Structure-property relationships for self-assembled zinc chlorin light-harvesting dye aggregates
Structure-property relationships for self-assembled zinc chlorin light-harvesting dye aggregates
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DOI：
10.1002/chem.200800764
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发表时间：
2008-01-01
影响因子：
4.3
通讯作者：
Wuerthner, Frank
中科院分区：
文献类型：
--
作者：
Huber, Valerie;Sengupta, Sanchita;Wuerthner, Frank
通过对天然叶绿素a的修饰，合成了一系列具有不同结构特征的3(1)-羟甲基氯化锌10a-e和3(1)-羟乙基氯化锌17，并用依赖于溶剂、温度和浓度的UV/Vis和CD光谱方法以及显微研究探讨了特定官能团和空间效应对这些锌氯化物自组装行为的重要性。半合成的氯化锌10a-e具有天然细菌叶绿素(BCHL)中与自组装相关的3个功能单元，即3(1)-OH基团、中心金属离子和沿Q(Y)轴的13(1)C=O基团，它们还含有各种17(2)-取代基。根据锌氯是否具有17(2)-疏水或亲水侧链，它们分别在非极性有机溶剂或水介质中自组装。具有至少两个长侧链的锌氯化合物提供了在溶液中长期稳定的可溶自聚集体，从而便于用光学光谱来阐明它们的性质。用原子力显微镜(AFM)研究了氯化锌聚集体的形态，揭示了氯化锌10b的纳米棒结构，高度约为6 nm。值得注意的是，这一大小与染料的管状排列很好地一致，类似于在绿色细菌的捕光绿体中观察到的天然BCHL对应物。此外，通过UV/Vis和CD光谱详细研究了具有疏水侧链的表位3(1)-羟乙基锌氯17的3(1)位手性中心对其聚集行为的影响。与锌氯10不同，3(1)-羟乙基锌氯17只形成较小的齐聚物，而不是较高的棒状聚集体结构，这可以归因于3(1)-位上额外的甲基所施加的空间效应。
A series of zinc 3(1)-hydroxymethyl chlorins 10a-e and zinc 3(1)-hydroxyethyl chlorins 17 with varied structural features were synthesized by modifying naturally occurring chlorophyll a. Solvent-, temperature-, and concentration-dependent UV/Vis and CD spectroscopic methods as well as microscopic investigations were performed to explore the importance of particular functional groups and steric effects on the self-assembly behavior of these zinc chlorins. Semisynthetic zinc chlorins 10a-e possess the three functional units relevant for self-assembly found in their natural bacteriochlorophyll (BChl) counterparts, namely, the 3(1)-OH group, a central metal ion, and the 13(1) C=O moiety along the Q(y) axis, and they contain various 17(2)-substituents. Depending on whether the zinc chlorins have 17(2)-hydrophobic or hydrophilic ;side chains, they self-assemble in nonpolar organic solvents or in aqueous media, respectively. Zinc chlorins possessing at least two long side chains provide soluble self-aggregates that are stable in solution for a prolonged time, thus facilitating elucidation of their properties by optical spectroscopy. The morphology of the zinc chlorin aggregates was elucidated by atomic force microscopy (AFM) studies, revealing well-defined nanoscale rod structures for zinc chlorin 10b with a height of about 6 nm. It is worth noting that this size is in good accordance with a tubular arrangement of the dyes similar to that observed in their natural BChl counterparts in the light-harvesting chlorosomes of green bacteria. Furthermore, for the epimeric 3(1)-hydroxyethyl zinc chlorins 17 with hydrophobic side chains, the influence of the chirality center at the 3(1)-position on the aggregation behavior was studied in detail by UV/Vis and CD spectroscopy. Unlike zinc chlorins 10, the 3(1)-hydroxyethyl zinc chlorins 17 formed only small oligomers and not higher rod aggregate structures, which can be attributed to the steric effect imposed by the additional methyl group at the 3(1)-position.