Design of two-tooth unidirectional rotary-ratchet molecular machines driven by linearly polarized ac fields.
An artificial molecular rotor system mounted in a biological membrane, which can unidirectionally rotate in response to weak pumping from a linearly polarized ac field, is modeled. The dynamics of the rotor unit are described by the Langevin equation for a particle in a two-dimensional bistable potential with a two-tooth ratchet structure. This model reveals effects due to the two-dimensionality of the ratchet and the polarization of the applied field. First, we demonstrate that a unidirectional rotation appears with stochastic resonance exhibiting a bell-shaped peak for noise intensity in the mean angular momentum (MAM) of the rotor. An analytical expression for the MAM, (L), is obtained on the basis of a four-state Markov approximation. Second, a significant effect due to torsional nonlinearity (representing the ratchet-like structure) in the potential geometry is quantified: in the absence of torsion, the MAM depends on the polarization angle φ of the applied field as (L) sin(2φ), whereas in the presence of torsion, an additional bias appears in the MAM as (L)(bias + sin(2φ)). It is found that this effect can be used to make the rotor system robustly maintain rotation in a single direction independent of the mounting conditions. Possible designs for an artificial molecular rotor system using the torsion effect are discussed.
Department of Applied Analysis and Complex Dynamical Systems, Graduate School of Informatics, Kyoto University, Kyoto 606-8501, Japan.
Hiroki
H
Tutu
Yuta
Y
Hoshino
D032701:Biomimetics / Q000379:methods*; D008962:Models, Theoretical; D020409:Molecular Motor Proteins / Q000378:metabolism; D012399:Rotation
D020409:Molecular Motor Proteins