faster dynamics for substituted residues with reference to unsubstituted residues along a given polymer chain. In addition, significant correlations between local hydration and polymer dynamics / structure in terms of relaxation times and order parameters was observed across differently substituted hydrated xylan systems, such that the polymer dynamics could be expressed as a local hydration water dependent component and a second partially stochastic component. In addition, the molecular structure of mixed linkage (1,3 and 1,6) as well as 1,3 linked glucans elucidated the effect of the nature of glycosidic linkage on the molecular structure of glucan oligosaccharides. A combination of glucan linkages and the ratio of different conformation states of the hydroxymethyl dihedral angle was observed to yield linear, twisted and extended structures in mutans, or helical coils of varying pitch sizes in alternans. Further modeling of structure-dynamics dependencies in hydrated xylan systems and analysis of the effect of alignment / chemical substitutions at the nanoscale is to be correlated with scattering or related experimental techniques in the future to understand the dynamics of hydrated xylan aggregates in typically aqueous solutions at varying intermediate length / timescales. In addition, the methodologies derived in this work to identify atom-specific, temporally sensitive, structural / dynamical parameters for analysing structural / dynamical variations at the nanoscale can be extended to study other hydrated biopolymeric systems. The role of substitutions, involving its polar nature and interactions with other xylans, can be extended to neutral groups such as arabinose sugars to broaden knowledge in carbohydrate science as well as being analysed further to improve effective functionalisation for tailoring physical properties influencing phenomena like aggregation / dispersion.