Abstract：
Primary excitation energy transfer and charge separation in photosystem I (PSI) from the extremophile desert green alga Chlorella ohadii grown in low light were studied using broadband femtosecond pump-probe spectroscopy in the spectral range from 400 to 850 nm and in the time range from 50 fs to 500 ps. Photochemical reactions were induced by the excitation into the blue and red edges of the chlorophyll Qy absorption band and compared with similar processes in PSI from the cyanobacterium Synechocystis sp. PCC 6803. When PSI from C. ohadii was excited at 660 nm, the processes of energy redistribution in the light-harvesting antenna complex were observed within a time interval of up to 25 ps, while formation of the stable radical ion pair P700+A1- was kinetically heterogeneous with characteristic times of 25 and 120 ps. When PSI was excited into the red edge of the Qy band at 715 nm, primary charge separation reactions occurred within the time range of 7 ps in half of the complexes. In the remaining complexes, formation of the radical ion pair P700+A1- was limited by the energy transfer and occurred with a characteristic time of 70 ps. Similar photochemical reactions in PSI from Synechocystis 6803 were significantly faster: upon excitation at 680 nm, formation of the primary radical ion pairs occurred with a time of 3 ps in ~30% complexes. Excitation at 720 nm resulted in kinetically unresolvable ultrafast primary charge separation in 50% complexes, and subsequent formation of P700+A1- was observed within 25 ps. The photodynamics of PSI from C. ohadii was noticeably similar to the excitation energy transfer and charge separation in PSI from the microalga Chlamydomonas reinhardtii; however, the dynamics of energy transfer in C. ohadii PSI also included slower components.
摘要：
使用宽带飞秒泵浦-探针光谱法，在400至850nm的光谱范围内和时间范围内，研究了在弱光下生长的极端微生物沙漠绿藻小球藻的光系统I（PSI）中的初级激发能量转移和电荷分离。从50fs到500ps。光化学反应是通过激发叶绿素Qy吸收带的蓝色和红色边缘而引起的，并与蓝细菌集胞藻的PSI中的类似过程进行了比较。PCC6803。当C.ohadii的PSI在660nm处被激发时，在高达25ps的时间间隔内观察到光捕获天线复合体中的能量再分配过程，而稳定的自由基离子对P700A1-的形成在动力学上是异质的，特征时间为25和120ps。当PSI被激发到715nm的Qy波段的红色边缘时，在一半的配合物中，主要的电荷分离反应发生在7ps的时间范围内。在其余的复合物中，自由基离子对P700A1-的形成受到能量转移的限制，并且以70ps的特征时间发生。在6803集胞藻的PSI中类似的光化学反应明显更快：在680nm激发后，在〜30％的络合物中，初级自由基离子对的形成时间为3ps。在720nm处的激发导致在50％的复合物中动力学上不可分辨的超快一次电荷分离，随后在25ps内观察到P700+A1-的形成。来自C.ohadii的PSI的光动力学与来自微藻衣藻的PSI中的激发能量转移和电荷分离明显相似；但是，C.ohadiiPSI中的能量转移动力学也包括较慢的成分。
