Molecular pumping and separation in a symmetric channel
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Molecular pumping and separation in a symmetric channel D. Fleishmana, A.E. Filippovb and M. Urbakha a School of Chemistry, Tel Aviv University, 69978 Tel Aviv, Israel. b Donetsk Institute for Physics and Engineering of NASU, 83144, Donetsk, Ukraine. ABSTRACT A mechanism responsible for directed transport and molecular separation in a symmetric channel is proposed. We found that under the action of spatial harmonic oscillations of the channel, the system exhibits a directed transport in either direction, presenting multiple current reversals as the amplitude and/or frequency of the oscillations are varied. The particles of different masses may be forced to move with different velocities in the same or in the opposite directions by properly adjusting driving parameters. The directed transport can be produced in both directions even in the absence of thermal noise, the latter can speed up or slow down the transport depending on the system parameters. INTRODUCTION In recent years there has been an increasing interest in studies of molecular pumps and channels [1-7]. These investigations have been motivated by a desire to understand how biological molecular pumps operate and to develop new strategies for a fabrication of synthetic pumps. Most studies in this field rely on the idea of particles moving in spatially asymmetric (ratchet) potentials, [8-12]. So far such studies have been focused on directed motion of particles through a rigid channel without considering fluctuations of its structure. However, dynamics of internal degrees of freedom of the channel proteins is in many cases essential for net directional motion to occur [13]. From the viewpoint of physics, it should also be interesting to explore the interconnections between the channel’s intrinsic dynamics and directed transport. The closely related concept of dynamical control of motion has received much attention recently in the context of molecular engines [14-17]. It has been shown that directed motion can be induced dynamically and no static asymmetry is required which is built into in the system. In this paper we propose a pumping mechanism driven by spatial fluctuations of a symmetric channel. We demonstrate that an effective pumping and separation of particles can be achieved by correlated oscillations of the walls of the channel in the lateral (along the channel axis) and normal (perpendicular to the channel axis) directions. The space oscillations of the channel lead to a modulation of the particle-wall interactions those produce temporally asymmetric forces acting on the particles. The main advantages of the proposed mechanism of pumping are: (a) the directionality of motion is determined dynamically and does not require any spatial asymmetry of the channel, (b) the transport velocity can be varied in a wide range, independent of the direction, (c) the pump allows a separation of particles according to their masses or/and interaction with the channel walls, (d) the pump can induce motion uphill a gradient of electrochemical potential, (e) de
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