CO2 in Supramolecular Chemistry: Preparation of Switchable Supramolecular Polymers

Triethanolamine-modified layered double oxide for efficient CO2 capture with low regeneration energy

Various adsorbents for CO2 capture have been developed to mitigate the greenhouse effect. In this work, a novel CO2 adsorbent was fabricated by depositing triethanolamine (TEOA) onto the surface of nickel-cobalt-aluminum layered double oxide (NiCoAl-LDO) via the impregnation method. The CO2 capacity of the TEOA-LDO composite reached 1.27 mmol/g at 0 °C and 100 kPa, which was twice that of unmodified NiCoAl-LDO. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that the hydroxyl groups (-OH) on the surface of NiCoAl-LDO played a significant role in facilitating CO2 adsorption, similar to CO2 adsorption in the presence of H2O, where CO2 is not converted to carbamates but to bicarbonates through base-catalyzed hydration. This bicarbonate pathway doubles the theoretical amine efficiency, increases the CO2 capacity, and reduces the energy consumption during CO2 desorption. The work provides valuable insights into the development of CO2 adsorbents with high capacity, excellent cycling stability, and low regeneration energy.

Development and Applications of CO2-Responsive Gels in CO2 Flooding and Geological Storage

Gel systems are widely used as plugging materials in the oil and gas industry. Gas channeling can be mitigated by reducing the heterogeneity of the formation and the mobility ratio of CO2 to crude oil. Cracks and other CO2 leaking pathways can be plugged during the geological storage of CO2 to increase the storage stability. By adding CO2-responsive groups to the classic polymer gel's molecular chain, CO2 responsive gel is able to seal and recognize CO2 in the formation while maintaining the superior performance of traditional polymer gel. The application of CO2 responsive gels in oil and gas production is still in the stage of laboratory testing on the whole. To actually achieve the commercial application of CO2 responsive gels in the oil and gas industry, it is imperative to thoroughly understand the CO2 responsive mechanisms of the various types of CO2 responsive gels, as well as the advantages and drawbacks of the gels and the direction of future development prospects. This work provides an overview of the research progress and response mechanisms of various types of CO2 responsive groups and CO2 responsive gels. Studies of the CO2 responsive gel development, injectivity, and plugging performance are comprehensively reviewed and summarized. The shortcomings of the existing CO2 responsive gels system are discussed and the paths for future CO2 responsive gel development are suggested.

A fluorescent controllable supramolecular crosslinked polymer constructed by complementary metal coordination interaction

In this work, two different monomers M1 and M2 were designed and synthesized. M1 + M2 + Zn(OTf)2 could self-assemble to form a supramolecular crosslinked polymer (SCP) based on complementary terpyridine-based metal coordination interaction. The self-assembly of M1 + M2 + Zn(OTf)2 was studied by various techniques, such as 1H NMR, 2D COSY NMR, 2D NOESY NMR, UV-Vis analysis, fluorescence analysis, viscosity measurement, and TEM. The experimental result indicated that the molecular weight of the SCP depended on the initial monomer concentration. The SCP could further turn into supramolecular polymer gel at high concentrations, and the reversible gel-sol transformation could be realized by heating/cooling. Moreover, the fluorescence quenching/enhancement of the SCP could be adjusted by adding base/acid.

Carbon dioxide enhances sulphur-selective conjugate addition reactions

Sulphur-selective conjugate addition reactions play a central role in synthetic chemistry and chemical biology. A general tool for conjugate addition reactions should provide high selectivity in the presence of competing nucleophilic functional groups, namely nitrogen nucleophiles. We report CO₂-mediated chemoselective S-Michael addition reactions where CO₂ can reversibly control the reaction pHs, thus providing practical reaction conditions. The increased chemoselectivity for sulphur-alkylation products was ascribed to CO₂ as a temporary and traceless protecting group for nitrogen nucleophiles, while CO₂ efficiently provide higher conversion and selectivity sulphur nucleophiles on peptides and human serum albumin (HSA) with various electrophiles. This method offers simple reaction conditions for cysteine modification reactions when high chemoselectivity is required.

Ethylene Control Technologies in Extending Postharvest Shelf Life of Climacteric Fruit

Fresh fruit is important for a healthy diet. However, because of their seasonal production, regional specific cultivation, and perishable nature, it is essential to develop preservation technologies to extend the postharvest shelf life of fresh fruits. Climacteric fruit adopt spoilage because of ethylene, a key hormone associated with the ripening process. Therefore, controlling ethylene activity by following safe and effective approaches is a key to extend the postharvest shelf life of fruit. In this review, ethylene control technologies will be discussed aiming for the need of developing more innovative and effective approaches. The biosynthesis pathway will be given first. Then, the technologies determining the postharvest shelf life of climacteric fruit will be described with special attention to the latest and significant published works in this field. Special attention is given to 1-methylcyclopropene (1-MCP), which is effective in fruit preservation technologies. Finally, the encapsulation technology to improve the stability of 1-MCP will be proposed, using a potential encapsulation agent of 1-MCP, calixarene.

Dynamic Covalent Chemistry of Carbon Dioxide: Opportunities to Address Environmental Issues

Extraction and purification of basic chemicals from complex mixtures has been a persistent issue throughout the development of the chemical sciences. The chemical industry and academic research have grown over the centuries by following a deconstruction-reconstruction approach, reminiscent of the metabolism process. Chemists have designed and optimized extraction, purification, and transformation processes of molecules from natural deposits (fossil fuels, biomass, ores), in order to reassemble them into complex adducts. These highly selective and cost-effective techniques arose from developments in physical chemistry but also in supramolecular chemistry, long before the term was even coined. Thanks to the extremely diverse toolbox currently available to the scientific community, artificial molecular systems of increasing complexity can be built and integrated into high-technology products. If humanity has proven through the ages how gifted it can be at this deconstruction-reconstruction game, which has transformed the natural world to a human-shaped one, it has been confronted for more than a century by a new challenge: the deconstruction and reconstruction from a new type of deposit, the waste resulting from the mass production of disposable manufactured goods. In this Account, we will explore the potential contribution of controlled molecular and supramolecular self-assembly phenomena to the challenge of selective and efficient capture of valuable target molecules from mixtures found in postconsumer waste. While it may appear paradoxical to add more molecular ingredients to an already compositionally complex system in order to address a purification issue, we will compare the selectivity, yield, and cost of such an atypical procedure with traditional physical techniques. In the context of carbon dioxide capture or release, we will specifically focus on the coupling between this reversible covalent fixation of the gas by amines and an additional chemical equilibrium. This equilibrium may involve covalent or noncovalent bond formation between a supplementary species and either the unloaded reactant or the CO₂-loaded product. Thereby, this new reactive species may act as a CO₂ capture agonist or antagonist by either thermodynamically favoring the carbamation or decarbamation direction. Indeed, superagonism, the increase of CO₂ loading per amine site upon carbamation beyond the theoretical limit of 0.5, can be achieved using tightly bound cationic metal counterions. In all cases, upon binding and adduct formation, a mutual selection process occurs between one member of the CO₂-based dynamic combinatorial library and one agonist or antagonist, which can itself be contained in a complex mixture of analogues. If this adduct is the only species that, upon formation, can self-aggregate into a separate solid phase, selection and binding are accompanied by translocation, rendering the purification procedure operationally straightforward. This general strategy, based on a simple design of coupled molecular systems, may easily be implemented within new, disruptive technologies for selective extraction of target molecules, thereby providing a substantial environmental and economic benefit.

CO2-responsive polymeric materials: synthesis, self-assembly, and functional applications

CO2 is an ideal trigger for switchable or stimuli-responsive materials because it is benign, inexpensive, green, abundant, and does not accumulate in the system. Many different CO2-responsive materials including polymers, latexes, solvents, solutes, gels, surfactants, and catalysts have been prepared. This review focuses on the preparation, self-assembly, and functional applications of CO2-responsive polymers. Detailed discussion is provided on the synthesis of CO2-responsive polymers, in particular using reversible deactivation radical polymerization (RDRP), formerly known as controlled/living radical polymerization (CLRP), a powerful technique for the preparation of well-defined (co)polymers with precise control over molecular weight distribution, chain-end functional groups, and polymer architectural design. Self-assembly in aqueous dispersed media is highlighted as well as emerging potential applications.

A guide to the selection of switchable functional groups for CO2-switchable compounds

CO₂-responsive species in water interconvert between neutral and bicarbonate forms, but only if the species has appropriate basicity.

Reduced Reactivity of Amines against Nucleophilic Substitution via Reversible Reaction with Carbon Dioxide

The reversible reaction of carbon dioxide (CO₂) with primary amines to form alkyl-ammonium carbamates is demonstrated in this work to reduce amine reactivity against nucleophilic substitution reactions with benzophenone and phenyl isocyanate. The reversible formation of carbamates has been recently exploited for a number of unique applications including the formation of reversible ionic liquids and surfactants. For these applications, reduced reactivity of the carbamate is imperative, particularly for applications in reactions and separations. In this work, carbamate formation resulted in a 67% reduction in yield for urea synthesis and 55% reduction for imine synthesis. Furthermore, the amine reactivity can be recovered upon reversal of the carbamate reaction, demonstrating reversibility. The strong nucleophilic properties of amines often require protection/de-protection schemes during bi-functional coupling reactions. This typically requires three separate reaction steps to achieve a single transformation, which is the motivation behind Green Chemistry Principle #8: Reduce Derivatives. Based upon the reduced reactivity, there is potential to employ the reversible carbamate reaction as an alternative method for amine protection in the presence of competing reactions. For the context of this work, CO₂ is envisioned as a green protecting agent to suppress formation of n-phenyl benzophenoneimine and various n-phenyl–n-alky ureas.

CO₂-Responsive Pillar[5]arene-Based Molecular Recognition in Water: Establishment and Application in Gas-Controlled Self-Assembly and Release

Here we developed a novel CO2-responsive pillararene-based molecular recognition motif established from a water-soluble pillar[5]arene and an anionic surfactant, sodium dodecyl sulfonate (SDS). The inclusion complex acted as a supramolecular amphiphile and self-assembled into spherical bilayer vesicles as confirmed by DLS, SEM, and TEM experiments. These vesicles were disrupted upon bubbling N2 or adding much more SDS to eliminate the inclusion complex. The assembly and disassembly of vesicles were successfully employed in gas and surfactant triggered releases of calcein, a water-soluble dye.

The exchangeable self-assembly behaviour of bis-pseudorotaxanes with metallo-bisviologens (CH3PyTpyFeTpyPyCH34+) and crown ether (Tpy = 2,2′:6′,2′′-terpyridine)

Two different terpyridine chelated Fe²⁺ complexes which contain two methyl-pyridinium salts could be self-assembled with dibenzo-24-crown-8 ether to generate exchangeable double metallo-pseudorotaxanes.

pH sensitive smart gels of cetylpyridinium chloride in binary solvent mixtures: phase behaviour, structure and composition

Figure showing the effect of pH on CPC gel formation at 25 °C and fluorescence emission spectra of CPC solutions at pH ∼ 11.8.