Schiff Base Condensation Reaction Research Articles

A Simple and Rapid Quinoline Schiff Base as a Fluorescent Probe for Zn2+ and Its Application in Test Strips

AbstractA simple fluorescent probe, (E)‐N‐(3‐methoxy‐4‐methylphenyl)‐1‐(quinolin‐2‐yl)methanimine (L), was synthesized via Schiff base condensation reaction between quinoline‐2‐carboxaldehyde and 3‐methoxy‐4‐methylaniline. L can be used as a ′turn‐on′ fluorescent probe for the selective and sensitive detection of Zn2+ ions in a CH3OH/HEPES medium. The detection limit was 1.04×10−7 M. Job plot analysis shows that the binding stoichiometry of L and Zn2+ is 1 : 1, further verified by the single crystal structure. The fluorescence‐enhanced response of L towards Zn2+ ions may be related to the chelation‐enhanced fluorescence (CHEF) supported by theoretical calculations. By adding EDTA, the reversibility of the probe binding to Zn2+ ions is demonstrated, enabling the construction of a functional molecular logic circuit. In addition, probe L was successfully incorporated into test strips for the quantitative detection of Zn2+.

Preparation of Anderson-type CoMo6-2NH2@ECOF for highly active catalysis on aerobic oxidative desulfurization of fuel under O2

Deep desulfurization with high-efficiency is imperia for environmental demands with increasing stringent standard of sulfur content in fuels. To develop high efficiency heterogeneous catalyst for aerobic oxidative desulfurization (AODS) of fuel, an Anderson-type CoMo6-2NH2 (POM) as active site, which was considered to be very effective in catalyzing the activation of O2, was successfully anchored on the sub-stoichiometric ECOF as a carrier by Schiff-base condensation reaction between –NH2 groups in CoMo6-2NH2 and –CHO groups in ECOF. The anchoring of CoMo6-2NH2 on ECOF by covalent bond resulted in the heterogenization of CoMo6-2NH2 enabled CoMo6-2NH2@ECOF to be recyclable during the AODS process. When CoMo6-2NH2@ECOF was applied as catalyst for AODS of fuel with surfactant (OTAC) under O2, it exhibited excellent catalytic activity with almost 100 % removal rates under 95 °C for 6 h. Moreover, the catalyst can be recycled 7 times without significant loss of catalytic activity. Further, the structure-activity relationship was investigated and the reaction mechanism of AODS of fuel was verified by ESR, XPS analysis and selective quenching experiments.

A wafer scale thin film of ultra-small Sc2O3 nanocrystals on a 2D COF with high rigidity.

Scandium oxide (Sc2O3) has a wide range of applications in metallurgy, chemical industry, electronics and many other high-tech fields. However, most Sc2O3 materials exist in the powder or bulk form, while nanostructured Sc2O3 has rarely been reported as there is a lack of a common method to control its dimensionality, hindering the understanding of new properties and potential applications of nano-Sc2O3 materials. In this paper, we establish a procedure to synthesize a two-dimensional (2D) Sc2O3-covalent organic framework (COF) composite film where the crystal size of Sc2O3 domains is as small as ∼3 nm. The composite film is prepared by a Schiff base condensation reaction at the sharp n-pentane/water interface using a combination of surfactant-monolayer-assisted interfacial synthesis and laminar assembly polymerization methods. Then the conditions of nucleation and uniform film formation of the 2D Sc2O3/COF are explored further. Meanwhile, an atomic force microscopy indentation test shows that the material has a high Young's modulus of 89.1 ± 3.8 GPa, which is much higher than those of the majority of reported 2D polymer materials. We further extended this synthesis method to the preparation of Yb2O3 (ytterbium oxide) and/or Er2O3 (erbium oxide)-incorporated 2D COF composite films, verifying the universality of this strategy. This work provides an opportunity to vary the dimensionality of many kinds of metal oxides and explore the potential applications of low-dimensional Sc2O3 materials.

Post-synthetic molecular modifications based on Schiff base condensation reactions for designing functional paddlewheel diruthenium(II,II) complexes.

A new synthetic route for constructing functional paddlewheel diruthenium(II,II) complexes ([RuII,II2]) was developed by utilizing Schiff base condensation reactions of formyl-substituted benzoate-bridged [RuII,II2] complexes with various aromatic monoamines under mild conditions. Cyclic voltammetry and DFT calculations revealed that the attached Schiff base groups significantly affected the electronic states of the resulting [RuII,II2] complexes.

Preparation of Well-Constructed and Metal-Modified Covalent Organic Framework Nanoparticles for Biosensing Design with Cascade Catalytic Capability.

Uniform covalent organic framework nanoparticles (COF NPs) with a well-defined pore structure may provide a robust platform for scaffolding enzymes. Herein, bipyridine-based spherical COF NPs have been successfully prepared in this work through the Schiff base condensation reaction. Moreover, they are functionalized by metal modification and are further used for biosensor fabrication. Experimental results reveal that the metal-modified COF NPs also display impressive peroxidase-like catalytic activities, while they can load enzymes, such as glucose oxidase (GOx) and sarcosine oxidase (SOx), to develop a cascade catalysis system for design of various kinds of biosensors with very well performance. For example, the optimized GOx@Fe-COFs can achieve a sensitive detection of glucose with a low limit of detection (LOD) of 12.8 μM. Meanwhile, the enzymes also exhibit a commendable preservation of 80% enzymatic activity over a span of 14 days under ambient conditions. This work may pave the way for advancing cascade catalysis and the analysis of different kinds of biological molecules based on COF NPs.

Coordination-Driven Heterochiral Self-Assembly: Construction of Cd(II) Coordination Polymers with Sorption Behaviors for Iodine and Dyes.

A racemic bispyridyl ligand (L) was synthesized via a Schiff base condensation reaction. Four Cd(II) complexes, {[CdL2Cl2]·2DMF}n (1), [CdLI2]n (2), {[CdL2Br2]·4H2O}n (3), and {[CdL2(H2O)2](NO3)2·2CH3OH·8H2O}n (4), were synthesized and further characterized based on this ligand. Single-crystal structures show that the coordination-driven assembly of the bispyridyl ligand with Cd(II) salts bearing different counteranions can lead to multidimensional coordination polymers via a heterochiral self-discrimination process. Complex 1 exists as a one-dimensional (1D) looped chain polymer, and complex 2 exists as a 1D zigzag chain polymer. Complex 3 is a 2D grid coordination polymer, and complex 4 exists as a 3D framework polymer. Furthermore, the iodine sorption capacities of the four complexes were investigated in the solution of n-hexane and water as well as in the iodine steam. The dye sorption behaviors were investigated in water, which showed that complex 2 exhibited good adsorption for crystal violet (CV), while complex 4 had good adsorption capability toward direct yellow 4 (DY).

Crystal structure and luminescent mechanochromism of a quinoline-appended acylhydrazone ligand and its Zn(II) complex

In the work, a quinoline-appended acylhydrazone H2L was designed and prepared via a Schiff base condensation reaction of quinoline-2-formaldehyde and salicylhydrazide. Further, a new zinc(II) complex, [Zn(HL)2]·H2O was synthesized by the reacting of the ligand H2L and Zn(NO3)2·6H2O in dichloromethane/ethanol solution. The ligand and its Zn(II) complex were elucidated via UV–Vis, FT-IR, DFT calculation, Hirshfeld surfaces, MEP & IRI analyses, and X-ray single-crystal diffractions. The results of Hershfield surface analysis showed that there are obvious hydrogen bond interactions and CH···π mutual effect in the Zn(II) complex. In addition, solid-state photoluminescence properties indicated that H2L and its Zn(II) complex represent uncommon luminescent mechanochromism tuned via intermolecular hydrogen bonds.

Synthesis of calix [4]arene-based nanohybrids: An efficient route for the electrochemical detection of dCO2 and its sustainable transformation for the production of formic acid, a industrially valuable chemical

CO2 exposure has damaging effects on human health and environment; therefore, its detection and sustainable capture and conversion has applications for both industrial and domestic use. Electrochemical method is a simple and reliable technique for selective quantification of dCO2 and gCO2. Herein, we have developed electrochemical method for determination of dissolved CO2 (dCO2) employing calix [4]Arene-based nanohybrids using NaHCO3 as the carbon source exhibiting limit of detection (LOD) of 0.006 μM (1.5 × 10−6 hPa CO2). The nanohybrids were produced by reducing Ag(I) on the surface of organic nanoparticles developed from calix [4]arene molecule. The calix [4]arene based dipodal receptor was synthesized using a Schiff base condensation reaction and organic nanoparticles were prepared by reprecipitation method. To reduce the carbon footprint, we have attempted to convert dCO2 into formic acid (yield >97%) electrochemically employing AgNPs nanohybrids as an efficient catalyst in slightly acidic medium and the conversion was characterized using NMR and FT-IR spectroscopy. The proposed method is highly efficient, simple and sustainable method to reduce CO2 into formic acid and the practical utility of the proposed methodology was validated on bottled beverages (carbonated drinks), aquarium water, algae containing water, distilled water and fresh river water.

Construction of N-Rich Aminal-Linked Porous Organic Polymers for Outstanding Precombustion CO2 Capture and H2 Purification: A Combined Experimental and Theoretical Study.

A large number of scientific investigations are needed for developing a sustainable solid sorbent material for precombustion CO2 capture in the integrated gasification combined cycle (IGCC) that is accountable for the industrial coproduction of hydrogen and electricity. Keeping in mind the industrially relevant conditions (high pressure, high temperature, and humidity) as well as good CO2/H2 selectivity, we explored a series of sorbent materials. An all-rounder player in this game is the porous organic polymers (POPs) that are thermally and chemically stable, easily scalable, and precisely tunable. In the present investigation, we successfully synthesized two nitrogen-rich POPs by extended Schiff-base condensation reactions. Among these two porous polymers, TBAL-POP-2 exhibits high CO2 uptake capacity at 30 bar pressure (57.2, 18.7, and 15.9 mmol g-1 at 273, 298, and 313 K temperatures, respectively). CO2/H2 selectivities of TBAL-POP-1 and 2 at 25 °C are 434.35 and 477.93, respectively. On the other hand, at 313 K the CO2/H2 selectivities of TBAL-POP-1 and 2 are 296.92 and 421.58, respectively. Another important feature to win the race in the search of good sorbents is CO2 capture capacity at room temperature, which is very high for TBAL-POP-2 (15.61 mmol g-1 at 298 K for 30 to 1 bar pressure swing). High BET surface area and good mesopore volume along with a large nitrogen content in the framework make TBAL-POP-2 an excellent sorbent material for precombustion CO2 capture and H2 purification.

Chitosan immobilized Chinese gallotannin: A potential adsorbent to enrich the rare metals Ge (Ⅳ), Ga (Ⅲ), and In (Ⅲ)

In this study, a solid adsorbent based on Chinese gallotannin and chitosan was generated and applied to adsorb rare and scattered metals, including Ge (Ⅳ), Ga (Ⅲ), and In (Ⅲ), from simulated zinc plant leachates. Fourier-transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance (SSNMR) were performed to characterize the grafting way of Chinese gallotannin on the chitosan matrix. It was clearly showed that Chinese gallotannin was immobilized on the chitosan by Schiff-base condensation and phenol-formaldehyde reaction at the molar ratio of glutaraldehyde to tannin of 2:1. And the amount of chitosan amino groups was ten times that of tannin, with an initial pH of 4. The adsorption experiments showed that an appropriate increase in pH was more beneficial to enhance the adsorption capacity of immobilized Chinese gallotannin (ICGT). At a temperature exceeding 30 °C, the immobilized tannin became less sensitive to temperature. Adsorption kinetics studies showed that the adsorption of the three scattered metals by ICGT followed a quasi-second-order kinetic equation, with chemisorption as the mechanism. The adsorption isotherm was well fitted by the Langmuir model, indicating uniform adsorption sites on the surface of ICGT. The adsorption capacities of Ge (Ⅳ), Ga (Ⅲ), and In (Ⅲ) in solution by the adsorption model of monolayer were 61.39 mg/g, 63.82 mg/g, and 59.92 mg/g, respectively. Mechanical property and stability tests showed that ICGT had good resistance to harsh adsorption conditions of scattered metal ions.

A tetraphenylethylene-based acylhydrazone Schiff base macrocycle exhibiting aggregation-induced emission and “turn-on” detection of Al3+ ions

A tetraphenylethylene-based acylhydrazone macrocycle (H8L) was designed and synthesized via Schiff base condensation reaction. The [2 + 2] molecular structure of H8L was determined via 1H NMR, 13C NMR, elemental analysis, ESI-MS, and single crystal X-ray diffraction. The “ESIPT + AIE” and selective recognition properties of macrocycle H8L were investigated via UV–vis absorption spectra and fluorescence emission spectra. The results showed that macrocycle H8L exhibited an obvious AIE characteristic in THF/H2O solution with varying water fraction, and displayed a selective “turn-on” response to Al3+ ions in the solution of THF/H2O (V: V = 4: 1). In addition, the visualization of latent fingerprints and the application of H8L on test strips were performed as well.

Five Porous Complexes Constructed from a Racemic Ligand: Synthesis, Chiral Self-Assembly, Iodine Adsorption, and Desorption Properties.

Herein, a chiral bispyridyl ligand (L) was designed and synthesized using a Schiff base condensation reaction, followed by a 1,3-H shift. Five complexes, [Zn2L2(OAc)4] (1), {[CdLCl2(DMF)]·4H2O}n (2), [Cd2L2I4]·4H2O (3), {[CdL2(H2O)2](NO3)2·2CH3OH}n (4), and [Hg2L2Cl4]·2DMF (5), were synthesized and characterized upon its reaction with Zn(II), Cd(II), or Hg(II) ions, respectively. X-ray crystallography shows that the organic compound exists as a racemic ligand with equal amounts of its R- and S-isomers, and all of the synthesized complexes exhibit heterochiral self-assembly via a chiral self-discrimination process. Complexes 1, 3, and 5 exist as centrosymmetric binuclear metallamacrocycles, while complexes 2 and 4 exist as 1D looped-chain coordination polymers. Inspired by the assembled structures of the five complexes, I2 adsorption/desorption measurements for the complexes were carried out. The results show that complexes 1 and 5 exhibit good adsorption capacities toward I2 in n-hexane and in water, respectively.

Strategical design of bridged vanillic Schiff-bases as jet fuel antioxidants

Two vanillic Schiff-base antioxidants, 2-methoxy-4-(((4-(phenylamino)phenyl)imino)methyl)phenol (PPIMP) and 2-methoxy-4-(((4-(phenylamino)phenyl)amino)methyl)phenol (PPAMP), have been synthesized through the Schiff-base condensation reaction and hydrogenation to improve the thermal-oxidative stability of hydrocarbon fuels. Both novel antioxidants exhibited remarkable performance in decalin and JP-10 fuel. For example, pressurized differential scanning calorimetry (P-DSC) tests showed that adding 100 ppm of PPIMP or PPAMP to JP-10 improved the oxidation induction time from 9.5 min to 19.2 and 27.8 min, respectively. JFTOT tests showed that adding 100 ppm of either antioxidant helped alleviate JP-10 deposition. Theoretical calculations on electron properties and orbital conformation revealed that the C = N bridge in PPIMP had an electron donation effect and conjugative stabilization effect, which can stabilize intermediate antioxidant radicals and improve the antioxidants’ reactivity. The hydrogenation of C = N further enhanced the performance of PPAMP by introducing an additional antioxidant group. Therefore, both C = N and C-N in the synthesized antioxidants were found to be essential. The chemical combination of small molecular antioxidants achieves 1 + 1 > 2 synergism with the assistance of the azomethine group.

A BODIPY-Based 1D Covalent Organic Framework for Photocatalytic Aerobic Oxidation.

Covalent organic frameworks (COFs) as metal-free photocatalysts have attracted extensive interest. However, the organic transformations photocatalyzed by COFs under mild conditions remain a challenge. Herein, a boron-dipyrromethene (BODIPY) based 1D COF, namely JNM-12, was facilely constructed by Schiff-base condensation reaction. JNM-12 exhibited strong visible-light harvesting abilities and suitable photocatalysis energy potentials, enabling the activation of O2 to superoxide anions (O2 ⋅- ) and singlet oxygen (1 O2 ) under visible light irradiation. Benefiting from these properties, JNM-12 delivered excellent photocatalytic activity in the O2 ⋅- -mediated oxidative coupling of amines and 1 O2 -engaged aerobic oxidation of enamines. Our work paves a new way for synthesis of COFs as efficient, economical, and green photocatalysts for organic synthesis.

Synthesis, structures, and gas adsorption properties of Hg(II) and Cd(II) complexes constructed from two acylhydrazone ligands with multiple coordination sites

Two chain-like acylhydrazone ligands (L1 and L2) were synthesized from Schiff base condensation reaction of 3,3′-(1,4-piperazine-bis-(methylene)-bis-(2-hydroxy-5-methylbenzaldehyde)) (b) with isonicotinic hydrazide or nicotinic hydrazide, respectively. In the presence of Hg(II) or Cd(II) ions and in DMF/methanol solution, three complexes, formulated as {[Hg3L1Br6]·4DMF}n (1), {[Hg2L2I4]·2DMF}n (2), and [Cd4(L2)2I8(H2O)2]·4DMF (3), were synthesized and further characterized via elemental analysis, FT-IR spectra and single-crystal X-ray diffraction. Complex 1 exists as a 1D zag-zig chain polymer and complex 2 exists as a 1D looped chain polymer. Complex 3 exists as a rare tetranuclear structure. The structural differences of the three complexes and the coordination competition among the coordination sites were analyzed, and the results showed that the pyridyl nitrogen atoms have an obvious coordination ability prior to other sites. Furthermore, gas adsorption measurements were carried out, which show that the three complexes exhibit good adsorption capacity towards CH3OH over N2, H2, O2, and CO2.

A Handy Chemical Sensor Based on Benzaldehyde and Imidazo[1,2-a]pyridine Mixture for Naked-eye Colorimetric and Fluorescent Detection of F.

Upon the Schiff base condensation reaction of imidazo[1,2-a]pyridine-2-carbohydrazide and 2,5-dihydroxybenzaldehyde, a bimodal colorimetric and fluorescent chemosensor 1o for assaying fluoride (F-) in DMSO was synthesized. The characterization of 1o structure was obtained by 1H NMR, 13C NMR and MS.The structure of 1o was characterized by 1H NMR, 13C NMR and MS. Under the presence of various anions, 1o could be applied for naked-eye and fluorescent detection of F- (naked eye: colorless to yellow; fluorescence: dark to green) and displayed promising performance, such as high selectivity and sensitivity, as well as a low detection limit. Upon calculation, the detection limit of chemosensor 1o for F- was 193.5nM, which is well below the allowed maximum value of F- (1.5mg/L) by WHO. As the intermolecular proton transfer mechanism induced "turn-on" fluorescent signal and naked-eye color change of F- to 1o through deprotonation effect, which was confirmed by Job's plot curve, mass spectrometry and 1H NMR titration. Alternatively, the chemosensor 1o can be effectively manufactured into test strips to detect fluoride in solid state, which is user-friendly with no additional equipment required.

Structural and Morphological Transformations of Covalent Organic Nanotubes

AbstractCovalent organic nanotubes (CONTs) are porous one‐dimensional frameworks connected through imine bonds via Schiff base condensation between aldehydes and amines. The presence of two amine groups at the ortho position in the structurally demanding tetraaminotriptycene (TAT) building block leads to multiple reaction pathways between the ditopic aldehyde and the tetratopic amine. We have synthesized five different monomers of CONT‐1 by the Schiff base condensation reaction between TAT and o‐anisaldehyde. The conversion of imine to imidazole bonding in a monomer is probed using NMR, mass spectrometry, and X‐ray diffraction techniques. Solid‐state NMR provide insights into the CONTs’ structural connectivity. A theoretical investigation suggests that the π‐π stacking could be the driving force for rapid imine to imidazole conversion within the CONT‐1. Microscopic imaging sheds further light on the self‐assembly process of the CONTs, indicating both head‐to‐head and side‐by‐side assembly.

Structural and Morphological Transformations of Covalent Organic Nanotubes.

Covalent organic nanotubes (CONTs) are porous one-dimensional frameworks connected through imine bonds via Schiff base condensation between aldehydes and amines. The presence of two amine groups at the ortho position in the structurally demanding tetraaminotriptycene (TAT) building block leads to multiple reaction pathways between the ditopic aldehyde and the tetratopic amine. We have synthesized five different monomers of CONT-1 by the Schiff base condensation reaction between TAT and o-anisaldehyde. The conversion of imine to imidazole bonding in a monomer is probed using NMR, mass spectrometry, and X-ray diffraction techniques. Solid-state NMR provide insights into the CONTs' structural connectivity. A theoretical investigation suggests that the π-π stacking could be the driving force for rapid imine to imidazole conversion within the CONT-1. Microscopic imaging sheds further light on the self-assembly process of the CONTs, indicating both head-to-head and side-by-side assembly.

Design of Smartphone-Assisted Point-of-Care Platform for Colorimetric Sensing of Uric Acid via Visible Light-Induced Oxidase-Like Activity of Covalent Organic Framework.

Monitoring of uric acid (UA) levels in biological samples is of great significance for human health, while the development of a simple and effective method for the precise determination of UA content is still challenging. In the present study, a two-dimensional (2D) imine-linked crystalline pyridine-based covalent organic framework (TpBpy COF) was synthesized using 2,4,6-triformylphloroglucinol (Tp) and [2,2'-bipyridine]-5,5'-diamine (Bpy) as precursors via Schiff-base condensation reactions and was characterized with scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy, and Brunauer-Emmett-Teller (BET) assays. The as-synthesized TpBpy COF exhibited excellent visible light-induced oxidase-like activity, ascribed to the generation of superoxide radicals (O2•-) by photo-generated electron transfer. TpBpy COF could efficiently oxidase the colorless substrate 3,3',5,5'-tetramethylbenzydine (TMB) into blue oxidized TMB (oxTMB) under visible light irradiation. Based on the color fade of the TpBpy COF + TMB system by UA, a colorimetric procedure was developed for UA determination with a detection limit of 1.7 μmol L-1. Moreover, a smartphone-based sensing platform was also constructed for instrument-free and on-site detection of UA with a sensitive detection limit of 3.1 μmol L-1. The developed sensing system was adopted for UA determination in human urine and serum samples with satisfactory recoveries (96.6-107.8%), suggesting the potential practical application of the TpBpy COF-based sensor for UA detection in biological samples.

Unsymmetrically bi-functionalized 1,1′-ferrocenyl bi-hydrazone and hydrazone-cyanovinyl molecules as fluorescent “on–off” sensor: Synthesis, cytotoxicity and cancer cell imaging behavior

Unsymmetrically bi-functionalized ferrocenyl compounds are significant class of multifunctional molecule having unique structural features, varied conformational orientations, tunable electrochemical behavior and wide functional prospects. Strategic design of these unsymmetrical derivatives involving multifunctional components containing sandwich based electroactive fragment, heterocyclic moieties and a highly emissive photo-responsive unit can create flexible, biocompatible fluorescent single molecule - probe for sensor and signaling based molecular devices. Therefore, synthesis of fluorophoric 1,1′-unsymmetrical bi-functionalized ferrocenyl molecular receptor have been carried out using two different types of solid supported condensation reactions, one using Schiff base condensation reaction to link hydrazone based heterocyclic moieties and the other involving a Knoevenagel condensation to link cyano-vinyl based donor–acceptor system, to obtain 1,1′-ferrocenyl rhodaminyl-pyridyl hydrazones and 1,1′-ferrocenyl hydrazone-cyanovinylester derivatives. The unsymmetrical nature of the molecules has been established by single crystal diffraction study and explored for their fluorescence and electrochemical based signaling and sensing behavior of metal cations in solution and subcellular level. The study showed significant intracellular metal recognition and imaging characteristics for their potential in applications related to bioimaging of heavy metal ions. DFT study revealed distinct interaction of the metal ion leading to a change in structural conformation due to the rotational flexibility within the ferrocenyl axis. Molecules were also explored for their cytotoxic behavior and protein binding interaction to understand their biological potential.