Analytical Applications of Nonlinear Infrared Spectroscopy

威斯康星大学的约翰·赖特教授的这一项目是基于最近的关键实验，这些实验表明，带有振动跃迁的共振可以充分地增强原子核的极化率，足以超过非共振的电子极化率，并且模耦合足够大，以至于多个共振可以成倍地增强非线性光学过程。这些实验证明了一类新的多共振振动增强型非线性光学光谱仪的可行性。这些光谱类似于二维核磁共振方法，它们对分子内和分子间的相互作用特别敏感。从生物学的角度来看，它们可以被认为是一种双色染料，允许可视化分子相互作用并鉴定相互作用中涉及的功能。随着新技术的空间成像能力的发展，这种类比在未来可能会变得重要。该项目寻求将这些新方法应用于生物化学中的核心问题，在这些问题中，相互作用发挥着核心作用。有许多不同的分子相互作用，但这项建议将集中在应用新的方法来研究生物分子结构中由氢键引起的光谱相关性。这种相关性既体现在二维光谱中交叉峰的相对强度，从而反映了两个共振之间的相互作用，也体现在线条收窄的交叉峰的线位移上。在分子水平上，生物分子的结构在很大程度上取决于氢键的相互作用。虽然氢键可以在相对简单的系统中被理解，但在复杂的三维生物分子结构中氢键的性质和程度要难得多。将在该项目主持下完成的光谱实验为完成这一表征提供了一种灵敏和直接的手段。随着人们更好地了解氢键的作用，复杂的生物分子结构可能会被建模，甚至可能被预测为合成的天然分子的类似物。

This project by Professor John Wright of the University of Wisconsin is predicated on recent key experiments that have demonstrated that resonance with vibrational transitions can enhance the nuclear polarizability sufficiently to exceed the nonresonant electronic polarizability, and that mode coupling is sufficiently large that multiple resonances can multiplicatively enhance nonlinear optical processes. These experiments demonstrate the feasibility for a new family of multiresonant vibrationally enhanced nonlinear optical spectroscopies. These spectroscopies are analogous to 2-dimensional NMR methods and they are uniquely sensitive to intra- and intermolecular interactions. From a biological perspective, they can be considered as a two- color stain that allows visualization of molecular interactions and identification of the functionalities involved in the interaction. This analogy might become important in the future as the spatial imaging capabilities of the new technology are developed. The project seeks to apply these new approaches to central problems in biochemistry where interactions play a central role. There are many different molecular interactions but this proposal will focus on applying the new method to study of the spectral correlations that are induced by the hydrogen bonding in a biomolecule structure. The correlations will be evidenced both in the relative intensities of cross-peaks in the 2-D spectra, thus reflecting the interactions between the two resonances, and in the line position shifts in line-narrowed cross-peaks.At the molecular level, the structures of biomolecules depend to a large degree on the interactions known as hydrogen bonding. Although hydrogen bonding may be understood in relatively simple systems, the nature and extent of hydrogen bonding in a complex three-dimensional biomolecular structure is far more difficult to characterize. The spectroscopic experiments to be completed under the auspices of this project provide a sensitive and direct means to complete that characterization. With the role of hydrogen bonding better understood, complex biomolecular structures may be modeled and perhaps even predicted for synthetic analogs of natural molecules.