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Interactions between 2-methylisoborneol and C-phycocyanin: Binding site analysis and effects of complexation on
Sihong Li1, Yuhui Ma2, Maoxia He2
1Shandong Key Laboratory of Synergistic Control of Complex Multi-Media Pollution, School of Environmental Science and Engineering, Shandong University, Qingdao, 266237, China.
Abstract:
2-Methylisoborneol (2-MIB), predominantly produced by cyanobacteria in drinking water sources, is a major off-flavor compound responsible for earthy-musty odors at extremely low concentrations. Recent evidence suggests that a substantial fraction of 2-MIB exists in a bound state associated with algal-derived proteins, yet the mechanism governing this association and its influence on 2-MIB removal during advanced oxidation processes (AOPs) remain poorly understood. In this study, the influence of protein binding on 2-MIB degradation was systematically investigated in UV/H2O2 and UV/Cl2 processes using C-phycocyanin (C-PC) as a representative algal protein. Relative to the freshly mixed system, the pre-equilibrated 2-MIB/C-PC system showed consistently lower 2-MIB degradation efficiencies and apparent reaction rate constants under both UV-AOPs. At an initial 2-MIB concentration of 1.0 μg/L, C-PC binding decreased the 2-MIB removal efficiency at 40 min in the UV/H2O2 and UV/Cl2 processes from 85.8% to 74.8% and from 63.0% to 57.3%, respectively. Spectroscopic analyses, molecular docking, and molecular dynamics simulations collectively showed that 2-MIB could be accommodated within a hydrophobic pocket of C-PC, where van der Waals interactions dominated the overall binding stability. Density functional theory calculations further revealed that a residue-specific hydrogen bond involving lysine altered the electrostatic potential around the hydroxyl group of 2-MIB and reduced its local radical reactivity. In contrast, free lysine did not form a stable association with 2-MIB in bulk water, highlighting the essential role of the confined protein microenvironment. These findings indicate that protein-associated binding states should be considered when optimizing UV-AOPs for odor control in bloom-impacted drinking water sources, as weakening protein-2-MIB associations may enhance 2-MIB accessibility to reactive species and thereby improve oxidative removal of 2-MIB.
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