Macromolecular diffusion in strongly confined geometries and crowded environments is still to a large extent an open subject in soft matter physics and biology. In this paper, we employ large-scale Langevin dynamics simulations to investigate how the diffusion of a tracer is influenced by the combined action of excluded-volume and weak attractive crowder-tracer interactions. We consider two species of tracers, standard hard-core particles described by the Weeks-Chandler-Andersen (WCA) repulsive potential and core-softened (CS) particles, which model, e.g., globular proteins, charged colloids and nanoparticles covered by polymeric brushes. These systems are characterized by the presence of two length scales in the interaction and can show water-like anomalies in their diffusion, stemming from the inherent competition between different length scales. Here we report a comprehensive study of both diffusion and structure of these two tracer species in an environment crowded by quenched configurations of polymers at increasing density. We analyze in detail how the tracer-polymer affinity and the system density affect transport as compared to the emergence of specific static spatial correlations. In particular, we find that, while hardly any differences emerge in the diffusion properties of WCA and CS particles, the propensity to develop structural order for large crowding is strongly frustrated for CS particles. Surprisingly, for large enough affinity for the crowding matrix, the diffusion coefficient of WCA tracers display a non-monotonic trend as their density is increased when compared to the zero affinity scenario. This water-like anomaly turns out to be even larger than what observed for CS particle and appears to be rooted in a similar competition between excluded-volume and affinity effects.
Enhanced diffusion of colloidal tracers due to enzymatic activity
California State University Fullerton（加州州立大学富勒顿分校）；Lewis-Sigler Institute for Integrative Genomics, Princeton University（普林斯顿大学整合基因组学刘易斯-西格勒研究所）；Université de Toulouse（图卢兹大学）；Valencia High School（瓦伦西亚高中）；Syracuse University（雪城大学）；Brandeis University（布兰迪斯大学）；CNRS, Laboratoire de Physique Théorique（法国国家科学研究中心理论物理实验室）；CNRS, Centre de Biologie Intégrative（法国国家科学研究中心综合生物学中心）
