Stabilization of an asymmetric bolaamphiphilic sugar-based crown ether hydrogel by hydrogen bonding interaction and its sol–gel transcription

Functionality mediated colour shifting gels from cetyltrimethylammonium bromide and 6-amino caproic acid

A charge transfer gel from a cetyltrimethylammonium bromide (CTAB) and an additive 6-aminocaproic acid (6-ACA), in a two-component solvent mixture at a critical solvent composition of 3 : 1 v/v water : toluene is reported. The pale yellow colour of the gel arising from charge transfer interactions between the amine group (-NH2) of hexylamine and the ammonium ion (N+) of CTAB was confirmed after performing a set of trial experiments with CTAB-heptanoic acid and CTAB-hexylamine systems. The process of gelation, gel phase development and its microstructure were investigated using spectroscopy, microscopy, and small-angle X-ray scattering (SAXS) techniques. The gel formed a lamellar organization while preserving a loose-packed arrangement of a bilayer of CTAB and 6-ACA molecules, maintaining H-bonding along with significant charge transfer interactions. The SAXS pattern revealed a distinct crystalline form of the lamellar gel, indicating a stable phase characterized by alternating layers of crystalline and amorphous structures. This unique gelation nature was inferred from the interplanar spacings, demonstrating its non-conducive properties in highly polar solvents such as methanol and ethanol, as well as in less polar solvents like cyclohexane and carbon tetrachloride, when the organic solvent polarity was altered in the presence of water in the mixed amphiphilic system.

Glycosylated lanthanide cyclen complexes as luminescent probes for monitoring glycosidase enzyme activity

The development of synthetic chemical probes for the detection of enzymes is extremely important for biological, medicinal, and industrial applications. Here we report the synthesis of an array of novel glycosylated Tb(iii) complexes, their photophysical properties in solution, and their ability to function as luminescent probes for observing glycosidase enzyme activity in real time. Our initial studies into the application of these complexes for the detection of the Concanavalin A (ConA) lectin is also reported, highlighting the broad scope of these novel chemical probes.

Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping address fundamental questions about the mechanisms or the consequences of the self-assembly of molecules, including low molecular weight ones. Finally, we provide a perspective on supramolecular hydrogelators. We hope that this review will serve as an updated introduction and reference for researchers who are interested in exploring supramolecular hydrogelators as molecular biomaterials for addressing the societal needs at various frontiers.

Differential response of cholesterol based pyrimidine systems with oxyethylene type spacers to gelation and mesogen formation in the presence of alkali metal ions

A new series of lipophilic cholesteryl derivatives of 2,4,6-trichloro-pyrimidine-5-carbaldehyde has been synthesized. Oxyethylene spacers of variable lengths were inserted between the hydrogen bonding promoting pyrimidine core and the cholesteryl tail in order to understand their effect on the self-assembly of these compounds. Only compound 1a with the shortest spacer formed a gel in organic solvents such as n-butanol and n-dodecane. While other members (1b and c) having longer spacers led to sol formation and precipitation in n-butanol and n-dodecane respectively. The self-assembly phenomena associated with the gelation process were investigated using temperature-dependent UV-Vis and CD-spectroscopy. The morphological features of the freeze-dried gels obtained from different organic solvents were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The solid phase behaviours of these molecules and their associated alkali metal ion complexes were explored using polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The molecular arrangements in the xerogel and in the solid state were further probed using a wide-angle X-ray diffraction (WAXD) technique. Analysis of the wide-angle X-ray diffraction data reveals that this class of molecules adopts a hexagonal columnar organization in the gel and in the solid state. Each slice of these hexagonal columnar structures is composed of a dimeric molecular-assembly as a building block. Significant changes in the conformation of the oxyethylene chains could be triggered via the coordination of selected alkali metal ions. This led to the production of interesting metal ion promoted mesogenic behaviour.

A correlation study between hydrogen-bonded network and gelation ability of three galactose derivatives

The hydrogen bonding network in the crystals of the three saccharides was correlated with their gelling ability or inability, and unexpectedly, a 2D hydrogen-bonded system was found to show efficient gelation, whereas a 1D hydrogen bonding system was a nongelator.

Roles of both amines and acid in supramolecular hydrogel formation of tetracarboxyl acid-appended calix[4]arene gelator

A tetracarboxylic acid-appended calix[4]arene derivative 1 which were insoluble in water could form a supramolecular hydrogel upon addition of both amines and HCl.

Organogelation and hydrogelation of low-molecular-weight amphiphilic dipeptides: pH responsiveness in phase-selective gelation and dye removal

The search for efficient low-molecular-weight gelators (LMWGs) with possible structure-activity correlation is on the rise. The present work reports a novel set of amphiphilic dipeptide-based carboxylic acids capable of efficiently gelating organic solvents. More interestingly, their sodium salts showed enhanced efficiency in organogelation with the additional ability to gelate water. Electrostatic interactions present in the aggregation of the sodium carboxylates of amphiphilic dipeptides seem to be important because some of the nongelator carboxylic acids turned out to be excellent gelators upon salt formation. The combinations and sequence of the amino acids in the dipeptide moiety were systematically altered to understand the collective importance of the nonpolar aliphatic/aromatic substitution in amino acids in the self-assembling behavior of amphiphiles. Almost a 20-fold enhancement in the gelation ability was observed on reversing the sequence of the amino acid residues, and in some cases, nongelators were transformed to efficient gelators. Spectroscopic and microscopic studies of these thermoreversible organo/hydrogels revealed that balanced participation of the noncovalent interactions including hydrogen bonding and van der Waals interactions are crucial for organo/hydrogelation. These dipeptides selectively gelate organic solvents from their mixtures with water, and the xerogels prepared from these organogels showed time-dependent adsorption of dyes such as crystal violet. The most remarkable feature of these gelators is the pH responsiveness, which was aptly utilized for the pH-dependent phase-selective gelation of either solvent in a biphasic mixture of oil and water. The dissimilar gelation ability of the acid and its salt originating from the pH responsiveness of the amphiphilic dipeptide was employed in the instant removal of large amounts of dyes for wastewater treatment.

Synthesis and characterization of monosaccharide-derived carbamates as low-molecular-weight gelators

Sugar-based low-molecular-weight gelators are an interesting new class of compounds that are important in supramolecular chemistry and for the preparation of advanced materials. Previously, we synthesized a series of ester and carbamate derivatives of 4,6-O-benzylidene methyl-alpha-D-glucopyranoside and found that monosubstituted alkynyl esters with five to seven carbons and monosubstituted carbamates with saturated five- and seven-carbon chains are good gelators. To understand the structural requirement for the gelation of the carbamate derivatives (O-linked carbamates), a diverse series of analogs, including alkynyl, aryl, and alkyl halide derivatives, were prepared and analyzed. We found that for gelation the O-linked carbamate derivatives have different structural preferences than the ester derivatives. To exhibit gellation, the ester analogs favor alkyl-containing terminal acetylene groups and the carbamoyl derivatives prefer saturated hydrocarbons. Both the esters and the carbamates showed good gelation properties when they were functionalized with aryl side chains. We also synthesized and screened a new series of carbamates (N-linked carbamates) in which the nitrogen atom of the carbamate group is directly attached to the sugar ring. The N-linked carbamates are good gelators for aqueous DMSO and ethanol solutions, and two of the compounds are also able to form gels in pure water. Optical microscopy and scanning electron microscopy were used to characterize several representative gels. In general, long, narrow, uniform fibrous networks were observed for effective gelators. The structure-gelation correlation obtained here can be used in the design of new sugar-based low-molecular-weight gelators.

Synthesis and structural analysis of a series of D-glucose derivatives as low molecular weight gelators

Low molecular weight gelators are an interesting new type of compounds that are important in supramolecular chemistry and advanced materials. Previously, we had synthesized several acyl derivatives of methyl 4,6-O-benzylidene-alpha-D-glucopyranoside and found that a number of terminal acetylene-containing esters are good gelators. To understand the structure requirement of the acyl chains, we synthesized a series of analogs containing different functional groups including aryl, alkenyl, and halogen derivatives. X-ray crystal structures of a monoester and a diester derivative were also obtained to help understand the relationship between structure and gelation. For good gelation properties, the carboxyl derivatives should possess alkyl groups containing a terminal acetylene group and aryl derivatives.