Postsynthetic Modifications Research Articles

Amine Chemistry of Porous CO2 Adsorbents.

ConspectusAs renewable energy and CO2 utilization technologies progress to make a more significant contribution to global emissions reduction, carbon capture remains a critical component of the mission. Current CO2 capture technologies involve operations at point sources such as fossil fuel-based power plants or source-agnostic like in direct air capture. Each strategy has its own advantages and limitations, but in common, they all employ sorption-based methods with the use of sorbents strongly adhering to CO2. Amine solutions are the most widely used absorbents for industrial operations due to the robust chemical bonds formed between amines and CO2 under both dry and humid conditions, rendering excellent selectivity. Such strong binding, however, causes problematic regeneration. In contrast, purely physisorptive porous materials with high surface areas allow for the confinement of CO2 inside narrow pores/channels and have a lower regeneration energy demand but with decreased selectivity and capacity. The most promising solution would then be the unification of both types of sorbents in one system, which could bring about a practical adsorption-desorption process. In other words, the development of porous solid materials with tunable amine content is necessary to leverage the high contact surface of porous sorbents with the added ability to manipulate amine incorporation toward lower CO2 binding strength.To answer the call to uncover the most feasible amine chemistry in carbon capture, our group has devoted intense effort to the study of amine-based CO2 adsorbents for the past decade. Oriented along practicality, we put forth a principle for the design of our materials to be produced in no more than three synthetic steps with economically viable starting materials. Porous organic polymers with amine functionalities of various substitutions, meaning primary, secondary, and tertiary amines, were synthesized and studied for CO2 adsorption. Direct synthesis proved to be feasibly applicable for secondary and tertiary amine-incorporated porous polymers whereas primary-amine-based sorbents would be conveniently obtained via postsynthetic modifications. Sorbents based on tertiary amines exhibit purely physical adsorption behavior if the nitrogen atoms are placed adjacent to aromatic cores due to the conjugation effect that reduces the electron density of the amine. However, when such conjugation is inhibited, chemisorptive activity is observed. Secondary amine adsorbents, in turn, express a higher binding strength than tertiary amine counterparts, but both types can merit a strengthened binding by the physical impregnation of small-molecule amines. Sorbents with primary-amine tethers can be obtained via postsynthetic transformation of precursor functionalities, and for them, chemical adsorption is mainly at work. We conclude that mixed-amine systems could exhibit unprecedented binding mechanisms, resulting in exceptionally specific interactions that would be useful for the development of highly selective sorbents for CO2.

Linkage conversions in single-crystalline covalent organic frameworks.

Single-crystal X-ray diffraction is a powerful characterization technique that enables the determination of atomic arrangements in crystalline materials. Growing or retaining large single crystals amenable to it has, however, remained challenging with covalent organic frameworks (COFs), especially suffering from post-synthetic modifications. Here we show the synthesis of a flexible COF with interpenetrated qtz topology by polymerization of tetra(phenyl)bimesityl-based tetraaldehyde and tetraamine building blocks. The material is shown to be flexible through its large, anisotropic positive thermal expansion along the c axis (αc = +491 × 10-6 K-1), as well as through a structural transformation on the removal of solvent molecules from its pores. The as-synthesized and desolvated materials undergo single-crystal-to-single-crystal transformation by reduction and oxidation of its imine linkages to amine and amide ones, respectively. These redox-induced linkage conversions endow the resulting COFs with improved stability towards strong acid; loading of phosphoric acid leads to anhydrous proton conductivity up to ca. 6.0 × 10-2 S cm-1.

2'-Modified Thymidines with Bioorthogonal Cyclopropene or Sydnone as Building Blocks for Copper-Free Postsynthetic Functionalization of Chemically Synthesized Oligonucleotides.

The development of facile methods for conjugating relevant probes, ligands, or delivery agents onto oligonucleotides (ONs) is highly desirable both for fundamental studies in chemical biology and for improving the pharmacology of ONs in medicinal chemistry. Numerous efforts have been focused on the introduction of bioorthogonal groups onto phosphoramidite building blocks, allowing the controlled chemical synthesis of reactive ONs for postsynthetic modifications. Among these building blocks, alkyne, cyclooctynes, trans-cyclooctene, and norbornene have been proved to be compatible with automated solid-phase chemistry. Herein, we present the development of novel 2'-functionalized nucleoside phosphoramidite monomers comprising bioorthogonal methylcyclopropene or sydnone moieties and their introduction for the first time to ON solid-phase synthesis. Traceless ON postsynthetic modifications with reactive complementary probes were successfully achieved through either inverse electron-demand Diels-Alder (iEDDA) reactions or strain-promoted sydnone-alkyne cycloaddition (SPSAC). These results expand the set of bioorthogonal phosphoramidite building blocks to generate ONs for postsynthetic labeling.

A Triphenylphosphine-Based Microporous Polymer for a Wittig Reaction Cycle in the Solid State.

The Wittig reaction is a key step in industrial processes to synthesise large quantities of vitamin A and various other important chemicals that are used in daily life. This article presents a pathway to achieve the Wittig reaction in a solid network. A highly porous triphenylphosphine-based polymer was applied as a solid Wittig reagent that undergoes, in a multi-step cycle, in total six post-synthetic modifications. This allowed for regeneration of the solid Wittig reagent and reuse for the same reaction cycle. Of particular industrial relevance is that the newly developed material also enables a simple way of separating the product by filtration. Therefore, additional costly and difficult separation and purification steps are no longer needed.

Pd Immobilization Phenanthroline-2,9-Dicarbaldehyde Modified Magnetic CuBDC MOF as a Reusable Heterogeneous Catalyst for Suzuki-Miyaura Cross-Coupling Reactions

A porous magnetic multifunctional copper-based metal-organic framework (MOF) was developed through combined covalent and dative post-synthetic modification (PSM) of the CuBDC. In this regard, a novel magnetic metal-organic framework (MMOF) consisting of supported 1,10-phenanthroline-2,9-dicarbaldehyde (Fe3O4@Cu(BDC)-NH2-PHD) has been fabricated by post-synthetic modifications of Fe3O4@Cu(BDC)-NH2. Subsequently, the prepared nanocomposites were modified using palladium chloride ions (Fe3O4@Cu(BDC)-NH2-PdPHD) to impart catalytic sites. As a result, the fabricated magnetic porous catalyst exhibited great catalytic activity in Suzuki-Miyaura cross-coupling reactions. Some of the essential advantages of the synthesized catalyst are; high catalytic activity, short reaction times, mild conditions, high thermal stability, and reusability. Moreover, his porous magnetic nanomaterial can be used as a new support to immobilize other metals in different catalytic reactions.

Efficient Synthesis of Quinolines from 2‐Aminoaryl Ketones with α‐Methylene Carbonyl Derivatives: Exploiting the Dual Acid Sites of Metal Organic Framework Catalyst

AbstractWe report on the use of heterogeneous metal organic framework (MOF) catalysts for the Friedländer synthesis of 2‐aminoaryl ketone with α‐methylene carbonyl derivatives, a versatile and widely used method for the synthesis of quinoline derivatives. The importance of the Lewis and Brønsted acid sites and their spatial proximity have been explored. Postsynthetic modifications were made to introduce the Brønsted −SO3H acid sites in the pristine MIL‐53(Al). Two modifications were carried out, resulting in two different MOFs: MIL‐53(Al)−NH−(CH2)3−SO3H, in which there is a significant spatial distance between the Lewis and Brønsted sites, and MIL‐53(Al)−SO3H, where the two sites are in close proximity. The availability of sulfonic acid groups has a significant impact on their catalytic performance. The sulfonated MIL‐53(Al) material exhibited a high yield of quinoline derivatives under solventless and mild reaction conditions, with a wide substrate scope and good reusability. Mechanistic studies revealed that the dual acidic sites of the catalysts play an important role in the reaction mechanism.

Isonitrile-Tetrazine Click-and-Release Chemistry for Controlling RNA-Guided Nucleic Acid Cleavage.

With the increasing demand for the regulation of CRISPR systems, a considerable number of studies have been conducted to control their excessive activity levels. In this context, we propose a method that involves a bioorthogonal cleavage reaction between isonitrile and tetrazine to modulate the cleavage activity of the CRISPR system. Importantly, isonitrile demonstrates significant potential for modifying sgRNAs, making it a promising candidate for bioorthogonal reactions, a phenomenon that has not been previously reported. Our approach utilizes the 3-isocyanopropyl-carbonate group as a caging group to deactivate the CRISPR systems, while tetrazine acts as an activator to restore their activities. Through the implementation of post-synthetic modifications and click-and-release chemistry, we have successfully achieved the regulation of RNA-guided nucleic acid cleavage, which holds great promise for controlling gene editing in human cells.

Versatile Post-synthetic Modifications of Helical β-Peptide Foldamers Derived from a Thioether-Containing Cyclic β-Amino Acid.

We introduce a novel cyclic β-amino acid, trans-(3S,4R)-4-aminotetrahydrothiophene-3-carboxylic acid (ATTC), as a versatile building block for designing peptide foldamers with controlled secondary structures. We synthesized and characterized a series of β-peptide hexamers containing ATTC using various techniques, including X-ray crystallography, circular dichroism, and NMR spectroscopy. Our findings reveal that ATTC-containing foldamers can adopt 12-helical conformations similar to their isosteres and offer the possibility of fine-tuning their properties via post-synthetic modifications. In particular, chemoselective conjugation strategies demonstrate that ATTC provides unique post-synthetic modification opportunities, which expand their potential applications across diverse research areas. Collectively, our study highlights the versatility and utility of ATTC as an alternative to previously reported cyclic β-amino acid building blocks in both structural and functional aspects, paving the way for future research in the realm of peptide foldamers and beyond.

Advances in Chalcogenide Crystal Growth: Flux and Solution Syntheses, and Approaches for Postsynthetic Modifications

Advances in Chalcogenide Crystal Growth: Flux and Solution Syntheses, and Approaches for Postsynthetic Modifications

Blue light photocatalytic oxidation of sulfides to sulfoxides with oxygen over a thiazole-linked 2D covalent organic framework

With permanent porosity and intrinsic crystallinity, covalent organic frameworks (COFs) have great potential for solar energy conversions. However, the crystallinity of COFs necessitates reversible linkages like imine, leading to inadequate chemical stability of COFs as photocatalysts. To overcome this inadequacy, post-synthetic modifications (PSMs) transform an imine-linked COF, TTI-COF, into a thiazole-linked COF, TTT-COF. The morphology and crystallinity of TTT-COF are similar to that of TTI-COF. Compared to TTI-COF, TTT-COF secures evident amelioration of stability and optoelectronic properties supported by both experiments and theoretical calculations. Consequently, these two COFs are exploited for the photocatalytic oxidation of organic sulfides. Under blue light-emitting diode irradiation, TTI-COF marginally impels the reaction. In contrast, TTT-COF emerges with significantly better activity for selective oxidation of organic sulfides with oxygen in ethanol. This work sheds light on the transformative power of PSMs for tailoring COFs in visible light photocatalysis for oxidations.

Polymers of Intrinsic Microporosity Based on Dibenzodioxin Linkage: Design, Synthesis, Properties, and Applications.

The development of polymers of intrinsic microporosity (PIMs) over the last two decades has established them as a distinct class of microporous materials, which combine the attributes of microporous solid materials and the soluble nature of glassy polymers. Due to their solubility in common organic solvents, PIMs are easily processable materials that potentially find application in membrane-based separation, catalysis, ion separation in electrochemical energy storage devices, sensing, etc. Dibenzodioxin linkage, Tröger's base, and imide bond-forming reactions have widely been utilized for synthesis of a large number of PIMs. Among these linkages, however, most of the studies have been based on dibenzodioxin-based PIMs. Therefore, this review focuses precisely on dibenzodioxin linkage chemistry. Herein, the design principles of different rigid and contorted monomer scaffolds are discussed, as well as synthetic strategies of the polymers through dibenzodioxin-forming reactions including copolymerization and postsynthetic modifications, their characteristic properties and potential applications studied so far. Towards the end, the prospects of these materials are examined with respect to their utility in industrial purposes. Further, the structure-property correlation of dibenzodioxin PIMs is analyzed, which is essential for tailored synthesis and tunable properties of these PIMs and their molecular level engineering for enhanced performances making these materials suitable for commercial usage.

Expedient Access to Enantioenriched 1-Azaspiro Cyclobutanones Enabled by Modified Heyns Rearrangement.

Leveraging the unexplored regions of chemical space, the integration of spirocyclic cyclobutane in a molecular scaffold opens up a new vista in modern drug discovery. Despite recent advancements in achieving the synthesis of such motifs, strategies for their asymmetric construction have not been well-recognized and remain a formidable challenge. Herein, for the first time, we have demonstrated a chiral Brønsted acid-catalyzed enantioselective synthesis of 1-azaspiro cyclobutanone enabled by an unusual reactivity of enamine that explore the potentiality of Heyns rearrangement upon electrophilic modification. This design strategy offers viable access to a wide range of cyclobutanone containing spiroindoline and spiropyrrolidine derivatives in good yields with excellent stereoselectivities (up to >99 % ee, >20 : 1 dr). Furthermore, the practicality of this methodology has been shown by a scale-up synthesis of spirocyclic products and their facile post-synthetic modifications.

High single Zn-ion conductive porous organic conductors decorated with dense acidic groups via double post-synthetic sulfonations

Solid Zn-ionic conductors are one of the important components of rechargeable aqueous Zn-ion batteries. Although ion-conductive porous materials have been intensively studied due to their effective conduction pathways through large surface areas and tunable functionalities, porous material-based Zn ion conductors have been rarely reported because the strong electrostatic bonding properties of divalent Zn2+ ions generally lead to slow diffusion rates and low conductivity. Herein, we prepared porous organic polymer (POP)-based Zn-ion conductors via multiple post-synthetic modifications. The porous conductor with a large number of Zn-ion-incorporated sites exhibited a conductivity value of 3.24×10−4 S cm−1, and a transference number of 0.94, which are the highest values among other porous materials. The long-term performance of conductivity was retained for at least one week. This work highlights the remarkable effectiveness of multiple post-synthetic modifications to achieve high Zn-ion conductivity and provides the first demonstration of a Zn-ion POP conductor.

Pd-Coordinated Salinidol-Modified Mixed MOF: An Excellent Active Center for Efficient Nitroarenes Reduction and Selective Oxidation of Alcohols.

Selective oxidation of active and inactive alcohol substrates and reduction of nitroarenes is a highly versatile conversion that remains a challenge in controlling functionality and adjustments in metal-organic frameworks (MOFs). On the other hand, it offers an attractive opportunity to expand their applications in designing the next generation of catalysts with improved performance. Herein, a novel mixed MOF consisting of supported 2-hydroxybenzamide (mixed MOF-salinidol) has been fabricated by post-synthetic modifications of mixed MOF. Subsequently, the prepared nanocomposites were modified to impart catalytic sites using palladium chloride ions mixed with MOF-salinidol/Pd (II). After successfully designing and structurally characterizing nanocomposites, we evaluated their activity in oxidizing primary and secondary alcohols using aerobic conditions with molecular oxygen and an air atmosphere. In addition, the stability of (mixed MOF-salinidol/Pd (II)) catalysts under catalytic conditions was also demonstrated by comparing the Fourier-transform infrared spectrum, scanning electron microscopy image, and ICP-OES method before and after catalysis. Based on the results, the active surface area of the synthesized nanocatalyst is large, which highlights its unique synergistic effect between post-synthetic modified MOF and Pd, and furthermore, the availability of catalytic sites from Pd, as demonstrated by outstanding catalytic activity.

Room Temperature Curable Copper Nanowire-Based Transparent Heater.

Copper nanowires (Cu NWs) are a promising alternative to silver NWs to develop transparent conducting films (TCFs) due to their comparable electrical conductivity and relative abundance. Postsynthetic modifications of the ink and high-temperature postannealing processes for obtaining conducting films are significant challenges that need to be addressed before commercial deployment of these materials. In this work, we have developed an annealing-free (room temperature curable) TCF with Cu NW ink that requires minimal postsynthetic modifications. Organic acid pretreated Cu NW ink is used for spin-coating to obtain a TCF with a sheet resistance of 9.4 Ω/sq. and optical transparency of 67.4% at 550 nm. For oxidation protection, the Cu NW TCF is encapsulated with polydimethylsiloxane (PDMS). The encapsulated film is tested as a transparent heater at various voltages and shows good repeatability. These results demonstrate the potential of Cu NW-based TCFs as a replacement for Ag-NW based TCFs for a variety of optoelectronic applications, such as transparent heaters, touch screens, and photovoltaics.

Eu(III)-functionalized iCOF hybrids by “tandem post-synthetic modifications” for fluorescent detection of folic acid and trimethoprim: A logical judgment by combination of neural networks and logic gates

A universal strategy called “tandem post-synthetic modifications” is applied to combine lanthanide ions with cationic covalent organic frameworks by using anionic carboxylate ligand as “molecular bridge”. In the first step, anionic carboxylate ligand is introduced into cationic COFs by ion exchange, which is then coordinated to Eu3+ ions in the second step. Herein, 2,2-biquinoline-4,4-dicarboxylic acid disodium (BCA) is selected to verify the feasibility of this strategy and successfully introduce Eu3+ to EB-TFP, resulting in the hybrid system Eu3+@BCA@EB-TFP. Based on the “turn-off” mechanism, Eu3+@BCA@EB-TFP can be used as a probe for the detection of folic acid (FA) and trimethoprim (TMP). The limits of detection (LOD) for FA and TMP in ethanol solution can reach to 0.142 and 0.139 μM at 282 nm respectively. The fluorescence properties are then explored to uncover the potential of the probe for detection of FA and TMP in serum. Interestingly, FA remains the quenching ability under excitation at 342 nm, while TMP has no response, which provides great convenience in distinguishing between them. In addition, according to the experimental results and through the combination of neural networks and logic gates, a theoretical scenario for determining the tolerance of bacteria to TMP is also presented for reference.

Controlled Growth of a Photocatalytic Metal–Organic Framework on Conductive Plates by Mixing Direct Synthesis and Postsynthetic Modification Strategies

In this work, we develop a two-step process for the controlled growth of a thin layer of a functionalized and photosensitive metal–organic framework (MOF), namely Ru–Ti–UiO-67, on the surface of a plate coated with indium tin oxide (ITO), a transparent conductive oxide (TCO). In the first step, the in situ controlled growth of a layer of UiO-67-based MOF doped with a photosensitizer (ruthenium complex), herein referred to as Ru–UiO-67, is carried out on the surface of the ITO-coated plate, leading to Ru–UiO-67/ITO. The obtained MOF layer is relatively thin, allowing increased interactions between the MOF material and the TCO surface, and consists of crystals in the near-nanometer particle size. In the second step, a postsynthetic modification (PSM) process is applied to Ru–UiO-67/ITO to integrate Ti catalytic sites into the MOF framework, leading to Ru–Ti–UiO-67/ITO (containing both the photosensitizer and catalyst) while maintaining the MOF’s structure and morphology in addition to its strong interaction with the substrate. Importantly, on the synthetic level, this work demonstrates the possibility to form a homogeneous surface anchored with MOF on a transparent conductive surface, whereby the obtained MOF layer is strongly bound to the substrate and postsynthetic chemical modifications are enabled without any loss of material. Furthermore, the obtained material is proven to exhibit an efficient visible-light-driven photodegradation activity in aqueous solution.

Post-Combustion Capture of Carbon Dioxide by Natural and Synthetic Organic Polymers

The elevation of carbon dioxide (CO2) levels in the atmosphere is responsible for global warming which in turn causes abrupt climate change and consequently poses a threat to living organisms in the coming years. To reduce CO2 content in the atmosphere CO2 capture and separation is highly necessary. Among various methods of CO2 capture post-combustion capture is very much useful because of its operational simplicity and applicability in many industries and power sectors, such as coal-fired power plants. Polymers with high surface area, high volume and narrow pores are ideal solid sorbents for adsorption-driven post-combustion CO2 capture. Natural polymers, such as polysaccharides are cheap, abundant, and can be modified by various methods to produce porous materials and thus can be effectively utilized for CO2 capture while the surface area and the pore size of synthetic porous organic polymers can be tuned precisely for high CO2 capturing capacity. A significant amount of research activities has already been established in this field, especially in the last ten years and are still in progress. In this review, we have introduced the latest developments to the readers about synthetic techniques, post-synthetic modifications and CO2 capture capacities of various biopolymer-based materials and synthetic porous organic polymers (POPs) published in the last five years (2018–2022). This review will be beneficial to the researchers to design smart polymer-based materials to overcome the existing challenges in carbon capture and storage/sequestration.

The synthesis of gmelinite microspheres and their post-synthetic modification for improved defluoridation

ABSTRACT A method for synthesizing microspheres of the zeolite gmelinite (GME) with mean diameter 8 µm, and narrow dispersion, has been developed and establishes the key role of aging the gel prior to heating to produce a narrow size distribution. Fluoride adsorption from acidic media has been evaluated for GME microspheres following post-synthetic modifications by calcium ion exchange, iron(III) surface modification, and dealumination. In each instance, the post-synthetic modification leads to appreciable equilibrium fluoride loadings, with the highest loadings observed for dealuminated GME microspheres, capable of 97.4% fluoride removal from acidified 22 ppm fluoride solutions at equilibrium. Accordingly, dealuminated GME microspheres show promise as a potential adsorbent for reducing the aqueous fluoride content in dangerously high natural sources (up to 30 ppm) to safe drinking levels (≤1.5 ppm) in one treatment.

Recent progress in novel zeolite catalysts for selective catalytic reduction of nitrogen oxides

Selective catalytic reduction (SCR) using zeolite catalysts is a key technology for the abatement of nitrogen oxides (NOx) from lean-burn heavy-duty vehicles. With the increasing stringency of emission regulations, researchers are now devoting more efforts to enhancing the efficiency and durability of zeolite catalysts. This paper intends to summarize the very recent (mainly in the last five years) advancements in the development and application of novel zeolites as SCR catalysts. Specifically, we first provide a detailed overview of the synthesis, structure-performance relationship, and potential application of small-pore zeolites with different topologies (CHA, AEI, LTA, AFX, SFW, KFI, ERI/EAB, LEV and RHO) as catalysts in SCR with NH3 as the reductant. Then, advances in the post-synthetic modifications of small-pore zeolites for NH3-SCR are reviewed, followed by an introduction of Cu-free small-pore zeolites as NH3-SCR catalysts. We also summarize the recent mechanistic understandings of NH3-SCR chemistry over small-pore zeolite catalysts, mainly over Cu-SSZ-13, using in situ or operando spectroscopy. The application of zeolites as catalysts in SCR with hydrocarbons (e.g., CH4, CH3OH) or H2 as the reductant is also briefly discussed. Finally, we discuss the potential of several novel small-pore zeolites, such as Cu-SSZ-39, for real application in NH3-SCR and the development of new SCR systems with minimized formation of byproducts, such as the greenhouse gas N2O and the toxic HCN.