Amino Acid-Containing Phase-Selective Organogelators: A Water-Based Delivery System for Oil Spill Treatment

Enantioseparation via Chiral Supramolecular Gels Comprising Ambidextrous Gelators Based on β-Peptide-type Primary Amines

While β-peptides have been paid attention due to their diverse secondary structures, their application to the design of low-molecular-weight gelators (LMWGs) is less explored. In this work, chiral cyclic β-amino acid-based β-peptides were developed as ambidextrous LMWGs, wherein multiple hydrogen bonds between the amide moieties led to high gelation ability. Their molecular assembly was elucidated using spectroscopies, microscopy, and X-ray analysis. Further, the supramolecular gel was used as a platform for the enantioselective extraction of (S)-naproxen from its racemate under optimized conditions. These findings have expanded the utility of β-peptides and shown the potential of supramolecular gels as a distinct dynamic medium for enantiomer separation.

Development of Low-Molecular-Weight Organogelators from Cyclic β-Amino Acid: Effect of Stereochemistry and their Application on Visual Chiral Recognition of Amines

This study reports the formation of low-molecular-weight gelators based on carboxylic acids derived from chiral cyclicβ-amino acids. The effect of their stereochemistry on the gelation of organic solvents was investigated, and their assemblies with the intermolecular interactions in the xerogels were proposed via infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and crystallographic details of the related model compounds. The effect of the alkyl chain length on the gelators was studied, and they were applied to the chiral recognition of amines. Only one diastereomeric salt with amines afforded gels, whereas the others resulted in precipitates. Chiral recognition was also achieved in the gel state, and the appearance of the as-prepared gel changed upon the addition of each amine enantiomer, thus enabling the visual detection of their chirality.

Low-Molecular-Weight Organogelators Based on N-dodecanoyl-L-amino Acids-Energy Frameworks and Supramolecular Synthons

Lauric acid was used to synthesize the low-molecular-weight organogelators (LMOGs), derivatives of two endogenous (L)-alanine, (L)-leucine, and three exogenous (L)-valine, (L)-phenylalanine, and (L)-proline amino acids. The nature of processes responsible for the gel formation both in polar and in apolar solvents of such compounds is still under investigation. Knowing that the organization of surfactant molecules affects the properties of nano scale materials and gels, we decided to elucidate this problem using crystallographic diffraction and energy frameworks analysis. The single crystals of the mentioned compounds were produced successfully from heptane/^tBuOMe mixture. The compounds form lamellar self-assemblies in crystals. The energetic landscapes of single crystals of a series of studied amphiphilic gelators have been analyzed to explore the gelling properties. The presented results may be used as model systems to understand which supramolecular interactions observed in the solid state and what energy contributions are desired in the designing of new low-molecular-weight organic gelators.

Facile and Efficient Phase-Selective Powder Polymer Organogelator for Oil Spill Remediation

Phase-selective organogelators that gel oils from oil/water mixtures are useful to remediate oil spills on water. We designed and synthesized polymer organogelators, poly(styrene-co-10-undecenoic acid) with five different 10-undecenoic acid contents that could be added as powders at room temperature to gel oils with different viscosities. The morphologies and mechanical strengths of the gels were investigated using field-emission electron microscopy and rheological measurements, respectively. The gels formed porous fibrillar structures and had high stiffness. Fourier transformm infrared (FTIR) spectroscopy studies of these gels showed that hydrogen bonding and van der Waals forces helped create three-dimensional networks. The straightforward synthesis procedure, room-temperature conditions, and easy powder delivery make poly(styrene-co-10-undecenoic acid) an attractive alternative to existing oil spill response methods.

Carboxylate Group-Based Phase-Selective Organogelators with a pH-Triggered Recyclable Property

Phase-selective organogelators (PSOGs) have recently attracted more attention because of their advantages in handling oil spills and leaked organic solvents. However, it is difficult to separate and recover the organic phase and PSOGs from organic gels due to the strong interaction between them. Aiming to enhance the separation and recovery performance of the organic phase and PSOGs, we synthesized a series of pH-responsive PSOGs by using itaconic anhydride and fatty amines with carbon chain lengths of C₁₂-C₁₈. Here, PSOGs have an excellent gelation ability in that amounts of organic solvents and fuel oil can be solidified at a low concentration (<3 wt %). It is worth noting that these gels are stronger, which is more convenient for removal by a salvage operation. More importantly, compared with traditional organogelators, pH-responsive PSOGs can easily recover the organic phase and fuel oil with an adjustment of the pH without extraction or distillation. Because of the transformation between the hydrophilicity and hydrophobicity of PSOGs by pH stimulation, 83.15% PSOGs are recovered in three-cycle experiments. In addition, the recycled PSOGs can be used to realize the removal of the organic phase again. Herein, we find that pH-responsive PSOGs could be used as promising and sustainable materials for separating and recovering organic solvents/oils and PSOGs.

Manipulating the Self-Assembly of Multicomponent Low Molecular Weight Gelators (LMWGs) through Molecular Design

Multicomponent low molecular weight gelators (LMWGs) may self-assemble by co-assembly (CA), social self-sorting (SSS), or narcissistic self-sorting (NSS). Understanding the nuances of the self-assembly processes is important to predict the behavior of multicomponent organogels. Here, we investigate the effect of molecular structure on self-assembly in a series of amino-acid based bicomponent LMWGs that differ in headgroup and alkyl chain length. Packing preference of the organogels was determined using differential scanning calorimetry, nuclear magnetic resonance spectroscopy and small angle X-ray scattering. From 66 bicomponent samples we found 50 CA, 14 SSS and 2 NSS. Furthermore, we performed statistical analysis to investigate the role of hydrophobicity and chain length on the overall pathway of self-assembly for these systems. We found the hydrophobicity of the headgroup strongly affected the assembly preference of the organogel, but alkyl chain length only played a small role.

Preparation and Application of Superhydrophobic Copper Mesh by Chemical Etching and In-situ Growth

Oily sewage and floating oil in the ocean post a huge threat to the ecological environment, therefore, developing an efficient separation for oil/water mixtures is an urgent need. Currently, superhydrophobic materials exhibit excellent oil/water separation ability. In this study, a superhydrophobic copper mesh prepared by the chemical etching method and the in-situ growth method and the performance evaluation are introduced. The oxide layer on the surface of the copper mesh is first removed by pickling, and then immersed in FeCl3 solution for chemical etching to make the surface rough, stearic acid (SA) is used for in-situ growth to reduce the surface energy, a superhydrophobic oil-water separation copper mesh is obtained. The water contact angle (WCA) of the copper mesh is more than 160°. The copper mesh is chemically stable and can effectively adsorb floating oil and separate the oil-water mixture. After several oil-water separation experiments, the oil-water separation efficiency can still be above 98%. The effects of the concentration of FeCl3 and SA on the contact angle and oil-water separation efficiency are investigated, the results show that when the concentration of FeCl3 is 2% and SA is 1.5%, the WCA and oil-water separation efficiency are the largest. The research used a simple and environmentally friendly method to prepare the oil-water separation copper mesh, which has important application significance for water quality restoration.

Exploring the Tunable Optical and Mechanical Properties of Multicomponent Low-Molecular-Weight Gelators

A class of amino acid-based low-molecular-weight gelators (LMWGs) was used for single and multicomponent gel studies to investigate their tunable optical properties and their self-assembly process. The optical properties of multicomponent gels were found to be easily tuned by changing the proportion of the components, varying from opaque to highly transparent gels as analyzed using ultraviolet-visible spectroscopy. This phenomenon allows tunability without introducing another variable into the system. Scanning electron microscopy, differential scanning calorimetry, and small-angle X-ray scattering (SAXS) were used to investigate the structures of the gels. It was found that because of the structural similarities of the molecules, the gelators favor coassembly packing over self-sorting. The emergence of transparency was ascribed to changes in the fiber diameters. Moreover, analysis of the SAXS data allowed us to compare the molecular order present in the gel phase with single-crystal X-ray diffraction (SCXRD) data. Our analysis suggests that the packing of molecules seen in the crystalline phase is translated into the gel network. This reveals that the structure of the crystalline phase seen through SCXRD is a useful tool to aid in understanding the molecular packing in the gel phase.

Demonstrating Aqueous-Phase Low-Molecular-Weight-Gel Wicking of Oil for the Remediation of Oil Spilled into Surface Water

Oils spilled into surface water require effective and timely treatment. In this paper, we report on a low-molecular-weight gelator that can form gels in organic and aqueous phases. The aqueous gel was observed to absorb oils, which is proposed as a new class of materials for remediating oil spilled into surface water. The gels and the low-molecular-weight gelator have both fundamental and applied significance. Fundamentally, identifying the mechanisms that govern the formation of these gels and their resultant mechanical properties is of interest. Subsequently, these fundamental insights aid in the optimization of these gels for addressing spilled oil. First, we briefly compare the organic and aqueous gels qualitatively before focusing on the aqueous gel. Second, we demonstrate the ability of the aqueous gel to wick oils through experiments in a Hele-Shaw cell and compare our results to the Washburn equation for porous media. The Washburn equation is not entirely adequate in describing our results due to the change in volume of the porous media during the wicking process. Finally, we investigate mechanisms proposed to govern the formation of low-molecular-weight gels in the literature through rheological shear measurements during gel formation. Our experiments suggest that the proposed mechanisms are applicable to our aqueous gels, growing as anisotropic crystal networks with fractal dimensions between one and two dimensions from temporally sporadic nucleation sites.