Structural and spectroscopic details of polysaccharide–bile acid composites from molecular dynamics simulations

Abstract

Interactions of a prototypical bile acid (cholic acid, ‘Ch’) and its corresponding sodium salt (sodium cholate, ‘NaCh’) with a standard dietary β-glucan (β-G), bearing β-D-glucopyranose units having mixed 1-4/1-3 glycosidic linkages are studied using molecular dynamics simulation and density functional theory (DFT) calculations. Self-aggregation of the biliary components and their interaction with fifteen strands of the decameric mixed linkage β-glucan is elucidated by estimating varieties of physical properties like the coordination number, moment of inertia and shape anisotropy of the biggest cluster formed at different time instants. Small angle scattering profiles indicate formation of compact spheroidal aggregates. The simulated results of small angle scattering and ¹H NMR chemical shifts are compared to spectroscopic data, wherever available. Density functional theory calculations and estimation of the ¹H NMR chemical shifts of Ch-protons lying close to the β-G chains reveal change in chemical shift values from that in absence of the polysaccharide. Hydrogen bonding and non-bonding interactions, primarily short range van der Waals interactions and some extent of inter-molecular charge transfer are found to play significant role in stabilizing the complex soft assemblies of bile acid aggregates and β-G.

Communicated by Ramaswamy H. Sarma

Keywords:

• Polysaccharide
• glucan
• bile acid
• molecular dynamics
• small angle scattering
• density functional theory
• NMR

Acknowledgements

SP and DR acknowledge gratefully the computation time provided on the high performance computing facility, Sharanga, at the Birla Institute of Technology and Science – Pilani, Hyderabad Campus.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

Data pertaining to the paper are available from the authors upon reasonable request.

Additional information

Funding

DR is obliged to the Science and Engineering Research Board, India (SERB, CRG/2018/000949 and SPG/2021/002390) for generous funding. SP is thankful to BITS-Pilani, Hyderabad for PhD fellowship.