(13)C MAS NMR and photo-CIDNP reveal a pronounced asymmetry in the electronic ground state of the special pair of Rhodobacter sphaeroides reaction centers.
(13)C MAS NMR and photo-CIDNP reveal a pronounced asymmetry in the electronic ground state of the special pair of Rhodobacter sphaeroides reaction centers.
复制标题
(13)13C MAS NMR 和 photo-CIDNP 揭示了特殊的球形红细菌反应中心对的电子基态存在明显的不对称性。
作者：
E. Schulten;J. Matysik;Alía;S. Kiihne;J. Raap;J. Lugtenburg;P. Gast;A. Hoff;H. D. de Groot
野生型球形红杆菌的反应中心被选择性地（13）c同位素标记在细菌叶绿素和细菌内生素中。（13）利用C固态CP/MAS NMR和photocidnp在原子尺度上深入研究了主电子给体和主电子受体的电子结构。第一个二维光化学诱导动态核极化（photocidnp） （13）C-(13)C固态MAS NMR谱显示，主供体的两个BChl环的负电荷通过局部静电相互作用参与了蛋白质中这些辅助因子氧化电位的基态调谐。特别是，（13）C位移在电子基态的特殊对的两个BChl分子之间显示出适度的电子结构差异，这可归因于其中一个BChl分子的氢键。电子自旋密度的主要部分在特殊对的两个BChl分子和光化学活性的BPhe上强烈地离域。π -自旋密度的一小部分分布在第四个分量上，该分量分配给附件BChl。将光- cidnp数据与在超高场下获得的“暗”核磁共振波谱进行比较，表明光反应时存在刚性的特殊对环境，表明特殊对中两个BChl分子的芳族大环的结构变化对与电荷转移过程相关的重组能没有显著贡献。
Reaction centers of wild-type Rhodobacter sphaeroides were selectively (13)C-isotope labeled in bacteriochlorophyll and bacteriopheophytin. (13)C solid-state CP/MAS NMR and photo-CIDNP were used to provide insight into the electronic structure of the primary electron donor and acceptor on the atomic scale. The first 2-dimensional photochemically induced dynamic nuclear polarization (photo-CIDNP) (13)C-(13)C solid-state MAS NMR spectra reveal that negative charging of the two BChl rings of the primary donor is involved in ground-state tuning of the oxidation potential of these cofactors in the protein via local electrostatic interactions. In particular, the (13)C shifts show moderate differences in the electronic structure between the two BChl molecules of the special pair in the electronic ground state, which can be attributed to hydrogen bonding of one of the BChl molecules. The major fraction of the electron spin density is strongly delocalized over the two BChl molecules of the special pair and the photochemically active BPhe. A small fraction of the pi-spin density is distributed over a fourth component, which is assigned to the accessory BChl. Comparison of the photo-CIDNP data with "dark" NMR spectra obtained in ultra high field indicates a rigid special pair environment upon photoreaction and suggests that structural changes of the aromatic macrocycles of the two BChl molecules of the special pair do not significantly contribute to the reorganization energy associated with the charge-transfer process.