Physics Department, University of California Santa Barbara, Santa Barbara, California 93106, USA.
Materials Department, University of California Santa Barbara, Santa Barbara, California 93106, USA.
J Chem Phys. 2024 Jun 7;160(21). doi: 10.1063/5.0204125.
Liquid-liquid phase separation in biology has recently been shown to play a major role in the spatial control of biomolecular components within the cell. However, as they are phase transitions, these processes also display nontrivial dynamics. A model phase-separating system of DNA nanostars provides unique access to nucleation physics in a biomolecular context, as phase separation is driven near room temperature by highly thermo-responsive DNA hybridization and at modest DNA concentrations. By measuring the delay time for phase-separated droplets to appear, we demonstrate that the dynamics of DNA nanostar phase separation reflect that of a metastable binary mixture of patchy particles. For sufficiently deep temperature quenches, droplets undergo spinodal decomposition and grow spontaneously, driven by Brownian motion and coalescence of phase-separated droplets, as confirmed by comparing experimental measurements to particle-based simulations. Near the coexistence boundary, droplet growth slows substantially, indicative of a nucleation process. The temperature dependence of droplet appearance times can be predicted by a classical nucleation picture with mean field exponents and demonstrates that a theory previously used to predict equilibrium phase diagrams can also distinguish spinodal and nucleation dynamical regimes. These dynamical principles are relevant to behaviors associated with liquid-liquid phase separating systems, such as their spatial patterning, reaction coupling, and biological function.
近年来，液-液相分离在生物学中被证明在细胞内生物分子成分的空间控制中起着重要作用。然而，由于它们是相变，这些过程也显示出非平凡的动力学。DNA 纳米星的模型相分离系统为研究生物分子环境中的成核物理提供了独特的途径，因为在接近室温的条件下，高度热敏性的 DNA 杂交驱动相分离，且在适度的 DNA 浓度下即可发生。通过测量相分离液滴出现的延迟时间，我们证明了 DNA 纳米星相分离的动力学反映了具有斑点粒子的亚稳二元混合物的动力学。对于足够深的温度淬火，液滴在布朗运动和相分离液滴的聚结的驱动下经历旋节线分解并自发生长，这通过将实验测量与基于粒子的模拟进行比较得到证实。在共存边界附近，液滴的生长明显减慢，表明存在成核过程。液滴出现时间的温度依赖性可以通过具有平均场指数的经典成核图来预测，并表明先前用于预测平衡相图的理论也可以区分旋节线和成核动力学区域。这些动力学原理与与液-液相分离系统相关的行为有关，例如它们的空间图案形成、反应耦合和生物学功能。
