Self-aggregation of synthetic zinc oxo-bacteriochlorins bearing substituents characteristic of chlorosomal chlorophylls
Self-aggregation of synthetic zinc oxo-bacteriochlorins bearing substituents characteristic of chlorosomal chlorophylls
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DOI：
10.1021/jo048263p
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发表时间：
2005-02-04
影响因子：
3.6
通讯作者：
Tamiaki, H
中科院分区：
文献类型：
--
作者：
Kunieda, M;Tamiaki, H
我们制备了新的锌8-乙基-8-甲基-7-氧代-和7-乙基-7-甲基-8-氧代-菌绿素1和2，其具有叶绿体叶绿素的特征取代基，仅在光合绿色细菌的膜外捕光天线中观察到。单体1和2在THF中的电子吸收光谱明显不同，前者的Q（y）最大值为724，后者的Q（y）最大值为683 nm。这种观察到的光谱差异清楚地解释了理论ZINDO/S计算的能量最小化的分子。单体1/2的光学性质受7/8-氧代基团的电子效应控制。通过用100/200倍体积的环己烷稀释1/2的单体THF溶液，在电子、CD和FT-IR吸收光谱中的特定光谱变化表明形成了由13-C=O... H-O（3（1））. Zn和π-π堆积。特别是在自聚集的1/2的Q1带的红移值为2450/1970 cm（-1），表明在I的自聚集中复合分子之间的激子相互作用比在2的自聚集中强。基于平行链排列的1/2十二聚体的分子模型计算给出了部分不同的超分子结构; 2-十二聚体中的特定氢键距离大于1-十二聚体中的特定氢键距离，而两种配位给出了相同的Zn-O距离。这些建模结果表明，1在自聚集体中更紧密地堆积，从而通过自聚集在Q1带中产生比2更大的红移值。超分子结构的差异主要归因于8/7-二烷基在1/2自聚集体中的空间效应。
We prepared novel zinc 8-ethyl-8-methyl-7-oxo- and 7-ethyl-7-methyl-8-oxo-bacteriochlorins 1 and 2 possessing substituents characteristic of chlorosomal chlorophylls, exclusively observed in extramembraneous light-harvesting antennas of photosynthetic green bacteria. The electronic absorption spectra of monomeric 1 and 2 in THF were obviously different: the Q(y) maximum of the former was 724 and that of the latter was 683 nm. This observed spectral difference was clearly explained by theoretical ZINDO/S calculation of their energetically minimized molecules. The optical properties of monomeric 1/2 were controlled by the electronic effect of the 7/8-oxo groups. Specific spectral changes in the electronic, CD, and FT-IR absorption spectra by dilution of the monomeric THF solutions of 1/2 with a 100/200-fold volume of cyclohexane showed the formation of chlorosomal self-aggregation species constructed by 13-C=O...H-O(3(1))...Zn and pi-pi stacking. Especially, the red-shift values in the Q, band of 1/2 by self-aggregation were 2450/1970 cm(-1), indicating that exciton interaction among the composite molecules in the self-aggregation of I was stronger than in those of 2. Molecular model calculations for dodecamers of 1/2 based on a parallel chain arrangement gave partially different supramolecular structures; the specific hydrogen-bonding distances in 2-dodecamer were larger than those of 1-dodecamer, while both coordinations gave the same Zn-O distance. These modeling results showed that 1 was more tightly packed in the self-aggregates to give a larger red-shift value in the Q, band by self-aggregation than 2. The difference in the supramolecular structures is mainly ascribable to the steric effect of 8/7-dialkyl groups in self-aggregates of 1/2.