Tailoring acidic deep eutectic solvents for selenylation of locust bean gum: Elucidating acidity and polarity effects on selenium incorporation and molecular weight.

In the field of food colloids, selenium (Se) modification is considered a promising strategy for the development of organic selenium additives. However, the synthesis of Se-polysaccharide is frequently hindered by low selenium incorporation and uncontrolled molecular weight (MW) degradation. In this study, a collection of acidic deep eutectic solvents (ADESs), formulated from choline chloride paired with diverse carboxylic acids were developed as dual-functional media for the selenylation of locust bean gum (LBG). The resulting selenized LBG (SeLBG) exhibited a markedly enhanced Se content (up to 11,038 μg/g), representing a significant improvement over HNO3/Na2SeO3 and DMSO-based methods. Further analysis revealed significant correlations between ADES acidity (H0), polarity (ETN) and selenylation efficiency, with stronger acidity and higher polarity generally associated with increased Se incorporation. FT-IR and 13C NMR characterization confirmed the formation of selenite esters, primarily through substitution at the C-6 hydroxyl groups of mannose residues. Moreover, MW analysis demonstrated that polysaccharide degradation was modulated by both solvent acidity and polarity, where higher polarity was associated with greater molecular-weight reduction, which may be related to enhanced polysaccharide solvation and conformational changes.. Importantly, computational analyses rooted in density functional theory (DFT) alongside molecular dynamics (MD) modeling indicated enhanced hydrogen-bonding affinity between ADESs and LBG enhanced solvation and exposed more reactive sites, thereby facilitating improved selenylation efficiency. This work demonstrated that tailoring the physicochemical properties of ADESs enables precise control over the Se content and MW of Se-polysaccharides, providing a robust strategy for the structure-oriented synthesis of bioactive glycan derivatives.