First principles modelling of the ion binding capacity of finger millet

Wei Cong Matthew Yong; Apramita Devi; Tsair-Fuh Lin; Helen F Chappell

doi:10.1038/s41538-024-00270-1

First principles modelling of the ion binding capacity of finger millet

NPJ Sci Food. 2024 May 14;8(1):28. doi: 10.1038/s41538-024-00270-1.

Authors

Wei Cong Matthew Yong¹, Apramita Devi^{2

3}, Tsair-Fuh Lin³, Helen F Chappell⁴

Affiliations

¹ School of Food Science and Nutrition, University of Leeds, Leeds, UK.
² Department of Viticulture and Enology, University of California, Davis, CA, USA.
³ Department of Environmental Engineering, National Cheng Kung University, Tainan, Taiwan.
⁴ School of Food Science and Nutrition, University of Leeds, Leeds, UK. [email protected].

Abstract

Finger millet, a cereal grain widely consumed in India and Africa, has gained more attention in recent years due to its high dietary fibre (arabinoxylan) and trace mineral content, and its climate resilience. The aim of this study was to understand the interactions between potassium (K⁺), calcium (Ca²⁺) and zinc (Zn²⁺) ions and the arabinoxylan structure and determine its ion-binding capacity. Three variations of a proposed model of the arabinoxylan structure were constructed and first principles Density Functional Theory calculations were carried out to determine the cation-binding capacity of the arabinoxylan complexes. Zn²⁺-arabinoxylan complexes were highly unstable and thermodynamically unfavourable in all three models. Ca²⁺ and K⁺ ions, however, form thermodynamically stable complexes, particularly involving two glucuronic acid residues as a binding pocket. Glucuronic acid residues are found to play a key role in stabilising the cation-arabinoxylan complex, and steric effects are more important to the stability than charge density. Our results highlight the most important structural features of the millet fibre regarding ion-storage capacity, and provide valuable preliminary data for confirmatory experimental studies and for the planning of clinical trials where the bioavailability of bound ions following digestion may be tested.