Porphyrin-based organogels: control of the aggregation mode by a pyridine-carboxylic acid interaction.
Porphyrin-based organogels: control of the aggregation mode by a pyridine-carboxylic acid interaction.
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DOI：
10.1021/la047070u
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发表时间：
2005-02
期刊：
影响因子：
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通讯作者：
Satoshi Tanaka;Michihiro Shirakawa;K. Kaneko;M. Takeuchi;S. Shinkai
中科院分区：
文献类型：
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作者：
Satoshi Tanaka;Michihiro Shirakawa;K. Kaneko;M. Takeuchi;S. Shinkai
为了寻找一种新的设计基于卟啉的有机凝胶剂的策略，在卟啉(1CP或1EP)的外围位置引入了给氢键(羧酸)/接受(吡啶)取代基或给电子(二烷氨基)/脱电子(吡啶)取代基，并与含有两个吡啶取代基或两个酯基(分别为1PP或1EE)的对称参比化合物的凝胶性能进行了比较。结果表明，对称分子的溶解度比1CP和1EP分子的溶解度要差得多，1CP和1EP分子具有偶极矩，在大多数有机溶剂中都有沉淀。1CP、1EP和1EE分别与环己烷、甲基环己烷和几种醇类溶剂形成凝胶，但扫描电子显微镜和透射电子显微镜观察表明，它们在有机凝胶中形成的超结构有很大不同。在环己烷中，1CP形成片状结构，而1EP和1EE形成纤维状结构。这种差异归因于1CP中由卟啉-卟啉pi-pi堆积和羧酸-吡啶氢键组成的二维相互作用力。事实上，当氢键相互作用被醇类溶剂或加入吡啶或N，N-二甲氨基吡啶削弱时，片状结构转变为纤维状结构。通过紫外-可见(UV-Vis)、傅立叶变换红外光谱(FT-IR)、X射线衍射(XRD)等光谱分析手段，进一步详细分析了它们的聚集模式。在此基础上，讨论了这些外围取代基对凝胶形成和聚集方式的影响。
To find a new strategy for designing porphyrin-based organogelators, hydrogen-bond-donating (carboxylic acid)/accepting (pyridine) substituents or electron-donating (dialkylamino)/withdrawing (pyridine) substituents were introduced into peripheral positions of a porphyrin (1cp or 1ep, respectively), and the gelation properties were compared with those of symmetrical reference compounds bearing two pyridyl substituents or two ester groups (1pp or 1ee, respectively). It was found that the symmetrical molecules show a solubility that is quite inferior to that of 1cp and 1ep having a dipole moment and precipitate from most organic solvents. 1cp, 1ep, and 1ee formed gels with cyclohexane, methylcyclohexane, and several alcoholic solvents, but scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations revealed that their superstructures constructed in the organogels are very different. In cyclohexane, 1cp resulted in a sheetlike structure, whereas 1ep and 1ee resulted in a fiberlike structure. The difference is attributed to the two-dimensional interactive forces in 1cp consisting of the porphyrin-porphyrin pi-pi stacking and the carboxylic acid-pyridine hydrogen bonding. In fact, when the hydrogen-bonding interaction was weakened by alcoholic solvents or by adding pyridine or N,N-(dimethylamino)pyridine, the sheetlike structure was transfigured to the fiberlike structure. Further detailed analyses of their aggregation modes were conducted by spectroscopic methods such as ultraviolet-visible (UV-vis) absorption, Fourier transform infrared (FT-IR), and X-ray diffraction (XRD). On the basis of these findings, the influence of these peripheral substituents on the gel formation and the aggregation mode was discussed.