Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
J Phys Chem B. 2010 May 13;114(18):6207-15. doi: 10.1021/jp100688u.
Magic-angle spinning (MAS) (13)C-(13)C correlation NMR spectroscopy was used to resolve the electronic ground state characteristics of the bacteriochlorophyll a (BChl a) cofactors in light-harvesting 1 (LH1) complexes of Rhodopseudomonas acidophila (strain 10050). The BChl a (13)C isotropic chemical shifts of the LH1 complexes are compared to the (13)C chemical shifts for BChl a dissolved in acetone-d(6) and to (13)C NMR data that has been obtained for the B800 and B850 BChl molecules in Rps. acidophila peripheral light-harvesting complexes (LH2). Since both complexes contain BChl a cofactors, we can address the chemical shift variability for specific carbon responses between the two types of antennae. The global shift pattern of the LH1 BChl's resembles the shift patterns of the LH2 alpha- and beta-B850 BChl's, while some carbon responses, in particular the C3 and C3(1), show significant deviations. A comparison with density functional theory (DFT) shift calculations provides insight into the BChl concomitant structural and electronic interactions in the ground state. The differences in the LH1 BChl observed chemical shifts relative to the (13)C responses of BChl a in solution cannot be explained by local side chain interactions, such as hydrogen bonding or nonplanarity of the C3 acetyl, but appear to be dominated by protein-induced macrocycle distortion. Such shaping of the macrocycle will contribute significantly to the red shift of the BChl Q(y) absorbance band in purple bacterial light-harvesting complexes.
魔角旋转（MAS）（13）C-（13）C 相关 NMR 光谱用于解析嗜酸性红假单胞菌（菌株 10050）光捕获 1（LH1）复合物中细菌叶绿素 a（BChl a）辅因子的电子基态特征。将 LH1 复合物的 BChl a（13）C 各向同性化学位移与丙酮-d（6）中溶解的 BChl a 的（13）C 化学位移进行比较，并与在嗜酸性红假单胞菌周边光捕获复合物（LH2）中获得的 B800 和 B850 BChl 分子的（13）C NMR 数据进行比较。由于这两个复合物都含有 BChl a 辅因子，因此我们可以研究两种天线之间特定碳响应的化学位移可变性。LH1 BChl 的整体位移模式类似于 LH2 alpha-和 beta-B850 BChl 的位移模式，而一些碳响应，特别是 C3 和 C3（1），则表现出明显的偏差。与密度泛函理论（DFT）位移计算的比较提供了对基态中 BChl 伴随结构和电子相互作用的深入了解。与在溶液中 BChl a 的（13）C 响应相比，LH1 BChl 观察到的化学位移的差异不能用局部侧链相互作用（如氢键或 C3 乙酰基的非平面性）来解释，但似乎主要由蛋白质诱导的大环变形引起。大环的这种塑造将对紫细菌光捕获复合物中 BChl Q（y）吸收带的红移产生重大影响。
