Sol-gel polycondensation of tetraethyl orthosilicate (TEOS) in sugar-based porphyrin organogels: inorganic conversion of a sugar-directed porphyrinic fiber library through sol-gel transcription processes.
Sol-gel polycondensation of tetraethyl orthosilicate (TEOS) in sugar-based porphyrin organogels: inorganic conversion of a sugar-directed porphyrinic fiber library through sol-gel transcription processes.
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DOI：
10.1002/chem.200305042
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发表时间：
2004-01
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影响因子：
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通讯作者：
Shin‐ichiro Kawano;S. Tamaru;Norifumi Fujita;S. Shinkai
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文献类型：
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作者：
Shin‐ichiro Kawano;S. Tamaru;Norifumi Fujita;S. Shinkai
本文设计了一类新型的糖基卟啉（1a-e）凝胶剂。这些化合物中的一些具有形成一维聚集体的趋势，这些聚集体足够稳定以显示对于DMF-醇混合溶剂的成功凝胶化能力。通过紫外-可见光谱（UV/维斯）、圆二色性（CD）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）详细评价了特定柱状超结构中的聚集模式。从1a-c得到的糖附加的卟啉凝胶的所有紫外-可见光谱都表现出Soret带吸收，其向较低波长移动并且显著加宽。这一现象表明，这些卟啉核强烈相互作用，在H-聚集体的方式，这驱动了一维卟啉堆积阵列的产生。来自Ia和I B的有机凝胶（其为端基异构体）的CD光谱表现出几乎对称的图案，而来自Ic的凝胶给出完全不同的图案。这意味着凝胶原纤维以右手或左手方式缠绕自己;这反映了胶凝因子的特定分子结构中的手性。凝胶原纤维的SEM结果与CD图谱吻合较好。图1 a中的凝胶原纤维具有左旋螺旋，而图1 B中的凝胶原纤维自身右旋缠绕。宏观螺旋形态在分子水平上很好地反映了微观结构，这给出了凝胶原纤维的结构多样性，这可以通过糖库来定义。通过溶胶-凝胶转录过程的有机螺旋纤维的无机转化成功地给出了螺旋二氧化硅结构，其精细地继承了有机形态。一个引人注目的观察是，单分子的卟啉堆叠阵列也转录成二氧化硅纤维时，选择最佳的溶胶-凝胶反应条件。因此，卟啉凝胶中的糖基有机纤维库通过溶胶-凝胶转录过程提供了多种无机材料。
Sugar-appended porphyrins (1 a-e) with monosaccharide groups at their periphery have been rationally designed for a new class of gelating reagents. A few of these compounds have the tendancy to form one-dimensional aggregates stable enough to show successful gelation ability for DMF-alcohol mixed solvents. The aggregation mode in the specific columnar super structures has been evaluated in detail by UV-visible spectrometry (UV/Vis), circular dichroism (CD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). All UV-visible spectra of sugar-appended porphyrinic gels obtained from 1 a-c exhibit Soret band absorptions, which shift to lower wavelength and are significantly broadened. This phenomenon indicates that these porphyrin cores strongly interact with each other in an H-aggregate fashion, which drives the generation of a one-dimensional porphyrin-stacking array. The CD spectra of the organogels from 1 a and 1 b, which are in anomers, exhibit an almost symmetric pattern, whereas the gel from 1 c gives a completely different pattern. This implies that the gel fibrils wind themselves in a right- or left-handed fashion; this reflects chirality in the specific molecular structure of the gelators. The results from SEM for the gel fibrils are in good agreement with the CD patterns. The gel fibrils in 1 a possess left-handed helicity, whereas those in 1 b wind themselves right-handedly. Macroscopic helical morphology reflects the microscopic structure well at a molecular level, which gives structural variety of the gel fibrils, which can be defined by the sugar library. Inorganic conversion of the organic helical fibrils by a sol-gel transcription process successfully gives the helical-silica structures, which finely inherit the organic morphology. A striking observation is that a unimolecular porphyrin-stacking array is also transcribed into silica fibers when the optimized sol-gel reaction conditions are selected. A sugar-based organic-fiber library in porphyrinic gels thus provides a variety of inorganic materials through the sol-gel transcription process.