ELECTRONIC SPECTROSCOPY OF SIMPLE PORPHYRINS AND BACTERIORHODOPSIN

简单卟啉和细菌视紫红质的电子光谱

• 批准号: 6271614
• 负责人: LAWRENCE William JOHNSON
• 金额: $ 18.63万
• 依托单位: YORK COLLEGE
• 依托单位国家: 美国
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-06-01 至 1999-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6271614
• 关键词: alkanes; bacteriorhodopsins; chemical synthesis; chlorin; chromophore; dipole moment; electronic spectra; laser spectrometry; metal complex; metalloporphyrins; photochemistry; porphyrin structure

The research described in this proposal is a continuation, extention and modification of the work being carried out under our current MBRS grant. It is a study of simple porphyrins in the solid-state at 5K with respect to their electronic ground and excited state properties using single site excitation, optical hole-burning and the Stark effect. The fundamental hypothesis driving this research is that the excited states and the presence of low energy Npi* transitions. In this phase of our work both free base and metal complex forms of these molecules will be studied: e.g. porphin, chlorin, tetraazaporphin. These simple porphyrins are the parent compounds of biomedically important moieties (e.g. hemes, cytochromes, chlorophylls and photodynamic photosensitizers). Porphyrins are and have been actively studied, however most of the spectroscopic data sis from room temperature solutions which yield only broad bands. Our approach is to place the molecules in n-alkane host crystals; at liquid helium temperatures highly resolved (about 2 cm-1) spectra are obtained. The spectrum of molecules in a particular crystal environment can then be isolated by using single site-excitation. This high resolution can be improved even more by using optical hole-burning. When a molecule is dissolved in a matrix, its electronic spectrum is inhomogeneously broadened; when a narrow bandwidth laser is employed for excitation it is sometimes possible to burn holes in the inhomogeneously broadened bands; holes result from photochemistry, transient storage or molecular reorientation. When the narrow bands of single site spectra, or optical holes are coupled with the Stark effect, they provide a sensitive proble of molecular electronic states. Our overall methodology involves the growth of single mixed crystals (porphyrin/n-alkane) or making low temperature glassy solutions. The sample is immersed in liquid N2 or He and an absorption or emission spectrum obtained. Single site spectra are made or optical holes burned and scanned with a narrow band laser. For Stark effect experiments, a coniscopically oriented crystal is placed between electrodes. The electric field can be applied either DC or pulsed depending on the need. The primary long-term objective of this project is to use these techniques to extract detailed excited state information (e.g., vibrational energies, dipole moments, pi pi* and npi* origin energies, coupling, etc.) from these biomedically important chromophores. (Of particular interest now is that we seem to be finding strong evidence for the presence of low energy pi* lesser--- n transitions in some of these simple porphyrins). This research will involve two MBRS students. Each one will be responsible for a separate chromophore and will carry out its preparation, purification and run low and medium resolution spectra. Laser and Stark experiments will be done with the PI. Most of the spectroscopic data now available on these chromophores is low resolution because of substantial inhomogeneous broadening of the electronic bands. Optical hole-burning, single site excitation and the Stark effect will provide a clearer picture of the electronic states of these biomedically important molecules.

本课题所描述的研究是一个延续、延伸和