A wave-mechanical model of incoherent quasielastic scattering in complex systems
A wave-mechanical model of incoherent quasielastic scattering in complex systems
复制标题
复杂系统中非相干准弹性散射的波力学模型
DOI：
10.1073/pnas.1411781111
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
R. Young
中科院分区：
文献类型：
--
作者：
H. Frauenfelder;P. Fenimore;R. Young
准弹性非相干中子散射（QENS）是研究复杂系统（如液体、聚合物、玻璃和生物分子）的重要工具。目前已有相当数量的中子设施，而且正在计划建造更多的设施。了解QENS对于理解和应用科学以及有效利用设施都很重要。我们主张目前对QENS的解释是不完整的。我们提出了一个波动力学模型，符合中子衍射。它是基于自由能的景观和对待中子作为布罗意波包。该模型得到了实验的支持，并具有预测能力。它提供了对蛋白质动力学的重要见解，并可能导致更好地理解生物过程。准弹性非相干中子散射（QENS）是研究生物分子、液体和玻璃等复杂系统动力学的重要工具。动力学反映在散射中子的能谱中。通常这些谱被分解成窄的弹性线和宽的准弹性带。该频带被解释为由于目标分子的空间运动而引起的多普勒展宽。我们提出了一个量子力学模型，其中没有单独的弹性线。准弹性带由两倍于自然线宽的尖锐线条组成，通过蛋白质在目标分子的自由能景观中的随机行走从中心移位。行走是由振动和外部波动驱动的。我们首先探讨了具有穆斯堡尔效应的模型。在QENS的后续应用中，我们将入射中子视为布罗意波包。当波包通过蛋白质和水化壳层中的质子时，它在大约100 ns的通过时间内与蛋白质交换能量。能量交换拓宽了系综光谱。由于交换涉及蛋白质的自由能景观，QENS不仅提供了对蛋白质动力学的洞察，而且还可以照亮蛋白质-溶剂系统的自由能景观。
Significance Quasielastic incoherent neutron scattering (QENS) is a key tool for the exploration of complex systems, such as liquids, polymers, glasses, and biomolecules. A considerable number of neutron facilities exist and more are being planned. Understanding QENS is important, both for comprehending and applying the science and making efficient use of the facilities. We claim that the present explanation of QENS is incomplete. We propose a wave-mechanical model, consistent with neutron diffraction. It is based on the free-energy landscape and treats the neutrons as de Broglie wave packets. The model is supported by experiments and has predictive power. It provides significant insight into the dynamics of proteins and may lead to a better understanding of biological processes. Quasielastic incoherent neutron scattering (QENS) is an important tool for the exploration of the dynamics of complex systems such as biomolecules, liquids, and glasses. The dynamics is reflected in the energy spectra of the scattered neutrons. Conventionally these spectra are decomposed into a narrow elastic line and a broad quasielastic band. The band is interpreted as being caused by Doppler broadening due to spatial motion of the target molecules. We propose a quantum-mechanical model in which there is no separate elastic line. The quasielastic band is composed of sharp lines with twice the natural line width, shifted from the center by a random walk of the protein in the free-energy landscape of the target molecule. The walk is driven by vibrations and by external fluctuations. We first explore the model with the Mössbauer effect. In the subsequent application to QENS we treat the incoming neutron as a de Broglie wave packet. While the wave packet passes the protons in the protein and the hydration shell it exchanges energy with the protein during the passage time of about 100 ns. The energy exchange broadens the ensemble spectrum. Because the exchange involves the free-energy landscape of the protein, the QENS not only provides insight into the protein dynamics, but it may also illuminate the free-energy landscape of the protein–solvent system.