Resonance Raman spectra of bacteriochlorophyll and its electrogenerated cation radical. Excitation of the Soret bands by use of stimulated Raman scattering from hydrogen and deuterium
Resonance Raman spectra of bacteriochlorophyll and its electrogenerated cation radical. Excitation of the Soret bands by use of stimulated Raman scattering from hydrogen and deuterium
复制标题
细菌叶绿素及其电生阳离子自由基的共振拉曼光谱。
DOI：
10.1021/ja00541a002
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发表时间：
1980
影响因子：
15
通讯作者：
R. V. Duyne
中科院分区：
文献类型：
--
作者：
T. Cotton;K. D. Parks;R. V. Duyne
在细菌叶绿素(BCHL)及其电生阳离子自由基的Soret带区产生激光波长的新实验方法的发展，使人们能够比以前更详细地研究激发波长对共振拉曼(RR)光谱的影响。高压下H/sub2/或D/sub2/的受激拉曼散射(SRS)是由Nd：YAG激光器的二次或三次谐波驱动的。产生的波长范围从396.7到502.9 nm。在中性BCHL中，最高能量波长位于最强的Soret跃迁的肩上。在该波长下获得了高质量的RR光谱，并且没有观察到光降解的证据。然而，对于BCHL阳离子自由基，激发波长的影响更为显著，因为利用可用的激光谱线可以激发出三个不同的强电子跃迁的近共振。此外，所得到的光谱清楚地表明，BCHL的单电子氧化导致其RR光谱发生明显的变化。在BCHL/sup+/谱中出现的两个强RR带在相应的BCHL谱中不存在(1414 cm/sup-1/)或仅弱观察到(1340 cm/sup-1/)。这些结果表明，使用416.0 nm激发结合1414或1340 cm/sup-1/拉曼峰的检测，可以选择性地监测体内阳离子自由基的形成和衰变动力学。根据最近关于Soret区电子跃迁性质的从头算组态相互作用计算，研究了BCHL和BCHL/sup+/的RR谱。共振增强拉曼光谱与分子几何结构的变化定性一致，这是基于激发电子态相对于基态的分子轨道组成而预期的。(7位数字，3个表)。
The development of a new experimental method for producing laser wavelengths in the Soret band region of bacteriochlorophyll (BChl) and its electrogenerated cation radical permits a more detailed study of the effect of excitation wavelength on the resonance Raman (RR) spectrum than was previously possible. Stimulated Raman scattering (SRS) from H/sub 2/ or D/sub 2/ under high pressure is driven with the second or third harmonics of a Nd:YAG laser. Wavelengths ranging from 396.7 to 502.9 nm are generated. The highest energy wavelength is on the shoulder of the strongest Soret transition in neutral BChl. Good quality RR spectra are obtained at this wavelength, and no evidence of photodegradation is observed. In the case of BChl cation radical, however, the effect of excitation wavelength is more dramatic because it is possible to excite near resonance with three different intense electronic transitions by using the available laser lines. In addition, the resulting spectra show clearly that one-electron oxidation of BChl causes distinctive changes in its RR spectrum. Two intense RR bands seen in the BChl/sup +/ spectrum are absent (1414 cm/sup -1/) or only weakly observed (1340 cm/sup -1/) in the corresponding spectra for BChl. These results indicate that selective RRmore » monitoring of the formation and decay kinetics of the cation radical in vivo should be possible by using 416.0-nm excitation together with detection of the 1414- or 1340-cm/sup -1/ Raman peaks. The RR spectra of BChl and BChl/sup +/ are examined in terms of recent ab initio configuration interaction calculations regarding the nature of the electronic transitions in the Soret region. The resonance enhanced Raman spectra agree qualitatively with changes in the molecular geometry which might be expected on the basis of the molecular orbital composition of the excited electronic state relative to the ground state. (7 figures, 3 tables).« less