ELECTRONIC SPECTROSCOPY OF SIMPLE PORPHYRINS

这里描述的研究是我们目前的MBR赠款下正在进行的工作的继续和延伸。这主要是利用位置激发、光学烧孔和斯塔克效应研究了简单的、未被取代的卟啉在5K下的固态与其电子基态和激发态蛋白质的关系。这项研究的基本假设是，卟啉的激发态比目前所认识的更复杂。多年来，人们一直在积极研究卟啉，但大多数光谱数据来自产生宽带的室温溶液。我们的方法是在液氦温度下将分子放置在正构烷烃主体晶体或低温玻璃中。用单SIT激发或光学烧孔可以获得高分辨率(约2 cm/-1)的光谱。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态的灵敏探测器。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、异细菌碘氯)；它们是生物医学上重要部分的母体化合物(例如，血红素、叶绿素)。现在对简单卟啉的电子结构特别感兴趣的是，我们发现了第一和第二激发态之间存在振动耦合的证据，以及存在低能pi*-n跃迁的证据。这两个观测结果都将通过斯塔克效应实验进行进一步研究。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，以及我们以前获得的关于简单卟啉的详细光谱信息，来研究具有生物医学活性的基于卟啉的部分的电子状态。由于我们在等细菌碘氯方面的丰富经验，我们将从亚硫酸盐还原酶开始这一倡议；这种酶的特征是存在一种与Fe4S4簇相连的铁铁血红素(铁等细菌氯)。该项目的主要长期目标是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*起源能量、耦合等)。从生物医学上重要的卟啉发色团，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.