Acid Schiff Base Research Articles

Efficient Synthesis of a Schiff Base Copper(II) Complex Using a Microfluidic Device

The efficient synthesis of amino acid Schiff base copper(II) complexes using a microfluidic device was successfully achieved. Schiff bases and their complexes are remarkable compounds due to their high biological activity and catalytic function. Conventionally, products are synthesized under reaction conditions of 40 °C for 4 h using a beaker-based method. However, in this paper, we propose using a microfluidic channel to enable quasi-instantaneous synthesis at room temperature (23 °C). The products were characterized using UV–Vis, FT–IR, and MS spectroscopy. The efficient generation of compounds using microfluidic channels has the potential to significantly contribute to the efficiency of drug discovery and material development due to high reactivity.

Synthesis and Characterization of New Bis-Schiff Bases Linked to Various Imide Cycles

This research includes the synthesis of new bis-Schiff bases linked to different imide cycles. There were some steps involved in the synthesis of the novel Schiff bases with succinimide, phthalimide, tetrachlorophthalimide, and tetrabromophthalimide cycles. The first step involved the preparation of 4,4`-bis[(4-aminophenyl) methyl benzylidene]tolidine (1) via the condensation reaction of 3,3'-dimethyl-(1,1'-biphenyl)-4,4'-diamine with 4-amino acetophenone. In the second step, compound 1 reacted with various cyclic anhydrides, affording bis-amic acid Schiff bases 2-5. In the third step, the products 2-5 were dehydrated using the fusion method to produce the target bis-imidyl Schiff bases 6-9. This work also involved the synthesis of bis-imidyl Schiff base 10 directly by fusion of compound 1 with 1,8-naphthalic anhydride. The prepared compounds were characterized depending on their FT-IR, 1H NMR, and 13C NMR spectra. The newly synthesized target compounds are expected to be very active biologically since their molecules are essential components of two active groups (imine and imide).

Preferential Enrichment of Enantiomer from Amino Acid Schiff Bases by Coordination Interaction and Crystallization.

In this paper, preferential enrichment (PE) is described for three pairs of novel amino acid Schiff base Cu(II)/Cu(I) complexes. Single crystal X-ray diffraction indicated that 1-S/R are one-dimensional coordination polymers (CPs) with helical structures, and 2-S/R and 3-S/R are one-dimensional CPs with auxiliary ligands. By tuning the pH, the solvent and second ligands, the 1-S/R, 3-S/R underwent polymorphic transitions, resulting in enantioselective liberation of excess enantiomers into solution, until the deposited crystals were slightly enriched with the opposite enantiomer, thereby successfully exhibiting PE. However, under the effects of Cu(II), the solvent and low pH, 2-S/R did not exhibit PE and resulted in enrichment of racemic compounds, which was attributed to amino acid Schiff base chiral complex mechanisms of PE. The three pairs of Cu complex structures were characterized by UV-vis, MS and X-ray photoelectron spectroscopy (XPS). All chiral properties were studied by circular dichroism (CD) in the solid and liquid.

Polymeric Copper(II) Complexes with a Newly Synthesized Biphenyldicarboxylic Acid Schiff Base Ligand—Synthesis, Structural and Thermal Characterization

The newly synthesized biphenyldicarboxylic acid Schiff base and its complexes with Cu(II) were synthesized, and their spectroscopic and structural analysis was performed. The reaction of the ligand and copper(II) acetate in different solvents resulted in the formation of two solvatomorphic complexes, one with MeOH, and the other with DMF molecules, in the crystal lattice. The differences in the results of the thermal analysis could be explained by the different polarities of the solvents present. SC-XRD analysis revealed that the ligand is coordinated as a dianion, in a pentadentate manner, through two phenoxide oxygen atoms, two azomethine nitrogen atoms, and with the oxygen atom of one carboxylate functioning as a bridge that connects the monomeric units. The coordination polyhedron was described with several parameters obtained from different methods of calculation. The presence of different solvents in the crystal structure results in differences in the H-bond networks, and an overall different crystal packing of the structural units in the obtained complexes.

Novel Enrofloxacin Schiff Base Metal Complexes: Synthesis, Spectroscopic Characterization, Computational Simulation and Antimicrobial Investigation against Some Food and Phyto-Pathogens

Condensation of the reaction between enrofloxacin and ethylenediamine in the existence of glacial acetic acid produced a new N,N-ethylene (bis 1-cyclopropyl-7-(4-ethylpiperazin-1-yl)-6-fluoro-1,4-dihydroquinoline-3-carboxylic acid Schiff base (H2Erx-en). H2Erx-en was used as a tetra-dentate ligand to produce novel complexes by interacting with metal ions iron(III), yttrium(III), zirconium(IV), and lanthanum(III). The synthetic H2Erx-en and its chelates had been detected with elemental analysis, spectroscopic methods, mass spectrometry, thermal studies, conductometric and magnetic measurements experiments. The calculated molar conductance of the complexes in 1 × 10−3 M DMF solution shows that iron(III), yttrium(III) and lanthanum(III) are 1:1 electrolytes, however the zirconium(IV) complex is non-electrolyte. The infrared spectra of H2Erx-en chelates indicated that the carboxylic group is deprotonated and H2Erx-en is associated with metals as a tetra-dentate through nitrogen and oxygen atoms. The disappearance of the carboxylic proton in all complexes corroborated information concerning H2Erx-en deprotonation and complexation with metal ions, according to 1H NMR data. Thermal analysis revealed the abundance of H2O particles in the chelates’ entrance and outlet spheres, indicating the disintegration pattern of H2Erx-en and their chelates. The Coats–Redfern and Horowitz–Metzeger approaches were utilized to calculate the thermodynamic items (Ea, ΔS *, ΔH *, and ΔG *) at n = 1 and n ≠ 1. The resulting data reveal better organized chelate building activation. Density functional theory (DFT) was created to properly grasp the optimal architecture of the molecules. The chelates are softer than H2Erx-en, with estimates varying between 95.23 eV to 400.00 eV, compared to 31.47 eV for H2Erx-en. The disc diffusion technique was utilized to assess H2Erx-en and their chelates in an antimicrobial assay against various food and phytopathogens. The zirconium(IV) chelate has the most potent antibacterial action and is particularly efficient against Salmonella typhi.

Schiff Base-functionalized Metal-organic Frameworks for Selective Sensing of Chromate and Dichromate in Water.

In this research, Zn- or Cd-based metal-organic frameworks (coded ZnMOF-1 and CdMOF-1) containing benzene-1,4-dicarboxylic acid (H2bdc) and pyridyl-based Schiff base (4-pyridylcarboxaldehydeisonicotinoylhydrazone (L)) dual ligands were successfully assembled via a conventional solvothermal method. The photoluminescence quenching response of ZnMOF-1 and CdMOF-1 and their sensing sensitivity and selectivity towards various inorganic anions were evaluated in aqueous media. Crystallographic and thermogravimetric studies confirm the formation of both MOFs with good crystallinity and thermal stability. Photoluminescence studies also verify the selectivity of ZnMOF-1 and CdMOF-1 for efficient sensing of inorganic oxyanions (like chromate/dichromate: CrO42- and Cr2O72-). Further, it was noted that only chromate/dichromate (CrO42-/Cr2O72-) anions showed a significant turn-off quenching effect while other anions (like F-, Br-, I-, Cl-, ClO4-, SCN-, SO42-, NO3-, and NO2-) have a low/negligible effect on the photoluminescence intensity of both MOFs. The limit of detection (LOD) of chromate/dichromate by ZnMOF-1 and CdMOF-1 was 9.79/10.94µM and 2.68/1.48µM, respectively. A probable mechanism for turn-off quenching response towards chromate and dichromate anions could be attributed to the spectral overlap of both excitation and emission spectra of ZnMOF-1/CdMOF-1 with the absorption spectra ofchromate/dichromate anions. As a result, the energy transfer from ZnMOF-1 or CdMOF-1 to the target chromate and dichromate anions decreased fluorescence intensity (i.e., fluorescence quenching effect).

Synthesis, structural characterization, and cytotoxic activity in tumor cells of Cu(II) and Co(II) complexes with o‐vanillin amino acids Schiff bases

Two new families of Cu(II) and Co(II) mononuclear complexes with mixed ligands, [Cu(VanTrpt)(bipy)]·MeOH (CuVanTrpt), [Cu(VanSer)(bipy)]·4H2O (CuVanSer), [Cu(VanTyr)(bipy)]·H2O (CuVanTyr), [Cu(VanThr)(bipy)]·MeOH (CuVanThr), [Co(VanTrpt)(bipy)(OH2)]·H2O·MeOH (CoVanTrpt), [Co(VanSer)(bipy)(OH2)]·MeOH (CoVanSer), [Co(VanTyr)(bipy)(OH2)]·3H2O·MeOH (CoVanTyr), and [Co(VanThr)(bipy)(OH2)] (CoVanThr), (VanX are Schiff base proligands resulted from the condensation of o‐vanillin with D,L‐tryptophan (VanTrpt), L‐serine (VanSer), L‐tyrosine (VanTyr), and L‐threonine (VanThr), respectively, and bipy is 2,2′‐bipyridine), have been obtained and characterized on the basis of elemental analysis, magnetic measurements, and spectral data (FT‐IR and UV–Vis–Nir spectroscopy). Crystal structures of CuVanTrpt, CuVanSer, and CuVanTyr have been solved by single‐crystal X‐Ray diffraction. Biological evaluation revealed that they are cytotoxic in HeLa (human carcinoma of the uterine cervix) and LSR‐SF‐SR (rat sarcoma induced by Rous sarcoma virus strain Schmidt‐Ruppin) cells, showing an enhancement of cytotoxicity dependent of concentration and treatment time. The most pronounced cytotoxic effect is expressed by CuVanSer and CoVanSer. Various cytopathological changes of both types of cancer cells were observed after treatment with Cu(II) and Co(II) complexes for 72 h at concentrations of 100 and 200 μg ml−1. LSR‐SF‐SR cells were found to be relatively more sensitive to the cytotoxic effect of the complexes investigated as compared to HeLa cells.

Synthesis, Identification and Antibacterial Activities of Amino Acid Schiff Base Cu(II) Complexes with Chlorinated Aromatic Moieties

Amino acid Schiff base Cu(II) complexes were synthesized under microwave irradiation using methanol as a solvent, to maximize the best conditions to obtain the attained compounds, containing aromatics possessing no, one or two chlorine atoms. The compounds’ antibacterial activities were tested against Gram-positive and Gram-negative bacteria, and the most active were tested for their antioxidant activities, and as E. coli, in particular, was found to be sensitive to these compounds, their interaction with this bacterium was investigated. It was found that, depending on the amino acid used for the formation of the Schiff base ligand, its LogPo/w mono-chlorinated or bis-chlorinated compounds are the most efficient against the tested bacteria.

Anti-tumor effect of novel amino acid Schiff base nickel (II) complexes on oral squamous cell carcinoma cells (CAL-27) in vitro

Anti-tumor effect of novel amino acid Schiff base nickel (II) complexes on oral squamous cell carcinoma cells (CAL-27) in vitro

Catalytic Dehydrogenative β-Alkylation of Amino Acid Schiff Bases with Hydrocarbon.

A synthetic method for the synthesis of a highly congested α,β-dehydroamino acid through the β-C-H bond activation of an amino acid Schiff base is described. Abundant hydrocarbon feedstock could be used as an alkylating reagent to afford an α,β-dehydroamino acid bearing a quaternary carbon at the γ-position with an exclusively (Z)-geometry. Notably, a tetrasubstituted olefin could be constructed from saturated starting materials. The transformation of the synthesized α,β-dehydroamino acid into unnatural α-amino acid derivatives was also demonstrated.

Spectroscopic study, theoretical calculations, and optical nonlinear properties of amino acid (glycine)-4-nitro benzaldeyhyde-derived Schiff base

Schiff base of amino acid salt: potassium 2-((4-nitrobenzylidene)amino)acetate 4 (C 9 H 7 KN 2 O 4 ), derived from the condensation reaction of amino acid (glycine) 1 and 4-nitro benzaldeyhyde 3 is synthesized and fully characterized by magnetic nuclear resonance ( 1 H and 13 C NMR), infrared (IR), mass, UV–visible spectroscopies and melting point. The optical nonlinear (ONL) properties of amino acid Schiff base salt 4 are studied using continuous wave (cw), visible, single transverse fundamental mode, low power, 473 nm laser beam. Ring diffraction patterns (RDPs) and Z-scan techniques are adopted to calculate the nonlinear index of refraction (NIR) together with testing the sample property of optical limiting (OLg). RDPs are simulated numerically using the integral of Fresnel-Kirchhoff and compared with experimental findings. • The Schiff base compound was synthesized and characterized by magnetic nuclear resonance ( 1 H and 13 C NMR). • We studied the nonlinear optical properties of Schiff base compound. • The nonlinear refractive index of this sample is determined using diffraction ring patterns and Z-scan techniques. . • Optical limiting threshold of Schiff base compound is found to be 9 mW.

Novel amino acid Schiff base Zn(II) complexes as new therapeutic approaches in diabetes and Alzheimer's disease: Synthesis, characterization, biological evaluation, and molecular docking studies.

Schiff bases are compounds that have gained importance in the paint industry due to their colorful nature and in the field of chemistry and biochemistry due to their biological activities. Various biological applications of Schiff bases, such as antitumor, antifungal, antibacterial, antioxidant, antituberculosis, and anthelmintic, have been widely studied. Within the scope of the study, 5-bromo-2-hydroxybenzaldehyde and amino acid methyl esters (isoleucine, phenylalanine, and methionine) and amino acid Schiff bases were synthesized first. The synthesis of the new Zn(II) complexes of these Schiff bases was carried out by the reaction of synthesized Schiff bases and Zn(OAc)2 ·2H2 O. The structures of the synthesized complexes were elucidated using elemental analysis, Fourier transform infrared, nuclear magnetic resonance, UV-visible, and thermal analysis spectroscopy techniques. These synthesized salts were found to be effective inhibitor compounds for the α-glycosidase, and acetylcholinesterase enzyme with Ki values in the range of 30.50 ± 3.82-38.17 ± 6.26 µM for α-glycosidase, 3.68 ± 0.54-10.27 ± 1.68 µM for butyrylcholinesterase, and 6.26 ± 0.83-15.73 ± 4.73 µM for acetylcholinesterase, respectively.

Antimicrobial Activities of Schiff Base Metal Complexes of First Transition Series

The correlative antimicrobial analysis of amino acid Schiff base and derivatized tren metal complexes: A= [MLCl2], B= [ML(CH3OH)2], respectively, against fungal strains, Candida parapsilosis, Candida albicans, Candida krusei, and Cryptococcus neoformans and (Gram-negative) P. aeruginosa, E. coli, S. typhimurium, and S. pyogenes, Methicillin-resistant Staphylococcus aureus (MRSA), S. mutans (Gram-positive) bacterial strains had been done by disk diffusion method following McFarland protocol. [CuLCl2] and [Cu (CH3OH)2] manifest overwhelming activity against microbes than other metal complexes of cobalt, nickel and zinc. Minimum inhibition concentration data also shows that copper complexes have the lowest MIC values against these tested microorganisms. The significance of this investigation is to uncover shielding and constructive therapeutic agents that wield against bacterial and fungal infection.

Punica granatum pericarp extract catalyzed green chemistry approach for synthesizing novel ligand and its metal(II) complexes: Molecular docking/DNA interactions

The gallic acid (GA) obtained from the ethanolic extract of Pomegranate(Punica granatum) pericarp, was successfully applied as a green and effective natural catalyst for the synthesis of novel quinoline based amino acid Schiff base ligand, L (C16H14N4O3) and its divalent metal complexes (where M = Fe(II), Co(II), Ni(II), Cu(II); L=(E)-2-(((2-hydroxyquinolin-3-yl)methylene)amino)-3-(1H-imidazol-5-yl)propanoic acid) through condensation of 2-hydroxyquinoline-3-carbaldehyde with L-histidine, employing a simple physical grinding technique. The ligand and the complexes denoted as [M(LH2)2] were characterized by advanced spectroscopic and analytical techniques. The configuration of the as synthesized complexes is deduced to be octahedral. The molecular docking experiments were performed by using an Autodock-4 tool to find the binding mode of the metal(II) complexes to B-DNA dodecamer. The metal complex interactions with CT-DNA were studied using spectroscopic techniques, viscosity analysis and thermal denaturation method. In UV-visible irradiation with pUC19 DNA the photo-induced cleavage studies interpreted the photonuclease characteristics of the metal(II) complexes.

New Amino Acid Schiff Bases as Anticancer Agents via Potential Mitochondrial Complex I-Associated Hexokinase Inhibition and Targeting AMP-Protein Kinases/mTOR Signaling Pathway.

Two series of novel amino acid Schiff base ligands containing heterocyclic moieties, such as quinazolinone 3–11 and indole 12–20 were successfully synthesized and confirmed by spectroscopic techniques and elemental analysis. Furthermore, all compounds were investigated in silico for their ability to inhibit mitochondrial NADH: ubiquinone oxidoreductase (complex I) by targeting the AMPK/mTOR signaling pathway and inhibiting hexokinase, a key glycolytic enzyme to prevent the Warburg effect in cancer cells. This inhibitory pathway may be an effective strategy to cause cancer cell death due to an insufficient amount of ATP. Our results revealed that, out of 18 compounds, two (11 and 20) were top-ranked as they exhibited the highest binding energies of −8.8, −13.0, −7.9, and −10.0 kcal/mol in the docking analysis, so they were then selected for in vitro assessment. Compound 11 promoted the best cytotoxic effect on MCF-7 with IC50 = 64.05 ± 0.14 μg/mL (0.135 mM) while compound 20 exhibited the best cytotoxic effect on MDA-231 with IC50 = 46.29 ± 0.09 μg/mL (0.166 mM) Compounds 11 and 20 showed significant activation of AMPK protein and oxidative stress, which led to elevated expression of p53 and Bax, reduced Bcl-2 expression, and caused cell cycle arrest at the sub-G0/G1 phase. Moreover, compounds 11 and 20 showed significant inhibition of the mTOR protein, which led to the activation of aerobic glycolysis for survival. This alternative pathway was also blocked as compounds 11 and 20 showed significant inhibitory effects on the hexokinase enzyme. These findings demonstrate that compounds 11 and 20 obeyed Lipinski’s rule of five and could be used as privileged scaffolds for cancer therapy via their potential inhibition of mitochondrial complex I-associated hexokinase.

Reduced Amino Acid Schiff Base‐Iron(III) Complexes Catalyzing Oxidation of Cyclohexane with Hydrogen Peroxide

AbstractThe reduced amino acid Schiff base ligands have been prepared and were coordinated with ferric chloride to generate the iron(III) complexes. The ligands and complexes have been characterized using FT‐IR, UV‐vis, elemental analysis, ICP‐AES analysis, mass spectra etc. After the structural characterization, these complexes were applied for the oxidation of cyclohexane using hydrogen peroxide as the oxidant under mild conditions. The activity tests showed that the L‐phenylalanine‐derived reduced Schiff base iron(III) complex(Ph−FeCl) afforded the highest yield of cyclohexanol and cyclohexanone(total yield up to 23.2 %). Notably, the Ph−FeCl complex catalyzes the reaction via a heterogeneous approach, allowing the complex to be separated and recycled conveniently after the oxidation reaction. Besides, the Ph−FeCl catalyst can also be extended for the selective oxidation of other alkanes and aromatics into alcohols, ketones and phenols etc. Finally, the reaction mechanism of cyclohexane oxidation on the iron(III) complex was proposed as well by the free radical inhibitors and EPR study of active intermediates.

Crystal structure and SOD activity of a hybrid lysozyme including an amino acid Schiff base copper complex

Crystal structure and SOD activity of a hybrid lysozyme including an amino acid Schiff base copper complex

Enhanced enantioselectivity in heterogeneous manganese-catalyzed asymmetric epoxidation with nanosheets modified amino acid Schiff bases as ligands by modulating the orientation and the arrangement order

Catalytic enantioselective epoxidation of olefins plays an important role in the production of optically-active epoxy. Transition-metal complexes prove efficient for the catalytic epoxidation of un-functionalized olefins by employing privileged chiral ligands with rotational symmetry and bulky substituents, which usually require complicated multistep synthesis and are often very expensive. Here, this work proposes an efficient strategy to promote the enantioselectivity of Mn(III)-catalyzed indene epoxidation, which simply utilizes the nanosheets of layered double hydroxides (LDHs) to modify α-amino acid derivatives as chiral ligands, achieving an enantioselectivity of more than 91.0%, much higher than that (<35%) in the previous reports using chiral ligands without any rotational-symmetry. By virtue of “flexible” interlayer spaces of LDHs, intercalated L-tert-leucine, L-valine, L-leucine, and L-phenylalanine anions have further been derived in situ to L-tert-leucine, L-valine, L-leucine, and L-phenylalanine Schiff base anions. Over the Mn(III) coordinated with L-phenylalanine Schiff base anion intercalated LDHs, an indene conversion of 81.0 ± 1.0%, a chem-selectivity of 89.0 ± 1.0%, and an enantiomeric excesses (ee) value of 94.5 ± 0.5% for (1S,2R)-1,2-epoxyindane have been afforded. The spatial effects of LDH nanosheets on the enantioselectivity have been investigated, focusing on the interlayer orientation and arrangement order of intercalated amino acid derivative anions. The strategy has been proved valid for the epoxidation of functionalized olefins, which is more challenging, including allylic alcohols, chalcone, and chromene derivatives.

Weakly Non-Covalent Docking of Amino-Acid Schiff Base Zn(II) Complex to Lysozyme

Artificial metal enzymes that combine proteins with synthesized unnatural metal complexes as cofactors are attracting attention. The preparation of artificial metal enzymes not only clarifies the behavior of metal ions in biology, but also leads to the development of synthetic chemistry fields such as the discovery of new catalytic reactivity and substrate selectivity that are not observed in nature. In addition, a certain Schiff base zinc (II) complex is known to exhibit antioxidant and anticancer activity, too. Therefore, in this study, we investigated a rapid synthesis method of two known amino acid Schiff base zinc (II) complexes using microwave method and the complexation of zinc (II) complex with chicken egg white lysozyme, which is a relatively low molecular weight protein. Furthermore, investigation of weakly non-covalent intermolecular interaction features between the zinc (II) complexes and lysozyme was also carried out using some spectroscopic measurements.

Mixed Ligand Oxovanadium (IV) Complexes of 5,6-Dimethyl-1,10-phenanthroline and Amino Acid Schiff Bases Containing Salicylaldehyde: Synthesis and Characterization with Antibacterial Properties

Mixed Ligand Oxovanadium (IV) Complexes of 5,6-Dimethyl-1,10-phenanthroline and Amino Acid Schiff Bases Containing Salicylaldehyde: Synthesis and Characterization with Antibacterial Properties