Decoding the molecular interaction mechanisms of tannic acid in modulating Fe3+‑sodium alginate microgel delivery systems

Abstract

While conventional studies of polysaccharide hydrogel networks emphasize singular polysaccharide-metal coordination, we hypothesized that synergistic interactions between hydrogen bonding and Fe³⁺-tannic acid coordination could enhance the structural stability and functional performance of alginate-based microgels. To test this, we investigated the binding mechanisms of tannic acid in Fe³⁺‑sodium alginate microgels as a model system. Using FTIR, XRD, and XPS analyses combined with molecular docking simulations, we systematically identified the dominant molecular interactions (hydrogen bonding/coordination) and their binding sites in tannic acid-modulated gels. Our results demonstrated that the proposed dual-interaction mechanism significantly reinforced the gel network, improving microgel stability and controlled release efficiency. Tannic acid-Fe³⁺‑sodium alginate microgels achieved a 34.1 % increase in folic acid bioaccessibility (encapsulation efficiency: 97.3 %), and synergistic antioxidant activity (86.4 % DPPH scavenging). This work validates the hypothesis that polyphenol-modulated dual interactions outperform single-coordination networks, providing a framework for designing advanced nutrient delivery systems with enhanced bioavailability and multifunctionality.