Self-assembly of 2,3-dihydroxycholestane steroids into supramolecular organogels as a soft template for the in-situ generation of silicate nanomaterials

Abstract

SummarySupramolecular 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.

Organogel formation rationalized by Hansen solubility parameters: dos and don'ts

“…In a few cases however, a very elongated or even two discontinuous gelation domains have been identified. 42,44 From a theoretical perspective, this is in fact not surprizing because a given gelator may not necessarily form fibres with the same crystalline structure in every tested liquid. 51,64,65 Therefore, the functional groups of the gelator that are exposed at the fibre surface can actually depend on the gelated liquid, 66 which obviously affects the interfacial energy.…”

“…42 Since then, several groups have tested our approach with new LMWGs and have confirmed the validity of the concept. [43][44][45][46] However, some concerns have been expressed about the mathematical difficulties involved in the method, 47,48 while several studies have proposed related approaches. [47][48][49][50][51][52][53][54][55][56] Therefore, the objective of the present report is both to better explain our approach to make it more accessible and to critically discuss the recent developments in the field.…”

Organogel Formation Rationalized by Hansen Solubility Parameters: Shift of the Gelation Sphere with the Gelator Structure

“…4 The next challenge in the field is to evaluate how small changes in the structure of a LMWG will affect the gelation domain. [27][28][29][30][31][32][33] In particular, we previously probed the influence of the length of an alkyl chain within a family of related gelators, but showed that it is difficult to rationalize the results without knowledge of the molecular packing. 33 To better correlate the molecular structure with the gelation domain, we selected a family of amide-based thiazole derivatives bearing a long aliphatic chain, for which the elucidation of the molecular packing seemed to be within reach ( Figure 1).…”

Organogel formation rationalized by Hansen solubility parameters: improved methodology

“…14 Some studies performed a simple qualitative description of the Hansen space (without determining a gelation sphere) or used a 1D or 2D projection of Hansen space (Teas Plot) to simplify the data treatment and representation. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] More interestingly, some studies proposed alternative procedures to determine a gelation domain from their specific experimental data. [30][31][32][33][34][35][36][37][38] While these modifications of the data treatment are certainly well suited to particular datasets, the natural question that arises is whether they are of general applicability.…”