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Abstract
New enantiomerically pure C16-alkyl diamides derived from trihydroxy cyclohexane-1,2-dicarboxylic acid have been synthesized from (−)-shikimic acid. The hydroxyl groups in these compounds are free or, alternatively, they present full or partial protection. Their gelling abilities towards several solvents have been tested and rationalized by means of the combined use of Hansen solubility parameters, scanning electron microscopy (SEM), and circular dichroism (CD), as well as computational calculations. All the results allowed us to account for the capability of each type of organogelator to interact with different solvents and for the main mode of aggregation. Thus, compounds with fully protected hydroxyl groups are good organogelators for methanol and ethanol. In contrast, a related compound bearing three free hydroxyl groups is insoluble in water and polar solvents including alcohols but it is able to gelate some low-polarity solvents. This last behavior can be justified by strong hydrogen bonding between molecules of organogelator, which competes advantageously with polar solvent interactions. As an intermediate case, an organogelator with two free hydroxyl groups presents an ambivalent ability to gelate both apolar and polar solvents by means of two aggregation patterns. These involve hydrogen bonding interactions of the unprotected hydroxyl groups in apolar solvents and intermolecular interactions between amide groups in polar ones.
Highlights
Low molecular weight organogelators (LMWOGs) are soft materials widely used at present in several fields that include products employed as lubricants, cosmetics, drug delivery systems, tissue regeneration materials, biosensors, molecular electronic devices or chiral catalysts [1,2,3,4,5]
Chiral pentasubstituted cyclohexane derivatives 2–5 show different gelling behavior depending on the degree of protection of the hydroxyl groups and, to some extent, depending on the relative cis/trans stereochemistry
These results are confirmed by the circular dichroism (CD) spectra that show of a bisignate spectrum for cis-2 and a monosignate positive band for trans-2, both as xerogels from methanol
Summary
Low molecular weight organogelators (LMWOGs) are soft materials widely used at present in several fields that include products employed as lubricants, cosmetics, drug delivery systems, tissue regeneration materials, biosensors, molecular electronic devices or chiral catalysts [1,2,3,4,5]. Applications of supramolecular gels as materials for environmental remediation [6] or for practical and eco-friendly oil spill recovery [7,8] have been reported. The gelling ability of molecules in different solvents has been the subject of a number of studies. The ultimate reasons for the hierarchical self-assembling of a gelator in a specific solvent still remain incomplete [9,10].
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