Dissipation in the mechanics of soft molecules

非技术性的。耗散，或称摩擦，与热力学第二定律有关，也就是时间之箭，也就是万物的生命。一个没有摩擦的世界是一个由开普勒轨道和钟摆组成的世界，时间是可逆的，是无意识的。但物质是由原子组成的，单个原子是非耗散系统。那么，“时间之箭”从多大规模开始形成呢？之前美国国家科学基金会资助的圆周率小组的研究为大分子形变中的耗散过程打开了一个新的实验窗口。在这一专业知识的基础上，PI和他的团队描述了酶工作中涉及的耗散。他们在分子的尺度上测量摩擦力，并寻找新的现象，如在他们的系统中发现的耗散动力学发出的光。因此，一小群年轻人，包括两名研究生和两名本科生，走上了科学发现的道路，同时获得了纳米科学领域最先进的技术技能。这个项目的主要目标是创造知识。更具体地说，这项研究的重点是发展一种新的生物分子材料科学，这项研究在PI即将出版的书《分子机器》中介绍。技术上的。纳米系统中摩擦的微观机制、耗散与非线性、非平衡过程之间的关系，都是纳米科学中不完全了解的、相互关联的基本问题。当用纳米流变学探测酶的力学时，这些主题以实验的即时性出现。利用直接测量折叠酶分子驱动变形中发生的耗散的独特能力，Pi和他的团队研究了这种分子级摩擦的来源，特别是包括水化层在内的分子表面的贡献。由纳米流变学探索的水化层动力学，也是本研究发展的物理化学课题--渗透(有序诱导)和杂化的新的、动态理解的起点。最后，该项目探索了动态应力分子发光的可能性，目的是开发一种新的光谱来表征分子尺度上的耗散。PI的实验室发明的纳米流变学允许以亚埃分辨率测量折叠的天然酶的应力-应变关系，并以不同的频率进行测量。通过最近的改进，该方法现在可以准确地测量机械响应的相位以及幅度，从而直接进入耗散。这个项目专注于动力学的耗散部分，这是这些分子大幅度变形的非线性(但可逆)机械机制。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical. Dissipation, or friction, relates to the Second Law of thermodynamics, thus the arrow of time, and everything living. A world without friction is a world of Kepler orbits and pendulums, time reversible, and unconscious. But matter is made of atoms, and individual atoms are non-dissipative systems. At what scale, then, does "the arrow of time" start to form? Previous NSF funded research in the PI's group opened a new experimental window on dissipative processes occurring in the deformation of big molecules. Building on this expertise, the PI and his group characterize the dissipation involved in the working of enzymes. They measure friction at the scale of molecules and look for new phenomena such as light emission from the dissipative dynamics discovered in their system. A small group of young people, comprising two graduate students and two undergrads, is thus set on a path of scientific discovery, while acquiring state-of-the-art technical skills in the field of nanoscience. The primary goal of this project is the creation of knowledge. More specifically, this research focuses on developing a new materials science of biomolecules, introduced in the PI's forthcoming book "Molecular Machines". Technical. Microscopic mechanisms of friction, the relation between dissipation and nonlinearity, non-equilibrium processes in nanoscale systems, are all incompletely understood, fundamental, interconnected problems in nanoscience. These topics appear with experimental immediacy when probing enzyme mechanics by nano-rheology. Using the unique capability of measuring directly dissipation occurring in the driven deformation of folded enzyme molecules, the PI and his group investigate the origin of this molecular scale friction, specifically the contribution of the surface of the molecule, which includes the hydration layer. Hydration layer dynamics, explored by nano-rheology, is also the starting point of a new, dynamic understanding of kosmotropic (order inducing) and chaotropic agents, a physical chemistry topic which this research develops. Finally, the project explores the possibility of light emission from dynamically stressed molecules, with the aim of developing a new spectroscopy to characterize dissipation at the molecular scale. Nano-rheology, invented in the PI's lab, allows the measurement of the stress - strain relations for a folded, native enzyme with sub-Angstrom resolution and at different frequencies. Through recent improvements, the method now allows accurate measurements of the phase of the mechanical response, as well as the amplitude, and thus gives direct access to the dissipation. This project focuses on the dissipative part of the dynamics, which is the nonlinear (but reversible) mechanical regime of large amplitude deformations for these molecules.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.