Departamento de Química Orgánica and UMYMFOR (CONICET-FCEN), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, Buenos Aires, C1428EGA, Argentina.
Beilstein J Org Chem. 2013 Sep 9;9:1826-36. doi: 10.3762/bjoc.9.213. eCollection 2013.
Supramolecular gels are an important and interesting class of soft materials that show great potential for many applications. Most of them have been discovered serendipitously, and understanding the supramolecular self-assembly that leads to the formation of the gel superstructure is the key to the directed design of new organogels. We report herein the organogelating property of four stereoisomers of the simple steroid 2,3-dihydroxycholestane. Only the isomer with the trans-diaxial hydroxy groups had the ability to gelate a broad variety of liquids and, thus, to be a super-organogelator for hydrocarbons. The scope of solvent gelation was analysed with regard to two solvent parameters, namely the Kamlet-Taft and the Hansen solubility parameters. The best correlation was observed with the Hansen approach that revealed the existence of two clear gelation zones. We propose a general model of self-assembly through multiple intermolecular hydrogen bonds between the 1,2-dihydroxy system, which is based on experimental data and computational simulations revealing the importance of the di-axial orientation of the hydroxy groups for the one-dimensional self-assembly. Under controlled conditions, the fibrillar superstructure of the organogel was successfully used as a template for the in-situ sol-gel polymerization of tetraethoxysilane and the further preparation of silica nanotubes. We propose that the driving forces for templating are hydrogen bonding and electrostatic interactions between the anionic silicate intermediate species and the self-assembled fibrillar network.
超分子凝胶是一类重要且有趣的软物质，它们在许多应用中具有很大的潜力。它们中的大多数都是偶然发现的，而理解导致凝胶超结构形成的超分子自组装是定向设计新的有机凝胶的关键。本文报告了简单甾体 2,3-二羟胆甾烷的四个立体异构体的有机凝胶性质。只有具有反式双轴向羟基的异构体才有能力胶凝各种液体，因此是碳氢化合物的超级有机凝胶剂。溶剂凝胶化的范围根据两个溶剂参数，即 Kamlet-Taft 和 Hansen 溶解度参数进行了分析。与 Hansen 方法的最佳相关性表明存在两个明确的凝胶化区。我们提出了一种通过 1,2-二羟基系统之间的多个分子间氢键进行自组装的一般模型，该模型基于实验数据和计算模拟，揭示了羟基的双轴向取向对一维自组装的重要性。在受控条件下，有机凝胶的纤维状超结构成功地用作正硅酸乙酯原位溶胶-凝胶聚合的模板，并进一步制备了二氧化硅纳米管。我们提出，模板的驱动力是阴离子硅酸盐中间体与自组装纤维状网络之间的氢键和静电相互作用。
