ELECTRONIC SPECTROSCOPY OF SIMPLE PORPHYRINS

这里描述的研究是在我们目前的MBRS资助下进行的工作的延续和扩展。这主要是一个简单的，未取代的卟啉在固态5K下的电子基态和激发态蛋白质的研究，使用位点激发，光学空穴燃烧和斯塔克效应。本研究的基本假设是卟啉的激发态比目前认识到的更复杂。卟啉已被积极研究多年，但大多数光谱数据是来自室温下产生宽频带的溶液。我们的方法是将分子置于正烷烃主体晶体或液氦温度下的低温玻璃中。高分辨率（约2厘米/-1）光谱可以获得使用单座激发或光学孔燃烧。当单位光谱的窄带或光学空穴与斯塔克效应耦合时，它们提供了分子电子状态的敏感探针。我们计划继续研究这些简单分子的游离碱和金属络合物形式（例如卟啉，氯，等细菌氯）；它们是生物医学上重要的部分（如血红素、叶绿素）的母体化合物。现在对简单卟啉的电子结构特别感兴趣的是，我们已经发现了第一和第二激发态之间的振动耦合以及低能pi*- n跃迁的证据。这两种观察结果将通过斯塔克效应实验进一步研究。然而，现在我们也将开始利用我们在获得高分辨率电子光谱方面的专业知识，以及我们以前在简单的卟啉上获得的详细光谱信息，来检查生物医学上活性卟啉基部分的电子状态。由于我们在异杆菌氯方面的丰富经验，我们将从亚硫酸盐还原酶开始这项倡议；该酶的特点是存在铁siroheme（铁等细菌氯）交换偶联到Fe4S4簇。该项目的主要长期目标是从生物医学上重要的卟啉发色团中提取详细的基态和激发态信息（例如振动能量，偶极矩，pi/pi*和npi*原点能量，耦合等）并了解它们的电子结构。

The research described here is a continuation and extension of work being carried out under our current MBRS grant. This is primarily a study of simple, unsubstituted porphyrins in the solid state at 5K with respect to their electronic ground and excited state proteins using site excitation, optical hole-burning and the Stark effect. The fundamental hypothesis of this research is that excited states of porphyrins are more complex than is currently recognized. Porphyrins have been actively studied for years, but most of the spectroscopic data is from room temperature solutions which yield broad bands. Our approach is to place the molecules in n-alkane host crystals or low temperature glasses at liquid helium temperatures. High resolution (approximately 2 cm/-1) spectra can be obtained using single sit excitation or optical hole-burning. When the narrow bands of single site spectra, or optical holes are coupled with the Stark effect, they provide a sensitive probe of molecule's electronic states. We plan to continue to study free base and metal complex forms of these simple molecules (e.g. porphin, chlorin, isobacteriochlorin); they are parent compounds of biomedically important moieties (e.g. hemes, chlorophylls). Of particular interest now in the electronic structure of the simple porphyrins, is that we have found evidence for vibronic coupling between the first and second excited states and for the presence of low energy pi*- n transitions. Both of these observations will be studied further with Stark effect experiments. However, now we will also begin to use our expertise in obtaining high resolution electronic spectra, and the detailed spectral information which we previously obtained on simple prophyrins, to examine the electronic states of biomedically active porphyrin based moieties. Because of our extensive experience with isobacteriochlorin we will start this initiative with sulfite reductase; this enzyme is characterized by the presence of an iron siroheme (iron isobacteriochlorin) exchanged coupled to a Fe4S4 cluster. The primary, long-term objective of this project is to extract detailed ground and excited state information (e.g. vibrational energies, dipole moments, pi/pi* and npi* origin energies, coupling, etc.) from biomedically important porphyrin chromophores and understand their electronic structure.