Heterocyclic Schiff Base Research Articles

Synthesis of a new heterocyclic Schiff base ligand “(E)-5-benzoyl-4-phenyl-1-((pyridin-2-ylmethylene) amino) pyrimidin-2(1H)-one”: An experimental and computational modeling study

In this study, a new heterocyclic Schiff base has been synthesized and characterized using FT-IR, NMR (1H NMR, 13C NMR), UV–Vis, Mass spectroscopies and single-crystal X-ray diffraction method. The molecular geometry obtained from the X-ray structure determination was optimized using Density Functional Theory (DFT/B3LYP) method with the 6-31G+(d, p) basis set in ground state. From the optimized geometry of the title molecule, the geometric parameters (bond lengths, bond angles and torsion angles), vibrational wavenumbers and chemical shifts were computed. In addition, the molecular electrostatic potential (MEP), frontier molecular orbitals (FMOs) and nonlinear optical (NLO) property of this molecule were determined using a DFT protocol at the B3LYP/6-31+G (d, p) level. For the purpose of the structural conformity of the title molecule, the theoretical results were compared with the experimental values. This comparison indicated that the theoretically calculated results are in agreement with the experimental data on the whole.

ESIPT reaction of potential bioactive heterocyclic Schiff base: Atomic visualization coupled with in vitro spectroscopy

Abstract The present study epitomizes the identification of ground state geometry, determination of X-ray structure and solvent dependent excited state intramolecular proton transfer (ESIPT) process of a potential bioactive benzothiazole Schiff base ligand viz (E)-2-((6-chlorobenzo[d]thiazol-2-ylimino)methyl)-5-(diethylamino)phenol (CBMDP) using 1H and 13C NMR, FTIR, single crystal XRD, electronic absorption, steady state emission, time resolved and 3D-fluorescence spectroscopic techniques. The experimental observations have further been corroborated with quantum chemical calculations using Density Functional Theory (DFT) and Time Dependent DFT (TDDFT) methods. Single crystal X-ray structure confirms the existence of enol-imine (N) form of CBMDP in the ground state due to strong intramolecular hydrogen bond between phenolic hydrogen and azomethine nitrogen. The photophysical studies reveal that on photoexcitation, the molecule undergoes structural changes via ESIPT reaction. Dual emission have been identified from the excited enol-imine (N*) and tautomeric keto-amine (T*) species in non-polar heptane. The redistribution of the electron density in the photoexcited CBMDP molecule is visualised from DFT and TDDFT calculations. This electronic redistribution enhances the in basic character of azomethine nitrogen which is reflected in the Mulliken partial atomic charges increases from −0.21 to −0.56, which ultimately leads to an intramolecular hydroxyl proton transfer in the excited state. The simultaneous emission from two states are also theoretically supported by the low energy difference (0.66 kcal/mol) between the N* and T* form in the potential energy surface diagram. The consolidated spectroscopic research, described herein, provides enormous information to open up the new avenues in designing and synthesizing potential bioactive benzothiazole Schiff bases for medicinal chemistry research.

Synthesis, antimicrobial activities and QSAR studies of heterocyclic Schiff base ligands with organosilicon(IV) halides

A series of heterocyclic Schiff base ligands 4-hydroxy-3-[1-{(2-hydroxy-aryl) imino}-ethyl]-6-methyl-pyran-2-one; aryl = phenyl, 4-methylphenyl, 4-chlorophenyl or 4-nitrophenyl (1–4) and their organosilicon(IV) complexes R2Si(L) (R = Et, Bu or Ph) (5–16) were synthesized and characterized. The elemental analyses, molar conductance and spectral (IR, 1H, 13C and 29Si NMR) data suggested pentacoordinated environment around the silicon atom, where tridentate ligands coordinate through the azomethine nitrogen and oxygen of hydroxyl groups. The ligands and their organosilicon complexes were tested in vitro against pathogenic bacteria and fungi to assess their antimicrobial properties. The activity of the ligands improved against most of the strains of the tested microorganisms on complexation to the organosilicon groups. The antimicrobial activities were correlated with QSAR studies using the linear free energy relationship model which indicate the importance of topological parameters, third-order and valence first-order molecular connectivity indices (3 χ v and 1 χ v ), to explain the antibacterial and antifungal activities of all synthesized compounds.

Spectroscopic and electrochemical investigations and antibacterial activity of binuclear Pd(II) and Pt(IV) complexes of newly synthesized tridentate heterocyclic compounds

New Pd(II) and Pt(IV) binuclear complexes with two heterocyclic Schiff base ligands of type ONO derived from condensation of salicylaldehyde with 4-aminoantipyrine have been synthesized and characterized using elemental analysis, IR, electronic absorption spectra, magnetic moments. It has been found that the stoichiometric ratio is metal:ligand (2:2) with Pd(II) or Pt(IV) ions forming binuclear complexes. The electrochemistry of the Pt complexes for Pt(IV)/Pt(II) redox couple was investigated by cyclic voltammetry. According to molar conductance, the complexes may be formulated as [Pd 2 (L1) 2 ], [Pt 2 (L1) 2 (H 2 O) 4 ]Cl 2 , [Pd 2 (L2) 2 ]Cl, and [Pt 2 (L2) 2 (H 2 O) 4 ]Cl 3 . On the basis of the magnetic moments, square planar geometry is suggested for Pd(II) complexes and octahedral geometry is suggested for Pt(IV) complexes. The antibacterial activity of the ligands and complexes were assessed against Gram‐positive bacteria B. subtilis and S. aureus and Gram‐negative bacteria S. typhi and Salmonella spp.

Novel Zinc(II) Complexes of Heterocyclic Ligands as Antimicrobial Agents: Synthesis, Characterisation, and Antimicrobial Studies.

The synthesis and antimicrobial activity of novel Zn(II) metal complexes derived from three novel heterocyclic Schiff base ligands 8-[(Z)-{[3-(N-methylamino)propyl]imino}methyl]-7-hydroxy-4-methyl-2H-chromen-2-one, 2-[(E)-{[4-(1H-1,2,4-triazol-1-ylmethyl)phenyl]imino}methyl]phenol, and (4S)-4-{4-[(E)-(2-hydroxybenzylidene)amino]benzyl}-1,3-oxazolidin-2-one have been described. These Schiff base ligands and metal complexes are characterised by spectroscopic techniques. According to these data, we propose an octahedral geometry to all the metal complexes. Antimicrobial activity of the Schiff base ligand and its metal complexes was studied against Gram negative bacteria: E. coli and Pseudomonas fluorescens, Gram positive bacteria: Staphylococcus aureus, and also against fungi, that is, C. albicans and A. niger. Some of the metal complexes show significant antifungal activity (MIC < 0.2 μg/mL). The “in vitro” data has identified [Zn(NMAPIMHMC)2]·2H2O, [Zn(TMPIMP)2]·2H2O, and [Zn(HBABO)2]·2H2O as potential therapeutic antifungal agents against C. albicans and A. niger.

Spectrophotometric and spectrofluorimetric studies of novel heterocyclic Schiff base dyes

Novel heterocyclic Schiff base dyes were prepared by the reaction of salicylaldehyde/2-Hydroxy-1-naphthaldehyde with different heterocyclic amines. Results of the newly synthesized compounds established by FT-IR, 1H-NMR, 13C-NMR and GC–MS spectroscopic experiments were consistent with their chemical structures. Resulted heterocyclic Schiff base dyes were found to be pure from data obtained by the elemental analysis. In addition, spectrophotometric and spectrofluorimetric studies showed that these dyes were good absorbent and fluorescent. Fluorescence polarity study data revealed that some of these compounds were sensitive to the polarity of the microenvironment provided by different solvents. Time-based fluorescence steady-state measurements also showed that these heterocyclic Schiff base dyes have high photostability against photobleaching.

Synthesis, spectroscopic and physicochemical investigations of environmentally benign heterocyclic Schiff base derivatives as antibacterial agents on the bases of in vitro and density functional theory

A series of Schiff bases were synthesized by the reaction of 4-dimethylamino-benzaldehyde and corresponding active amines under microwave irradiation. Results obtained from spectroscopic (FT-IR, 1H NMR, 13C NMR, GC–MS) and elemental analyses of synthesized compounds were in a very good agreement with their chemical structures. UV–Vis and fluorescence spectroscopy measurements provided that all compounds are good absorbent and fluorescent. Fluorescence polarity study demonstrated that these compounds were sensitive to the polarity of the microenvironment provided by different solvents. In addition, spectroscopic and physicochemical parameters, including singlet absorption, extinction coefficient, Stokes shift, oscillator strength and dipole moment, were investigated in order to explore the analytical potential of synthesized compounds. The antibacterial activity of these compounds was first studied in vitro by the disk diffusion assay against two Gram-positive and two Gram-negative bacteria. The minimum inhibitory concentration was then determined with the reference of standard drug tetracycline. The results displayed that compound 1 was better inhibitors of both types of the bacteria (Gram-positive and Gram-negative) than tetracycline. Based on the density functional theory calculations, LUMO and density of compounds (1–5) were calculated to support the antibacterial activities.

Co(II) and Cd(II) Complexes Derived from Heterocyclic Schiff-Bases: Synthesis, Structural Characterisation, and Biological Activity

New monomeric cobalt and cadmium complexes with Schiff-bases, namely, N′-[(E)-(3-hydroxy-4-methoxyphenyl)methylidene]furan-2-carbohydrazide (L1) and N′-[(E)-(3-hydroxy-4-methoxyphenyl)methylidene]thiophene-2-carbohydrazide (L2) are reported. Schiff-base ligands L1 and L2 were derived from condensation of 3-hydroxy-4-methoxybenzaldehyde (iso-vanillin) with furan-2-carboxylic acid hydrazide and thiophene-2-carboxylic acid hydrazide, respectively. Complexes of the general formula [M(L)2]Cl2 (where M = Co(II) or Cd(II), L = L1 or L2) have been obtained from the reaction of the corresponding metal chloride with the ligands. The ligands and their metal complexes were characterised by spectroscopic methods (FTIR, UV-Vis, 1H, and 13C NMR spectra), elemental analysis, metal content, magnetic measurement, and conductance. These studies revealed the formation of four-coordinate complexes in which the geometry about metal ion is tetrahedral. Biological activity of the ligands and their metal complexes against gram positive bacterial strain Bacillus (G+) and gram negative bacteria Pseudomonas (G−) revealed that the metal complexes become less resistive to the microbial activities as compared to the free ligands.

Synthesis of Peony-Like Cu(II) Complexes of Schiff Base Derived from 3,4-Dimethoxybenzaldehyde and p-Aminobenzoic Acid

Schiff bases and their metal complexes have been continuous received intensively attentions not only due to the easy with which they can be synthesized, but also owing to their widely range of potential applications in co-ordination chemistry, medicinal chemistry, catalysis, optical and magnetic materials. Schiff base ligands can coordinate with metal ions (transitionor alkali-) to form various Schiff base chelating complexes through O-, N-donors on the imino groups (-C=N-). These ligands have shown fascinating properties in antimicrobial, antifungal, anticancerous and antiproliferative activities. For example, Shebl et al. reported that Co(II), Ni(II) and Cu(II) of mono-, bi-and tri-nuclear metal complexes of a new Schiff base ligand was found to be biologically active. They showed high antimicrobial activity against gram positive bacteria, gram negative bacteria and fungi. Arjmand et al. synthesized a new chiral heterocyclic Schiff base moduted Cu(II) complexes, which exhibited a remarkable DNA cleavage activity with CT-DNA in presence of different activators compare to classical anticancer drug cisplatin. And also, flexible catalysis are exhibited by varieties of metal complexes of Schiff bases. A new oxovanadium(IV) was investigated by Grivani et al. which was very active and selective in the epoxidation of cyclooctene under optimized condition. Synthesis of Peony-Like Cu(II) Complexes of Schiff Base Derived from 3,4-Dimethoxybenzaldehyde and p-Aminobenzoic Acid

Synthesis, spectroscopic characterization, solid state d.c. electrical conductivity and biological studies of some lanthanide(III) chloride complexes with a heterocyclic Schiff base ligand

Condensation of 2-hydroxy-1-naphthaldehyde with 2-amino-3-carboxyethyl-4,5-dimethylthiophene in 1:1molar ratio, yielded a potentially tridentate Schiff base viz. 2-[N-(2′-hydroxy-1-naphthylidene)amino]-3-carboxyethyl-4,5-dimethylthiophene (HNAT). This ligand formed complexes with lanthanum(III), cerium(III), praseodymium(III), neodymium(III), samarium(III), europium(III) and gadolinium(III) chloride under well defined conditions. These complexes were characterized through elemental analysis, molar conductance, magnetic moment measurements, IR, UV–Vis, FAB mass and 1H NMR spectral studies. Analytical data showed that all the metal complexes exhibited 1:1 metal–ligand ratio. Molar conductance values adequately confirmed the non-electrolytic nature of the metal complexes. The proton NMR spectral observations supplement the IR spectral assignments. The spectral data revealed that the ligand acted as neutral tridentate, coordinating to the metal ion through azomethine nitrogen, ester carbonyl and naphtholate oxygen without deprotonation. The ligand and its lanthanum(III) chloride complex were subjected to XRD studies. The lanthanum(III) chloride complex has undergone a facile transesterification reaction. The solid state d.c. electrical conductivity of some selected complexes were measured as a function of temperature, indicating the semiconducting nature of the metal complexes. The antimicrobial activities were examined by disk diffusion method against some pathogenic bacterial and fungal species.

Corrosion Inhibition Study of a Heterocyclic Schiff Base Derived from Isatin

A Schiff base, 3-(phenylimino)indolin-2-one, was successfully obtained from the condensation reaction of isatin and aniline in absolute ethanol with a yield of 72%. The ligand was successfully characterized via physical and spectroscopic techniques namely melting point, Elemental Analysis (C, H, N), 1H Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FTIR) Spectroscopy. The corrosion inhibiting property of the Schiff base and that of a mixture of its starting materials on mild steel in 1 M HCl solution was studied through Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization Resistance (LPR). The concentration of the Schiff base and the precursor molecules were varied from 1 x 10-3 M to 1 x 10-5 M. The results showed that the percentage of inhibition efficiencies increased with the increase of compound’s concentrations. Comparing the two sets of results for the Schiff base and the mixture of its starting materials, it was shown that the Schiff base was a much better inhibitor than the mixture of the starting materials, clearly indicating the importance of the presence of imine group (C=N) bearing lone pairs of electrons and π electrons in corrosion inhibition.

Physico-chemical studies on some fluorescence sensors: DFT based ESIPT process

A group of novel heterocyclic Schiff base derivatives were synthesized and characterized by NMR spectra, mass and CHN analysis. Excited state intramolecular proton transfer (ESIPT) processes in o-hydroxy Schiff base have been studied using electronic spectral studies. Experimental and FT studies support that trans enol form predominates over the cis enol form. The fluorescence of Schiff bases quenched markedly with the gradual addition of Cu2+. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the Schiff base derivatives were performed and discussed. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state. The charge distribution has been calculated from the atomic charges by non-linear optical (NLO) and natural bond orbital (NBO) analysis. The energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels and the molecular electrostatic potential (MEP) energy surface studies evidenced the existence of intramolecular charge transfer (ICT) within the molecule.

Spectroscopic, Thermal, and Antimicrobial Studies of Co(II), Ni(II), Cu(II), and Zn(II) Complexes Derived from Bidentate Ligands Containing N and S Donor Atoms

Two new heterocyclic Schiff bases of 4-amino-5-mercapto-3-H/propyl-1,2,4-triazole and 5-nitrofurfuraldehyde [HL1-2] and their cobalt, nickel, copper, and zinc complexes have been synthesized and characterized by elemental analyses, spectral (UV-Vis, IR, 1H NMR, Fluorescence, and ESR) studies, thermal techniques, and magnetic moment measurements. The heterocyclic Schiff bases act as bidentate ligands and coordinate with metal ions through nitrogen and sulphur of the thiol group. The low molar conductance values in DMF indicate that the metal complexes are nonelectrolytes. The magnetic moments and electronic spectral data suggest octahedral geometry for the Co(II), Ni(II), and Zn(II) complexes and square planar for Cu(II) complexes. Two Gram-positive bacteria (Staphylococcus aureus MTCC 96 and Bacillus subtilis MTCC 121), two Gram-negative bacteria (Escherichia coli MTCC 1652 and Pseudomonas aeruginosa MTCC 741), and one yeast, Candida albicans, were used for the evaluation of antimicrobial activity of the newly synthesized compounds.

Spectroscopic Characterization and Biological Activity of Mixed Ligand Complexes of Ni(II) with 1,10-Phenanthroline and Heterocyclic Schiff Bases.

Mixed ligand complexes of Ni(II) with 1,10-phenanthroline (1,10-Phen) and Schiff bases L1(MIIMP); L2(CMIIMP); L3(EMIIMP); L4(MIIMNP); L5(MEMIIMP); L6(BMIIMP); L7(MMIIMP); L8(MIIBD) have been synthesized. These metal chelates have been characterized by elemental analysis, IR, 1H-NMR, 13C-NMR, Mass, UV-Vis, magnetic moments, and thermogravimetric (TG&DTA) analysis. Spectral data showed that the 1,10-phenanthroline act as neutral bidentate ligand coordinating to the metal ion through two nitrogen donor atoms and Schiff bases acts as monobasic bidentate coordinating through NO donor atoms. All Ni(II) complexes appear to have an octahedral geometry. The antimicrobial activity of mixed ligand complexes has been studied by screening against various microorganisms, it is observed that the activity enhances upon coordination. The DNA binding studies have been investigated by UV-Vis spectroscopy, and the experimental results indicate that these complexes bind to CT DNA with the intrinsic binding constant Kb = 2.5 ± 0.2 × 105 M−1. MTT is used to test the anticancer effect of the complexes with HL60 tumor cell. The inhibition ratio was accelerated by increasing the dosage, and it had significant positive correlation with the medication dosage.

Binuclear Cu(II) and Co(II) Complexes of Tridentate Heterocyclic Shiff Base Derived from Salicylaldehyde with 4-Aminoantipyrine

New binuclear Co(II) and Co(II) complexes of ONO tridentate heterocyclic Schiff base derived from 4-aminoantipyrine with salicylaldehyde have been synthesized and characterized on the bases of elemental analysis, UV-Vis., FT-IR, and also by aid of molar conductivity measurements, magnetic measurements, and melting points. It has been found that the Schiff bases with Cu(II) or Co(II) ion forming binuclear complexes on (1 : 1) “metal : ligand” stoichiometry. The molar conductance measurements of the complexes in DMSO correspond to be nonelectrolytic nature for all prepared complexes. Distorted octahedral environment is suggested for metal complexes. A theoretical treatment of the formation of complexes in the gas phase was studied, and this was done by using the HyperChem-6 program for the molecular mechanics and semi-empirical calculations. The free ligand and its complexes have been tested for their antibacterial activities against two types of human pathogenic bacteria: the first type (Staphylococcus aureus) is Gram positive and the second type (Escherichia coli) is Gram negative (by using agar well diffusion method). Finally, it was found that compounds show different activity of inhibition on growth of the bacteria.

Electrochemical and Gravimetric Corrosion Inhibition Investigations of A Heterocyclic Schiff Base Derived From 3- Formylindole

The corrosion inhibition efficiency of Schiff base, 3-formylindole-3-aminobenzoic acid (3FI3ABA) on mild steel (MS) in 1.0 M HCl solution have been investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies. 3FI3ABA exhibited good inhibition on mild steel in HCl medium even at low concentrations and the inhibition efficiencies increases with increase in concentration of the inhibitor. The adsorption of inhibitor on the surfaces of the corroding metal obeys Langmiur isotherm. Polarization studies revealed that 3FI3ABA act as a mixed type inhibitor. Thermodynamic parameters (Kads, ∆G 0 ads) were calculated using Langmiur adsorption isotherm.

Synthesis and Bioactivity of Three-Ring Heterocyclic Schiff Base Derivatives

Ten novel three-ring heterocyclic Schiff-base derivatives were designed and synthesized. Their structures of all these compounds were confirmed by H NMR, C NMR, IR spectra and elemental analysis. The preliminary result of bioassay showed that the title compounds exhibited some degree of antifungal activities on G. zeae, C. mandshurica and F. oxysporum under 50 mg/L concentration.

DNA interaction, antimicrobial, electrochemical and spectroscopic studies of metal(II) complexes with tridentate heterocyclic Schiff base derived from 2′-methylacetoacetanilide

A new Schiff base ligand (HL) was synthesized by the condensation reaction between 2′-methyleacetoacetanilide and 2-amino-3-hydroxypyridine. Its Co(II), Ni(II), Cu(II) and Zn(II) complexes were prepared by the interaction of the ligand with metal(II) chloride. They were characterized by elemental analysis, IR, 1H NMR, EPR, UV–Vis, magnetic susceptibility measurements, conductivity measurements and FAB-mass spectra. The interaction of the complexes with calf thymus DNA (CT-DNA) has been investigated by UV absorption, viscosity and cyclic voltammetry methods, and the mode of CT-DNA binding to the complexes has been explored. Furthermore, the DNA cleavage activity by the complexes was performed. It was found to be oxidative hydroxyl radical cleavage in the presence of 3-mercaptopropionic acid (MPA). The Schiff base and its complexes have been screened for their antibacterial ( Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa) and antifungal ( Aspergillus niger, Rhizopus stolonifer, Rhizoctonia bataicola and Candida albicans) activities and the data reveal that the complexes have higher activity than the free ligand.

Synthesis, characterization and biological studies on some transition metal complexes derived from a heterocyclic Schiff base ligand

Synthesis, characterization and biological studies on some transition metal complexes derived from a heterocyclic Schiff base ligand

ChemInform Abstract: The Asymmetric Transfer Hydrogenation of Benzoylpyridine: Preparation and Crystal Structure of Chiral Heterocyclic Schiff Base Ligands.

AbstractTwo new, optically active heterocyclic Schiff bases (I) are synthesized and successfully applied as ligands in the Ir‐catalyzed transfer hydrogenation of 4‐benzoylpyridine.