２０１４年４月２４日 Ziya Kalay氏 （終了）

日時： ２０１４年４月２４日（木）１６：００
場所： 首都大学東京　８号館３０２号室
講師： Ziya Kalay氏（京都大学 WPI-iCeMS）
題目： Lateral diffusion in a 2-D fluid with immobile heterogeneities

要旨： In this talk I will present the results of our recent study [1] motivated by the observation that the outermost membrane of many cells contains immobile proteins, hindering the lateral diffusion of membrane molecules. As shown previously, the presence immobile obstacles reduces diffusivity especially when fluid dynamic interactions are accounted for [2,3]. We investigated the effects of a distribution of immobile particles on diffusion, accounting for the discrete nature of the fluid, long-ranged fluid dynamical interactions and correlations in the distribution of immobile particles. By performing event driven molecular dynamics simulations on a hard disk system, we found that the diffusion coefficient sharply decreases with the fraction of immobile particles, dropping by a factor of ∼3 as the fraction of immobile particles increases from 0 to 0.1. By combining our results with earlier analytical calculations [3], we estimated that a factor-of-∼20 reduction in diffusion coefficients in live cell membranes, a puzzling finding in cell biology, can be accounted for when less than ∼22% of the particles in our model system is immobilized. Furthermore, we investigated the effects of confinement induced by a correlated distribution of immobile particles. Calculating the distribution of the time it takes for particles to escape from a corral, we showed that the mean escape time grows exponentially with the density of obstacles at the corral boundary, and is approximately proportional to the area of the corral. We believe that our findings will be useful in interpreting both the observations of diffusion in a heterogeneous fluid and results of particle based simulations that explore the effect of fluid dynamics on molecular transport in a 2-D fluid.

[1] Z. Kalay, T. K. Fujiwara, A. Otaka, and A. Kusumi, Phys. Rev. E 89:022724 (2014)
[2] S. J. Bussell, D. L. Koch, and D. A. Hammer, Biophys. J. 68:1836 (1995)
[3] N. Oppenheimer and H. Diamant, Phys. Rev. Lett. 107:258102 (2011)