Polar Solvent-Induced Unprecedented Supergelation of (Un)Weathered Crude Oils at Room Temperature

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.

Spatiotemporal Resolved Live Cell Membrane Tracking through Photo-click Reactions Enriched in Lipid Phase

A set of photo-switchable monopeptides derived from cis-β-dibenzodiazocine-l-alanine (cis-DBDAA) have been designed and synthesized, which are capable of photo-click reacting with diaryltetrazoles or diarylsydnones in a hydrophobic phospholipid bilayer environment. The DBDAA monopeptides include both a hydrophobic tail on C-terminal, providing high affinity toward lipid membrane, and a modularized functional moiety on N-terminal, enabling rapid optimization of the self-assembly strength to form multifunctional supramolecules. With the cis-DBDAA monopeptides photo-switched into trans-configuration, we were able to disrupt the supramolecular assembly through an efficient photo-click reaction across the lipid bilayer of liposomes. We reveal that the performance of the photo-click reactions between the monopeptides and photo-generated nitrile imine intermediates is significantly enhanced by enrichment of both reactants in the hydrophobic membrane lamel of liposomes. Enrichment of the DBDAA monopeptide in lipid phase serves as a convenient method to introduce bioorthogonal chemical handles on live cell membranes, which enables fluorescence labelling of single cell's membrane with high spatiotemporal resolution to facilitate the studies on cell membrane dynamics.

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.

How Far Are We in Combating Marine Oil Spills by Using Phase-Selective Organogelators?

Marine oil spills is one of the frequent natural disasters that adversely affect the economy and ecosystem. A variety of methods have been developed to combat marine oil spills. However, none of these methods is ideal and universal for tackling different kinds of oil spills. In addition, most of these methods do not offer the possibility for recovering the spilt oil. There is great interest in developing novel and better methods for combating marine oil spills that allow recovery of the spilt oil. The use of low molecular weight organogelators that can selectively congeal oil from oil-water mixtures have been proposed to be useful for oil spill recovery. From this initial proposal, the area has progressed gradually towards their practical implementation. The advancements and novel concepts in this area are reviewed.

Monopeptide-Based Powder Gelators for Instant Phase-Selective Gelation of Aprotic Aromatics and for Toxic Dye Removal

Through a combinatorial screening of 35 possible phase-selective monopeptide-based organogelators readily made at low cost, we identified five of them with high gelling ability toward aprotic aromatic solvents in the powder form. The best of them (Fmoc-V-6) is able to instantly and phase-selectively gel benzene, toluene, and xylenes in the presence of water at room temperature at a gelator loading of 6% w/v. This enables the gelled aromatics to be separated by filtration and both aromatics and the gelling material to be recycled by distillation. We also identified Fmoc-I-16 as the best gelator for benzyl alcohol, and the corresponding organogel efficiently removes toxic dye molecules by 82-99% from their highly concentrated aqueous solutions. These efficient removals of toxic organic solvents and dyes from water suggest their promising applications in remediating contaminated water resources.

Porous amorphous powder form phase-selective organogelator for rapid recovery of leaked aromatics and spilled oils

Phase-selective organogelators (PSOGs) have drawn wide attention due to their potential applications in recovery of leaked aromatics and spilled oils. However, powder form PSOGs with fast gelling abilities and broad applicabilities are still limited. Herein, we developed three D-gluconic acetal-based gelators with different alkyl chains, all of which show excellent gel properties for hydrocarbon solvents. The spectroscopic and X-ray results revealed that the gel formation was the synergy of hydrogen bonding, π-π stacking and van der Waals forces. Surprisingly, the powder form gelator A with a cis double bond in the alkyl chain could instantly and selectively gel aromatic hydrocarbons, and also rapidly solidify crude oils with widely ranging viscosities from seawater at room temperature within minutes. Further research revealed that A powder exhibited porous amorphous morphology because the cis double bonds broke the crystalline chain-chain interdigitation between the assemblies. Therefore, the fast dispersion and recombination of fibers under the action of oil molecules lead to the fast room temperature gel process. Overall, a non-toxic and low-cost powder form PSOG with rapid room temperature phase selective gelation ability for a wide range of oils makes it promising for the emergency treatment of oil spill and aromatics leakage.

A gelator–starch blend for dry powder based instant solidification of crude oil at room temperature

A sugar based organogelator and natural polymer blend has been found to be useful for the ultrafast, room temperature solidification of crude oil in a dry powder form.

Triazole Linked N-Acetylglucosamine Based Gelators for Crude Oil Separation and Dye Removal

Marine oil-spills have a long-lasting impact on the environment; therefore, it is a major concern in the scientific community to find a solution for remediation. Recently, phase selective organo-gelators emerged as potential materials for removal of oil from water through selective gelation. Herein, we report synthesis of a series of C-6 triazole linked N-acetylglucosamine derivatives, among which three have shown excellent selective gelation of organic solvents, diesel, petrol, and crude oils in water and seawater. We have studied phase selective gelation against different API grade crude oils (from light to heavy), and the gelation was achieved using nontoxic carrier solvent at room temperature in less than 15 min, and gelators were found useful for recovering crude oils. Critical gel concentration (CGC) of crude oil gelators was found to be 2.3-12% (w/v). The variable temperature NMR and FTIR experiments reveal that intermolecular hydrogen bonding was responsible for gel formation. Furthermore, a gelator was utilized for selective dye removal from water.

Development and application of an amylopectin-graft-poly(methyl acrylate) solidifier for rapid and efficient containment and recovery of heavy oil spills in aqueous environments

Effective oil spill preparedness and response are crucial to ensure environmental protection and promote the responsible development of the petroleum industry. Hence, interest in developing new approaches and/or improving existing oil spill response measures has increased greatly in the past decade. Solidifiers are an attractive and underutilized option to mitigate the effects of oil spills, as they interact with oil to contain the spill, prevent it from spreading, and facilitate its removal from the environment. In this work, we have synthesized an inexpensive and easy-to-make natural-based sorbent, a subclass of solidifiers. Our amylopectin-graft-poly(methyl acrylate) (AP-g-PMA) sorbent is highly oleophilic and hydrophobic, and selectively solidifies diluted bitumen and conventional crude oil from biphasic mixtures of oil and water. The complete solidification of conventional crude oil and diluted bitumen by the AP-g-PMA sorbent occurs within 8 and 32 min, respectively, and even a low solidifier-to-oil ratio of 4% w/w is sufficient to enable complete recovery of diluted bitumen. This innovative natural-based polymeric sorbent may be applied as a key component of oil spill response procedures, especially for heavy oils. The AP-g-PMA sorbent combines the biodegradability and non-toxicity of the amylopectin with the hydrophobicity and oleophilicity of the synthetic polymer poly(methyl acrylate).

Role of water in the formation of unusual organogels with cyclo(leucyl-leucyl)

The key role of water in the formation of cyclo(leucyl-leucyl) organogels was demonstrated. The conditions required for preparation of previously unknown gels with aliphatic hydrocarbons at room temperature were determined. Cyclo(leucyl-leucyl) self-assembles to form different structures depending on the medium used. The molecular organization of gels was studied by the methods of microscopy, spectroscopy and X-ray powder diffractometry. The organogel of cyclo(leucyl-leucyl) can reversibly change volume during the heating/cooling cycle. We showed the possibility of practical application of cyclo(leucyl-leucyl) for water purification. The results obtained give a new insight into the mechanism of gelation with cyclo(dipeptide)-based low-molecular-weight gelators and may be useful for the preparation of new physical gels.

Highly Efficient Recovery of Oils in Water via Serine-Based Organogelators

We report here the gelation of a series of petroleum products by serine derivatives. Among Fmoc (9-fluorenylmethoxycarbonyl) amino acids modified by long-chain amines with different substituents, serine-based compounds exhibit excellent performance in gel formation. Further studies on the variation of serine-based gelators demonstrate a considerable structure-property relationship between oil gelation performance and the molecular structure. Oils could be separated and collected by acid and distillation. Gelators exhibit the potential to be applied in an effective treatment of oil-containing water produced from frequent marine oil spills.

Smart Materials for Environmental Remediation Based on Two-Component Gels: Room-Temperature-Phase-Selective Gelation for the Removal of Organic Pollutants Including Nitrobenzene/O-Dichlorobenzene, and Dye Molecules from the Wastewater

Novel two-component gel systems based on aliphatic acid-hydroxy/base interaction were developed as smart materials for environmental remediation. The G1-A16 gelator could be used directly as a powder form to selectively gel aromatic solvents (nitrobenzene and o-dichlorobenzene) from their mixtures with wastewater (containing 0.5 M sodium nitrate and 0.5 M sodium sulfate) via a simple shaking strategy at room temperature without employing co-solvents and a heating-cooling process. Meanwhile, the two-component gel system can efficiently remove the toxic dyes from the aqueous solution. The dominant factors that drive gelation in the case of the gelator and nitrobenzene or water have been studied using FT-IR, 1H NMR, and XRD. Overall, our research provides an efficient two-component approach for facilely tuning the properties of one-component gel for the realization of high-performance functionalities of gels. At the same time, our study demonstrates potential industrial application prospect in removing pollutants efficiently (such as aromatic solvents and toxic dye removal).

Stearoyl-appended pendant amino acid-based hyperbranched polymers for selective gelation of oil from oil/water mixtures

Stearic acid-appended pendant amino acid-based poly(methacrylate) hyperbranched polymers were developed for the phase-selective organogelation of crude oil from a binary mixture of oil/water.