Synthesis,spectral characterization,X-ray crystal structure,electrochemical studies,and DNA interactions of a Schiff base pro-ligand and its homobimetallic complexes containing the cysteamine moiety

A Schiff base, N,N′-(3,4-dithiahexane-1,6-diyl)bis(5-methylsalicylideneimine), was synthesized and characterized by X-ray crystallography. Dimeric complexes of nickel(II), palladium(II), and vanadium(IV) were synthesized by the reactions of the Schiff base with nickel(II) acetate, palladium(II) acetate, and vanadyl acetylacetonate in 1:1 molar ratio. In all three complexes, the thiol group was deprotonated and coordinated to the metal. The X-ray structure of the Schiff base showed that in the crystalline form, the SH groups were oxidized to the corresponding disulfide. In the dimeric complexes, coordination took place through the azomethine nitrogen, enolic oxygen, and sulfur atoms. The metal-to-ligand ratio was 1:1, and molar conductance data revealed that the metal complexes were nonelectrolytes. The free Schiff base and its complexes showed photoluminescence in methanol at room temperature. The redox behavior of the compounds was studied by cyclic voltammetry in DMF, which showed both quasi-reversible and irreversible processes. The interaction of the complexes with DNA was investigated by electronic absorption spectroscopy.     

Europium and terbium Schiff base peptide complexes as potential antimicrobial agents against <Emphasis Type="Italic">Salmonella typhimurium</Emphasis> and <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>

Eu(III) and Tb(III) Schiff base complexes are applicable in various fields such as sensing, assays, screening protocols in vitro, and imaging studies in vitro or in vivo. Fluorescent europium and terbium complexes and their interaction with cell penetrating peptide (KKKRKC) can represent an excellent key for understanding pathway of peptide transportation though cell membrane and the application of Schiff base complexes as potential antibacterial drugs. The Schiff base–metal complexes and its conjugates with peptide were tested for their antibacterial activity against Pseudomonas aeruginosa and Salmonella typhimurium. Schiff base–metal complexes conjugated with peptide show minor toxicity in normal human PNT1A cells and high antibacterial activity against P. aeruginosa and S. typhimurium, where IC50 down to 125.9 and/or 36.1 µM were found for P. aeruginosa and S. typhimurium, respectively. Our results strongly suggest that Schiff base–metal complexes conjugated with peptide have great potential to be developed into highly effective antibacterial drug.     

Synthesis,structural and spectroscopic properties of asymmetric Schiff bases derived from 2,3-diaminopyridine

Two Schiff base derivatives, 4-(2-amino-3-pyridyliminomethyl)phenol (I) and 3-(2-amino-3-pyridyliminomethyl)nitrobenzene (II), were synthesised and characterised by spectroscopy. The structure of I was determined by single crystal X-ray diffraction studies. The asymmetric Schiff base derived from 2,3-diaminopyridine selectively recognise transition and heavy metal cations, and some anion. Ligands I and II form stable complexes with Cu²⁺, Zn²⁺, Pb²⁺, Al³⁺ whereas ligand I also binds F~ ions. The stoichiometry for the host: cation is 1: 1 and 2: 1. The addition of F~ ion in CH₃CN to ligand I causes a colour change of the solution from colourless to yellow. The binding behaviour of ligand I towards several ions was investigated using density functional theory calculations.     

Synthesis of silver(I) and palladium(II) <Emphasis Type="Italic">N</Emphasis>-heterocyclic carbene complexes and their use as catalysts for the direct C5 arylation of heteroaromatic compounds

Silver(I) N-heterocyclic carbene complexes were synthesized in good yields by the reactions of 1,3-dialkylperhydrobenzimidazolium salts with silver(I) oxide in dichloromethane. The silver complexes were used as carbene-transfer agents to synthesize palladium(II) N-heterocyclic carbene complexes. All of the complexes were characterized by physicochemical and spectroscopic methods. The new palladium complexes were tested as catalysts in the direct C5 arylation of 2-n-butylfuran, 2-n-butylthiophene and 2-n-propylthiazole with aryl bromides at 130 °C in N,N-dimethylacetamide. The arylation reactions proceeded selectively at the C5 position of the heteroaromatic compounds, and the corresponding coupling products were obtained in moderate to good yields by using 0.5 mol% of the palladium complex.     

Synthesis,characterization, spectroscopic and catalytic oxidation studies of Fe(III), Ni(II), Co(III), V(IV) and U(VI) Schiff base complexes with N,O donor ligands derived from 2,3-diaminopyridine

Fifteen new complexes of transition metals were designed using three Schiff base ligands and aldol condensation of 2,3-diaminopyridine with 5-R-2-hydroxybenzaldehyde (R = F, Cl, Br) in the 1:2 molar ratio. The tetradentate ligands N,N′-bis(5-R-2-hydroxybenzaldehyde) pyridine were acquired with the common formula H₂[(5-R-sal)₂py] and characterized by IR, UV–Vis spectra, ¹H-NMR and elemental analysis. These ligands produce 1:1 complexes M[(5-R-sal)₂py] with Fe(III), Ni(II), Co(III), V(IV) and U(VI) metal ions. The electronic property and nature of complexes were identified by IR, UV–Vis spectra, elemental analysis, X-ray crystallography and cyclic voltammetric methods. The catalytic activity of complexes for epoxidation of styrene with UHP as primary oxidant at minimal temperature (10 °C) has been planned. The spectral data of the ligands and their complexes are deliberate in connection with the structural changes which happen due to complex preparation. The electrochemical outcome has good conformability with what suggested for electronic interaction among metal center and ligand by the UV–Vis and IR measurements.     

Synthesis,X-ray crystal structures,and antibacterial activities of Schiff base nickel(II) complexes with similar tetradentate Schiff bases

Two new mononuclear complexes, [NiL¹] · CH₃OH (I) and [NiL²] (II), have been prepared from the tetradentate Schiff bases N,N'-bis(5-methylsalicylidene)ethylenediamine (H₂L¹) and N,N'-bis(5-methylsalicylidene)- o-phenylenediamine (H₂L₂), respectively. The complexes have been characterized by physico-chemical and spectroscopic methods, as well as single-crystal X-ray determination (CIF files nos. 1428969 (I), 1428968 (II)). Complex I crystallizes in the triclinic space group P1 with a = 6.7387(14), b = 10.7010(17), c = 12.681(2) Å, α = 87.059(2)°, β = 88.828(2)°, γ = 89.901(2)°, V = 913.0(3) ų, Z = 2. Complex II crystallizes in the monoclinic space group P2₁/n with a = 12.1437(11), b = 8.0537(8), c = 18.4545(18) Å, β = 105.088(2)°, V = 1742.7(3) ų, Z = 4. The nickel atoms in the complexes are coordinated by two phenolate O and two imine N atoms of the tetradentate Schiff base ligands, forming square planar coordination. The complexes and the Schiff base compounds were assayed for antibacterial activities against three Gram-positive bacterial strains (B. subtilis, S. aureus, and St. faecalis) and three Gram-negative bacterial strains (E. coli, P. aeruginosa, and E. cloacae) by MTT method. As a result, the complexes showed effective antimicrobial activity against the microorganisms tested.     

Synthesis,crystal structures,and antibacterial activity of copper(II) and cobalt(III) complexes derived from 2-[(2-dimethylaminoethylimino)methyl]-4-methylphenol

A new tetranuclear copper(II) complex (I) and a new mononuclear cobalt(III) complex (II) have been synthesized from the Schiff base compound 2-[(2-dimethylaminoethylimino)methyl]-4-methylphenol. The complexes have been characterized by physico-chemical and spectroscopic methods, as well as single crystal X-ray determination (CIF files CCDC nos. 1447778 (I) and 1447779 (II)). The Cu atoms in complex I are in square pyramidal coordination, and the Co atom in complex II is in octahedral coordination. Crystal structures of the complex are stabilized by hydrogen bonds and π···π interactions. The complexes and the Schiff base compound were assayed for antibacterial activities against three Gram-positive bacterial strains (B. subtilis, S. aureus, and St. faecalis) and three Gram-negative bacterial strains (E. coli, P. aeruginosa, and E. cloacae) by MTT method. As a result, the complexes showed effective antimicrobial activity against the microorganisms tested.     

Synthesis,crystal structures,and antibacterial activities of Schiff base nickel(II) and cadmium(II) complexes with tridentate Schiff bases

Reaction of tridentate Schiff bases with nickel and cadmium salts in methanol afforded two new mononuclear complexes, [Ni(L¹)₂] (I) and [Cd(L²)₂] (II), where L¹ and L² are the anions of 2-bromo-4-chloro-6-[(3-dimethylaminopropylimino)methyl]phenol (HL¹) and 2-bromo-4-chloro-6-[(3-morpholin-4-ylpropylimino)methyl]phenol (HL²), respectively. The complexes were characterized by singlecrystal X-ray diffraction (CIF files CCDC nos. 1428653 (I) and 1428654 for (II)), FT-IR, and elemental analysis. Complex I crystallizes in the monoclinic space group P2 ₁/c, with a = 8.8216(8), b = 14.0424(8), c = 11.8687(12) Å, β = 111.238(2)°, V = 1370.4(2) ų, Z = 2. Complex II crystallizes in the monoclinic space group P2 ₁/n, with a = 9.6774(4), b = 15.8970(6), c = 20.3144(7) Å, β = 90.408(2)°, V = 3125.1(2) ų, Z = 4. The metal atoms in the complexes are coordinated by two tridentate Schiff base ligands, forming octahedral coordination. The free Schiff bases and the complexes were assayed for antibacterial activities. Both complexes are more active against the bacteria than the free Schiff bases. Complex II has the MIC value of 0.39 μg mL^–1 against Bacillus subtilis.     

Syntheses,characterization, crystal structures and fluorescence property of Zinc(II) complexes with Schiff bases

Two new mononuclear Schiff base zinc(II) complexes, [ZnCl₂(L¹)] ? MeOH (I) and [Zn(L²)₂] (II) (L¹ = 2-bromo-4-chloro-6-[(2-ethylammonioethylimino)methyl]phenolate; L² = 2-bromo-4-chloro-6-(isopropyliminomethyl)phenolate), have been prepared and characterized by elemental analyses, infrared and UV-Vis spectroscopy, and single-cyrstal X-ray diffraction (CIF files CCDC nos. 1408962 (I), 1408961 (II)). Complex I crystallizes in the triclinic space group \(P\overline 1\) with unit cell dimensions a = 9.859(1), b = 13.015(2), c = 19.817(3) Å, α = 73.591(2)°, β = 76.032(2)°, γ = 82.966(2)°, V = 2363.0(5) ų, Z = 4, R ₁ = 0.0925, and wR ₂ = 0.2257. Complex II crystallizes in the monoclinic space group P2₁/c with unit cell dimensions a = 7.6387(7), b = 22.307(2), c = 21.443(2) Å, β = 96.216(3)°, V = 3632.4(6) ų, Z = 8, R ₁ = 0.0651, and wR ₂ = 0.1100. The both Zn atoms in I is four-coordinated in a tetrahedral geometry by the NO donor set of the Schiff base ligand, and two Cl ligands. The Zn atom in II is in a tetrahedral geometry by two N and two O atoms from two Schiff base ligands. Crystals of the complexes are stabilized by hydrogen bonds and weak π…π interactions. Fluorescence property of the complexes have been determined.     

Syntheses,crystal structures and in vitro anticancer activities of oxovanadium(IV) complexes of amino acid Schiff base and 1,10-phenanthroline ligands

Four oxovanadium(IV) complexes, namely [VO(desa-met)(phen)]·MeOH·2H₂O (1) (desa-met = Schiff base derived from 4-(diethylamino)salicylaldehyde and dl-methionine, phen = 1,10-phenanthroline), [VO(o-van-met) (phen)]·MeOH·CH₂Cl₂·3H₂O (2) (o-van-met = Schiff base derived from o-vanillin and dl-methionine), [VO(dtbs-napa)(phen)]·2H₂O (3) (dtbs-napa = Schiff base derived from 3,5-di-tert-butyl salicylaldehyde and 3-(1-naphthyl)-l-alanine) and [VO(hyna-napa)(phen)]·1.5H₂O (4) (hyna-napa = Schiff base derived from 2-hydroxy-1-naphthaldehyde and 3-(1-naphthyl)-l-alanine), were synthesized and characterized by IR, HRMS, UV–vis spectra, molar conductance and single-crystal X-ray diffraction (XRD). X-ray structural analysis showed that the V(IV) atoms in all four complexes are six-coordinated in a distorted octahedral environment. In the crystals of complexes 1 and 2, π–π stacking interactions together with hydrogen bonds connect the molecular units into 2D networks. Meanwhile, CH–π stacking interactions are observed between the aromatic rings in the crystals of 1 and 4, while the π–π stacking interactions between aromatic rings in the crystals of 2 and 3 are arranged with a face-to-face mode. The in vitro anticancer activities of these complexes against A-549 and HeGp2 cells were tested by MTT assay.     

Crystal structure,DFT study,antimicrobial properties and DNA cleavage potential and thermal behavior of some new mercury complexes

In this study, a new bidentate Schiff base ligand (L) entitled as N,N’-bis(dimethylaminocinnamaldehyde)-2,2-dimethyl-1,3-propanediamine and its mercury complexes were synthesized. The Schiff base ligand and its complexes were characterized using FT-IR, ¹H-, ¹³C-NMR spectroscopy, molar conductivity and electronic spectral study. Regarding physical and spectral data, the general formula for the complexes was suggested as HgLX₂ (L = Schiff base ligand and X = Cl^?, Br^?, I^?, SCN^?, N₃ ^?). For structural identification of these complexes, crystal structure of mercury iodide complex was analyzed as typical one. In the structure of this complex, Hg ion is surrounded by 2 iodide ions and 2 N atoms from the Schiff base ligand to form a four-coordinated mercury complex in triclinic system with space group of P ₁. Angular index (τ ₄) value was evaluated equal to 0.85, so the geometry around the mercury ion in this complex can be described as trigonal pyramid. A layered supramolecular structure for HgLI₂ complex is stabilized by C–H···I and C–H···π interactions in solid state. DFT study on the ligand and its complexes was also carried out, and then some calculated and experimental structural parameters of HgLI₂ were compared. Thermal behaviors of the titled compounds were investigated by thermogravimetric analyses. Furthermore, biological properties of the ligand and its complexes were examined against some Gram-negative and Gram-positive bacteria and also against 2 fungi. Finally, the interaction of the ligand and its complexes with DNA was investigated by electrophoresis method.     

Synthesis,crystal structures,and antibacterial activities of Schiff base zinc(II) complexes [Zn(L<Superscript>1</Superscript>)<Subscript>2</Subscript>] and [Zn(L<Superscript>2</Superscript>)<Subscript>2</Subscript>]

The reaction of cyclopentylamine with 2-hydroxy-1-naphthaldehyde and 5-nitrosalicylaldehyde, respectively, in methanol affords two new Schiff bases, 1-(cyclopentyliminomethyl)naphthalen-2-ol (HL¹) and 4-nitro-2-(cyclopentyliminomethyl)phenol (HL²). Two new zinc(II) complexes, [Zn(L¹)₂] (I) and [Zn(L²)₂] (II), derived from the Schiff bases, have been prepared and characterized by single-crystal X-ray diffraction, FT-IR, and elemental analysis. Complex I crystallizes in the monoclinic space group P2₁/c with a = 17.834(4), b = 14.738(3), c = 9.868(2) Å, β = 91.20(3)°, V = 2593.1(9) ų, Z = 4. Complex II crystallizes in the triclinic space group P \(\bar 1\) with a = 10.206(1), b = 10.502(1), c = 12.554(1) Å, α = 66.771(2)°, β = 78.133(2)°, γ = 76.292(2)°, V = 1191.8(1) ų, Z = 2. The Zn atom in each complex is coordinated by two N and two O atoms from two Schiff base ligands, forming a tetrahedral geometry. The Schiff bases and the complexes were assayed for antibacterial activities.     

Synthesis and spectral properties of unsymmetrical benzoporphyrins containing phenoxy groups or quinoxaline fragments

Condensation of phthalimide and 4-tert-butylphthalimide with zinc(II) acetate gave 3-(3-oxo-2,3-dihydro-1H-isoindol-1-ylidenemethyl)-1H-isoindol-1-one and 5-tert-butyl-3-(5-tert-butyl-3-oxo-2,3-dihydro-1H-isoindol-1-ylidenemethyl)-1H-isoindol-1-one, respectively. Their reactions with 4-phenoxyphthalimide and quinoxaline-2,3-dicarboximide in the presence of Zn(OAc)₂ led to the formation of zinc complexes of cis-4,4′-diphenoxytetrabenzoporphyrin and cis-di(4-tert-butylbenzo)diquinoxalinoporphyrin. The complexes were converted into the free bases by treatment with sulfuric acid. Spectral properties of the obtained porphyrin derivatives were studied.     

Synthesis,characterization, and crystal structures of two Schiff base zinc(II) complexes with urease inhibitory activities

Two Schiff base zinc(II) complexes, [ZnBr₂L¹] · 2CH₃OH (I) (I) and [ZnBr₂L²] (II), where L¹ is 4-chloro-2-[(2-piperazin-1-ylethylimino)methyl]phenol and L² is 4-chloro-2-[(3-diethylaminopropylimino)methyl]phenol were synthesized and structurally characterized. The crystal of I is monoclinic: space group P2₁/c, a = 9.831(3), b = 18.680(6), c = 11.879(4) Å, β = 94.660(6)°, V = 2174.3(11) ų, Z = 4. The crystal of II is monoclinic: space group P2₁/n, a = 7.2310(14), b = 16.037(3), c = 15.856(3), β = 90.01(3)°, V = 1838.7(6) ų, Z = 4. The Zn atom in each complex is four-coordinated by one phenolate O and one imine N atoms of the Schiff base ligand and two bromide atoms, forming a tetrahedral coordination. The urease inhibitory activities of the complexes were evaluated.     

Reaction of apple pectin modified by pharmacophores,with copper(II) cations

The reaction of apple pectin modified by organic pharmacophores (nicotinic, salicylic, 5-aminosalicylic, and anthranilic acids) with Cu(II) cations was studied by spectral methods. The compositions of the complexes were determined and their stability constants, as well as the thermodynamic parameters (ΔH ⁰, ΔG ⁰, ΔS ⁰) of the complex formation were calculated. The structure of the drug in the polymeric ligand was found to affect certain physicochemical properties of the metal complexes.     

Synthesis,crystal structure,and fluorescence properties of a two-dimensional copper(II) complex with Schiff base

A new Schiff base ligand C₁₉H₁₃NO₅(H₂L) was synthesized using 2-aminoterephthalic acid and 2-hydroxy-1-naphthaldehyde. A complex of this ligand [Cu(C₁₉H₁₁NO₅)(C₂H₆O)] _n was synthesized and characterized by IR, UV, fluorescence spectroscopy and X-ray diffraction single-crystal analysis. The crystal crystallizes in the monoclinic system, space group Pbca with a = 8.7745(18), b = 18.613(4), c = 24.644(5) Å, V = 4024.9(14) ų, Z = 8, F(000) = 1816, S = 1.009, ρ _calcd = 1.462 g cm^?3, μ = 1.122 mm^?1, the final R = 0.0477 and wR = 0.1594 for 4609 observed reflections (I > 2σ(I)). The Cu(II) is five-coordinated by one N atom and two O atoms from the Schiff base ligand and two carboxylate O atoms from another two ligands to form a distorted square-pyramidal geometry. Each ligand serves as a bridging ligand to link Cu²⁺ ions, leading to a two-dimensional coordination polymer. The fluorescence properties of the ligand and complex were also studied. The ligand shows strong fluorescence, and the fluorescence intensity is weakened after the Cu(II) complex formed.     

6,6'-[piperazine-1,4-diylbis(methylene)]bis[3,5-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-1,2- benzoquinone]: Synthesis and properties

Preparation method is developed for a new 6,6'-[piperazine-1,4-diylbis(methylene)]bis[3,5-di(tert-butyl)- 1,2-benzoquinone], including the stage of 3,5-di(tert-butyl)pyrocatechol aminoalkylation by Mannich reaction followed by oxidation. The molecular structure of one of its hydrolysis products, 4,6-di(tert-butyl)-2,3-dihydroxybenzaldehyde, is established by X-ray diffraction (XRD) analysis.     

Synthesis,structure, and antimicrobial activity of a cadmium(II) complex derived from N,N′-<Emphasis Type="Italic">bis</Emphasis>(5-chlorosalicylidene)propane-1,3-diamine

The Schiff base, N,N′-bis(5-chlorosalicylidene)propane-1,3-diamine (H₂L) derived from 5-chlorosalicylaldehyde and propane-1,3-diamine, and its cadmium(II) complex, bis(μ₂-acetato)bis(μ₂-N,N′-bis(5-chlorosalicylidene)-1,3-propanediamine)tricadmium(II) Cd[Cd(CH₃COO)L]₂ (I), have been prepared and characterized by elemental analyses, IR, and single-crystal X-ray diffraction analysis. The crystal of H₂L is monoclinic: space group P2₁/n, a = 11.252(4), b = 8.972(3), c = 16.981(6) Å, β = 96.005(4)°, V = 1705.0(10) ų, Z = 4. The crystal of complex I is monoclinic: space group P2₁/c, a = 11.056(1), b = 22.284(2), c = 8.398(1) Å, β = 91.779(1)°, V = 2068.0(3) ų, Z = 2. Complex I is a centrosymmetric trinuclear cadmium(II) complex. The deprotonated Schiff base ligand coordinates to the Cd atoms through the phenolate O and imine N atoms. The effect of the Schiff base ligand and the complex on the antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans was studied.     

Synthesis,crystal structures,and antimicrobial activity of a pair of isostructural dinuclear copper(II) complexes derived from 4-nitro-2-[(2-diethylaminoethylimino)methyl]phenol

A pair of isostructural azido- or thiocyanato-bridged centrosymmetric dinuclear copper(II) complexes, [Cu₂L₂(μ_1,3-N₃)₂] (1) and [Cu₂L₂(μ_1,3-NCS)₂] (2), derived from the Schiff base ligand 4-nitro-2-[(2-diethylaminoethylimino)methyl]phenol (HL), have been synthesized and characterized by elemental analysis, IR spectra and single crystal X-ray diffraction. Each Cu atom in the complexes is five-coordinate in a square pyramidal geometry by one O and two N atoms of one Schiff base ligand, and by two terminal donor atoms from two bridging azide or thiocyanate ligands. Both the azide and thiocyanate ligands adopt end-to-end bridging mode in the complexes. The distance between the two copper atoms is 5.205(2) Å for (1) and 5.515(2) Å for (2). The antimicrobial activity of the complexes has been tested.     

Supramolecular solid-state structure,potential energy surfaces and evaluation of antiproliferative effect of 2-benzothiazolylhydrazone derivatives in vitro

The in situ condensation reaction of 2-hydrazinobenzothiazole with salicylaldehyde, 3,4-dihydroxybenzaldehyde, 2,4-dihydroxybenzaldehyde, 2,5-dihydroxybenzaldehyde, 2,3-dihydroxybenzaldehyde, 2-hydroxy-1-naphthaldehyde, 2-methoxy-1-naphthaldehyde, 4-methoxy-1-naphthaldehyde and 6-methoxy-2-naphthaldehyde produced 9 hydrazone Schiff bases (L1–L9, respectively) which were identified and characterized by elemental analysis, IR and NMR spectroscopy. The crystal and molecular structures of four Schiff bases (L1, L7–L9) have been determined by the single-crystal X-ray diffraction method confirming the imino form of L1 and the amino tautomeric form of L7–L9 compounds. Molecular structure analysis also confirmed that reported compounds are E-isomers relative to exo C = N imino bond. The N_hydrazino–H group of amino tautomers forms N_hydrazino–H···N_thiazolyl intermolecular hydrogen bonds shaping molecules into R ₂ ² (8) rings, while imino tautomer of L1 forms C(4) infinite helical chains via N_thiazolyl–H···N_hydrazino type of intermolecular hydrogen bond. The methoxy group (L7–L9) further shaped these primary supramolecular synthons into different supramolecular arrangements via C–H···O, C–H···N and C–H···S intermolecular hydrogen bonds. The role of aryl substituents in the shaping and stabilization of supramolecular architectures of L1, L7–L9 is supported by quantum chemical calculations. Strong antiproliferative effects on tumor cells and cytotoxic effects on fibroblasts are shown for all ligands L1–L9 with exception of L6 and L7 that had no effect on fibroblast cells.