Heterocyclic Schiff Base Ligands Research Articles

Unveiling Anti-Malarial, Antimicrobial, Antioxidant Efficiency and Molecular Docking Study of Synthesized Transition Metal Complexes Derived From Heterocyclic Schiff Base Ligands.

Malaria, a persistent and ancient adversary, continues to impact vast regions worldwide, afflicting millions and severely affecting human health and well-being. Recently, despite significant progress in combating this parasitic disease, malaria remains a major global health concern, especially in areas with limited resources and vulnerable populations. Consequently, identifying and developing effective agents to combat malaria and its associated dysfunctions is essential therefore the two new Schiff base ligands incorporated Co(II), Ni(II), Cu(II) and Zn(II) ions were synthesized and thoroughly characterized. The synthesized compounds were assessed for in vitro anti-malarial and antimicrobial efficacy, compounds (9, 10) demonstrated highest potential with IC50=1.08±0.09 to 1.18±0.04 μM against P. falciparum and MIC=0.0058 μmol/mL against C. albicans and E. coli, respectively. The complexes (5, 6) were effectively reduce mitigate oxidative stress with lowest IC50 value of 2.69±0.12 to 2.87±0.09 μM. Moreover, the biological findings were reinforced by a molecular docking investigation involving the potential compounds (2, 7-10) against dihydroorotate dehydrogenase and sterol 14-alpha demethylase proteins which exposed complex's excellent biological response than their parent ligands. ADMET profiling was used to confirm the compounds' oral drug-like features. This research offers promising prospects for future multi-functional drug innovations targeting malaria, pathogenic infections, and oxidative stress.

Synthesis, structure elucidation, antioxidant, antimicrobial, anti-inflammatory and molecular docking studies of transition metal(II) complexes derived from heterocyclic Schiff base ligands

Synthesis, structure elucidation, antioxidant, antimicrobial, anti-inflammatory and molecular docking studies of transition metal(II) complexes derived from heterocyclic Schiff base ligands

Transition metal complexes of triazole-based bioactive ligands: synthesis, spectral characterization, antimicrobial, anticancer and molecular docking studies

In the present research work, four new heterocyclic Schiff base ligands (1–4) were synthesized by the condensation of 4-(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl)phenol with salicylaldehyde derivatives in 1:1 molar ratio. The synthesized Schiff base ligands were allowed for complexation with Co(II), Ni(II), Cu(II), Zn(II) metal ions. The structure of the newly synthesized compounds (1–20) was elucidated with the help of various spectral and physicochemical techniques. Spectroscopic data confirm the tridentate nature of ligands which coordinate to the metal via deprotonated oxygen, azomethine nitrogen and thiol sulphur. Conductivity data showed the non-electrolytic nature of complexes. Furthermore, the synthesized compounds were evaluated for their in-vitro antimicrobial activity against four pathogenic bacterial strains and two pathogenic fungal strains. The observed results of microbial activity reveals that compound 3 and its complexes (13–16) were found most potent against the pathogenic strains. In addition, the anticancer activity of all the synthesized compounds was evaluated against human carcinoma cell lines i.e. HCT-116, DU145 and A549 using MTT assay. Among the tested compounds 12, 19, and 20 were found to show promising potency against the cancer cell lines. To rationalize the preferred modes of interaction of most potent compounds with the active site of human EGFR protein (PDB id: 5XGM), molecular docking studies were performed.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s11164-021-04621-5.

Synthesis, characterization and quantum-chemical investigations of new fluorescent heterocyclic Schiff-base ligands and their cobalt(II) complexes

Two new fluorescent heterocyclic Schiff base ligands were synthesized and characterized by elemental analyses, IR, mass, and NMR spectra. Results from NOESY experiment confirmed the E configuration of Schiff-bases. Coordination of the bidentate ligands with Co(II) cation led to the formation of deep green complexes. The structures of the complexes have been confirmed by spectral, analytical data and Job’s method. Schiff-base ligands and cobalt complexes were spectrally characterized by UV–Vis and fluorescence spectroscopy. An efficient charge transfer of electron from p-orbital on ligand to Co(II) d-orbital can be proposed as the main reason for the color of the complexes. In addition, the DFT methods were employed to achieve deeper insight into geometry, spectral properties and energy difference between the HOMO and LUMO frontier orbitals of the synthesized compounds. The DFT-calculated spectral properties are in good agreement with the experimental values, confirming suitability of the optimized geometries for Co(II) complexes.

Design, synthesis, spectral, antibacterial activities and quantum chemical calculations of new Cu (II) complexes of heterocyclic ligands

New Cu (II) complexes were obtained by reaction of Cu (II) cation with new heterocyclic Schiff base ligands derived from benzo[1,2-c]isoxazoles. The ligands and their Cu (II) complexes were characterized by elemental analyses, IR, mass, and NMR spectra. The optical properties of the compounds were also investigated by UV–Vis and fluorescence spectroscopy. The DFT methods were employed to achieve deeper insight into geometry, spectral properties and energy difference between the frontier orbitals of the ligands and their Cu (II) complexes. The DFT-calculated spectral properties are in good agreement with the experimental values, confirming suitability of the optimized geometries for Cu (II) complexes. In addition, the new ligands and their Cu (II) complexes demonstrated potent antibacterial activity against a panel of strains of Gram negative bacterial and Gram positive species and their MIC was also determined. The results revealed that Cu (II) complexes, displayed greater antibacterial activity against Gram-negative and Gram positive bacteria than did the well known antibacterial agent Sulfamethoxazole.

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.

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.

Synthesis, characterization and crystal structure of some bidentate heterocyclic Schiff base ligands of 4-toluoyl pyrazolones and its mononuclear Cu(II) complexes

We depict the synthesis of a new set of six bidentate heterocyclic Schiff base ligands, formed by the condensation of three different 4-toluoyl pyrazolones with various aromatic amines in ethanolic medium. All of these ligands have been characterized on the basis of elemental analysis, IR, 1H NMR, 13C NMR and Mass spectral data. The molecular geometries of three of these ligands have been determined by single crystal X-ray study. It reveals that these ligands exist in amine-one tautomeric form in the solid state. The reaction of these ligands with copper(II) resulted in the formation of mononuclear complexes having the general composition [CuL 2(H 2O) 2] with two water molecules at axial positions. These complexes have been characterized on the basis of elemental analysis, Cu-estimation, molar conductivity, magnetic measurements, IR, UV–Visible, FAB–Mass, TG–DTA–DSC data, cyclic voltametric measurements and ESR spectral studies. ESR spectra and magnetic susceptibility measurements indicates distorted octahedral stereochemistry of Cu(II) complexes, while non-electrolytic behaviour of complexes indicates the absence of counter ion.

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

Two optically active heterocyclic imine ligands 3 (3a and 3b) have been synthesised for the iridium catalysed asymmetric transfer hydrogenation of 4-benzoylpyridine. 3b was characterised by single crystal X-ray diffraction analysis. The two ligands (3a and 3b) were applied to Ir-catalysed asymmetric transfer hydrogenation of 4-benzoylpyridine using 2-propanol as a source of hydrogen. The results showed that the corresponding chiral alcohol could be obtained with moderate yield and enantioselectivity at an optimum temperature.

Spectral, magnetic, biocidal screening, DNA binding and photocleavage studies of mononuclear Cu(II) and Zn(II) metal complexes of tricoordinate heterocyclic Schiff base ligands of pyrazolone and semicarbazide/thiosemicarbazide based derivatives

We depict the synthesis and characterization of copper(II) and zinc(II) coordination compounds of 4-(3',4'-dimethoxybenzaldehydene)2-3-dimethyl-1-phenyl-3-pyrazolin-5-semicarbazone (1a), 4-(3',4'-dimethoxybenzaldehydene)2-3-dimethyl-1-phenyl-3-pyrazolin-5-thiosemicarbazone (1b), 4-(3'-hydroxy-4'-nitrobenzaldehydene)2-3-dimeth yl-1-phenyl-3-pyrazolin-5-semicarbazone (1c) and 4-(3'-hydroxy-4'-nitrobenzal dehydene)2-3-dimethyl-1-phenyl-3-pyrazolin-5-thiosemicarbazone (1d). All the remote compounds have the general composition [ML(2)] (M=Cu(II) and Zn(II)); L=Schiff base (1a-1d). All the complexes were characterized by elemental analysis, molar conductivity, IR, (1)H NMR, UV-vis, ESI-Mass, magnetic susceptibility measurements, cyclic voltammetric measurements, and EPR spectral studies. It has been originated that the Schiff bases with Cu(II) and Zn(II) ions form mononuclear complexes on 1:2 (metal:ligand) stoichiometry. Distorted octahedral environment is suggested for the metal complexes. The conductivity data confirm the non-electrolytic nature of the complexes. The interaction of CuL(2)(1a-1d) complexes with CT DNA was investigated by spectroscopic, electrochemical and viscosity measurements. Results suggest that the copper complexes bind to DNA via an intercalative mode. Moreover, the complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365 nm. The Schiff bases and their metal complexes were screened for their antifungal and antibacterial activities against different species of pathogenic fungi and bacteria and their biopotency has been discussed.

Synthesis, Spectroscopic Characterization, Thermal Investigation and Antimicrobial Activity of S, O and N-Donor Heterocyclic Schiff Base Ligands and their Co(II), Cd(II), Hg(II), Fe(III) and UO2(II) Metal Complexes

Synthesis, Spectroscopic Characterization, Thermal Investigation and Antimicrobial Activity of S, O and N-Donor Heterocyclic Schiff Base Ligands and their Co(II), Cd(II), Hg(II), Fe(III) and UO2(II) Metal Complexes

Complexation of 4-amino-1,3 dimethyl-2,6 pyrimidine-dione derivatives with cobalt(II) and nickel(II) ions: synthesis, spectral, thermal and antimicrobial studies

Four heterocyclic Schiff-base ligands derived from condensation of 4-amino-1,3 dimethyl-2,6 pyrimidine-dione with 2-hydroxybenzaldehyde, 2-methoxybenzaldehyde, 4-hydroxy-3-methoxybenzaldehyde and 4-(dimethylamino) benzaldehyde, (HL1, L2, HL3and L4), respectively, and their Co(II) and Ni(II) complexes have been prepared and characterized via elemental analysis, molar conductance, magnetic moment, thermal and XRPD analysis as well as spectral data (IR, 1H-NMR, mass and solid reflectance). IR data reveal that the ligands are bidentate neutral ligands except HL1, which is monobasic tridentate with coordination sites azomethine (N), carbonyl (O) and phenolic (O). Conductance data suggest that all complexes are non-electrolytes, except cobalt(II) complexes of L2and HL3are 1 : 1 electrolytes. The mass spectra confirm the proposed structure of the ligands and their complexes. The solid reflectance spectral data and magnetic moment measurements suggest octahedral, tetrahedral and square planar geometrical structures for the metal complexes. The spectral data were utilized to compute the important ligand field parameters B, β and Dq; LFSE also was calculated. The thermal behavior is also studied. Antibacterial and antifungal properties of the ligands and their complexes show broad-spectrum activities and the metal complexes show higher activity than the free ligands.

Synthesis and Spectral Characterization of Some Transition Metal Complexes Containing Pentadentate SNNNS Donor Heterocyclic Schiff Base Ligands

A new Schiff base, 2,6-diacetylpyridine bis(3-methylsulfhydryl-4-amino-5-mercapto-1,2,4-triazole) (DPMAMT) is designed and synthesized by the condensation of 2,6-diacetylpyridine with 3-methylsulfhydryl-4-amino-5-mercapto-1,2,4-triazole, and structurally characterized. Copper(II), cobalt(II), nickel(II), manganese(II), zinc(II), cadmium(II) and oxovanadium(IV) complexes of DPMAMT have been prepared for the first time, and characterized on the basis of elemental analyses, conductance measurements, magnetic properties, spectral (i.r., 1H-n.m.r., u.v.–vis., e.p.r. and FAB-mass) and thermal studies. The complexes exhibit an octahedral geometry around the metal center. The pentadentate behavior of the ligand was confirmed on the basis of spectral studies.

Ruthenium(III) Schiff base complexes of [ONNO]-type mediated transfer hydrogenation of ketones

Stable ruthenium(III) Schiff base complexes of general formula [RuX(EPh 3)(LL′)] (X = Cl or Br; E = P or As; LL′ = [ONNO] donor of the heterocyclic Schiff base ligands) are accessible via simple and convenient synthesis. The complex [RuCl(PPh 3)(DHAphen)] is found to be efficient catalyst in the transfer hydrogenation of ketones in an excellent conversion up to 99% in the presence of isopropanol/KOH.

Isomeric complexes of ruthenium(II) with neutral heterocyclic schiff base ligands. High resolution proton resonance spectra of trans- cis isomeric pairs of RuX 2L 2 (L  2-arylpyridinecarboxaldimine, X  Cl, Br) and comparison of their physical properties

The reaction of 2-arylpyridinecarboxaldimine [RH 4C 6NC(H)Py, L ( 1)] with hydrated RuX 3 (X  Cl, Br) in boiling C 2H 5OH affords dark crystals of RuX 2L 2. Two geometrical isomers of the compound have been isolated and characterized by analytical and spectroscopic data. The trans isomer of RuCl 2L 2 shows a single sharp band for ν(RuCl), whereas two bands are observed for the corresponding cis isomer. The highresolution 1H NMR spectra of the isolated complexes are reported and completely assigned. All the complexes have multiple t 2→π *(L) transitions in the visible region. Each of the complexes display a quasi-reversible oxidative response due to an Ru III/Ru II couple in the range 0.25–0.40 V vs S.C.E. at a platinum working electrode. The formal potentials of this couple obey the Hammett relationship. The ligand-based irreversible oxidations are also briefly noted.