Graduate School of Life Sciences, Ritsumeikan University, 525-8577, Kusatsu, Shiga, Japan.
Photochem Photobiol Sci. 2020 Mar 1;19(3):332-340. doi: 10.1039/c9pp00373h. Epub 2020 Jan 29.
Two heterodyads were prepared from the chemical modification of naturally occurring (bacterio)chlorophyll-a and composed of a chlorin π-skeleton linked to a porphyrin or bacteriochlorin π-system. Zinc methyl pyropheophorbide-a, one of the chlorophyll-a derivatives, was covalently linked with its 17,18-didehydrogenated species (zinc methyl pyroprotopheophorbide-a) or its trans-7,8-dihydrogenated analog (zinc methyl pyrobacteriopheophorbide-a as one of the bacteriochlorophyll-a derivatives) through ethylene glycol diester at their 17-propionate residues. In benzene, the central zinc atoms of the synthetic conjugates were coordinated by two methanol molecules which were hydrogen-bonded with the 13-keto-carbonyl groups in a dyad molecule. The methanol locked, y-axis aligned, and slipped cofacial conformers showed two apparent Qy bands at longer wavelengths than those of the composite zinc complex monomers. The red-shifted Qy bands are ascribable to the exciton coupling of the two different π-systems in the folded heterodyad conformers. The synthetic heterodyads could be models of chlorophyll-a/c dimers in the light-harvesting antennas of chromophytes including fucoxanthin-chlorophyll proteins in diatoms and also chlorophyll-a species interacting with bacteriochlorophyll-a or g species in the charge-separating reaction centers of green sulfur bacteria or heliobacteria, respectively.
两个杂种由天然（细菌）叶绿素-a 的化学修饰而成，由连接到卟啉或细菌叶绿素-π 系统的氯代啉π 骨架组成。锌甲基原卟啉-a 是叶绿素-a 的衍生物之一，通过乙二醇二酯将其 17,18-去氢化物（锌甲基原紫质-a）或其反式 7,8-氢化类似物（锌甲基细菌紫质-a）与 17-丙酸酯残基共价连接。在苯中，合成共轭物的中心锌原子通过两个甲醇分子与二联体分子中的 13-酮羰基形成氢键配位。甲醇锁定、y 轴对齐、滑移共面构象在比复合锌配合物单体更长的波长处显示出两个明显的 Qy 带。红移的 Qy 带归因于折叠杂种构象中两个不同 π 系统的激子耦合。合成杂种可以作为藻类包括硅藻中的叶黄素-叶绿素蛋白的光捕获天线中的叶绿素-a/c 二聚体的模型，也可以作为与绿硫细菌或嗜热菌的细菌叶绿素-a 或 g 种相互作用的叶绿素-a 种的模型，分别在电荷分离反应中心。
