Imine Condensation Reactions Research Articles

Enhanced Ammonia Capture for Adsorption Heat Pumps Using a Salt-Embedded COF Aerogel Composite

Adsorption heat pumps (AHPs) have garnered significant attention due to their efficient use of low-grade thermal energy, eco-friendly nature, and cost-effectiveness. However, a significant challenge lies in developing adsorbent materials that can achieve a high uptake capacity, rapid adsorption rates, and efficient reversible release of refrigerants, such as ammonia (NH3). Herein, we developed and synthesized a novel salt-embedded covalent organic framework (COF) composite material designed for enhanced NH3 capture. This material was prepared by encapsulating sodium bromide (NaBr) within a porous and densely functionalized sulfonic acid-based COF. The COF was synthesized through a Schiff base (imine) condensation reaction, providing a robust platform for effective NaBr impregnation. The COF-based aerogel composite powder was investigated for its potential in ammonia-based AHPs, benefiting from both the porous, highly functionalized COF structure and the strong NH3 affinity of the impregnated NaBr. The composite adsorbent demonstrates an impressive NH3 adsorption capacity, adsorption rate, and stability. The exceptional NH3 adsorption performance of the COF-based aerogel composite powder is primarily attributed to the uniformly dispersed NaBr within the COF, the coordination of NH3 molecules with Na+ ions, and the hydrogen bonding interaction between NH3 and Br- ions. These findings highlight the potential of the salt-embedded COF composite for use in NH3-based AHPs, gas separation, and other related applications.

A vanillin-based vitrimer matrix for recyclable and sustainable carbon fibre-reinforced composites

Recently, economic and environmental concerns over the accumulation of end-of-life carbon fibre composite wastes have led to the extensive search for sustainable materials offering a lower environmental impact. Lately, vitrimers – a modern class of covalent adaptable networks – appeared as an innovative polymer, bridging the gap between thermoplastics and thermosets. However, the synthesis of vitrimers often involves the consumption of petrochemicals, increasing the carbon footprint and conflicts with the sustainability regulations in the “green” polymer industry. Herein, a biobased vitrimer from vanillin was successfully prepared via a catalyst-free imine condensation reaction. The Fourier Transform Infrared absorption peak at 1644 cm−1 represents the imine bond in the vanillin-based vitrimer (v-vitrimer). The thermal gravimetric analysis of the v-vitrimer shows good thermal stability (Td5% ∼ 240 °C) compared to the control polyimine vitrimer (285 °C) and the industry-grade vitrimer (Vitrimax) (299 °C). Differential scanning calorimetry (DSC) shows that v-vitrimer exhibits a higher glass transition temperature (85 °C) than that obtained from the control vitrimer (75 °C) and Vitrimax vitrimer (55 °C). Dynamic mechanical analysis shows that v-vitrimer exhibits rapid stress relaxation, reaching a relaxation time (37% relaxation) within 30 s. Owing to the fast stress relaxation at elevated temperatures, v-vitrimer can be thermally reprocessed by hot-press at their glass transition temperature (85 °C). Moreover, v-vitrimer can be chemically recycled via both acid hydrolysis and transamination thanks to reversible imine bonds in the v-vitrimer system. This work proposed a promising procedure to synthesise vitrimer from biobased materials with reprocessability and recyclability.

Toward Molecular Textiles: Synthesis and Characterization of Molecular Patches.

This works describes a new step into the assembly of molecular textiles by the use of covalent templating. To establish a well-founded base and to tackle pre-mature obstacles, expected during the fabrication of the desired 2D-material, we opted to investigate the in-solution synthesis of molecular patches e. g. cut-outs of a textile. A bi-functional cross-shaped monomer was designed, synthesized and was in-detail characterized by means of 1H-NMR and chiro-optical spectroscopy. In addition, x-ray structure crystallography was used to assess the absolute configuration. The monomer was used in an in-solution oligomerization to assemble the molecular patches via imine condensation, which revealed the formation of predominately dimeric patches. The imine-oligomer mixtures were further analyzed by reduction and cleaved to investigate the conditions required post mono-layer assembly. All reaction stages were followed by FT-IR and 1H-NMR analysis. Finally, we address the adsorption of the cross-shaped monomer onto a Au(111) surface, via high vacuum electrospray deposition. The subsequent annealing of the interface induced the on-surface imine condensation reaction, leading to unidimensional oligomers co-adsorbed with clusters of cyclic-dimers. Nc-AFM analysis revealed the tridimensional molecular structures, and together with electrospray deposition technique showed to be a promising pathway to investigate potential monomer candidates.

A Citrus Serenade: An Improved Procedure for the Imine Condensation Reaction in Undergraduate Laboratories

A Citrus Serenade: An Improved Procedure for the Imine Condensation Reaction in Undergraduate Laboratories

Hydrogen‐bond‐regulated mechanochemical synthesis of covalent organic frameworks: cocrystal precursor strategy for confined assembly

Two‐dimensional imine covalent organic frameworks (2D imine‐COFs) are crystalline porous materials with broad application prospects. Despite the efforts into their design and synthesis, the mechanisms of their formation are still not fully understood. Herein, a one‐pot two‐step mechanochemical cocrystal precursor synthetic strategy is developed for efficient construction of 2D imine‐COFs. The mechanistic investigation demonstrated that the cocrystal precursors of 4,4',4''‐(1,3,5‐triazine‐2,4,6‐triyl)trianiline (TAPT) and p‐toluenesulphonic acid (PTSA) sufficiently regulate the crystalline structure of COF. Evidenced by characterizations and theoretical studies, a helical hydrogen‐bond network was constructed by the N‐H···O supramolecular synthons between amine and sulfate in TAPT‐PTSA, demonstrating the role of cocrystals in promoting the organized stacking of interlayer π‐π interactions, layer arrangement, and interlayer spacing, thus facilitating the orderly assembly of COFs. Moreover, the protonation degree of TAPT amines, which tuned nucleophilic directionality, enabled the sequential progression of intra‐ and interlayer imine condensation reactions, inhibiting the formation of amorphous polymers. The transformation from cocrystal precursors to COFs was achieved through comprehensive control of hydrogen bond and covalent bond sites. This work significantly advances the concept of hydrogen‐bond‐regulated COF assembly and its mechanochemical method in the design and synthesis of 2D imine‐COFs, further elucidating the mechanistic aspects of their mechanochemical synthesis.

Hydrogen-Bond-Regulated Mechanochemical Synthesis of Covalent Organic Frameworks: Cocrystal Precursor Strategy for Confined Assembly.

Two-dimensional imine covalent organic frameworks (2D imine-COFs) are crystalline porous materials with broad application prospects. Despite the efforts into their design and synthesis, the mechanisms of their formation are still not fully understood. Herein, a one-pot two-step mechanochemical cocrystal precursor synthetic strategy is developed for efficient construction of 2D imine-COFs. The mechanistic investigation demonstrated that the cocrystal precursors of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline (TAPT) and p-toluenesulphonic acid (PTSA) sufficiently regulate the crystalline structure of COF. Evidenced by characterizations and theoretical studies, a helical hydrogen-bond network was constructed by the N-H⋅⋅⋅O supramolecular synthons between amino and sulfonic groups in TAPT-PTSA, demonstrating the role of cocrystals in promoting the organized stacking of interlayer π-π interactions, layer arrangement, and interlayer spacing, thus facilitating the orderly assembly of COFs. Moreover, the protonation degree of TAPT amines, which tuned nucleophilic directionality, enabled the sequential progression of intra- and interlayer imine condensation reactions, inhibiting the formation of amorphous polymers. The transformation from cocrystal precursors to COFs was achieved through comprehensive control of hydrogen bond and covalent bond sites. This work significantly advances the concept of hydrogen-bond-regulated COF assembly and its mechanochemical method in the design and synthesis of 2D imine-COFs, further elucidating the mechanistic aspects of their mechanochemical synthesis.

A Type of Ferrocene-Based Derivative FE-1 COF Material for Glycopeptide and Phosphopeptide Selective Enrichment.

In this work, a new type of FE-1 COF material is prepared by a reversible imine condensation reaction with diaminoferrocene and diaminodiformaldehyde as materials. The material is connected by imine bonds to form a COF skeleton, and the presence of plenty of nitrogen-containing groups gives the material good hydrophilicity; the presence of metal Fe ions provides the material application potential in the enrichment of phosphopeptides. According to the different binding abilities of N-glycopeptide and phosphopeptide on FE-1 COF, it can simultaneously enrich N-glycopeptide and phosphopeptide through different elution conditions to realize its controllable and selective enrichment. Using the above characteristics, 18 phosphopeptides were detected from α-casein hydrolysate, 8 phosphopeptides were detected from β-casein hydrolysate and 21 glycopeptides were detected from IgG hydrolysate. Finally, the gradual elution strategy was used; 16 phosphopeptides and 19 glycopeptides were detected from the α-casein hydrolysate and IgG hydrolysate. The corresponding glycopeptides and phosphopeptides were identified from the human serum. It proves that the FE-1 COF material has a good enrichment effect on phosphopeptides and glycopeptides.

The Me(almIM)<sub>2</sub> structural ZIFs: Synthesis, characterization and application

The Me(almIM)2 structural ZIFs are formed from the metal ions Me2+ and the linker 4-methyl-5-imidazolecarboxaldehyde (HalmIM), with the Me–almIM–Me bond angle similar to the Si–O–Si angle in zeolites (145o). Depending on the type of bond formed, Me(almIM)2 material has RHO or SOD structure with good thermal and chemical stability. With pore diameter of about 3.0-3.7 Å connected to large cavities with sizes from 9.1-17.9 Å and a structural frameworks containing two groups –CH3 and –CHO with hydrophilic properties, when the –CHO groups is modified by amine groups through imine condensation reaction, we can create hydrophobic materials for diverse applications in adsorption, separation, sensing, biomedical and catalysis. This review report collects results from more than 100 research papers related to Me(almIM)2 from 2010 to present and provides some recommendations on their synthesis, characterization and application in the future.

3D Covalent Organic Framework with "the" Topology.

Discovery of new topology covalent organic frameworks (COFs) is a mainstay in reticular chemistry and materials research because it not only serves as a stepwise guide to the designed construction of covalent-organic architectures but also helps to comprehend function from structural design point-of-view. Proceeding on this track, the first 3D COF, TUS-38, with the topology is constructed by reticulating a planar triangular 3-c node of D3h symmetry with a tetragonal prism 8-c node of D2h symmetry via [3+8] reversible imine condensation reaction. TUS-38 represents a twofold interpenetrated multidirectional pore network with a high degree of crystallinity and structural integrity. Interestingly, stemming from the nitrogen-rich s-triazine rings with electron-deficient character and ─C═N─ linkages composing the TUS-38 framework that benefit to the charge-transfer and hence dipole-dipole electrostatic interactions between the framework and iodine in addition to exclusive topological characteristics of the exotic the net, TUS-38 achieves an exemplary capacity for iodine vapor uptake reaching 6.3gg-1. Recyclability studies evidence that TUS-38 can be reused at least five times retaining 95% of its initial adsorption capacity; while density functional theory (DFT) calculations have heightened the understanding of the interactions between iodine molecules and the framework.

Enhancing Fluorescence in Both Solution and Solid States Induced by Imine Cage Formation.

Developing luminescent materials that exhibit strong emissions in both solution and solid phases is highly desirable and challenging. Herein, we report imine-bond directed formation of a rigid organic cage (TPE-cage) that was synthesized by [2+4] imine condensation of a TPE-cored tetra-aldehyde (TPE-TA) with a clip-like diamine (XA) to illustrate confinement-induced fluorescence enhancement. Compared to the non-emissive TPE-TA (ϕF =0.26 %) in the dichloromethane (DCM) solution, the TPE-cage achieved a remarkable (~520-fold) emission enhancement (ϕF =70.38 %). In contrast, a monomeric tetra-imine model compound (TPE-model) showed only a minor enhancement (ϕF =0.56 %) in emission compared to the parent tetra-aldehyde TPE-TA. The emission of TPE-cage was further enhanced by ~1.5-fold (ϕF =80.96 %) in the aggregated state owing to aggregation-induced emission enhancement (AIEE). This approach establishes the potential for synthesizing luminescent materials with high emission in both solution and solid-state by employing a single-step imine condensation reaction.

A chiral emissive porous organic cage used for high-resolution gas chromatography separations

The illustration of a chiral and porous tubular organic molecular cage (3P-1) was obtained through a [3+6] imine condensation reaction that used as the chiral stationary phase for preparing a 3P-1-coated capillary column by the static coating method.

Streamlining the automated discovery of porous organic cages.

Self-assembly through dynamic covalent chemistry (DCC) can yield a range of multi-component organic assemblies. The reversibility and dynamic nature of DCC has made prediction of reaction outcome particularly difficult and thus slows the discovery rate of new organic materials. In addition, traditional experimental processes are time-consuming and often rely on serendipity. Here, we present a streamlined hybrid workflow that combines automated high-throughput experimentation, automated data analysis, and computational modelling, to accelerate the discovery process of one particular subclass of molecular organic materials, porous organic cages. We demonstrate how the design and implementation of this workflow aids in the identification of organic cages with desirable properties. The curation of a precursor library of 55 tri- and di-topic aldehyde and amine precursors enabled the experimental screening of 366 imine condensation reactions experimentally, and 1464 hypothetical organic cage outcomes to be computationally modelled. From the screen, 225 cages were identified experimentally using mass spectrometry, 54 of which were cleanly formed as a single topology as determined by both turbidity measurements and 1H NMR spectroscopy. Integration of these characterisation methods into a fully automated Python pipeline, named cagey, led to over a 350-fold decrease in the time required for data analysis. This work highlights the advantages of combining automated synthesis, characterisation, and analysis, for large-scale data curation towards an accessible data-driven materials discovery approach.

Pore Space Partition Synthetic Strategy in Imine-linked Multivariate Covalent Organic Frameworks.

Partitioning the pores of covalent organic frameworks (COFs) is an attractive strategy for introducing microporosity and achieving new functionality, but it is technically challenging to achieve. Herein, we report a simple strategy for partitioning the micropores/mesopores of multivariate COFs. Our approach relies on the predesign and synthesis of multicomponent COFs through imine condensation reactions with aldehyde groups anchored in the COF pores, followed by inserting additional symmetric building blocks (with C2 or C3 symmetries) as pore partition agents. This approach allowed tetragonal or hexagonal pores to be partitioned into two or three smaller micropores, respectively. The synthesized library of pore-partitioned COFs was then applied for the capture of iodine pollutants (i.e., I2 and CH3I). This rich inventory allowed deep exploration of the relationships between the COF adsorbent composition, pore architecture, and adsorption capacity for I2 and CH3I capture under wide-ranging conditions. Notably, one of our developed pore-partitioned COFs (COF 3-2P) exhibited greatly enhanced dynamic I2 and CH3I adsorption performances compared to its parent COF (COF 3) in breakthrough tests, setting a new benchmark for COF-based adsorbents. Results present an effective design strategy toward functional COFs with tunable pore environments, functions, and properties.

Synthesis, Structure and Magnetic Properties of Some Copper(II) Complexes Supported by Pendant Calix[4]arene Ligands

AbstractThe synthesis and characterization of three new calix[4]arene ligands bearing two pendant acylhydrazone arms and some of their Cu2+ complexes, namely [Cu(L1‐2H)(MeOH)] (3), [Cu(L1’‐H)(Cl)(2‐hydroxy‐1‐naphthaldehyde)] (4), [Cu2(L2‐2H)2] (5) and [Cu4(L3‐2H)2(OH)2(ClO4)2] (6) are described. The ligands are obtained by simple imine condensation reactions between calix[4]arene‐1,3‐bis‐acyl‐hydrazides and the corresponding carbaldehydes. The Cu2+ ions are always situated in 5‐membered chelate rings, either in a deprotonated −O−CR=N−N=CHR (enolate) or a neutral O=CR−NH−N=CHR (keto) form. In 3 and 4 a 5‐membered chelate ring is formed through interaction of the Cu2+ ion with the naphtholato group. Additional MeOH, chlorido or naphthaldehyde ligands complete the planar (3) or square pyramidal (4) coordination spheres. The thiophenes in 5 do not interact with the Cu2+ ions and dimerization of [CuL] entities occurs to produce centrosymmetric 2 : 2 complexes with four‐coordinated Cu2+ ions. In 6, two dinuclear [Cu2(L3‐2H)(OH)] subunits are connected by μ1,3‐bridging ClO4− ions. The magnetic properties of polycrystalline samples of 5 and 6 were studied by variable temperature magnetic susceptibility measurements. The χ′′(T) vs T plots indicate antiferromagnetic exchange interactions. The exchange interactions in 6 (J=−4.8 cm−1) were found to be stronger than in 5 (J=−0.54 cm−1). This is also supported by broken symmetry DFT calculations.

Click nanosponge – A novel amine-rich β-cyclodextrin-based crosslinked polymer for heterogeneous catalysis

Cyclodextrin-based nanosponges are promising materials for heterogeneous catalysis due to their inherent synthetic versatility, tunable porosity and nontoxicity. In this work, a primary amine-rich β-cyclodextrin nanosponge was synthesized via click imine condensation reaction between 1,6-hexamethylamine-functionalized β-cyclodextrin (CDAM) and glutaraldehyde (GLT) to afford CDGLAM, in mild conditions. The crosslinked polymer exhibited a BET surface area of 36.39 m2 g−1, an average pore diameter of 3.09 nm (as assessed by the BJH method), and thermal stability up to 253 °C. CDGLAM was tested as heterogeneous catalyst for the metal-free Henry and Knoevenagel reactions, between aromatic aldehydes and nitromethane or ethyl cyanoacetate, respectively, affording the products in moderate to very high yields. These results show the ease of preparation of β-CD-based nanosponges from a green chemistry perspective, as well as their potential for future use in catalytic systems.

Single-Crystal Three-Dimensional Covalent Organic Framework Constructed from 6-Connected Triangular Prism Node.

The limited structural diversity of three-dimensional covalent organic frameworks (3D COFs) greatly restricts their application exploration. Therefore, there is an urgent need to expand their library of molecular building blocks, such as the development of highly connected (>4 reaction sites) polyhedral nodes. Herein, by precisely controlling the precursor conformation, we rationally designed a new 6-connected triangular prism node derived from the triphenylbenzene molecule and further used it to construct a novel 3D COF (3D-TMTAPB-COF) via imine condensation reaction. Surprisingly, without the addition of competing reagents, 3D-TMTAPB-COF crystallized directly into single crystals of ∼15 μm in size and was determined to adopt a rare 6-fold interpenetrated (Class IIIa interpenetration) acs topology. In addition, 3D-TMTAPB-COF showed a high SF6 adsorption capacity (60.9 cm3 g-1) and good SF6/N2 selectivity (335) at 298 K and 1 bar, superior to those of most crystalline porous materials. This work not only confirms the possibility of growing large-size single-crystal 3D COFs formed with strong covalent bonds by a solvothermal method in the absence of modulators, but also reports a novel triangular prism node for future construction of 3D COFs with interesting applications.

Microwave-Assisted Semisynthesis and Leishmanicidal Activity of Some Phenolic Constituents from Lichens

Leishmaniasis is considered one of the most untreated tropical diseases in the world. In this study, we investigated the in vitro leishmanicidal activity and cytotoxicity of various isolated lichen substances, including atranorin (1), usnic acid (2), gyrophoric acid (3), salazinic acid (4), galbinic acid (5), and parietin (6), and some semi-synthetic imine derivatives of usnic acid (7, 8, 9) and atranorin (10, 11, 12, 13). Imine condensation reactions with hydrazine and several amines were assisted by microwave heating, an efficient and eco-friendly energy source. The most interesting result was obtained for compound 2, which has high leishmanicidal activity but also high cytotoxicity. This cytotoxicity was mitigated in its derivative, 9, with better selectivity and high antileishmanic activity. This result may indicate that the usnic acid derivative (9) obtained using condensation with two cyclohexylamine groups is a promising lead compound for the discovery of new semisynthetic antiparasitic drugs.

Simultaneous determination of tert-butylhydroquinone, butylated hydroxyanisole and phenol in plant oil by metalloporphyrin-based covalent organic framework electrochemical sensor

In this study, a Zinc porphyrin based covalent organic framework (COF-366-Zn) was synthesized by imine condensation reaction. And the multi-walled carbon nanotubes(MWCNTs) were interspersed on COF-366-Zn to enhance the electron transfer between the material and the electrode surface. The composite material was used to design a COF-366-Zn/MWCNTs/Nafion/GCE sensor. The sensor performance for simultaneous electrochemical detection of antioxidants was investigated. It was found that the COF-366-Zn/MWCNTs/Nafion/GCE sensor could simultaneously detect tert-butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA) and phenol in actual samples with good detection performance. At the same time, the mutual interference between the three analytes was studied. The detection limits are 0.025 μM, 0.056 μM and 0.051 μM, respectively. In addition, the sensor also exhibits excellent anti-interference performance and storage performance.

Constructing a 3D Covalent Organic Framework from 2D hcb Nets through Inclined Interpenetration.

Three-dimensional covalent organic frameworks (3D COFs) have been of great interest due to their inherent numerous open sites and pore confinement effect. However, it has remained challenging to build 3D frameworks via interdigitation (also known as inclined interpenetration) by generating an entangled network formed by multiple 2D layers inclined with respect to each other. Herein, we report the first case of constructing a 3D COF, termed COF-904, through interdigitating 2D hcb nets, which was formed via [3+2] imine condensation reactions by the use of 1,3,5-triformylbenzene and 2,3,5,6-tetramethyl-1,4-phenylenediamine. The single-crystal structure of COF-904 is solved, and the locations of all non-hydrogen atoms are determined by 3D electron diffraction with a resolution up to 0.8 Å. These results not only broaden the strategy for achieving 3D COFs via interdigitation but also demonstrate that structurally complex extended frameworks can arise from simple molecules.

Investigation of microwave assisted synthesis of Schiff Base derived Metal-Chelates by liquid invert sugar containing D-Glucose

The ethanol-soluble (6E,6'E)-6,6'-(1,2-phenylenebis(azan-1-yl-1-ylidene))dihexane-1,2,3,4,5-pentaol (LISPDA) and (E)-6-(2-hydroxyphenylimino)hexane-1,2,3,4,5-pentaol (LISAP) were investigated in this study. Condensation of 1,2-phenylenediamine and 2-aminophenol with 2,3,4,5,6-pentahydroxyhexanal (GL) in the presence of weak acid as a catalyst under mono-mode microwave heating yielded the glucose-Schiff base product. A one-pot microwave-assisted reaction in a short reaction time was required to complete the imine condensation reaction with 90% yield and no byproducts. The molecular structures of these were discovered to be in an extended conformation, with the aromatic moiety coplanar with that of the imine bond and the imine bond exhibiting trans-geometry. Schiff base metal complexes were successfully synthesized by combining 1,2-phenylenediamine and 2-aminophenol with D-glucose and Co(II), Ni(II), and Cu(II). Elemental analysis, magnetic susceptibility, thermal analysis, and electronic and infrared spectral studies were used to determine the structural assessment of ML2 complexes.