Dissipative Particle Dynamics Studies on the Self-Assembling Dynamics of the Peptide Amphiphiles
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1135-CC06-02
Dissipative Particle Dynamics Studies on the Self-Assembling Dynamics of the Peptide Amphiphiles Taiga Seki1, Noriyoshi Arai1, Taku Ozawa2, Tomoko Shimada3, Kenji Yasuoka1 and Atsushi Hotta1 1 Graduate School of Science and Technology, Keio University, Yokohama, Japan. 2 JRI Solutions, Ltd., Tokyo, Japan. 3 Asahi Kasei Co., Tokyo, Japan. ABSTRACT A coarse-grained model of peptide amphiphiles (PA) dissolved in aqueous solution was presented, where the effects of PA concentration, temperature and shear stress upon the selfassembly of PA were numerically studied by dissipative particle dynamics (DPD) simulation. We technically investigate the repulsion parameter aHW which indicates the repulsion force between the hydrophilic head of PA and water molecules, hence, at the same time, indicating the change in temperature. It was found that aHW played an important role in the self-assembly dynamics and in the resulting micro-structures of PA. By imposing shear strain on the simulation system, the formation of wormlike PA micelles was accelerated. The simulation results were in good agreement with our previous experimental results and the mechanism of shear-induced transition was proposed. INTRODUCTION Self-assembly of amphiphilic molecules is attracting considerable interests for its wide variety of application largely due to the ability to construct supermolecular structures such as spherical micelles, wormlike micelles, lamellar and vesicles [1]. It is known that such selfassembling behavior of general amphiphilic molecules dissolved in solution depends on temperature, pH, and the concentration of the solution [1]. Recent development in computer technology has greatly improved such existing numerical techniques as molecular dynamics (MD), Monte Carlo (MC) and dissipative particle dynamics (DPD) simulations and numerous works have successfully unraveled the debatable self-assembly behavior of surfactants [2, 3] and copolymers [4, 5]. Shear stress was regarded as another key factor influencing the self-assembled structures, and several investigations concerning shear-induced structural transitions of aggregates under particular conditions have been reported [6-8]. Peptide amphiphile (PA) which is composed of hydrophilic peptides and hydrophobic alkyl chains is one of the most prospective materials in biological and biomedical fields [9-11], targeting e.g. drug delivery systems and cell culturing. For practical use of PA, computational studies on the dynamics and the mechanism of the self-assembly are indispensable. Quite a few experimental studies have been carried out on self assembly of PA [10-16]. Nowak et al. [13] and Ding et al. [14] reported the effect of chain conformation on the selfassembly behavior of PA. They found that the microscopic conformation of peptides played an important role in determining macroscopic aggregate structures. Our recent experimental studies on specific PA, which was named C16-W3K, revealed that the PA exhibited simultaneous structural transitions both in aggregate structures
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