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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Stark Hole-Burning Studies of Three Photosynthetic Complexes
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Stark Hole-Burning Studies of Three Photosynthetic Complexes

机译：三种光合复合物的纯净孔灼研究

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摘要

Stark hole-burning spectroscopy at 1.8 K was used to determine the dipole moment changes f△μ (f, the local field correction factor) for the B800 absorption band of the light harvesting 2 (LH2) complex of Rhodobacter sphaeroides, Rhodopseudomonas acidophila (strain 10050), and Rhodospirillum molischianum. Hole-burning values of f△μ for the lowest energy exciton level (B870) associated with LH2's B850 band have recently been reported (R#itsep et al. Spectrochim. Acta, in press). Values for the lowest energy exciton level (B896) associated with the B875 band of the LH1 complex of Rb. sphaeroides (wild-type chromatophores and an LH 1-only mutant) and the 825 nm band of the bacteriochlorophyll a (FMO) antenna complex of Chlorobium tepidum are also reported. For each band, f△μ was determined for burn laser polarization parallel and perpendicular to the Stark field Es and several burn frequencies. The dependencies on laser polarization and burn frequency are typically quite weak. Importantly, f△μ values for the above bands are small, falling in the range ～0.5-1.2 D, with the lowest and highest values associated with the 825 nm band of the FMO complex and B800 band of the LH2 complex, respectively. For the B896 band of the LH1 complex, fA/a 0.8 D. Such small values are consistent with the very weak linear electron-phonon coupling of antenna protein complexes as determined by hole-burning spectroscopy. Overall, the values for f△μ from classical Stark modulation (CSM) studies (Gottfried et al. Biochim. Biophys. Acta 1991, 1059, 63; Beekman et al. J. Phys. Chem. B 1997, 101, 7293) are larger, in the cases of B850 and B875, by a factor of 3-4. (In CSM spectroscopy, one analyzes the response of the entire absorption band to the external field.) Discussion of the discrepancies between the two Stark techniques is given. It appears that difficulties inherent to the analysis procedure of CSM spectroscopy can lead to unreliable values for dipole moment and polarizability changes associated with absorption bands of photosynthetic complexes, especially when several excitonic levels contribute to the band, e.g., B850 and B875. An explanation for the small hole-burning values of f△μ for the B870 and B896 levels associated with C↓(n) cyclic arrays of strongly coupled BChl a dimers is given based on structural, symmetry, and energy disorder considerations. A key point is that, in the absence of energy disorder, the component of △μ↓(j) (j labeling the exciton level) perpendicular to the C↓(n) axis is zero. Energy disorder, which destroys the C↓(n) symmetry and leads to localization effects results in nonzero values which may depend on j when the protein-induced contribution to △μ↓(j) is taken into account.
机译：使用1.8 K的Stark空穴燃烧光谱法确定球形红球菌，嗜酸红假单胞菌（菌株）的光收集2（LH2）络合物的B800吸收带的B800吸收带的偶极矩变化f△μ（f，局部场校正因子）。 10050），以及红景天螺旋藻。最近已经报道了与LH2的B850谱带相关的最低能量激子能级（B870）的f△μ烧孔值（R＃itsep等人，Spectrochim。Acta，印刷中）。与Rb的LH1络合物的B875谱带相关的最低能量激子能级（B896）的值。还报道了球根茎线虫（野生型色谱和仅LH 1突变体）和温和绿球藻细菌叶绿素a（FMO）天线复合体的825 nm带。对于每个波段，对于平行和垂直于Stark场Es的燃烧激光偏振以及几个燃烧频率，确定f△μ。对激光偏振和燃烧频率的依赖性通常很弱。重要的是，上述谱带的f△μ值很小，在〜0.5-1.2 D范围内，最低和最高值分别与FMO复合物的825 nm谱带和LH2复合物的B800谱带有关。对于LH1复合物的B896谱带，fA / a为0.8D。如此小的值与通过空穴燃烧光谱法确定的天线蛋白复合物的非常弱的线性电子-声子耦合相符。总体而言，经典斯塔克调制（CSM）研究（Gottfried等人，Biochim。Biophys。Acta 1991，1059，63; Beekman等人，J。Phys。Chem。B 1997，101，7293）的f△μ值是对于B850和B875，则为3-4倍。 （在CSM光谱中，一种分析了整个吸收带对外部场的响应。）讨论了两种Stark技术之间的差异。似乎CSM光谱分析程序固有的困难可能导致偶极矩值和与光合配合物吸收谱带相关的极化率变化不可靠，尤其是当几个激子能级对该谱带起作用时，例如B850和B875。基于结构，对称性和能量无序的考虑，给出了与强耦合BChl a二聚体的C↓（n）循环阵列相关的B870和B896能级的f△μ小烧孔值的解释。关键是，在没有能量紊乱的情况下，垂直于C↓（n）轴的△μ↓（j）（j表示激子能级）的分量为零。能量紊乱破坏了C↓（n）对称性并导致定位效应，导致非零值，当考虑蛋白质诱导的对Δμ↓（j）的贡献时，该值可能取决于j。

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