Schiff Base Moiety Research Articles

Poly(azomethine-epoxy-ether) containing phenyl and etoxy moieties: synthesis, characterization and fluorescence property

The design and synthesis of poly(azomethine-epoxy-ether) (PAZ-EP) containing epoxide moiety was described. The purpose of the research was the improvement of poly(azomethine-ether) containing epoxide by introduction of Schiff base moiety. PAZ-EP was synthesized using epichlorohydrin (EP). The structure of the Schiff base (SB) and PAZ-EP were verified by FT-IR, 1H-NMR, 13C-NMR and UV–Vis spectroscopic analyses. Further characterization was employed using photophysical, electrochemical and fluorescence (PL) measurements. Application of TGA and differential scanning calorimetry analyses revealed thermal stability and thus propose a thermal processibility, which makes them potential materials for many contemporary practices. The number of average molecular weight of polymer with a polydispersity index of 1.14 was found to be 6750 Da using a gel permeation chromatography instrument. The highest occupied–lowest unoccupied energy levels and electrochemical ( $$E_{\text{g}}^{'}$$ ) band gap values of PAZ-EP were determined by cyclic voltammetry (CV) measurement. Scanning electron microscopy (SEM) images were illustrated at different magnifications to study the morphologic property of PAZ-EP.

Structural effects of highly π-conjugated mesogenic Schiff-base moiety on the cationic polymerization of benzoxazine and formation of ordered morphologies

A Schiff-base moiety was introduced into the chemical structure of benzoxazine through the Mannich reaction. With alternative imine groups (CN) and benzene rings in the chain segment, these highly π-conjugated systems favored the formation of strong intermolecular hydrogen bonds to the hydroxyl groups generated during polymerization, leading to a thermally initiated cationic polymerization mechanism. Compared with the bisphenol-A-based benzoxazine, the benzoxazine with the Schiff-base moiety needs higher energy to facilitate the realization of polymerization and to increase polymerization degree. In addition to the influences on the polymerization, the highly π-conjugated Schiff-base acting as a mesogenic moiety is found to form liquid crystal (LC) phases, like the nematic phase and smectic phase. Interestingly, some LC-rich domains can be stabilized by the polybenzoxazine network, which will contribute to form nitrogen-rich ordered porous carbon at the carbonization stage. For N2 and CO2 adsorption–desorption process, the carbon exhibits an enhanced CO2 adsorption performance, suggesting their capture and separation capacity for CO2.

Discovery of 2-aminothiazolyl berberine derivatives as effectively antibacterial agents toward clinically drug-resistant Gram-negative Acinetobacter baumanii

Aminothiazolyl berberine derivatives as potentially antimicrobial agents were designed and synthesized in an effort to overcome drug resistance. The antimicrobial assay revealed that some target compounds exhibited significantly inhibitory efficiencies toward bacteria and fungi including drug-resistant pathogens, and the aminothiazole and Schiff base moieties were helpful structural fragments for aqueous solubility and antibacterial activity. Especially, aminothiazolyl 9-hexyl berberine 9c and 2,4-dichlorobenzyl derivative 18a exhibited good activities (MIC = 2 nmol/mL) against clinically drug-resistant Gram-negative Acinetobacter baumanii with low cytotoxicity to hepatocyte LO2 cells, rapidly bactericidal effects and quite slow development of bacterial resistance toward A. baumanii. Molecular modeling indicated that compounds 9c and 18a could bind with GLY-102, ARG-136 and/or ALA-100 residues of DNA gyrase through hydrogen bonds. It was found that compounds 9c and 18a were able to disturb the drug-resistant A. baumanii membrane effectively, and molecule 9c could not only intercalate but also cleave bacterial DNA isolated from resistant A. baumanii, which might be the preliminary antibacterial action mechanism of inhibiting the growth of A. baumanii strain. In particular, the combination use of compound 9c with norfloxacin could enhance the antibacterial activity, broaden antibacterial spectrum and overcome the drug resistance.

Synthesis and mesomorphism of novel multi-arm liquid crystals with cholic acid as chiral centre linking Schiff base moieties as mesogens

ABSTRACTA new series of multi-arm chiral liquid crystals (LCs) D1–D3 were synthesised and characterised. Cholic acid was used as the core and ω-[4-(p-alkoxybenzoloxy)phenoxycarbonyl]valeric acid (B1–B3) was used as the mesogenic arms, containing different terminal substituent X (B1: X= -OCH3, B2:X= -CH3, B3: X= -Cl). Their structures and mesomorphic properties were investigated by Fourier-transform infrared spectroscopy, nuclear magnetic resonance hydrogen spectrometer, differential scanning calorimetry, polarised optical microscopy and X-ray diffraction, respectively. The mesogenic B1–B3 displayed smectic B phase. The multi-arm LC D1 displayed cholesteric, while D2 and D3 exhibited nematic phase. The formation of cholesteric phase of D1 was affected by both the chiral core – the bulky cholic acid and the polarity of the terminal substituent of the mesogenic arm. That D1 displayed cholesteric phase but D2–D3 did not indicated that the stronger polarity of the terminal group OCH3 of D1 played an important part in stabilising the cholesteric phase. The multi-arm LCs D1–D3 all showed ultraviolet activity. The wavelength of maximum absorption of D1–D3 was affected by the terminal substituent of the mesogenic arm.

Post-synthetic modification of IRMOF-3 with an iminopalladacycle complex and its application as an effective heterogeneous catalyst in Suzuki-Miyaura cross-coupling reaction in H2O/EtOH media at room temperature

A novel iminopalladacycle complex was successfully immobilized onto a metal–organic framework (MOF) through post-synthetic modification of IRMOF-3. Initially, the IRMOF-3 was modified with benzaldehyde to achieve a Schiff-base moiety in the pores of IRMOF-3 (IRMOF-3-BI) which could anchor the palladium by the addition of palladium acetate (IRMOF-3-BI-Pd). The catalyst was fully characterized by using a variety of methods such as attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), energy dispersive X-ray (EDX), inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). Also, the structural unities of MOFs have been confirmed by scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) analysis. Moreover, the prepared catalyst has shown excellent turnover frequencies as a heterogonous catalyst in the Suzuki C-C coupling reaction for aryl iodides, bromides and chlorides in H2O/EtOH media at room temperature. Additionally, the catalyst can be easily isolated from the reaction mixture and recycled for five sequential runs without incredible decrease in catalytic efficiency.

Visual chiral recognition of 1,1′-binaphthol through enantioselective collapse of gel based on an amphiphilic Schiff-base gelator

A novel gelator that contained both Schiff base and L-lysine moieties was synthesized and its gelation behavior was tested. This gelator can form gels in various organic solvents. The resulting gel can be applied as a fascinating platform for visual recognition of enantiomeric 1-(2-hydroxynaphthalen-1-yl)naphthalen-2-ol (BINOL) through selective gel collapse. In addition, the mechanism for the reaction of the gel with chiral BINOL was investigated by scanning electron microscope and 1H nuclear magnetic resonance.

MCM-41-supported NNO type Schiff base complexes: a highly selective heterogeneous nanocatalyst for esterification, Diels–Alder and aldol condensation

Solid catalysts have been synthesized by anchoring transition metal complexes into organically modified MCM-41. First, the surface of Si-MCM-41 was modified with 3-aminopropyl-triethoxysilane (3-APTES), the imine group of which upon condensation with DFP (4-methyl-2,6-diformylphenol) affords a N2O-type Schiff base moiety in the mesoporous matrix. The Schiff base moieties were used to anchor Ni (II) and Cu (II) ions. The prepared catalyst have been characterized by DRS (Diffuse Reflectance Spectroscopy), FTIR (Fourier transform infrared) spectroscopy, small-angle X-ray diffraction (SAX), FESEM (Field Emission Scanning Electron Microscope), EDX (Energy-dispersive X-ray spectroscopy) and nitrogen sorption studies. The decrease of crystallinity in the multistep synthesis procedure, as evidenced by SAX (Small-angle X-ray) measurements, was observed. The prepared materials proved to be efficient catalysts for organic transformations such as esterification, Diels–Alder and Aldol condensation at ambient conditions. The immobilized complex does not leach or decompose during the catalytic reactions, showing practical advantages over the free metal complex.

Redox-Switchable New Phthalocyanines Containing Hydrazono-Thiazole-Carboxylate Fragments: Synthesis, Electrochemical, Spectroelectrochemical and Electrocolorimetric Investigation.

New phthalonitrile compound with Schiff base, carbothioamide and thiazole moieties as substituents and its corresponding metal-free and metallophthalocyanines (Zn(II), Ni(II), Co(II), and Cu(II)) were synthesized and characterized for the first time. The solubilities of these novel phthalocyanines were high in organic solvents. The redox properties of the compounds have been researched by cyclic voltammetry, square wave voltammetry, controlled-potential coulometry and in situ spectroelectrochemistry in dimethylsulfoxide. The compounds displayed metal and/or phthalocyanine ring-based, generally reversible or quasi-reversible reduction and oxidation processes. The effect of aggregation on the redox behavior of these complexes was also discussed. In general, decreased intensity and broadening in the main Q absorption band and the appearance of a new blue-shifted band confirmed the presence of H-type aggregates in the solutions of the complexes 4, 6 and 8 in DMSO/TBAP. The color changes associated with the redox processes and electrogenerated anionic and cationic redox species were also recorded with in situ electrocolorimetric measurements. In situ UV-vis spectral and associated color changes monitored during the reduction processes of the complexes suggested their applicability in the fields of the electrochemical technologies.

A reactive oxygen species-generating, cyclooxygenase-2 inhibiting, cancer stem cell-potent tetranuclear copper(ii) cluster.

Tetranuclear copper(ii) complexes containing multiple diclofenac and Schiff base moieties, 1-4, are shown to kill bulk cancer cells and cancer stem cells (CSCs) with low micromolar potency. The most effective complex, 1, elicits its cytotoxic effect by elevating the intracellular reactive oxygen species (ROS) levels and inhibiting cyclooxygenase-2 (COX-2) expression.

Grafting of chitosan Schiff base on graphene oxide and its characterization

ABSTRACTIn order to enhance the modification effect, and graphene oxide was also reported could be efficiently modified via covalent attachment. Herein, chitosan Schiff base was chosen to grafting on the surface of graphene oxide. Firstly, chitosan and parahydroxybenzaldehyde were used as raw materials to synthesizing chitosan Schiff base, which was abbreviated as CSb. Secondly, modified graphene oxide with CSb, and chitosan Schiff base moieties were grafted on the surface of graphene oxide, we called it SGO at here. The chemical structure of CSb and SGO were characterized by FT-IR, respectively. The XPS results confirmed that there was 2% nitrogen, 24% oxygen, and 74% carbon existed on the surface of SGO. The curing behavior of GO was characterized by DSC, there was only one exothermic peak during cure and its temperature was 172°C. After grafted with biological groups, appeared one endothermic peak around 76°C, one exothermic peak at 212°C during the cure of SGO. The thermal stability was studied by TGA. The results demonstrated that the thermal stability of SGO improved after modification and obtained 36.4% char yield at 800°C. The fractures properties of SGO were also characterized by FESEM in this paper.

Spectroscopic and Catalytic Discussions of the Alkaline Earth Metal Schiff Base Chelations Derived from Condensation of Furan-2-Carbaldehyde with 2-Chlorophenyl Hydrazine

Mg(II), Ca(II), Sr(II) and Ba(II) metal chelates with formulas, [Mg(HL)2(H2O)2] · Cl2, [Ca(HL)2(Cl)2], [Sr(HL)2(H2O)2] · Cl2 · 6H2O and [Ba(HL)2(H2O)2] · Cl2 that HL is the Schiff base moiety formed from condensation of furan-2-carbaldehyde with 2-chlorophenyl hydrazine have been prepared and characterized by elemental analysis and spectroscopic measurements (infrared, Mass and 1H-NMR). The microanalytical analyses (%C, %H and %N elements) of the Schiff base complexes deduce the 1:2 ratio of metal-to-ligand. The infrared spectra of the new Schiff base complexes led to identify the chelating around the respected metal ions via both nitrogen and oxygen atoms of 2-chlorophenyl hydrazine (–Ph–NH-) group and furan ring.

Molecular docking studies and biological evaluation of 1,3,4-thiadiazole derivatives bearing Schiff base moieties as tyrosinase inhibitors

1,3,4-Thiadiazole derivatives bearing Schiff base moieties were designed, synthesized, and their tyrosinase inhibitory activities were evaluated. Some compounds displayed potent tyrosinase inhibitory activities, especially, 4-(((5-mercapto-1,3,4-thiadiazol-2-yl)-imino)methyl)-2-methoxy-phenol (14) exhibited superior inhibitory effect to the other compounds with an IC50 value of 0.036μM. The structure–activity relationships (SARs) were preliminarily discussed and docking studies showed compound 14 had strong binding affinity to mushroom tyrosinase. Hydroxy might be the active groups. The inhibition kinetics study revealed that compounds (13 and 14) inhibited tyrosinase by acting as uncompetitive inhibitors. The LD50 value of the compound 14 was 5000mg/kg.

Second-Generation Phenylthiazole Antibiotics with Enhanced Pharmacokinetic Properties.

A series of second-generation analogues for 2-(1-(2-(4-butylphenyl)-4-methylthiazol-5-yl)ethylidene)aminoguanidine (1) have been synthesized and tested against methicillin-resistant Staphylococcus aureus (MRSA). The compounds were designed with the objective of improving pharmacokinetic properties. This main aim has been accomplished by replacing the rapidly hydrolyzable Schiff-base moiety of first-generation members with a cyclic, unhydrolyzable pyrimidine ring. The hydrazide-containing analogue 17 was identified as the most potent analogue constructed thus far. The corresponding amine 8 was 8 times less active. Finally, incorporating the nitrogenous side chain within an aromatic system completely abolished the antibacterial character. Replacement of the n-butyl group with cyclic bioisosteres revealed cyclohexenyl analogue 29, which showed significant improvement in in vitro anti-MRSA potency. Increasing or decreasing the ring size deteriorated the antibacterial activity. Compound 17 demonstrated a superior in vitro and in vivo pharmacokinetic profile, providing compelling evidence that this particular analogue is a good drug candidate worthy of further analysis.

Synthesis and Properties of Hemostatic and Bacteria-Responsive in Situ Hydrogels for Emergency Treatment in Critical Situations.

Immediate hemorrhage control and infection prevention are pivotal for saving lives in critical situations such as battlefields, natural disasters, traffic accidents, and so on. In situ hydrogels are promising candidates, but their mechanical strength is often not strong enough for use in critical situations. In this study, we constructed three hydrogels with different amounts of Schiff-base moieties from 4-arm-PEG-NH2, 4-arm-PEG-NHS, and 4-arm-PEG-CHO in which vancomycin was incorporated as an antimicrobial agent. The hydrogels possess porous structures, excellent mechanical strength, and high swelling ratio. The cytotoxicity studies indicated that the composite hydrogel systems possess good biocompatibility. The Schiff bases incorporated improve the adhesiveness and endow the hydrogels with bacteria-sensitivity. The in vivo hemostatic and antimicrobial experiments on rabbits and pigs demonstrated that the hydrogels are able to aid in rapid hemorrhage control and infection prevention. In summary, vancomycin-loaded hydrogels may be excellent candidates as hemostatic and antibacterial materials for first aid treatment of the wounded in critical situations.

The preparation of a new type of ferrocene-based compounds with large conjugated system containing symmetrical aromatic vinyl with Schiff base moieties and the study of their third-order nonlinear optical properties

Herein we reported the preparation of a new type of ferrocene-based compounds with large conjugated system containing symmetrical aromatic vinyl and Schiff base moieties and the study of their third-order nonlinear optical (NLO) properties. Their third-order NLO properties were measured using femtosecond laser and degenerate four-wave mixing (DFWM) technique. The obtained χ(3), n2 and γ values of these molecules were found in the range of 0.998–1.429×10−12esu,1.847–2.646×10−11esu and 1.026–1.449×10−30esu, respectively. The response time ranged from 43.65fs to 61.71fs. The results indicate that these compounds have potential nonlinear optical applications.

Crystal structure of 1,2-bis-((benzyl-sulfan-yl){2-[1-(2-hy-droxy-phen-yl)ethyl-idene]hydrazin-1-yl-idene}meth-yl)disulfane.

The title compound, C32H30N4O2S4, consists of two Schiff base moieties, namely two S-benzyl-β-N-(2-hy-droxy-phenyl-ethyl-idene)di-thio-carbazate groups, which are connected through an S-S single bond. These two moieties are twisted with respect to each other, with a dihedral angle of 87.88 (4)° between the S2C=N planes. A bifurcated intra-molecular O-H⋯(N,S) hydrogen bond is observed in each moiety. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds into inversion dimers. The dimers are further stacked in a column along the b axis through weak C-H⋯π inter-actions.

Luminescence properties of a thermal-responsive organogel to various metal cations

A new gelator (L) containing Schiff base, benzoimidazol and naphthayl moieties was synthesized and its self-assembly was investigated in various solvents. Gelation test revealed that it could form a thermal-responsive gel in ethylene glycol (GL) or the mixture solution of ethylene glycol and DMF. Different fluorescence behaviors were observed upon adding different metal ions. The addition of Mg2+ maintained the gelating ability of L, meanwhile the Mg2+-ion-mediated organogel in ethylene glycol can enhance the fluorescence of GL. The addition of Al3+ can destroy GL and lead to a state transition from gel to clear solution; the solution can give a brilliant blue emission excited at 365nm UV. Interestingly, the luminescence of GL increased sharply at first but decreased finally. The fluorescence of GL was quenched when other metal cations were added.

2-Aminobenzothiazole Containing Novel Schiff Bases Derivatives: Search for New Antibacterial Agents

The benzothiazole and Schiff base moieties are crucial functionalities due to their wide variety of biological activities and have a wide range of therapeutic properties. Keeping in view the importance of these organic moieties, a new series of 2-Aminobenzothiazole containing novel Schiff bases derivatives were synthesized by sequential reaction. The structures of the synthesized compounds were confirmed by their analytical and spectral data. The synthesized compounds were evaluated for their in vitro antibacterial activity against gram positive and gram negative bacteria. Synthesized compounds showed significant activity against microorganisms, which can be correlated with the privileged heterocyclic structural scaffolds.

2-Aminobenzothiazole Containing Novel Schiff Bases Derivatives: Search for New Antibacterial Agents

The benzothiazole and Schiff base moieties are crucial functionalities due to their wide variety of biological activities and have a wide range of therapeutic properties. Keeping in view the importance of these organic moieties, a new series of 2-Aminobenzothiazole containing novel Schiff bases derivatives were synthesized by sequential reaction. The structures of the synthesized compounds were confirmed by their analytical and spectral data. The synthesized compounds were evaluated for their in vitro antibacterial activity against gram positive and gram negative bacteria. Synthesized compounds showed significant activity against microorganisms, which can be correlated with the privileged heterocyclic structural scaffolds.

Synthesis of Schiff base-Based 1,2,4-Oxadiazole Derivative as Fluorescence Turn-On Sensor for High Selectivity of Pb(2.).

A new probe based on oxadiazole derivative (OXD) containing Schiff base moiety was synthesised as fluorescence turn-on sensor S1 . Furthermore, its fluorescents spectra (FS) result demonstrate that S1 selectively senses bivalent lead ion (Pb(2+)) in HEPES buffer solution (10mM, pH = 7.0,DMF-H2O, 9:1, v/v), so S1 was a viable candidate as fluorescent receptor for a new Pb(2+) sensor. And the results of fluorescent spectral titration showed this sensor formed 1:1complex with Pb(2+).