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Shew, Chwen-Yang

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Title Conformations of Single Semiflexible Chains in Poor Solvents: Density-of-States Monte Carlo SimulationAuthor(s)Shew, Chwen-YangCitation物性研究 (2006), 87(1): 197-198Issue Date2006-10-20URL http://hdl.handle.net/2433/110578RightType Departmental Bulletin PaperTextversionpublisherKyoto University「ソフトマターの物理学 2006JConformations of Single Semiflexible Chains in Poor Solvents Density-of-States Monte Carlo Simulation Dept. of Chemistry， Graduate Center， City Univ. of New York Chwen-Yang Shew 1 1 Introduction The conformational behavior of a single semiflexible chain has been investigated by using Monte Carlo simulations. In contrast to the continuous transition of a neutral flexible polymer， a semiflexible chain undergoes a discontinuous conformational transition， as solvent quality is decreased. Such a transition is analogous to the first-order ph錨 etransition， with coexistent elongated and compact conformational stat四・ [1]In this work， computer simulations are carried out to manifest the elongated and compact conformational states for a short semiflexible chain. 2 乱10delHere the semiflexible chain is modeled as a nonlinear elastic chain (FENE) of 8-mers， subjected to a bending energy due to local chain sti宜ness.[2] Also， monomers interact through a repulsive Lenna訂rd-Jofromr陀ef伽e位re印nc印e2. To model poor solvents， an attractive Yukawa potential is incorporated between monomers， with an adjustable interaction strength f. In the simulations， chain conformation is relaxed by using random walks for monomers， equivalent to monomer Brownian motion. [3] 3 Results and Discussion Our simulations show that for smaller f， chain conformation remains coiled-like， but for larger ε， chain tends to contract. Once chain reaches the folded state， areverse process is applied to unfold chain conformation by decreasing f in the simulations. A hysteresis loop for the folding-unfolding cycle of a stif enough chain is observed. A further study is carried out via the density-of-states Monte Carlo method (DOSMC) [4] to discern the stability of the two di百erentconformational states for a given εin the hysteresis loop. We find that the energy distribution obtained from DOSMC is close to that of the folded state (in figure 1)， indicating its thermodynamic stability. 1 E-mail: shew@mail.csi.cuny.edu ?????研究会報告0.25 foo訓 C→ uwiCompact state 0.2 015 a 0.1 0.05 。-80 マ60 40 20 20 E Figure 1: Comparison of the simulated energy distribution of elongated (unfolded) and compact (folded) conformational states (solid lines) with that of DOSMC (dotted line). 4 Conclusions The conformational behavior of a short semiflexible chain is investigated by using Monte Carlo simulations. The traditional Monte Carlo method generates a conformational hysteresis loop for a stif enough chain. The elongated and compact conformational stat田 aredominated for the folding and unfolding processes， respectively. From the simulations of the density of states， we find that the folded state can be more favorable thermodynamically in the hysteresis loop. Acknowledgment This work is partially supported by PSC-CUNY award， and CePM and MMA at CSljCUNY. Also， CYS thanks Prof. Kenichi Yoshikawa for stimulating discussions and suggestions. References [1] K. Yoshikawa， Adv. Drug Delivery Rev. 52 (2∞1) 235. [2] M. J. Stevens， Biophys. J. 80 (2001) 130. [3] A. Milchev， K. Binder and A. Bhattacharya， J.Chem. Phys. 22 (2004) 6042. [4] F. Wa昭如dD. P. Landau， Phys. Rev. Lett. 86 (2001) 2050. -198-

Conformations of Single Semiflexible Chains in Poor Solvents : Density-of-States Monte Carlo Simulation

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Conformations of Single Semiflexible Chains in Poor Solvents : Density-of-States Monte Carlo Simulation

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