Chirality, Gelation Ability and Crystal Structure: Together or Apart? Alkyl Phenyl Ethers of Glycerol as Simple LMWGs

Abstract

Chiral recognition plays an important role in the self-assembly of soft materials, in particular supramolecular organogels formed by low molecular weight gelators (LMWGs). Out of 14 pairs of the studied racemic and enantiopure samples of alkyl-substituted phenyl ethers of glycerol, only eight enantiopure diols form the stable gels in nonane. The formation of gels from solutions was studied by polarimetry, and their degradation with the formation of xerogels was studied by the PXRD method. The revealed crystalline characteristics of all studied xerogels corresponded to those for crystalline samples of the parent gelators. In addition to those previously investigated, crystalline samples of enantiopure para-n-alkylphenyl glycerol ethers [alkyl = pentyl (5), hexyl (6), heptyl (7), octyl (8), nonyl (9)] and racemic 3-(3,5-dimethylphenoxy)propane-1,2-diol (rac-14) have been examined by single crystal X-ray diffraction analysis. Among 22 samples of compounds 1-14 studied by SC-XRD, seven different types of supramolecular motifs are identified, of which only two are realized in crystals of supramolecular gelators. An attempt was made to relate the ability to gel formation with the characteristics of the supramolecular motif of a potential gelling agent, and the frequency of formation of the motif, required for gelation, with the chiral characteristics of the sample.

Intermolecular Hydrogen Bonding in Alpha-Hydroxy Carboxylic Acids Crystals: Connectivity, Synthons, Supramolecular Motifs

“…It is curious to note that in their good-quality study of the crystal organization of the representative set of mandelic acids, the authors of [41] Previously, using examples of homogeneously organized sets of chiral compounds of different classes [10,11,42], we noted that cyclic synthons begin to dominate over linear synthons upon passing from a single-enantiomeric to a racemic crystalline environment. In this work, we demonstrate that the chiral characteristics of the sample also play an important role in the choice of realizable cyclic synthons.…”

“…It is curious to note that in their good-quality study of the crystal organization of the representative set of mandelic acids, the authors of [41] Previously, using examples of homogeneously organized sets of chiral compounds of different classes [10,11,42], we noted that cyclic synthons begin to dominate over linear Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/cryst12101479/s1, Tables S1 and S2: Crystallographic summary of compounds rac-1-4, 6 (Table S1) and (S)-1-5, (R)-6 (Table S2). Schemes S1-S18: Connectivity diagrams in crystals of the studied compounds.…”

“…However, most α-hydroxycarboxylic acids are chiral, and it is often this feature that makes them interesting for practice. Previously, using the example of a uniformly organized series of chiral compounds, we showed that the crystal packings of racemic and enantiopure crystals differ at the level of supramolecular motifs predominating in them [10,11]. In this work, we will analyze the crystal structure of lactic acids (structure II in Scheme 2).…”

Solubility- and melting-based approaches to evaluate the inner-crystal enantiophobia and enantiophilia undergoing a structural change within a homologous series, exemplified by chiral glycerol ethers

“…This involves comparing compounds within a kindred or homologous series of chiral substances. [29][30][31][32][33][34][35] Comparison of the energy characteristics of crystal phases with the features of their crystal structures, as determined by X-ray diffraction, can also provide valuable information for this assessment.…”