A low-temperature dynamical transition has been reported in several proteins. We provide the first observation of a "protein-like" dynamical transition in nonbiological aqueous environments. To this aim, we exploit the popular colloidal system of poly-N-isopropylacrylamide (PNIPAM) microgels, extending their investigation to unprecedentedly high concentrations. Owing to the heterogeneous architecture of the microgels, water crystallization is avoided in concentrated samples, allowing us to monitor atomic dynamics at low temperatures. By elastic incoherent neutron scattering and molecular dynamics simulations, we find that a dynamical transition occurs at a temperature T_d ~ 250 K, independently from PNIPAM mass fraction. However, the transition is smeared out on approaching dry conditions. The quantitative agreement between experiments and simulations provides evidence that the transition occurs simultaneously for PNIPAM and water dynamics. The similarity of these results with hydrated protein powders suggests that the dynamical transition is a generic feature in complex macromolecular systems, independently from their biological function.

中文翻译：

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浓缩微凝胶中低温动态转变的证据。

已经报道了几种蛋白质中的低温动态转变。我们首次观察到非生物水环境中的“类蛋白质”动态转变。为此，我们利用流行的聚-N-异丙基丙烯酰胺（PNIPAM）微凝胶胶体系统，将他们的研究扩展到前所未有的高浓度。由于微凝胶的异质结构，浓缩样品中避免了水结晶，使我们能够监测低温下的原子动力学。通过弹性非相干中子散射和分子动力学模拟，我们发现在温度T _d发生动态转变~ 250 K，独立于 PNIPAM 质量分数。然而，过渡在接近干燥条件时被抹去。实验和模拟之间的定量一致性为 PNIPAM 和水动力学同时发生转变提供了证据。这些结果与水合蛋白粉的相似性表明，动态转变是复杂大分子系统的一般特征，与它们的生物学功能无关。