Development of Multidimensional Resonance Raman Spectroscopies for Studies of Photochemical Dynamics

在这项由化学测量和成像计划资助的项目中，北卡罗来纳大学的安德鲁·莫兰教授正在开发基于激光的实验方法，以研究血红素蛋白质中的光解离和电子转移动力学。本研究项目中的目标血红素蛋白令人感兴趣，因为它们介导了生命系统中的电子和氧气传输。例如，血红蛋白负责在血液中运输氧气，而细胞色素在线粒体的电子传输链中起着核心作用。这个项目的重点是这些系统发生基本核运动的飞秒时间尺度。脉冲激光技术是解决这种快速动力学问题的独特设备。除了促进对这些特定蛋白质的理解外，该项目中开发的实验方法还可以被其他研究人员修改，以应用于更广泛的系统和过程。进行这项研究的研究生和本科生发展了广泛的技术技能(例如，光学、仪器开发、机械加工、计算机编程)。该项目涉及开发二维共振拉曼(2DRR)光谱仪，其中五束非共线激光诱导化学体系的光发射。反应机理是通过在不同的光谱维度上分离反应物和产物的共振来揭示的，这在传统的共振拉曼光谱中是不可能的。这些技术的无背景特性促进了快速数据采集速率，并提高了对弱信号的灵敏度。二维拉曼光谱受到非共振系统(即不吸收入射激光的系统)中被称为级联的不受欢迎的非线性的挑战。通常可以理解，在非共振条件下遇到的问题的根源在于所需的非线性光学过程中的“禁止”步骤。相比之下，这项建议中开发的实验是在共振条件下进行的，在那里这种不幸的选择规则不适用。各种对照实验被用来排除来自级联的影响。

In this project funded by the Chemical Measurement and Imaging Program, Professor Andrew Moran of the University of North Carolina is developing laser-based experimental methods for studies of photodissociation and electron transfer dynamics in heme proteins. The heme proteins targeted in this research project are of interest, because they mediate electron and oxygen transport in living systems. For example, hemoglobin is responsible for transporting oxygen in blood, whereas cytochrome plays a central role in the electron transport chain in mitochondria. This project focuses on the femtosecond time scale in which elementary nuclear motions of these systems take place. Pulsed laser techniques are uniquely equipped to resolve such fast dynamics. In addition to advancing the understanding of these particular proteins, the experimental methods developed in this project can be adapted by other researchers for applications to a much wider range of systems and processes. The graduate and undergraduate students who conduct this research develop a wide range of technical skills (e.g., optics, instrument development, machining, computer programming).This project involves the development of two-dimensional resonance Raman (2DRR) spectroscopies in which five noncollinear laser beams induce light emission from a chemical system. Reaction mechanisms are exposed by separating resonances of the reactants and products in separate spectroscopic dimensions, which is not possible in traditional resonance Raman spectroscopies. The background-free nature of these techniques facilitates fast data acquisition rates and enhances sensitivity to weak signals. Two-dimensional Raman spectroscopies are challenged by undesired nonlinearities known as cascades in off-resonant systems (i.e., systems that do not absorb the incoming laser beams). It is generally understood that "forbidden" steps in the desired nonlinear optical processes are the origin of the problems encountered under off-resonant conditions. In contrast, the experiments developed in this proposal are carried out under resonant conditions, where such unfortunate selection rules do not apply. A variety of control experiments are used to rule out contributions from cascades.