Water-in-Oil Emulsion Gels Stabilized by a Low-Molecular Weight Organogelator Derived from Dehydroabietic Acid

Toroidal micelles formed in viscoelastic aqueous solutions of a double-tailed surfactant with two quaternary ammonium head groups

Innovation in surfactant structures is an effective way to prepare new soft materials with novel applications. In this study, we synthesized a double-tailed surfactant containing two quaternary ammonium head groups (Di-C12-N2). The Di-C12-N2 solution behavior was investigated by surface tension, fluorescence, rheology, and cryo-TEM methods. Although Di-C12-N2 contained a large double-tailed hydrophobic group, the solubility of Di-C12-N2 was ∼90 mmol L-1 at 25 °C with a Krafft temperature of ∼1 °C. The increase in Di-C12-N2 concentration in the solutions led to the formation of various aggregates, including spherical micelles, worm-like micelles, multi-layered vesicles, and a rare type of small toroidal micelles. The two quaternary ammonium head groups in Di-C12-N2 led to strong electrostatic interactions between molecules, which was critical for the formation of toroidal micelles. Moreover, with an added NaCl concentration of 40 mmol L-1, the viscosity of the 5 mmol L-1Di-C12-N2 solution increased by ∼1000 times compared to the pure 5 mmol L-1Di-C12-N2 solution, revealing the high sensitivity of the unique head groups to ionic strength. This study enriches the research on the self-assembly principles of surfactants and brings new potential applications for new soft materials.

Stimuli responsive gelation of tert-butylacetic acid based LMOGs - applications in remediation of marine oil spills, dye removal and heavy metal sensing

Tert-butylacetic acid based amides containing a structural backbone, a hydrogen bonding linker and a bulky end group have been synthesized (TBA1-TBA6) and explored for gelation of fuel oils and organic solvents. The importance of the tert-butyl group in driving the assembly towards gelation has been highlighted in our previously reported pivalamide-based phase selective organogelators (PSOGs). Both groups of compounds have been scrutinized and the effect of an additional methylene group in the newly synthesized series of compounds (on the gelation behavior, single crystal structure, non-covalent interactions responsible for gelation, morphology, dye absorption, etc.) were probed. Compounds TBA1-TBA6 were also utilized for sensing heavy metal ions and transition metal ions present in aqueous medium. They display phase-selective gelation of oil in the presence of biphasic systems (oil-sea water) when added in powder form as well as in solution form, and hence, make excellent candidates for containing oil spills in water bodies. Overall, both these libraries form a class of smallest molecules ever employed for successful organogelation behavior.

Synthesis and Self-assembly of Novel Nanofeather-like Fluorescent Alkyloxy-Containing Diphenyl Ether Organogelators

In this study, novel fluorescent low molecular-weight organogelators are derived from diphenyl ethers and substituted with para-alkoxy groups of different aliphatic chain lengths. The present research promotes the preparation of innovative nanofeather-like assemblies from the synthesized diphenyl ether-derived organogelators. The gelation performance of the prepared alkoxy-substituted diphenyl ethers was reported. The synthesis procedure was achieved by using a base-catalyzed reaction of hydroxyl-substituted diphenyl with various alcohols of different aliphatic chain lengths. The chemical structures of the synthesized diphenyl ether derivatives were studied by ¹H/¹³C NMR and infrared spectroscopy. Fluorescence and UV-vis absorption spectral analyses showed solvatochromism. The diphenyl ether derivatives with longer alkoxy terminal substituents showed enhanced thermoreversible gelation activity as compared to the diphenyl ether derivatives with shorter alkoxy terminal substituents. The morphological properties of the self-assembled diphenyl ethers were studied by transmission electron microscopy and scanning electron microscopy, which showed supramolecular architectures of highly ordered nanofeathers, enforced by van der Waals interactions and π-stacks. Depending on the length of the aliphatic tail, different morphologies were detected, including nanofeathers, nanofibers, and nanosheets. The antimicrobial and cytotoxic properties of the prepared diphenyl ether-derived organogelators were examined to confirm their possible use in various fields like drug delivery systems.

Synthesis and Properties of a New Type of Terpyridine Cholesterol Derivative Gelator with Applications to Medical Treatments

Low molecular mass gelators (LMMGs), as a new type of intelligent soft material, possess good response properties to light, electricity, heat, and ultrasound and have many potential applications in fields such as intelligent sensing, biological materials, and drug release. Additionally, steroid derivatives have been a focus in the study of LMMGs for their desirable properties as well, such as their rigid framework, multichiral center, and strong van der Waals accumulation. Furthermore, the coordination ability of terpyridine has been an emphasis in the study of supramolecular chemistry and coordination chemistry as well. Attempts have been made with terpyridine groups that have special responses, such as terpyridine with steroid derivatives, to build more specialized and functional gelators. In this study, we used 2-acetylpyridine, 2-formaldehyde, and cholesterol to synthesize 6-(2,2:6 ${}^{\prime }$ ,2 ${}^{″}$ -terpyridine-4 ${}^{\prime }$ -carboxamide group) hexanoic acid (with a yield of 64.39%, P1), glycine cholesterol ester (with a yield of 70.36%, P2), and DMTCP (with a yield of 88.92%). Infrared spectroscopy, nuclear magnetic resonance spectroscopy, mass spectrometry, elemental analysis, and gelator performance tests were then conducted to measure the gelation effect of the materials and to explore their gelation mechanisms. Compared to P1 and P2, the DMTCP synthesized by P1 and P2 was able to form gel in more kinds of solvents. In addition, when it contains both terpyridine and cholesterol functional groups, the gelation properties of DMTCP were also significantly improved, and all the gels prepared in the four solvents in which DMTCP can form gels were stimulus responsive.