Ghosh Surya K, Cherstvy Andrey G, Metzler Ralf
Institute for Physics & Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany.
Phys Chem Chem Phys. 2015 Jan 21;17(3):1847-58. doi: 10.1039/c4cp03599b. Epub 2014 Dec 4.
We study the diffusion of a tracer particle, which moves in continuum space between a lattice of excluded volume, immobile non-inert obstacles. In particular, we analyse how the strength of the tracer-obstacle interactions and the volume occupancy of the crowders alter the diffusive motion of the tracer. From the details of partitioning of the tracer diffusion modes between trapping states when bound to obstacles and bulk diffusion, we examine the degree of localisation of the tracer in the lattice of crowders. We study the properties of the tracer diffusion in terms of the ensemble and time averaged mean squared displacements, the trapping time distributions, the amplitude variation of the time averaged mean squared displacements, and the non-Gaussianity parameter of the diffusing tracer. We conclude that tracer-obstacle adsorption and binding triggers a transient anomalous diffusion. From a very narrow spread of recorded individual time averaged trajectories we exclude continuous type random walk processes as the underlying physical model of the tracer diffusion in our system. For moderate tracer-crowder attraction the motion is found to be fully ergodic, while at stronger attraction strength a transient disparity between ensemble and time averaged mean squared displacements occurs. We also put our results into perspective with findings from experimental single-particle tracking and simulations of the diffusion of tagged tracers in dense crowded suspensions. Our results have implications for the diffusion, transport, and spreading of chemical components in highly crowded environments inside living cells and other structured liquids.
我们研究了示踪粒子的扩散，该粒子在具有排除体积的晶格、固定的非惰性障碍物之间的连续空间中移动。特别地，我们分析了示踪粒子与障碍物相互作用的强度以及拥挤剂的体积占有率如何改变示踪粒子的扩散运动。从示踪粒子在与障碍物结合时的捕获状态和体扩散之间的扩散模式分配细节，我们研究了示踪粒子在拥挤剂晶格中的局域化程度。我们从系综平均和时间平均的均方位移、捕获时间分布、时间平均均方位移的幅度变化以及扩散示踪粒子的非高斯性参数等方面研究了示踪粒子扩散的性质。我们得出结论，示踪粒子与障碍物的吸附和结合引发了瞬态反常扩散。从记录的单个时间平均轨迹的非常窄的分布中，我们排除了连续型随机游走过程作为我们系统中示踪粒子扩散的潜在物理模型。对于适度的示踪粒子 - 拥挤剂吸引力，发现运动是完全遍历的，而在更强的吸引力强度下，系综平均和时间平均均方位移之间会出现瞬态差异。我们还将我们的结果与实验单粒子追踪以及标记示踪粒子在密集拥挤悬浮液中扩散的模拟结果进行了对比。我们的结果对活细胞和其他结构化液体内部高度拥挤环境中化学成分的扩散、传输和扩散具有启示意义。
