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Abstract
Understanding the dynamics of complex molecular systems is often facilitated by analysis of underlying free energy landscapes. In particular, activated transitions between metastable states of a system are frequently investigated assuming that the system follows a minimum energy path (MEP) connecting these states. However, the MEP assumption becomes invalid if the timescale of the system relaxation towards the MEP is comparable with the timescale of the system motion along the MEP. We demonstrate that such non-adiabatic dynamics takes place during molecular transport across flexible membranes and interfaces. This phenomenon is illustrated by a case study of penetration of a hydrophobic nanoparticle into a lipid bilayer. This system is investigated using constrained molecular dynamics simulations. Motion of this system along the MEP involves significant changes in the membrane shape in response to the nanoparticle position. It is shown that the timescale associated with these shape changes exceeds the timescale of the translational motion of the nanoparticle, which leads to non-adiabatic coupling between the nanoparticle transport and the membrane fluctuations. Implication of this coupling to analysis of the constrained simulations is discussed.
Acknowledgements
This research was supported by the National Science Foundation through CAREER Award (Grant CBET-0644089) and the Environmental Protection Agency (STAR programme Grant No. R832635). R.A. Tasseff received support from the University Scholars Programme at the University of Florida.
Notes
1. Present address: ACI Unit Process Development Group, Samsung Electro-Mechanics, 314, Maetan 3-Dong, Yeongtong-Gu, Suwon-Si, Gyeonggi-Do 443-743, South Korea. Email: [email protected]
2. Present address: School of Chemical & Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA. Email: [email protected]