Shreve A P, Cherepy N J, Franzen S, Boxer S G, Mathies R A
Department of Chemistry, University of California, Berkeley 94720.
Proc Natl Acad Sci U S A. 1991 Dec 15;88(24):11207-11. doi: 10.1073/pnas.88.24.11207.
Rapid-flow resonance Raman vibrational spectra of bacterial photosynthetic reaction centers from the R-26 mutant of Rhodobacter sphaeroides have been obtained by using excitation wavelengths (810-910 nm) resonant with the lowest energy, photochemically active electronic absorption. The technique of shifted excitation Raman difference spectroscopy is used to identify genuine Raman scattering bands in the presence of a large fluorescence background. The comparison of spectra obtained from untreated reaction centers and from reaction centers treated with the oxidant K3Fe(CN)6 demonstrates that resonance enhancement is obtained from the special pair. Relatively strong Raman scattering is observed for special pair vibrations with frequencies of 36, 94, 127, 202, 730, and 898 cm-1; other modes are observed at 71, 337, and 685 cm-1. Qualitative Raman excitation profiles are reported for some of the strong modes, and resonance enhancement is observed to occur throughout the near-IR absorption band of the special pair. These Raman data determine which vibrations are coupled to the optical absorption in the special pair and, thus, probe the nuclear motion that occurs after electronic excitation. Implications for the interpretation of previous hole-burning experiments and for the excited-state dynamics and photochemistry of reaction centers are discussed.
利用与最低能量、具有光化学活性的电子吸收共振的激发波长（810 - 910 nm），获得了球形红杆菌R - 26突变体细菌光合反应中心的快速流动共振拉曼振动光谱。在存在大量荧光背景的情况下，采用位移激发拉曼差光谱技术来识别真正的拉曼散射带。从未经处理的反应中心和用氧化剂K3Fe(CN)6处理过的反应中心获得的光谱比较表明，特殊对可实现共振增强。对于频率为36、94、127、202、730和898 cm-1的特殊对振动，观察到相对较强的拉曼散射；在71、337和685 cm-1处观察到其他模式。报告了一些强模式的定性拉曼激发轮廓，并且观察到在特殊对的近红外吸收带中都出现了共振增强。这些拉曼数据确定了哪些振动与特殊对中的光吸收耦合，从而探测了电子激发后发生的核运动。讨论了对先前空穴燃烧实验解释以及对反应中心激发态动力学和光化学的影响。
