Schiff Base Condensation Reaction Research Articles

Facile synthesis of Metal-Organic Framework/Chitosan cryogel as a robust Scavenger for Diclofenac sodium

Diclofenac sodium (DS), a commonly detected contaminant in aquatic environments, poses a a significant risk to both the ecological balance and the safety of aquatic products. Therefore, efficient removal of DS from water is ergently needed but remains a major challenge. In this study, an environmentally friendly Fe-based metal–organic framework/chitosan (NH2-MIL-53(Fe)/CS) cryogel was prepared through a Schiff base condensation reaction under mild conditions. Taking advantage of the catalytic role of the MOF in accelerating the reaction between CS and 1,3,5-triformylphloroglucinol, NH2-MIL-53(Fe) powders were incorporated into the polymeric networks within 30 s. Owing to the rich binding sites, the resulting NH2-MIL-53(Fe)/CS cryogel demonstrated remarkable efficacy in eliminating DS from water. The adsorption process reached equilibrium within 120 min with a maximum adsorption capacity of 728.6 mg g−1. A comprehensive mechanistic investigation revealed that the exceptional adsorption capability of the NH2-MIL-53(Fe)/CS cryogel for DS was attributed to the synergistic effect of multiple interactions, including favorable hydrophilicity, electrostatic forces, π-π stacking, hydrogen bonding, and coordination. Thus, this study provides a straightforward and rapid synthesis route for MOF/CS cryogel, offering a promising adsorbent that combines exceptional adsorption performance with ease of separation. The resulting MOF/CS cryogel holds great potential for the treatment of DS-contaminated wastewater.

Highly selective electrosynthesis of imines via electroreduction coupling of nitroarenes with aryl aldehydes on Co9S8 with positively charged sulfur vacancies

The electrocatalytic synthesis of imines through the reductive imination of nitroarenes with aldehydes is a facile, environmentally friendly, and valuable process. In this study, high selectivity electrosynthesis of imines was realized through the electrocatalytic C-N coupling reaction between nitroarenes and aryl aldehydes on Co9S8 nanoflowers with rich sulfur vacancies (Co9S8-Vs). Comparative experiments revealed that positively charged sulfur vacancies play a pivotal role in boosting catalytic selectivity towards imines. Electron-deficient sulfur vacancies intensified the adsorption of negatively charged Ph-NO2, thereby enhancing the conversion rate of the electrochemical nitrobenzene-reduction reaction (eNB-RR). Simultaneously, sulfur vacancies augmented the adsorption capability of negatively charged Ph-CHO, enriching Ph-CHO species at the electrode interface and expediting the Schiff base condensation reaction rate. The experimental results show that the reaction conditions can satisfy the different nitroarenes and aryl aldehydes in the electrocatalytic aqueous-phase system under mild conditions to obtain the corresponding imine products in high selectivity. This study provides a facile and environmentally friendly pathway for future electrocatalytic synthesis of imine.

Synthesis, Characterization, Biological Potency, and Molecular Docking of Co2+, Ni2+, and Pd2+ Complexes Derived From Carbohydrazone Ligand and Its Application in Dye Removal

ABSTRACTAs a result of the Schiff base condensation reaction between carbohydrazide and 4‐aminoacetophenone, novel HL ligand [(Z)‐N′‐((Z)‐1‐(4‐aminophenyl)ethylidene)‐2‐(1‐(4‐aminophenyl)ethylidene)hydrazine‐1‐carbohydrazide] and three coordination compounds were successfully obtained with the formulas of [Co2(L)(Cl)3(H2O)].Cl, [Ni2(L)(Cl)2(H2O)2].Cl.H2O, and [Pd (HL)(Cl)(H2O)].Cl, the obtained structures were analyzed using analytical and spectroscopic techniques such as Fourier‐transform infrared (FT‐IR), NMR, UV–Vis, molar conductivity, elemental analysis, and magnetic susceptibility measurements. Additionally, thermal stabilities, kinetic, and thermodynamic parameters were estimated utilizing thermogravimetric analysis. The structures were confirmed through quantum chemical computations. The antioxidant, anticancer, and antimicrobial biological efficacies of the ligand and its metal chelates were assessed. The ligand shows optimistic results as an antioxidant, while Co2+ and Pd2+ complexes showed the highest antimicrobial activities. The DNA binding affinity and cleavage of the isolated compounds were evaluated. Furthermore, the fluorescence spectrum of ligand in the absence and presence of Co2+ was recorded in order to investigate the interaction affinity along with the limit of detection. Another application of this work is the removal of methylene blue and crystal violet dyes from wastewater and reusability, through an inventive synthesis of a cellulose‐based material “LDC” Schiff base.

Design, synthesis, in vitro and in vivo trypanosomaticidal efficacy of novel 5-nitroindolylazines

Leishmaniasis and trypanosomiasis rank among lethal vector-borne parasitic diseases that are endemic in tropical and sub-tropical countries. There are currently no preventive vaccines against them, and once diagnosed, a handful of less effective drugs clinically accessible are the only therapeutic options offered to treat these ailments. And although curable, the eradication and elimination of these diseases are hampered by the emergence of multidrug-resistant strains of the causal pathogens. Hence, there is accrued necessity for the development of new, effective, and affordable drugs. In recent decades, several molecular scaffolds, including nitroaromatics, endoperoxides, etc., have been attempted as building blocks to generate new effective clinical antitrypanosomatid agents with low toxicity so far to no avail. In this regard, a series of nitroindolylazine derivatives was synthesised in a three-step process involving nucleophilic substitution (SN), hydrazination and Schiff base condensation reactions, and was evaluated against various Leishmania and Trypanosoma species and strains. Several promising hits portraying leishmanicidal and trypanocidal with in vitro submicromolar activities, and devoid of toxicity on mammalian cells were uncovered. Among these, nitrofurylazine 11 (Tc IC50: 0.08 ± 0.03 μM) and nitrothienylazine 13 (Tc IC50: 0.09 ± 0.01 μM) were evaluated in vivo against Trypanosoma congolense, the causative agent of nagana, which is livestock most virulent trypanosome species in mice-infected preliminary study. However, only partial efficacy was observed as all mice succumbed due to high parasitemia within 13 days post-infection during the treatment. The translational potential of antileishmanial and antichagasic hits, as well as further identification of their molecular targets, will be assessed in future research.

N-doping of β-ketoenamine based covalent organic frameworks (COFs) for enhancing photocatalytic oxidation activity

β-ketoenamine-based COFs are widely investigated due to their high stability, good crystallinity and tunable skeleton structures. Nitrogen doping is one of the effective ways to enhance the catalytic activity of COFs. Herein, N-doping of β-ketoenamine-based (0N-TP-COF, 1N-TP-COF, 2N-TP-COF) COFs were successfully constructed by the Schiff base condensation reaction between 1,3,5-tiformylphloroglucinol (TP) and p-phenylenediamine containing different numbers of nitrogen atoms. Studies showed that the as-prepared COFs exhibited more suitable electronic structure and more electron-rich active sites with the increasing of N atoms. Furthermore, the photocatalytic performance of 4-formylphenylboronic acid transformation was 0N-TP-COF (99 %, 48 h) < 1N-TP-COF (99 %, 32 h) < 2N-TP-COF (99 %, 16 h), and the photocatalytic performance of benzylamine coupling was 0N-TP-COF (99 %, 16 h) < 1N-TP-COF (99 %, 3.5 h) <2N-TP-COF (99 %, 1.5 h), respectively. Note that all N-doping COFs have excellent catalytic activity as well as stability, and 2N-TP-COF exhibits the highest catalytic activity. This work demonstrates that doping of nitrogen atoms is an effective way to enhance photocatalytic performance.

Room-temperature synthesis of covalent organic frameworks with dual functional groups for high-performance adsorption of diclofenac sodium from aqueous solution

Diclofenac sodium (DCF) are commonly found in ambient waterways due to its widespread use, and this poses significant risks to both human health and ecosystems. In this study, we have designed and synthesized a series of imine-linked covalent organic frameworks (COFs) with dual functional groups using a triple assembly strategy. Specifically, the platform molecules 2,5-dimethoxyterephthalaldehyde (DMTP), 2,5-dihydroxyterephthalaldehyde (DHTP), and 1,3,5-tris(4-aminophenyl)benzene (TAPB) were employed for the direct fabrication of COFs through Schiff base condensation reactions. As a proof of concept, three room-temperature synthesized COFs (COF TAPB-DMTP-[OH]n, where n represents the molar mass of DHTP, with n values of 0.02, 0.03, and 0.04) were used for DCF adsorption from water. The adsorption isotherms, kinetics, pH effects, ionic strength, co-existing ions, and COF regeneration for DCF were thoroughly investigated. The incorporation of methoxy (-OMe) and hydroxyl (-OH) groups serves as a functional strategy to facilitate hydrogen bonding interactions with DCF molecules. Consequently, the developed COFs, featuring an ultrahigh surface area and mesoporous structure, demonstrated a maximum adsorption capacity of 413.2 mg/g and a rate constant k2 of 0.0435 g/mg/min, which exceeds the performance of the majority of previously described adsorbents. The adsorption capacity toward DCF remained nearly unchanged after five regeneration cycles of the COF. Furthermore, the self-prepared adsorbent demonstrated efficient adsorption of DCF from real environmental water, indicating its potential for practical DCF removal applications.

β-Ketoenamine Porous Organic Polymers for High-Efficiency Carbon Dioxide Adsorption and Separation.

To mitigate the greenhouse effect, a number of porous organic polymers (POPs) has been developed for carbon capture. Considering the permanent quadrupole of symmetrical CO2 molecules, the integration of electron-rich groups into POPs is a feasible way to enhance the dipole-quadrupole interactions between host and guest. To comprehensively explore the effect of pore environment, including specific surface area, pore size, and number of heteroatoms, on carbon dioxide adsorption capacity, we synthesized a series of microporous POPs with different content of β-ketoenamine structures via Schiff-base condensation reactions. These materials exhibit high BET specific surface areas, high stability, and excellent CO2 adsorption capacity. It is worth mentioning that the CO2 adsorption capacity and CO2/N2 selectivity of TAPPy-TFP reaches 3.87 mmol g-1 and 27. This work demonstrates that the introduction of β-ketoenamine sites directly through condensation reaction is an effective strategy to improve the carbon dioxide adsorption performance of carbon dioxide.

A thiophene-sulfur doping porous organic Polymer/reduced graphene oxide composite for high-performance supercapacitor electrode

Porous organic polymers (POPs) are a type of promising materials which can be used in energy storage devices. In this study, we synthesized a novel thiophene-sulfur doping POPTAB-TPDA through Schiff-base condensation reaction between 1,3,5-triaminobenzene (TAB) and 2,5-thiphenedialdehyde (TPDA) at ambient temperature and pressure. With the reduced graphene oxide (rGO) as a template, thiophene-sulfur doping POPTAB-TPDA-rGO composite was obtained by in-situ synthesis under the same condition. As supercapacitor active electrode material, the stable value of specific capacitance of the POPTAB-TPDA-rGO composite (232.4 F g−1) is higher than that of pristine POPTAB-TPDA (193.5 F g−1) at a current density of 0.5 A g−1. The assembled asymmetric supercapacitor utilizing POPTAB-TPDA-rGO composite as positive material has an energy density of 38.7 W h kg−1 with the power density of 1619.2 W kg−1, displaying a better result than POPTAB-TPDA-based device. Furthermore, the POPTAB-TPDA-rGO-based supercapacitor exhibits an excellent cycle duration, with 81.7 % retention of its highest capacitance after 7000 cycles. This superior electrochemical performance of the composite could be attributed to three aspects: the reversible redox reaction processes of thiophene-sulfur units, the porous structure of POPTAB-TPDA facilitating ion transmission, and the good electron conductivity of rGO template.

Imine–linked covalent organic framework synthesis

Imine-linked covalent organic frameworks (COFs) are highly ordered polymer networks that are more chemically stable compared to their boron-linked counterparts making them more attractive for a variety of applications, including as energy storage devices, proton-conductive membranes, and catalytic supports. Furthermore, these imines linked COFs may be synthesized using a diverse spectrum of monomers, providing tremendous design freedom and versatility. We report a general method for synthesizing Imine linked COFs based on the Schiff-base condensation reaction of anilines. The synthesis of 4,4′,4′′-(benzene-1,3,5-triyltris(ethyne-2,1-diyl) trianiline, 4,4′-dicarbaldehyde, 4,4′-(ethyne-1,2-diyl) dibenzaldehyde (BPDA), and terephthalaldehyde (PDA) monomers produced by multistep coupling processes.

Synthesis, Characterization, Docking Study and Biological Activates of New 3-Aminorhodanine Derivatives

Abstract: Increase in fatalities among cancer patients is one of untreated facts and today cancer remains one of the main health issues. The most common cause of cancer death is lung cancer. Rhodanine has been recognized as a privileged scaffold in medicinal chemistry due to its well-known ability to demonstrate a broad range of biological activities, and most of its derivatives exhibited remarkable anticancer activity in the (μg/mL) concentration range, while causing negligible cytotoxicity to normal cells. New N- and 5- disubstituted aminorhodanine derivatives were synthesized by Schiff base and Knoevenagel condensation reactions over two consecutive steps. Human cancer cells and Hdfn (human dermal fibroblasts isolated from neonatal foreskin) cells line, were used to evaluate the synthesized compounds’ activity by MTT assay. The new compounds revealed higher anticancer activity against A549 lung cells cancer when compared with reference drug Erlotinib (anticancer drug) and determined no toxicity or safety on normal cell. Among the tested compounds, 2b2 compound show potent anticancer activity which have IC50 about (55.8 μg/mL).

A porous thiosemicarbazide functionalized covalent organic framework served as sensitive fluorescent sensor for Hg2+

The detection of heavy metal pollution in food and environment is of great significance for environmental pollution control and human health. 1,3,5-Tris(p-formylphenyl)benzene (TFPB) and thiosemicarbazide (TS) were used as building blocks to construct a thiosemicarbazide functionalized covalent organic framework (COF) through Schiff base condensation reaction. Hg2+ ions can significantly enhance the fluorescence of the prepared COF-TFPB-TS, and thus COF-TFPB-TS can be utilized for highly selective and sensitive detection of Hg2+ ions. Moreover, COF-TFPB-TS showed high performance for detecting Hg2+ in fresh fruit juice, mineral water and tap water, which demonstrated its ability to be applied in real sample testing.

Large Area Film of Highly Crystalline, Cleavable, and Transferable Semi-Conducting 2D-Imine Covalent Organic Framework on Dielectric Glass Substrate.

Two dimensional (2D) imine-based covalent organic framework (COF), 2D-COF, is a newly emerging molecular 2D polymer with potential applications in thin film electronics, sensing, and catalysis. It is considered an ideal candidate due to its robust 2D nature and precise tunability of the electronic and functional properties. Herein, we report a scalable facile synthesis of 2D imine-COF with control over film thickness (ranging from 100 nm to a few monolayers) and film dimension reaching up to 2 cm on a dielectric (glass) substrate. Highly crystalline 2D imine polymer films are formed by maintaining a quasi-equilibrium (very slow, ∼15 h) in Schiff base condensation reaction between p-phenylenediamine (PDA) and benzene-1,3,5-tricarboxaldehyde (TCA) molecules. Free-standing thin and ultrathin films of imine-COF are obtained using sonication exfoliation of 2D-COF polymer. Insights into the microstructure of thin/ultrathin imine-COF are obtained using scanning and transmission electron microscopy (SEM and TEM) and atomic force microscopy (AFM), which shows high crystallinity and 2D layered structure in both thin and ultrathin films. The chemical nature of the 2D polymer was established using X-ray photoelectron spectroscopy (XPS). Optical band gap measurements also reveal a semiconducting gap. This is further established by electronic structure calculation using density functional theory (DFT), which reveals a semiconductor-like band structure with strong dispersion in bands near conduction and valence band edges. The structural characteristics (layered morphology and microscopic structure) of 2D imine-COF show significant potential for its application in thin film device fabrication. In addition, the electronic structure shows strong dispersion in the frontier bands, making it a potential semiconducting material for charge carrier transportation in electronic devices.

Antiferromagnetic resorcinol bridged dinuclear square-planar copper (II) complexes: Syntheses, structural, spectroscopic and magnetic properties

A new C2-symmetric Schiff base ligand (H2L) featuring a core resorcinol bridging unit has been created, utilizing the Duff formylation reaction followed by the Schiff base condensation reaction. The ligand was characterized by various spectroscopic techniques. Cu(II) salts with varying coordinating anions (Cl− and SCN−) in methanol were allowed to react with this ligand in a 2:1 M ratio to create dinuclear Cu(II) complexes. The complexes were isolated in pure form and characterized by, elemental analysis,single crystal X-ray crystallography and various spectroscopic techniques. X-ray analysis discloses that both complexes are dinuclear, where the ligand (H2L) being tridentate in nature, coordinates to Cu(II) through its two N donor atoms and one O donor atom in the equatorial positions. The respective anions (−Cl− for 1 and –SCN− for 2) coordinate to Cu(II) to complete its square planar geometry. Temperature dependent magnetic susceptibility measurements indicate weak antiferromagnetic exchange interactions with a coupling constant of J = −5.9(1) cm−1 and g = 2.148(1) for 1 and J = −10.08(1) cm−1 and g = 2.106(1) for 2.

Ambient Synthesis of Porphyrin-Based Fe-Covalent Organic Frameworks for Efficient Infected Skin Wound Healing.

Reactive oxygen species (ROS) have emerged as a promising treatment option for antibacterial and biofilm eradication. However, their therapeutic efficacy is significantly hampered by the unique microenvironments of diabetic wounds. In this study, we designed and synthesized porphyrin-based Fe covalent organic frameworks (Fe-COF) through a Schiff base condensation reaction. Subsequently, Fe-COF were encapsulated with hyaluronic acid (HA) through electrostatic adsorption, resulting in a novel formulation named HA-Fe-COF for diabetic wound healing. HA-Fe-COF were engineered to respond to hyaluronidase in the infected wound, leading to the controlled release of Fe-COF. Those released Fe-COF served a dual role as photosensitizers, generating singlet oxygen and localized heating when exposed to dual light sources. Additionally, they acted as peroxidase-like nanozymes, facilitating the production of ROS through enzymatic reactions. This innovative approach enabled a synergistic therapeutic effect combining photodynamic, photothermal, and chemodynamic modalities. Furthermore, the sustained release of HA from HA-Fe-COF promoted angiogenesis, collagen deposition, and re-epithelialization during the diabetic wound healing process. This "all-in-one" strategy offers a novel approach for the development of antimicrobial and biofilm eradication strategies that minimize damage to healthy tissues in vivo.

Viologen-Cucurbit[7]uril Based Polyrotaxanated Covalent Organic Networks: A Metal Free Electrocatalyst for Oxygen Evolution Reaction.

Viologen-based covalent organic networks represent a burgeoning class of materials distinguished by their captivating properties. Here, supramolecular chemistry is harnessed to fabricate polyrotaxanated ionic covalent organic polymers (iCOP) through a Schiff-base condensation reaction under solvothermal conditions. The reaction between 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diium dichloride (DPV-NH2) and 1,3,5-triformylphloroglucinol (TPG) in various solvents yields an iCOP-1 and iCOP-2. Likewise, employing cucurbit[7]uril (CB[7]) in the reaction yielded polyrotaxanated iCOPs, denoted as iCOP-CB[7]-1 and iCOP-CB[7]-2. All four iCOPs exhibit exceptional stability under the acidic and basic conditions. iCOP-CB[7]-2 displays outstanding electrocatalytic Oxygen Evolution Reaction (OER) performance, demanding an overpotential of 296 and 332mV at 10 and 20mA cm-2, respectively. Moreover, the CB[7] integrated iCOP-2 exhibits a long-term stable nature for 30h in 1m KOH environment. Further, intrinsic activity studies like TOF show a 4.2-fold increase in generation of oxygen (O2) molecules than the bare iCOP-2. Also, it is found that iCOP-CB[7]-2 exhibits a high specific (19.48mA cm-2) and mass activity (76.74mAmg-1) at 1.59V versus RHE. Operando-EIS study evident that iCOP-CB[7]-2 commences OER at a relatively low applied potential of 1.5V versus RHE. These findings pave the way for a novel approach to synthesizing various mechanically interlocked molecules through straightforward solvothermal conditions.

GSH-depleted Cu-covalent organic frameworks for multimodal synergistic therapy against diabetic infections

Skin wound healing, particularly diabetic wound healing, is a common clinical challenge. Reducing bacterial infection and promoting angiogenesis are key strategies for diabetic wound healing. In this study, we construct the porphyrin-based Cu-covalent organic frameworks (Cu-COF) through a Schiff base condensation reaction, and then functionalize Cu-COF with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)] (mPEG-DSPE), denoted as PEG/Cu-COF, for enhancing diabetic wound healing. PEG/Cu-COF exhibits dual enzymatic properties (glutathione (GSH) oxidase-like and peroxidase (POD)-like nanozymes), facilitating the depletion of GSH and the generation of reactive oxygen species (ROS) through a self-cascading enzymatic reaction, thereby leading to chemodynamic therapy (CDT). Density functional theory (DFT) calculations are employed to investigate the catalytic mechanism and the results reveal that Cu-COF exhibits higher catalytic activity for POD. Moreover, porphyrin-based COF generates singlet oxygen and localize heating under white light and near-infrared irradiation, respectively. Both in vitro and in vivo experiments demonstrate that PEG/Cu-COF exhibits multimodal synergistic sterilization and promotes angiogenesis, collagen deposition, and re-epithelialization during diabetic wound healing. This work highlights the potential utilization of PEG/Cu-COF for self-supplying hydrogen peroxide (H2O2) and amplifying self-cascade reactions to address the limitations of enzymatic treatment, while the synergistic effect of phototherapy improves sterilization and minimizes side effects in vivo.

Construction of self-healing multifunctional hyper-crosslinked hyperbranched polymer @ metal–organic polyhedra (HHMOP) membranes

The preparation of hybrid membranes composed of polymer matrix and porous materials is a hot topic. Herein, a highly reversible hyper-crosslinked hyperbranched polymer @ metal–organic polyhedra (HHMOP) membrane was designed and synthesized using hyperbranched polyamide amine (HPMA), UiO-66-NH2, diethylenetriamine, and terephthalaldehyde through a multi-component Schiff-base condensation reaction of aldehyde and amine groups. The structures of HHMOP membranes were characterized by FTIR, XRD, and SEM. The mechanical properties, thermal properties, reversible self-healing properties, and biological activity of the membranes were studied. Introducing HPMA as hyper-crosslinking monomer and UiO-66-NH2 as porous comonomers into the network resulted in HHMOPs membranes with multiple functionalities: flexibility, humidity sensitivity, self-healing capacity, antibacterial capacity and better mechanical properties than the original polyimine films. The tensional intensity and breaking elongation of HHMOP membrane has been remarkably ameliorated, with the maximum tensile strength reached 54.64 MPa. The membranes showed humidity-sensitive mechanical properties and excellent self-healing performance, with 91.35 % strength revovered after 24-hours at room temperature and a relative humidity of 60 %, indicating that HPMA has a significant impact on the humidity responsiveness and self-healing performance of HHMOP membranes. The HHMOP membrane also demonstrated good antibacterial activity against common food lethal bacteria like the gram-positive Staphylococcus aureus and gram-negative Escherichia coli. This work will greatly enrich the devise and preparation of versatile membranes and broaden the use of MOFs.

1,2,3-triazole and chiral Schiff base hybrids as potential anticancer agents: DFT, molecular docking and ADME studies

A series of novel 1,2,3-triazole and chiral Schiff base hybrids 2–6 were synthesized by Schiff base condensation reaction from pre-prepared parent component of the hybrids (1,2,3-triazole 1) and series of primary chiral amines and their chemical structure were confirmed using NMR and FTIR spectroscopies, and CHN elemental analysis. Compounds 1–6 were evaluated for their anticancer activity against two cancer PC3 (prostate) and A375 (skin) and MRC-5 (healthy) cell lines by Almar Blue assay method. The compounds exhibited significant cytotoxicity against the tested cancer cell lines. Among the tested compounds 3 and 6 showed very good activity for the inhibition of the cancer cell lines and low toxicity for the healthy cell lines. All the compounds exhibited high binding affinity for Androgen receptor modulators (PDB ID: 5t8e) and Human MIA (PDB ID: 1i1j) inhibitors compared to the reference anticancer drug (cisplatin). Structure activity relationships (SARs) of the tested compounds is in good agreement with DFT and molecular docking studies. The compounds exhibited desirable physicochemical properties for drug likeness.

Chiral hydroxyl-controlled covalent organic framework-modified stationary phase for chromatographic enantioseparation.

Chiral covalent organic frameworks (CCOFs) possess asuperior chiral recognition environment, abundant pore configuration, and favorable physicochemical stability. In the post-synthetic chiral modification of COFs, research usually focused on increasing the density of chiral sites as much as possible, and little attention has been paid to the influence of the density of chiral sites on the spatial structure and chiral separation performance of CCOFs. In this article, 1,3,5-tris(4-aminophenyl) benzene (TPB), 2,5-dihydroxyterephthalaldehyde (DHTP), and 2,5-dimethoxyterephthalaldehyde (DMTP) served as the platform molecules to directly establish hydroxyl-controlled COFs through Schiff base condensation reactions. Then the novel chiral selectors 6-deoxy-6-[1-(2-aminoethyl)-3-(4-(4-isocyanatobenzyl)phenyl)urea]-β-cyclodextrin (UB-β-CD) were pended into the micropore structures of COFs via covalent bond for further construction the [UB-β-CD]x-TPB-DMTP COFs (x represents the density of chiral sites). The chiral sites density on [UB-β-CD]x-TPB-DMTP COFs was regulated by changing the construction proportion of DHTP to obtain a satisfactory CCOFs and significantly improve the ability of chiral separation. [UB-β-CD]x-TPB-DMTP COFs were coated on the inner wall of a capillary via a covalently bonding strategy. The prepared open tubular capillary exhibited strong and broad enantioselectivity toward a variety of chiral analytes, including sixteen racemic amino acids and six model chiral drugs. By comparing the outcomes of chromatographic separation, we observed that the density of chiral sites in CCOFs was not positively correlated with their enantiomeric separation performance. The mechanism of chiral recognition [UB-β-CD]x-TPB-DMTP COFs were further demonstrated by molecular docking simulation. This study not only introduces a new high-efficiency member of the COFs-based CSPs family but also demonstrates the enantioseparation potential of CCOFs constructed with traditional post-synthetic modification (PSM) strategy by utilizing the inherent characteristics of porous organic frameworks.

Mono- and bi-nuclear phosphine-phenolate neutral nickel catalysts via simple Schiff-Base condensation for ethylene polymerization

In catalytic olefin polymerization, a significant amount of effort has been invested to modify either phosphine substituent or ligand backbone in recently advanced phosphine-phenolate [P,O] neutral nickel catalysts. Unlike other commonly used ligands like phenoxy-imines [N,O] and α-diimines [N,N], [P,O] ligands often require a laborious synthesis technique, which has hindered the rational design of ligand structures and the development of new catalysts. Here we present a novel and effective strategy for creating catalysts using [N,O,P] hybrid ligands. The substituent adjacent to the phenoxy group can be efficiently modified through straightforward Schiff-base condensation reactions with various amines that have established synthetic routes and diverse structures. This process results in the preparation of a series of highly active [P,O] nickel catalysts (up to 1.7 × 107 g mol-1h−1) that are capable of producing ultrahigh molecular weight polyethylene (UHMWPE) (Mw = 243.7 × 104 g/mol) in ethylene polymerization. The additional binding site greatly facilitates modulation of catalytic properties by additives, and parameters such as catalytic activity, polymer molecular weight, and polymer branching can be tuned in this way. Furthermore, binuclear [P,O] neutral nickel catalysts for olefin polymerization are synthesized for the first time using a sequence of diamines. The strategy presented in this work greatly improves the efficiency for the design and synthesis of [P,O] nickel and related catalysts. These findings will be advantageous for future catalyst design and screening.