The Effect of the Side Chain on Gelation Properties of Bile Acid Alkyl Amides

Abstract

Six bile acid alkyl amide derivatives were studied with respect to their gelation properties. The derivatives were composed of three different bile acids with hexyl or cyclohexyl side chains. The gelation behaviour of all six compounds were studied for 36 solvents with varying polarities. Gelation was observed mainly in aromatic solvents, which is characteristic for bile‐acid‐based low molecular weight gelators. Out of 108 bile acid‐solvent combinations, a total of 44 gel systems were formed, 28 of which from lithocholic acid derivatives, only two from deoxycholic acid derivatives, and 14 from cholic acid derivatives. The majority of the gel systems were formed from bile acids with hexyl side chains, contrary to the cyclohexyl group, which seems to be a poor gelation moiety. These results indicate that the spatial demand of the side chain is the key feature for the gelation properties of the bile acid amides.

The Effect of Branched Alkyl Chain Length on the Properties of Supramolecular Organogels from Mono-N-Alkylated Primary Oxalamides

“…Despite the broad range of chemical structures of organic molecules known form supramolecular gels to date, the rational design of LMWGs for gelating specific liquids to give supramolecular gels with suitable properties for a certain application [3,13,19,20] remains a significant challenge. Towards this goal, many studies have been carried out in order to better understand the influence of molecular structure on the gelator self-assembly Gels 2023, 9, 5 2 of 20 process and gel properties, which involve the effect of slight structural changes on the gelation and gel properties for LMWGs such as hydroxystearic acids [21], glucosamines [22], stearates [23], stearamides [24], cholesterols [25], bile acids [26], coumarins [27], ureas [28], carbamates [29], alkylated amino acids [30], polyaromatics [31], dendritic supramolecules [32], as well as peptide-based hydrogelators [33] to name a few. Such studies have revealed that gel properties such as gelation ability with different solvents, critical gel concentration (CGC), gel strength and thermal stability can be modulated with minimal structural changes, without modifying the types of intermolecular interactions that drive the gel formation in a specific solvent allowing fine-tuning between gel properties and related applications [24].…”

Acid⋅⋅⋅Amide Supramolecular Synthon for Tuning Amino Acid‐Based Hydrogels’ Properties

“…In most cases, the attempt to tune the mechanical properties and release behavior of hydro-gels relied on the chemical modification of known gelling agents, or on the co-assembly of complementary-interacting LMWG. [4][5][6][7] An alternative approach recently envisaged the potential of noncovalent interactions involved in the crystal packing of supramolecular synthons, for predicting and modulating the macroscopic features of the corresponding gels. [8][9][10] Although the correlation between self-assembly in the solid state and in the gel phase is still under debate, [11] the application of crystal engineering principles to the design of LMWG afforded some promising results, [12][13][14][15] especially in the case of organic salts, [16][17][18][19] metallogels, [20][21] and sensing platforms for ions or bioactive molecules.…”

“…However, engineering supramolecular hydrogels with tailored properties remains a major challenge, as the lack of molecular insights on the self‐assembly process driving the gelation often hampers the design and choice of effective gelators. In most cases, the attempt to tune the mechanical properties and release behavior of hydrogels relied on the chemical modification of known gelling agents, or on the co‐assembly of complementary‐interacting LMWG [4–7] . An alternative approach recently envisaged the potential of noncovalent interactions involved in the crystal packing of supramolecular synthons, for predicting and modulating the macroscopic features of the corresponding gels [8–10] .…”