Exploring Molecular Recognition Pathways within a Family of Gelators with Different Hydrogen Bonding Motifs.

Abstract

General rights Copyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. AbstractWe report the synthesis of a family of gelators in which alkyl chains are connected to the amino groups of L-lysine methyl ester using a range of different hydrogen bonding linking groups (carbamate, amide, urea, thiourea and diacylhydrazine) using simple synthetic methodology based on isocyanate or acid chloride chemistry. The ability of these compounds to gelate organic solvents such as toluene or cyclohexane can be directly related to the ability of the linking group to form intermolecular hydrogen bonds. In general terms, the ability to structure solvents can be considered as:thiourea<carbamate<amide<urea∼diacylhydrazine. This process has been confirmed by thermal measurements, scanning electron microscopy (SEM) and infrared and circular dichroism spectroscopies. By deprotecting the methyl ester group, we have demonstrated that a balance between hydrophobic and hydrophilic groups is essential-if the system has too much hydrophilicity (e.g., diacylhydrazine, urea) it will not form gels due to low solubility in the organic media. However, the less effective gelators based on amide and carbamate linkages are enhanced by converting the methyl ester to a carboxylic acid. Furthermore, subsequent mixing of the acid with a second component (diaminododecane) further enhances the ability to form networks, and, in the case of the amide, generates a two-component gel, which can immobilise a wide range of solvents of industrial interest including petrol and diesel (fuel oils), olive oil and sunflower oil (renewable food oils) and ethyl laurate, isopropyl myristate and isopropyl palmitate (oils used in pharmaceutical formulation).The gels are all thermoreversible, and may therefore be useful in controlled release/formulation applications.

Supracolloidal Assemblies as Sacrificial Templates for Porous Silk-Based Biomaterials

“…A parameterized approach was used to investigate the ability of non-aqueous solvents to dissolve urea. Solvent–solute interactions play an important role in supramolecular chemistry which has led to quantitative studies of the role of solvents in self-assembly processes [ 19 , 20 , 21 , 22 , 23 , 24 ]. The bulk properties (e.g., boiling point, density) or molecular level properties (such as specific intermolecular forces) can be quantified and parameterized.…”

“…The parameters δ P and δ H are described in terms of a combined polar solubility parameter, δ a , and the Kamlet-Taft parameters, π* (a generalized polarity parameter), α (the ability to donate hydrogen bonds), and β (the ability to accept hydrogen bonds). The effects of solvents on the hierarchical assembly of supramolecular polymers in non-aqueous solvents have been studied for self-assembling peptides, and while there was a general correlation between the ability of supramolecular polymers to form and the polar solubility parameter, δ a [ 19 , 20 , 21 , 22 , 23 , 24 ], the precise hydrogen-bonding nature of the solvent in terms of Kamlet-Taft parameters ( i.e. , deconvolution of the hydrogen bond donors and acceptors) was important to fully understand the solvent effects [ 19 , 20 , 21 , 22 , 23 , 24 ].…”

Using EPR Spectroscopy as a Unique Probe of Molecular-Scale Reorganization and Solvation in Self-Assembled Gel-Phase Materials

“…This implies that the gel fibers are solvated and swollen by solvent, lowering the effective concentration of DLT and hence increasing the spin− spin distance as observed using EPR. Inspection of the SEM images of the DLD gel 29 (Figure S5) shows a network of intertwined narrow fibrils which presumably are swollen by solvent in wet gels.…”

Understanding the Role of H-Bonding in Self-Aggregation in Organic Liquids by Fatty Acid Amphiphiles with a Hydrocarbon Tail Containing Different H-Bonding Linker Groups

“…In the recent literature, the physical gelation of liquids by low-molecular-weight gelators (LMWGs) has been studied with a great deal of interest owing to their impacts in various fields including molecular self-assembly (SA), smart materials, and controlled drug release. − Over the last three decades, many LMWGs with excellent gelation abilities have been reported. These include steroids, amide- − and urea-type − compounds, sugar amphiphiles, − and so forth. Most of these gelators, however, were discovered by accident.…”

“…The LMWGs reported in the literature fall into two major classes, hydrogen-bond- and non-hydrogen-bond-type gelators. The H-bonding interaction is responsible for the gelation of organic liquids by amide compounds such as amino acids − and urea − and by hydroxyl compounds such as sugars. − However, anthracene, cholesterol, and tropone derivatives − are non-hydrogen-bond-based gelators. In fact, in most cases of organogelation, it was observed that H-bonding is the dominant factor.…”