Schiff Base Type Research Articles

English

This study reported the synthesis of the new ligands, 3,4-methylenedioxybenzyl-S-benzyldithiocarbazate (L1), p-chloro-benzyl-S-benzyldithiocarbazate (L2) and 2,6-dichlorobenzyl-S-benzyldithiocarbazate (L3). These three schiff base type ligands were respectively obtained by means of the reaction of 3,4-methylenedioxybenzaldehyde, p-chlorobenzaldehyde and 2,6-dichlorobenzaldehyde with S-benzyldithiocarbazate, at molar ratio 1:1. The respective Cu(II) complex C1, C2 and C3 were synthesized by the reaction of L1, L2 or L3, with CuCl2.2H2O, at molar ratio 1:1. The chemical identification of ligands and respective complexes was established through spectroscopic data (FT-IR, UV-Vis and 1H NMR). The ligand and complexes were subjected to in vitro radial diffusion assays against the gram-negative bacteria Escherichia coli and gram-positive Staphylococcus aureus and the fungus Candida albicans and Saccharomyces cerevisiae, with good results for some of these compounds. Due to its promising antimicrobial property, complex C1 was subjected to EPR analyses aiming to establish its conformational structure. The prediction of biological activities of ligands and complexes were evaluated through the simulation carried out in silico using the web tools PASSonline and ChemMapper. Key words: Aryl-S-benzyldithiocarbazate, Cu(II) complexes, antimicrobial activity, PASSonline, ChemMapper

New Fe(II) complexes with Schiff base ligand: Synthesis, spectral characterization, magnetic studies and thermal stability

New ligand (Z)-2-(1-methyl-2-(pyridine-2-ylmethylene)hydrazinyl)benzoxazole (L) reacts with Fe(II) ions what results in formation of mononuclear complexes of 2:1 stoichiometry (complexes 1 and 2), which crystallize in the rare space group Ia–3d (No. 230) with solvent–acetonitrile–molecules in the crystal structure. Obtained complexes were studied in terms of their properties in the solid state concerning thermal stability and magnetism. N3-donor Schiff base type L is a strong crystal field ligand, therefore both obtained Fe(II) complexes are diamagnetic at room temperature what has been confirmed by magnetic susceptibility measurements and Mössbauer spectroscopy. However, the reversible LS (1A1)↔HS (5T2) spin-transitions may be observed starting above room temperature, remaining incomplete even up to 400K. The thermal stability and electronic reflectance spectra of complexes were determined as well.

New NO donor ligands and complexes containing furfuryl or crown ether moiety: Syntheses, crystal structures and tautomerism in ortho-hydroxy substituted compounds as studied by UV–vis spectrophotometry

NO donor ligands were prepared by the condensation of methoxy substituted salicylaldehyde with 5-methylfurfurylamine (1 and 2) and 4′-aminobenzo-15-crown 5 (3–5). New crown ether ligands of Schiff base type (3–5) containing recognition sites for alkali metal and transition guest cations. Ni(II) complexes (1a–5a) have been synthesized with bidentate NO donor Schiff base ligands (1–5) with Ni(CH3COO)2.·4H2O. Monotopic crystalline 1:1 (Na+:ligand) sodium complexes (3b–5b) of the crown ether ligands were also prepared. Schiff bases (1–5) and complexes (1a–5a, 3b–5b) were characterized by elemental analyses, FT-IR, 1H-, 13C-NMR and mass spectroscopies. The crystal structures of 1, 1a and 2 were verified by X-ray diffraction analysis. The tautomeric equilibria (phenol-imine, O–H⋯N and keto-amine, O⋯H–N forms) have been systematically studied by using UV–vis spectrophotometry for the o-hydroxy substituted compounds (1–5). The UV–visible spectra of these ligands (1–5) were recorded and commented in polar, non-polar, acidic and basic media.

Experimental, theoretical and docking studies of 2-hydroxy Schiff base type compounds derived from 2-amino-4-chlorobenzenethiol

We report here synthesis, DFT, Docking and Fluorescence studies of three Schiff base organic compounds viz. 2-{(E)-[(5-chloro-2-sulfanylphenyl)imino]methyl}phenol (1); 2,4-dichloro-6-{(E)-[(5-chloro-2-sulfanylphenyl)imino]methyl}phenol (2) and 2-{(E)-[(5-chloro-2-sulfanylphenyl) imino] methyl}-5-(diethylamino) phenol (3). These compounds have been characterized by elemental, FTIR, electronic and 1H NMR spectral techniques. Spectroscopic studies reveal that all the compounds exist in enol-form in the solid state whereas keto and enol, both forms exist in solution. The fluorescence behavior has been studied in DMF solvents and 1 &2 compound exhibit more efficient fluorescence properties. The molecular geometry of all the compounds in the ground state has been computed using the Hartree–Fock (HF) and density functional theory (DFT) with the 6-31++G basis set. The theoretical electronic absorption spectra of the compounds have been predicted using TD-DFT and TD-HF methods and compared with experimental spectral results. The predicted nonlinear optical properties of all the compounds are higher than those of urea. In addition to DFT calculations; frequency calculations, mulliken charge distribution, HOMO-LUMO and molecular electrostatic potential (MEP) have also been computed at the same level of theory. Molecular docking studies of the compounds in the active site of CAII (PDB code: 1CNX) have been performed to predict their possible binding modes in the active site of target carbonic anhydrase II enzyme.

Theoretical studies of organotin(IV) complexes derived from ONO-donor type schiff base ligands.

In this work a molecular modeling study was carried out based on a series of organotin(IV) derivatives which were complexed with ONO-Donor type Schiff base ligands to build up a statistical data pool for researchers. For this purpose, various properties of the selected complexes such as energies, band gaps, chemical reactivity descriptors, polarizabilities, geometric parameters, (1)H-NMR, (13)C-NMR chemical shifting values were obtained through density functional theory using B3LYP, CAM-B3LYP, TPSSTPSS, TPSSh, HCTH, wB97XD, and MN12SX functionals. Empirical dispersion corrections were incorporated for some functionals and solvent effects were also taken into account through applying polarizable continuum model (PCM). (1)H-NMR, (13)C-NMR chemical shifts were calculated via linear regression analysis using either gauge invariant atomic orbital (GIAO) or continuous set of gauge transformations (CSGT) methods. While structural properties were being explored, quantitative effects of utilized functionals and empirical dispersion corrections over calculated properties were shown in detail.

Discriminating detection of multiple analytes (F− and CN−) by a single probe through colorimetric and fluorescent dual channels

Two novel Schiff base type receptors containing phenol hydroxyl group (1) or methoxy group (2) were designed and synthesized. The receptor 1 with phenol hydroxyl group exhibited different colorimetric and fluorimetric responses to fluoride and cyanide ions. In the colorimetric channel, the colorless solution turned to yellow towards F−, but red in the presence of CN−. In the fluorimetric channel, the nonluminous solution showed different “turn-on” response to F− and CN−, respectively. The distinguishing responses of receptor 1 to the two anions in dual channels were attributed to the disparate interaction mechanisms. F− was detected through the formation of hydrogen bonds and the subsequent deprotonation process. CN− initially formed hydrogen bonds and then it attacked the receptor via a nucleophilic addition reaction. In contrast, the receptor 2 with methoxy group only showed remarkable color change from colorless to yellow towards F−. These results proved that the phenol hydroxyl group played an important role in the discriminating detection of F− and CN−.

Immobilization of collagen peptide on dialdehyde bacterial cellulose nanofibers via covalent bonds for tissue engineering and regeneration.

Bacterial cellulose (BC) is an alternative nanostructured biomaterial to be utilized for a wide range of biomedical applications. Because of its low bioactivity, which restricted its practical application, collagen and collagen hydrolysate were usually composited into BC. It is necessary to develop a new method to generate covalent bonds between collagen and cellulose to improve the immobilization of collagen on BC. This study describes a facile dialdehyde BC/collagen peptide nanocomposite. BC was oxidized into dialdehyde bacterial cellulose (DBC) by regioselective oxidation, and then composited with collagen peptide (Col-p) via covalent bonds to form Schiff’s base type compounds, which was demonstrated by the results of microstructures, contact angle, Col-p content, and peptide-binding ratio. The peptide-binding ratio was further affected by the degree of oxidation, pH value, and zeta potential. In vitro desorption measurement of Col-p suggested a controlled release mechanism of the nanocomposite. Cell tests indicated that the prepared DBC/Col-p composite was bioactive and suitable for cell adhesion and attachment. This work demonstrates that the DBC/Col-p composite is a promising material for tissue engineering and regeneration.

Spectral and thermal characterization of salophen type Schiff base and its implementation as solid contact electrode for quantitative monitoring of copper(II) ion

Salophen templated Schiff base 2,3-bis(salicylaldimino)pyridine (H2IF) has been synthesized and fully characterized by a series of different spectroscopic methods and thermogravimetric analysis (TGA). It has been also further probed electrochemically and explored as a cation recognition ionophore in the form of a polymeric membrane as selective sensor for quantitative monitoring of Cu2+. Dielectric properties of the membrane have been studied by electrochemical impedance spectroscopy (EIS). The potentiometric results have demonstrated that the sensor exhibits very good selectivity and sensitivity towards Cu2+ over a wide variety of cations. The electrode has a linear response to Cu2+ with a detection limit of 4.46×10−8 and displays a Nernstian slope (29.14mV/decade) between pH 3.0 and 6.0 with a fast response time less than 10s. The solid contact electrodes have been exploited over five mounts period with good reproducibility. The analytical availability of the proposed electrode has been evaluated by applying in the determination of Cu2+ ions in water samples. The structural features and complexation of ionophore with Cu2+ have been monitored by UV–Vis spectroscopy and spectral findings have been further supported by DFT and TD-DFT calculations.

Spin crossover behavior in a series of iron(III) alkoxide complexes.

The synthesis, crystal structures, magnetic behavior, and electron paramagnetic resonance studies of five new Fe(III) spin crossover (SCO) complexes are reported. The [Fe(III)N5O] coordination core is constituted of the pentadentate ligand bztpen (N5) and a series of alkoxide anions (ethoxide, propoxide, n-butoxide, isobutoxide, and ethylene glycoxide). The methoxide derivative previously reported by us is also reinvestigated. The six complexes crystallize in the orthorhombic Pbca space group and show similar molecular structures and crystal packing. The coordination octahedron is strongly distorted in both the high- and low-temperature structures. The structural changes upon spin conversion are consistent with those previously observed for [Fe(III)N4O2] SCO complexes of the Schiff base type, except for the Fe-O(alkoxide) bond distance, which shortens significantly in the high-spin state. Application of the Slichter-Drickamer thermodynamic model to the experimental SCO curves afforded reasonably good simulations with typical enthalpy and entropy variations ranging in the intervals ΔH = 6-13 kJ mol(-1) and ΔS = 40-50 J mol(-1) K(-1), respectively. The estimated values of the cooperativity parameter Γ, found in the interval 0-2.2 kJ mol(-1), were consistent with the nature of the SCO. Electron paramagnetic resonance spectroscopy confirmed the transformation between the high-spin and low-spin states, characterized by signals at g ≈ 4.47 and 2.10, respectively. Electrochemical analysis demonstrated the instability of the Fe(II) alkoxide derivatives in solution.

Mixed-Ligand Chelate Formation of Co(II), Ni(II), Cu(II) and Zn(II) Ions with Schiff Base as Main Ligand and Amino Acid as Co-Ligand

A bidentate NO type Schiff base ligand (L) has been obtained by the condensation reaction of 4dimethylaminobenzaldehyde and 2-aminophenol and used as main ligand and l-Alanine as coligand (L 2 ), Four novel mixed ligand chelates of composition [M(L 1 L 2 )(H2O)2].nH2O, where M represents, Co(II), Ni(II), Cu(II) and Zn(II) ions, in which n= 1, 1.7, 5 and 7 as sited later for chelates. The resulting Schiff base and the mixed ligand chelates were characterized by CHN elemental analysis, molar conductivity, magnetic moment, UV/Vis, IR, H-NMR and mass spectra. All the obtained physiochemical data showed an octahedral structures. Original Research Article El-ajaily et al.; IRJPAC, 5(3): 229-237, 2015; Article no.IRJPAC.2015.020 230

Azo linked thiourea based effective dual sensor and its real samples application in aqueous medium

The azo linked thiourea type Schiff base has been synthesized and characterized which is found to sense F−, AcO− and Cd2+ ions in aqueous medium over other anions and cations. R1 gave rise to significant changes in the absorption spectrum and 1H NMR spectroscopic studies upon the titration with F−, AcO−. R1 detects anions and metal ions at nanomolar level. F− ion detection property of R1 in aqueous medium was also extended to the real samples like toothpaste and mouthwash.

ChemInform Abstract: Anion Recognition by Simple Chromogenic and Chromo‐Fluorogenic Salicylidene Schiff Base or Reduced‐Schiff Base Receptors

AbstractReview: 41 refs.

Synthesis, structure and magnetic properties of homotrinuclear Ni(II) complexes with asymmetric Schiff-base ligands

By using 1,3-propanediamine, 2-hydroxyacetophenone and salicylaldehyde an asymmetric ONNO type Schiff base, N(hydroxyphenylidene)-N′(2-hydroxyacetophenylidene)-1,3-propanediamine (H2metsalpn), has been prepared and isolated. This Schiff base has been reduced yielding N(2-hydroxybenzyl)-N′[1-(2-hydroxyphenyl)ethyl]-1,3-diaminopropane (H2metsalpnH) These two ligands were used in preparing three trinuclear Ni(II) complexes with catena-[Ni3] structural motif, where DMF and carboxylato (formato, acetato, benzoato) ligands occur. These complexes were characterized by EA, IR, TG, DTA and MS data. The X-ray diffraction confirms that the Ni(II) central atoms are in a distorted octahedral coordination environment: the terminal centers possess {NiN2O4} octahedral coordination sphere whereas the very central atom possesses {NiO6} chromophore. The coordinated DMF groups are liberated between 140–240°C. The SQUID magnetometry confirms presence of weak exchange coupling of the antiferromagnetic nature, J/hc=−2 to −7cm−1, with a moderate single-ion anisotropy reflected by the zero-field splitting D/hc=+4 to +7cm−1.

Synthesis, Characterization And Mesomorphic Properties of Side Chain Liquid Crystalline Oligomer Having Schiff Base Type Mesogenic Group

A new liquid crystalline oligomer OLC was synthesized from its monomer having Schiff-base type mesogenic group MLC via free radical polymerization. The chemical structures of all compounds were confirmed using UV, FTIR, 1 H NMR, 13 C NMR and MS spectroscopy. Schiff-base type thermotropic system based on side chain oligomer containing long aliphatic branching was studied to determine the change in mesophase behaviour of the Schiff-base type mesogenic groups. A combination of differantial scanning calorimetry (DSC) and polarize optical microscopy (POM) demonstrated that the oligomer behaves similar to its monomer and both of them exhibit enantiotropic SmC and monotropic SmX mesophases. The oligomerization of the liquid crystal monomer gives rise to decreased transition temperatures whereas it has no influence on the type and stability of the mesophase formed. Namely, simply through oligomerization, we can greatly vary transition temperatures of the mesogenic groups.

Synthesis, characterization, DNA interaction and pharmacological studies of substituted benzophenone derived Schiff base metal(II) complexes

A new bidentate NO type Schiff base ligand (HL), derived from 2-hydroxy-4-methoxyphenyl)phenylmethanone with aniline and its metal(II) [M = Mn, Co, Ni, Cu and Zn] complexes has been synthesized. The synthesized ligand and the metal(II) complexes were structurally characterized by analytical, spectral (FT-IR, UV–vis., 1H NMR, FAB-Mass, TGA/DTA and EPR) as well as molar conductance and magnetic studies. All the complexes are non-electrolytes having 1:2 stoichiometry. They adopt tetrahedral and octahedral geometry. Thermal behavior of metal(II) complexes (1a–1c) shows loss of coordinated water molecules in the first step followed by the decomposition of ligand moieties in a respective manner and leads to form an air stable metal oxide as the final residue. Micro crystalline nature and the presence of coordinated water molecules have been confirmed by powder XRD, SEM and thermal analyses. The ligand and its complexes have efficient bio-efficacy, DNA binding and cleavage ability.

Magnetic Study of a Pentanuclear {Co2IIICo3II} Cluster with a Bent {CoII3} Motif

AbstractWe have synthesised and structurally characterised a new pentanuclear mixed‐valent cobalt cluster of formula [CoII3CoIII2(OH)2(piv)6(L)2(H2O)4] (piv = trimethylacetate, H2L = salicylideneanthranillic acid) from reaction of a dinuclear cobalt pivalate precursor with a Schiff base type ligand under mild reaction conditions. The core structure can be conveniently described as two fused Co3–μ3–OH triangles with a strict unique sharing vertex point. A complete picture of the magnetic behaviour of this compound is presented. Through combined use of susceptibility, magnetisation, and EPR data as well as broken‐symmetry DFT calculations, we have supported the magnetic data that show weak and anisotropic exchange interaction between CoII ions affording an Seff = 1/2 ground state that is not completely isolated from the low‐lying excited doublets at low temperature. Under the optimum applied field of 2 kOe, a frequency‐dependent out‐of‐phase susceptibility signal can be observed below 4 K. However, no reliable relaxation rates could be extracted due to the narrow temperature range in which this behaviour was observed.

Graphene Coupled Schiff‐base Porous Polymers: Towards Nitrogen‐enriched Porous Carbon Nanosheets with Ultrahigh Electrochemical Capacity

Schiff-base type porous polymer sheets with ultrahigh nitrogen content have been successfully synthesized by utilizing aminated graphene oxide as a 2D structure-directing template via dynamic covalent chemistry. Nitrogen-enriched porous carbon nanosheets were thus prepared by thermal pyrolysis of the 2D porous polymers, showing exceptionally high capacitance up to 424 F g(-1) at 0.1 A g(-1) in 6 m KOH, superior to that of porous carbons without graphene involved.

Mononuclear and dinuclear salen type copper(II) Schiff base complexes: Synthesis, characterization, crystal structures and catalytic epoxidation of cyclooctene

A series of salen type Schiff base ligands and their mononuclear (CuLn, n=1–4) or dinuclear Cu(II) complexes (Cu2(L5)2) were synthesized and characterized by 1H NMR, IR and UV–Vis spectroscopy as well as elemental analyses. The ligands were synthesized from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with various salicylaldehyde derivatives (x-salicylaldehyde for H2Ln, x=H (n=1), 5-Br (n=2), 5-Br-3-NO2 (n=3), 3-OMe, (n=5)) and 2′-hydroxyacetophenone (n=4). Crystal structures of two complexes (CuL4 and Cu2(L5)2) were determined. Catalytic performance of the complexes was studied in the epoxidation of cyclooctene using tert-butylhydroperoxide (TBHP) as oxidant. Various factors including reaction temperature, solvent type, time, catalyst amount and substrate to oxidant ratio were optimized. High catalytic activity and epoxides selectivity was found. Solvent free epoxidation of cyclooctene was also studied and higher catalytic activity, epoxide selectivity and lower reaction times were observed.

Crystal structures and catalytic performance of three new methoxy substituted salen type nickel(II) Schiff base complexes derived from meso-1,2-diphenyl-1,2-ethylenediamine

Three new nickel(II) complexes of a series of methoxy substituted salen type Schiff base ligands were synthesized and characterized by IR, UV–Vis and 1H NMR spectroscopy and elemental analysis. The ligands were synthesized from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with n-methoxysalicylaldehyde (n=3, 4 and 5). Crystal structures of these complexes were determined. Electrochemical behavior of the complexes was studied by means of cyclic voltammetry in DMSO solutions. Catalytic performance of the complexes was studied in the epoxidation of cyclooctene using tert-butylhydroperoxide (TBHP) as oxidant under various conditions to find the optimum operating parameters. Low catalytic activity with moderate epoxide selectivity was observed in in-solvent conditions but in the solvent-free conditions, enhanced catalytic activity with high epoxide selectivity was achieved.

Synthesis, crystal structures and antibacterial studies of oxidovanadium(IV) complexes of salen-type Schiff base ligands derived from meso-1,2-diphenyl-1,2-ethylenediamine

A series of new derivatives and previously reported Schiff base ligands and their oxidovanadium(IV) complexes were synthesized, characterized and tested as potential antibacterial agents against four human pathogenic bacteria. These N2O2 type Schiff base ligands were derived from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with different salicylaldehyde derivatives, and their metal complexes were obtained from the reaction of these ligands with bis(acetylacetonato)oxidovanadium(IV). Our studies showed that the metal complexes had moderate antibacterial activity, and this activity was higher than that of the free ligands against both Gram-positive and Gram-negative bacteria. Besides, it was found that the presence of more substituents on the ligands increases the antibacterial activities of both the free ligands and their complexes. The crystal structures of H2L4 and its corresponding complex VOL4 were determined by X-ray crystallography.