Metal-ion-modulated dynamic affinity adsorption of α-amylase on β-cyclodextrin-functionalized polystyrene

Affinity-based adsorption enables selective enzyme separation through specific ligand–enzyme interactions under dynamic flow conditions. In this study, the dynamic affinity adsorption of α-amylase on β-cyclodextrin–diaminopropane–polystyrene (βCD–DAP–PS) was investigated, focusing on the influence of dissolved metal ions under continuous-flow operation. Dynamic adsorption experiments were conducted in the absence and presence of Na+, Ca2+, and Cu2+ ions (1–9 mM), and adsorption performance was evaluated using the maximum binding capacity (qm) and apparent affinity equilibrium constant (K) derived from Langmuir-type analysis. The adsorption behavior was adequately described by a Langmuir-type model under all conditions, indicating that the fundamental affinity interaction mechanism remained unchanged upon metal ion addition. Metal ions significantly influenced adsorption performance. Na+ and Cu2+ enhanced binding capacity, while Ca2+ exhibited a concentration-dependent effect, with reduced adsorption at higher concentrations. In contrast, all metal ions decreased the apparent affinity equilibrium constant, indicating reduced binding preference. Among the investigated conditions, Na+ at 7 mM provided the most favorable balance between adsorption capacity and apparent affinity. These findings demonstrate that solution chemistry can be used to modulate affinity-based separation performance under dynamic conditions, providing insight for optimizing operating conditions in cyclodextrin-based systems.