Zhao Guang-Jiu, Han Ke-Li
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China.
Biophys J. 2008 Jan 1;94(1):38-46. doi: 10.1529/biophysj.107.113738. Epub 2007 Sep 7.
The site-specific solvation of the photoexcited protochlorophyllide a (Pchlide a) in methanol solvent was investigated using the time-dependent density functional theory method for the first time to our knowledge. The intermolecular site-specific coordination and hydrogen-bonding interactions between Pchlide a and methanol molecules play a very important role in the steady-state and time-resolved spectra. All the calculated absorption and fluorescence spectra of the isolated Pchlide a and its coordinated and hydrogen-bonded complexes with methanol demonstrate that the novel fluorescence shoulder at approximately 690 nm of Pchlide a in methanol should be ascribed to the coordinated and hydrogen-bonded Pchlide a-(MeOH)(4) complex. This coordinated and hydrogen-bonded complex can also account for the intermediate state found in the time-resolved spectroscopic studies. Herein, we have theoretically confirmed that the intermolecular coordination and hydrogen bonds between Pchlide a and methanol molecules can be strengthened in the electronically excited state of Pchlide a. Furthermore, the site-specific solvation of the photoexcited Pchlide a can be induced by the intermolecular coordination and hydrogen-bond strengthening upon photoexcitation. Then the hydrogen-bonded intermediate state is formed in 22-27 ps timescales after the site-specific solvation. All the steady-state and time-resolved spectral features of Pchlide a in different solvents can be explained by the formation of this hydrogen-bonded intermediate state after the site-specific solvation, which is induced by the coordination and hydrogen-bond strengthening.
据我们所知，首次使用含时密度泛函理论方法研究了光激发原叶绿素酸酯a（Pchlide a）在甲醇溶剂中的位点特异性溶剂化作用。Pchlide a与甲醇分子之间的分子间位点特异性配位和氢键相互作用在稳态光谱和时间分辨光谱中起着非常重要的作用。孤立的Pchlide a及其与甲醇的配位和氢键复合物的所有计算吸收光谱和荧光光谱表明，甲醇中Pchlide a在约690 nm处的新型荧光肩应归因于配位和氢键结合的Pchlide a-(MeOH)(4)复合物。这种配位和氢键结合的复合物也可以解释时间分辨光谱研究中发现的中间态。在此，我们从理论上证实了Pchlide a与甲醇分子之间的分子间配位和氢键在Pchlide a的电子激发态下可以增强。此外，光激发Pchlide a的位点特异性溶剂化可以由光激发时分子间配位和氢键增强诱导产生。然后在位点特异性溶剂化后的22 - 27 ps时间尺度内形成氢键结合的中间态。Pchlide a在不同溶剂中的所有稳态和时间分辨光谱特征都可以通过这种由配位和氢键增强诱导的位点特异性溶剂化后形成的氢键结合中间态来解释。
