Influence of Positional Isomers on the Macroscale and Nanoscale Architectures of Aggregates of Racemic Hydroxyoctadecanoic Acids in Their Molecular Gel, Dispersion, and Solid States

Abstract

Inter/intramolecular hydrogen bonding of a series of hydroxystearic acids (HSAs) are investigated. Self-assembly of molecular gels obtained from these fatty acids with isomeric hydroxyl groups is influenced by the position of the secondary hydroxyl group. 2-Hydroxystearic acid (2HSA) does not form a molecular dimer, as indicated by FT-IR, and growth along the secondary axis is inhibited because the secondary hydroxyl group is unable to form intermolecular H-bonds. As well, the XRD long spacing is shorter than the dimer length of hydroxystearic acid. 3-Hydroxystearic acid (3HSA) forms an acyclic dimer, and the hydroxyl groups are unable to hydrogen bond, preventing the crystal structure from growing along the secondary axis. Finally, isomers 6HSA, 8HSA, 10HSA, 12HSA, and 14HSA have similar XRD and FT-IR patterns, suggesting that these molecules all self-assemble in a similar fashion. The monomers form a carboxylic cyclic dimer, and the secondary hydroxyl group promotes growth along the secondary axis.

Salicylato Titanocene Complexes as Cooperative Organometallic Lewis Acid and Brønsted Acid Catalysts for Three‐Component Mannich Reactions

“…In both the solid and gel states of all gelators, there is no evidence for free hydroxyl groups: only peaks at 3150–3400 cm −1 , and none at approximately 3600 cm −1 could be detected 25. There is no discernible frequency difference between the broad OH stretching bands in the spectra of neat HSA and 9,12 R ‐diol or their nitrobenzene gels.…”

“…Regardless, the data indicate that the carboxylic acid head groups in the solid and gel states prefer to exist as intermolecular cyclic dimers 16e. 25 The FT‐IR spectra of both the solid and gel phases of 9,12 R ‐diol (consisting of a 9:1 ratio of diastereomers) is the only gelator of the ones examined here that also displays a weak shoulder at approximately 1720 cm −1 , attributable to acyclic dimers of the carboxylic acid groups 16e. However, fibers (instead of platelets, found when acyclic dimers predominate)16e are still present in the AFM and POM images of the gels (Figure 2 and Figure 3).…”

“…Many criteria can be used to define gelator “efficiency”, such as the range of liquids gelated and the physical properties of the corresponding gels, including the minimum amounts of a gelator necessary to make a gel (critical gelator concentration, CGC ), the gel–sol transition temperatures ( T g ), magnitudes of viscoelastic properties, and lifetimes of the gels at room temperature 1a. 25 In this study, the range of liquids gelated is the major criterion employed, although several thermodynamic, structural, and dynamic (N.B., rheological) techniques have been used as well. Also, the relationship between liquids and a gelator has been explored using Hansen solubility parameters 7…”

“…In the trans diols, two intermolecular hydroxyl H‐bonds per molecule can be made along the axis orthogonal to the long molecular axis (promoting stabilization of fibrillar structures) 16e. 25 However, the cis diols are able to utilize only one hydroxyl group per molecule to construct a secondary H‐bonding network that is limited to pairs of molecules. The other two hydroxyl groups appear to contribute to intramolecular H‐bonding interactions.…”

Low-molecular-weight organogelators as functional materials for oil spill remediation

“…The relationship between the properties of the molecular gels formed from 12-HSA derivatives was extensively studied with different chemical structures by Rogers and Weiss (16a-16g, 17a-17f, 18a-18d). [29][30][31] Weiss's group also reported systematic studies of simple LMWGs and many organogelators that may be applicable for oil spill remediation and confirmed the formation of organogels composed of hydrophobic solvents, a liquid n-alkane (as a model for petroleum oil) and a gelator (longer n-alkanes C24, C28, C32 and C36, 19a-19g). [32] Moreover, they conducted a series of studies on organogels to clarify the influence of chemical modification of the n-alkane on its gelation ability, including the behavior of derivatives with amide 16a, 16d, 16e, [28] urea 20a-20i and thiourea 21a-21f, [33] and collected ample analytical data.…”