title: Binding structure and kinetics of surfactin monolayer formed at the air/water interface to counterions: A molecular dynamics simulation study.
abstract: The binding structure and kinetics of ionized surfactin monolayer formed at the air/water interface to five counterions, Li+, Na+, K+, Ca2+, and Ba2+ (molar ratios of surfactin to monovalent and divalent counterions are 1:2 and 1:1 respectively), have been studied using molecular dynamics simulation. The results show that surfactin exhibits higher binding affinity to divalent counterions, Ca2+, and Ba2+, and smaller monovalent counterion, Li+, than Na+ and K+. Both carboxyl groups in surfactin are accessible for counterions, but the carboxyl group in Glu1 is easier to access by counterions than Asp5. Salt bridges are widely built between carboxyl groups by counterions, and the probability of the formation of intermolecular salt bridge is markedly larger than that of intramolecular salt bridge. Divalent counterions perform well in forming salt bridges between carboxyl groups. The salt bridges mediated by Ca2+ are so rigid that the lifetimes are about 0.13 ns, and the break rates of these salt bridges are 1-2 orders of magnitude smaller than those mediated by K+ which is about 5 ps in duration. The positions of the hydration layer of carboxyl groups are independent of counterions, but the bound counterions induce the dehydration of carboxyl groups and disturb the hydrogen bonds built between carboxyl group and hydration water.
authors.affiliation: State Key Laboratory of Bioreactor Engineering and Applied Chemistry Institute, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, PR China.
authors.forename: Hongze
authors.initials: H
authors.lastname: Gang
authors.affiliation: State Key Laboratory of Bioreactor Engineering and Applied Chemistry Institute, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, PR China.
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Bioreactor Engineering and Applied Chemistry Institute, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, PR China; Shanghai Collaborative Innovation Center for Biomanufacturing Technology, 130 Meilong Road, Shanghai 200237, PR China. Electronic address: bzmu@ecust.edu.cn.
authors.forename: Bozhong
authors.initials: B
authors.lastname: Mu
mesh_terms: D000388:Air; D001665:Binding Sites; D003198:Computer Simulation; D007477:Ions / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D010456:Peptides, Cyclic / Q000737:chemistry*; D055672:Static Electricity; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D007477:Ions; D010456:Peptides, Cyclic; D013501:Surface-Active Agents; D014867:Water
keywords: Binding affinity; Break rate; Counterion; Salt bridge; Surfactin monolayer