Self-assembly and gelation behavior of tris(phenylisoxazolyl)benzenes.
Self-assembly and gelation behavior of tris(phenylisoxazolyl)benzenes.
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DOI：
10.1021/jo200766u
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发表时间：
2011-05
期刊：
影响因子：
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通讯作者：
Masahiro Tanaka;Toshiaki Ikeda;J. Mack;N. Kobayashi;T. Haino
中科院分区：
文献类型：
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作者：
Masahiro Tanaka;Toshiaki Ikeda;J. Mack;N. Kobayashi;T. Haino
合成了三苯基异恶唑基苯类低分子量有机胶凝剂（LMOG），并用1HNMR和UV-vis吸收光谱研究了其自组装行为。它们在非极性和高极性溶剂如甲基环己烷、乙醚、丙酮、二甲基亚砜等中均形成凝胶。场发射扫描电子显微镜（FESEM）观察具有饱和烷基链的1和3的干凝胶显示形成了发达的直纤维，而2的烷基链的不饱和末端促进右旋和左旋螺旋纤维的形成。用（1）H NMR和UV-vis光谱研究了化合物1、2和5在溶液中的自缔合行为。扁平芳香族化合物1通过π-π堆积相互作用沿其C（3）轴沿着以柱状方式堆积。组装受外围烷基取代基的调控;饱和烷基促进组装，而末端双键阻碍分子间缔合，支链取代基明显干扰堆叠的形成，可能是由于空间位阻要求。理论计算表明，异恶唑基团的三个偶极子采用圆形阵列。使用MacroModel V9.1对4的六聚体堆叠的构象搜索产生了两种主要的构象：一种是非螺旋的，另一种是螺旋的。通过圆二色性（CD）测量对手性5的组装体进行了进一步的详细结构分析，表明它们的组装体在溶液中采用螺旋结构。CD光谱和DFT计算表明，R-5形成左手超分子螺旋。R-和S-5的共组装显示出手性放大，因为5的手性信息被转移到1的螺旋组装体的超分子手性。少量的光学活性5提供了足够的手性刺激，产生了显着的手性响应和超分子螺旋结构的1。
Low-molecular-mass organic gelators (LMOG), tris(phenylisoxazolyl)benzenes, were synthesized, and their self-assembling behavior was examined using (1)H NMR and UV-vis absorption spectroscopies. They turned into a gel in both nonpolar and highly polar solvents such as methylcyclohexane, ether, acetone, dimethylsulfoxide, etc. Field emission scanning electron microscopy (FESEM) observation of the xerogels of 1 and 3 possessing the saturated alkyl chains revealed that well-developed straight fibers were formed, whereas the unsaturated termini of the alkyl chains of 2 promoted the formation of both the right- and left-handed helical fibers. The self-association behavior of 1, 2, and 5 in solution were investigated using (1)H NMR and UV-vis spectroscopies. The flat aromatic compound 1 stacked in a columnar fashion along its C(3) axis via π-π stacking interactions. The assemblies were regulated by the peripheral alkyl substituents; the saturated alkyl groups facilitated the assemblies while terminal double bonds impeded the intermolecular association, and the branched substituents obviously interfered in the formation of the stacks, probably due to steric requirements. Theoretical calculations suggest that the three dipoles of the isoxazole groups adopt the circular array. The conformational search of the hexameric stacks of 4 using MacroModel V9.1 gave rise to two major conformers: one is nonhelical and the other is helical. Further detailed structural analysis of the assemblies of chiral 5 using circular dichroism (CD) measurements indicated that their assemblies adopt helical structures in solution. CD spectra and DFT calculations revealed that R-5 forms a left-handed supramolecular helicate. The coassembly of R- and S-5 displayed chiral amplification, since the chiral information from 5 was transferred to the supramolecular chirality of the helical assemblies of 1. A small amount of optically active 5 provided enough chiral stimulus to produce a remarkable chiral response and supramolecular helical structures of 1.