Showing papers on "Schiff base published in 2003"
TL;DR: The chiral binaphthyl Schiff-base ligands have been shown to form stable complexes with metal ions of Al(III), Ti(IV), Cr(III) and Pd(II).
267 citations
TL;DR: The results indicate that the phen ligand is necessary for DNA binding of the complex, and both the sulfur-to-copper charge transfer band and copper d-d band excitations helped the DNA cleavage.
Abstract: A new class of ternary copper(II) complexes of formulation $[Cu(L^n)B](ClO_4)$ (1-4), where $HL^n$ is a NSO-donor Schiff base $(HL^1, HL^2)$ and B is a NN-donor heterocyclic base viz. 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (dmp), are prepared, structurally characterized, and their DNA binding and photocleavage activities studied in the presence of red light. Ternary complex $[Cu(L^3)(phen)](ClO_4)$ (5) containing an ONO-donor Schiff base and a binary complex $[Cu(L^2)_2]$ (6) are also prepared and structurally characterized for mechanistic investigations of the DNA cleavage reactions. While 1-4 have a square pyramidal (4 + 1) $CuN_3OS$ coordination geometry with the Schiff base bonded at the equatorial sites, 5 has a square pyramidal (4 + 1) geometry with $CuN_3O_2$ coordination with the alcoholic oxygen at the axial site, and 6 has a square planar trans-$CuN_2O_2$ geometry. Binding of the complexes 1-4 to calf thymus DNA shows the relative order: phen >> dmp. Mechanistic investigations using distamycin reveal minor groove binding for the complexes. The phen complexes containing the Schiff base with a thiomethyl or thiophenyl moiety show red light induced photocleavage. The dmp complexes are essentially photonuclease inactive. Complexes 5 and 6 are cleavage inactive under similar photolytic conditions. A $10 \mu M$ solution of 1 displays a 72% cleavage of SC DNA $(0.5 \mu g)$ on an exposure of 30 min using a 603 nm Nd:YAG pulsed laser (60 mJ/P) in Tris-HCl buffer (pH 7.2). Significant cleavage of 1 is also observed at 694 nm using a Ruby laser. Complex 1 is cleavage inactive under argon or nitrogen atmosphere. It shows a more enhanced cleavage in pure oxygen than in air. Enhancement of cleavage in $D_2O$ and inhibition with sodium azide addition indicate the possibility of the formation of singlet oxygen as a reactive intermediate leading to DNA cleavage. The d-d band excitation with red light shows significant enhancement of cleavage yield. The results indicate that the phen ligand is necessary for DNA binding of the complex. Both the sulfur-to-copper charge transfer band and copper d-d band excitations helped the DNA cleavage. While the absorption of a red photon induces a metal d-d transition, excitation at shorter visible wavelengths leads to the sulfur-to-copper charge transfer band excitation at the initial step of photocleavage. The excitation energy is subsequently transferred to ground state oxygen molecules to produce singlet oxygen that cleaves the DNA.
264 citations
TL;DR: The representative Schiff bases and their complexes were tested in vitro to evaluate their activity against fungi, namely, Aspergillus flavus (A. flavus) and Fusarium species.
206 citations
205 citations
169 citations
TL;DR: In this paper, neutral tetradentate chelate complexes of CuII, NiII, CoII, MnII, ZnII and VOII have been prepared in EtOH using Schiff bases derived from acetoacetanilido-4-aminoantipyrine and 2-aminophenol/2-aminothiophenol.
Abstract: Neutral tetradentate chelate complexes of CuII, NiII, CoII, MnII, ZnII and VOII have been prepared in EtOH using Schiff bases derived from acetoacetanilido-4-aminoantipyrine and 2-aminophenol/2-aminothiophenol. Microanalytical data, magnetic susceptibility, i.r., u.v.–vis., 1H-n.m.r. and e.s.r. spectral techniques were used to confirm the structures of the chelates. Electronic absorption and i.r. spectra of the complexes suggest a square-planar geometry around the central metal ion, except for VOII and MnII complexes which have square-pyramidal and octahedral geometry respectively. The cyclic voltammetric data for the CuII complexes in MeCN show two waves for copper(II) → copper(III) and copper(II) → copper(I) couples, whereas the VOII complexes in MeCN show two waves for vanadium(IV) → vanadium(V) and vanadium(IV) → vanadium(III) couples. The e.s.r. spectra of the CuII, VOII and MnII complexes were recorded in DMSO solution and their salient features reported. The in vitro antimicrobial activity of the investigated compounds was tested against the microorganisms such as Salmonella typhi, Staphylococcus aureus, Klebsiella pneumoniae, Bacillus subtilis, Shigella flexneri, Pseudomonas aeruginosa, Aspergillus niger and Rhizoctonia bataicola. Most of the metal chelates have higher antimicrobial activity than the free ligands.
158 citations
TL;DR: To evaluate the antibacterial role of the anion, these compounds have been screened for antibacterial properties against pathogenic strains such as Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa.
Abstract: Reaction of 2-acetamidobenzaldehyde with 2-amino-, 2-amino-4-methyl-, 2-amino-4-methoxy-, 2-amino-4-chloro-, 2-amino-6-nitro- and 2-amino-6-methylsufonylbenzothiazole afforded a series of Schiff bases. These compounds have been used for complexation reactions to obtain Zn(II) chelates having the same metal ion but different anions of the type [Zn(L)2]Xn [L = Schiff base derivative, X = SO4, NO3, C2O4 and CH3CO2 and n = 1 or 2] These complexes (Table I) have been characterized by physical, spectral, and analytical data. The Schiff bases act tridentately and their metal complexes were proposed to possess an octahedral geometry. To evaluate the antibacterial role of the anion, these compounds have been screened for antibacterial properties against pathogenic strains such as Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa.
153 citations
TL;DR: Schiff base 2,3-bis [(4-diethylamino-2-hydroxybenzylidene)amino]but-2enedinitrile (BDPMB) and its zinc complex with donor-acceptor-donor (D-A-D) type ICT properties in the neutral form were used as novel red-emitting dopants in OLEDs as discussed by the authors.
152 citations
TL;DR: With this model, high-resolution structural information is available for the initial bacteriorhodopsin, as well as the first five states in the transport cycle, which provide rationales for how relaxation of the distorted retinal causes movements of water and protein atoms that result in vectorial proton transfers to and from the Schiff base.
151 citations
TL;DR: In this article, the corrosion inhibition of mild steel with Schiff base compounds derived from salicylaldehyde and the corresponding amine was studied in relation to the concentration using electrochemical techniques, and the maximum inhibition efficiency (η) was obtained for the N-(2-methyl phenyl)salicyaldimine compound with threeelectrochemical techniques applied.
150 citations
TL;DR: In this article, a tetradentate Schiff base ligand was derived from the phenolic oxygen and azomethine nitrogen, and the results indicated that the Schiff base is a bivalent anion with tetralentate ONNO donors.
Abstract: New Mn(II), Co(II), Ni(II) and Cu(II) complexes of a tetradentate Schiff base ligand [bis(2-hydroxyanil)acetylacetone],“2-[{1-methyl-3-[(2-hydroxyphenyl)imino]butylidene}amino]phenol”, H 2 haacac, have been prepared and characterized by elemental analyses, IR and conductometry. The results suggest that the Schiff base is a bivalent anion with tetradentate ONNO donors derived from the phenolic oxygen and azomethine nitrogen. The formulae was found to be [M(haacac)] for the 1:1 non-electrolytic complexes. Alumina-supported [M(haacac)] complexes catalyze the oxidation of cyclohexene with tert -butylhydroperoxide (TBHP). The major products of the reaction were 2-cyclohexene-1-ol (OH), 2-cyclohexene-1-one (CO) and 2-cyclohexene-1-( tert -butylperoxy) (OO t Bu). The influence of temperature, solvent and time for the oxidation reaction has been studied. The selectivity of 2-cyclohexene-1-( tert -butylperoxy) varied with reaction temperature. Mn(haacac)-alumina shows significantly higher catalytic activity than other alumina-supported complexes.
TL;DR: A network of three water molecules near residue 219 in the crystal structure of the non-illuminated F219L mutant, where the residue replacement creates a cavity suggests that the hydration of the cytoplasmic region might have occurred spontaneously, beginning at an existing water molecule as nucleus, in the cavities from residue rearrangements in the photocycle.
TL;DR: The use of chiral 1,1′-binaphthyl-2,2′-diol and 2,2´-diamino-1,1''-binophthyl frameworks for the construction of ligands for coordination and metallosupramolecular chemistry is discussed in this article.
TL;DR: In this article, neutral tetradentate N2O2 type complexes of Cu(II, Ni(II), Co(II) and Zn(II)) have been synthesized using the Schiff base formed by the condensation of acetylacetone andp-anisidine.
Abstract: Neutral tetradentate N2O2 type complexes of Cu(II), Ni(II), Co(II) and Zn(II) have been synthesised using the Schiff base formed by the condensation of acetylacetone andp-anisidine. Microanalysis, molar conductance, magnetic susceptibility, IR, UV-Vis,1 H NMR, CV and EPR studies have been carried out to determine the structure of the complexes. From the data, it is found that all the complexes possess square-planar geometry. The EPR spectrum of the copper complex in DMSO at 300 K and 77 K was recorded and its salient features are reported. All the title complexes were screened for antimicrobial activity by the well diffusion technique using DMSO as solvent. The minimum inhibitory concentration (MIC) values were calculated at 37°C for a period of 24 h. It has been found that all the complexes are antimicrobially active and show higher activity than the free ligand.
TL;DR: The rhodium complex [Cp ∗ Rh(bpy)Cl]Cl shows efficient catalytic activity in the transfer hydrogenation of a wide variety of ketones in aqueous formic acid solution under mild reaction conditions as discussed by the authors.
Abstract: The rhodium complex [Cp ∗ Rh(bpy)Cl]Cl shows efficient catalytic activity in the transfer hydrogenation of a wide variety of ketones in aqueous formic acid solution under mild reaction conditions. In the asymmetric reduction using chiral Schiff base ligands, the asymmetric induction was observed in reduction of dialkyl ketones as well as aryl ketones, among which ortho-chloroacetophenone gave the highest ee of 84%. © 2002 Elsevier Science B.V. All rights reserved.
TL;DR: Polarization and impedance measurements were performed on steel in deaerated 5% HCl solution with and without Schiff base additives within the concentration range 1 −10 −4 −5 −× 10 −3 mol/dm 3.
TL;DR: In this article, the building block approach was identified as a useful alternative to the commonly used Bucherer−Berg method for the preparation of cyclic unusual α-amino acid derivatives.
Abstract: The building block approach was identified as a useful alternative to the commonly used Bucherer−Berg method for the preparation of cyclic unusual α-amino acid derivatives. The symmetrical building blocks were prepared by dialkylation of ethyl isocyanoacetate under solid−liquid phase transfer catalysis conditions while the unsymmetrical building blocks were prepared by a stepwise alkylation of the O'Donnell Schiff base. Metathesis reactions, Suzuki couplings, and cycloaddition reactions were utilized to assemble the building blocks.
TL;DR: In this paper, the photophysical behavior of Schiff-base complexes with several different metals has been investigated and it has been shown that if suitable groups are attached to the carboxylate function, supramolecular systems with interesting properties can be designed and characterised.
Abstract: The photophysical behaviour of Schiff-base complexes with several different metals has been investigated. Among these complexes, the one with aluminium (3) presents interesting features, showing good chemical stability, high absorption coefficients and fluorescence quantum yield. In addition, the fluorescence intensity of 3 udergoes appreciable changes in the presence of coordinating species, such as carboxylate anions, allowing the association process to be monitored with high sensitivity. In addition, we have demonstrated that, if suitable groups are attached to the carboxylate function, supramolecular systems with interesting properties can be designed and characterised.
TL;DR: In this article, a pentadentate phenol-containing ligand (H3L) with N2O3 donor atoms yields NiII2 (1), NiII4 (2), CuII2(3) and CuII4(4) complexes, which have been structurally characterized by X-ray diffraction.
Abstract: A pentadentate phenol-containing ligand (H3L) with N2O3 donor atoms yields NiII2 (1), NiII4 (2), CuII2 (3) and CuII4 (4) complexes, which have been structurally characterized by X-ray diffraction. Complex 1 contains a single-atom O-bridged urea. The compounds were characterized by IR, UV/Vis, mass spectrometry, electrochemistry and variable-temperature (2−295 K) magnetic susceptibility measurements. Analysis of the susceptibility data shows antiferromagnetic interactions between the metal centers indicating a diamagnetic ground state for complexes 1, 3 and 4, whereas complex 2, a tetranuclear NiII cubane, has a complicated low-lying magnetic structure with a non-diamagnetic ground state. A plot of J vs. Ni−O−Ni angles for all structurally characterized Ni4O4 cubane cores, including 2, irrespective of their symmetry exhibits a large variation of J values within a small range of Ni−O−Ni angles. The electrochemistry of all complexes was investigated in detail and the ligand-centered oxidation to a radical-ligand is inferred from the occurrence of oxidation processes at potentials which are similar. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
TL;DR: In this paper, vanadyl Schiff base complexes having a terminal carbon-carbon double bond pending alkyl chains of various lengths attached to the para position of the salen ligand have been prepared and anchored on three large surface area silicas, namely amorphous silica, ITQ-2, and MCM-41 through mercaptopropysilyl groups.
TL;DR: From the magnetic susceptibility measurements the complex 1 is found to exhibit very weak antiferromagnetic interaction whereas a weak ferromagnetic coupling has been established for complex 2, and the magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.
Abstract: A tridentate Schiff base carboxylate ligand, derived from the condensation of pyridine 2-carboxaldehyde with anthranilic acid, reacts with copper trifluoroacetate salt to give rise to the helical chain complex [Cu(C13H9N2O2)(F3CCO2)]n (1) and with copper nitrate to give rise to the tetranuclear complex [{Cu4(C13H9N2O2)4(H2O)4}·3.5NO3·0.5N3] (2) with the addition of azide salt. The structures of these complexes have been solved by X-ray crystallography. The Cu(II) ions are in a distorted square-pyramidal environment in complex 1. They are sequentially bridged by carboxylate groups in the syn−anti conformation, resulting in the formation of an infinite helix like chain along the crystallographic c-axis. The crystal structure of complex 2 consists of tetranuclear [Cu4(L)4(H2O)4]4+ (L = C13H9N2O2-) cations and isolated NO3- and N3- anions in the ratio 1:3.5:0.5, respectively, involving bridging carboxylate groups in the syn−anti conformation. For 1 the carboxylato−Cu(II) coordination is apical−basal, while fo...
TL;DR: This one-pot three-component reaction was successfully applied to a concise total synthesis of (5R,6S)-6-acetoxy-5-hexadecanolide, the oviposition attractant pheromone of the female Culex mosquito capable of transmitting the West Nile virus.
Abstract: This Communication reports the optimization of the first catalytic enantio- and diastereoselective hetero[4+2]/allylboration reaction to provide efficient access to alpha-hydroxyalkyl pyran derivatives. The key substrate 3-boronoacrolein pinacolate appears to be an exceptionally favorable heterodiene for use in Jacobsen's enantioselective reverse electron demand hetero[4+2] reaction with enol ethers, catalyzed by the tridentate (Schiff base)chromium complex 1. This one-pot three-component reaction was successfully applied to a concise total synthesis of (5R,6S)-6-acetoxy-5-hexadecanolide (2), the oviposition attractant pheromone of the female Culex mosquito capable of transmitting the West Nile virus.
TL;DR: In this article, a review summarizes the recent advances in the chemistry of oxovanadium(III-V) mononuclear complexes and their linear assemblies bearing tetradentate Schiff base ligands.
TL;DR: The tridentate Schiff base and its reduced form HISMIMA were synthesized and characterized and their mononuclear cis-dihalo copper(II) complexes 1 and 2, respectively were investigated by infrared, electronic, and EPR spectroscopies, cyclic voltammetry, and potentiometric equilibrium studies.
Abstract: The tridentate Schiff base [(2-(imidazol-4-yl)ethyl)(1-methylimidazol-2-yl)methyl)imine (HISMIMI) and its reduced form HISMIMA were synthesized and characterized, as well their mononuclear cis-dihalo copper(II) complexes 1 and 2, respectively. In addition, the dinuclear [CuII(μ-OH)2CuII]2+ complexes (3) and (4) obtained from complexes 1 and 2, respectively, were also isolated and characterized by several physicochemical techniques, including magnetochemistry, electrochemistry, and EPR and UV−vis spectroscopies. The crystal structures of 1 and 2 were determined by X-ray crystallography and revealed two neutral complexes with their tridentate chelate ligands meridionally coordinated. Completing the coordination spheres of the square-pyramidal structures, a chloride ion occupies the apical position and another is bonded in the basal plane. In addition, complexes 1 and 2 were investigated by infrared, electronic, and EPR spectroscopies, cyclic voltammetry, and potentiometric equilibrium studies. The hydrolyti...
TL;DR: The properties of these hexacoordinate complexes, such as electronic absorption, circular dichroism spectra, and 1H NMR spectra have been determined by X-ray structure analysis.
TL;DR: The question whether transport occurs at all under low pH conditions is revisited, and in both oriented membrane fragments and liposomes reconstituted with proteorhodopsin, transport at high pH but not at low pH is found.
Abstract: At pH >7, proteorhodopsin functions as an outward-directed proton pump in cell membranes, and Asp-97 and Glu-108, the homologues of the Asp-85 and Asp-96 in bacteriorhodopsin, are the proton acceptor and donor to the retinal Schiff base, respectively. It was reported, however [Friedrich, T. et al. (2002) J. Mol. Biol., 321, 821−838], that proteorhodopsin transports protons also at pH <7 where Asp-97 is protonated and in the direction reverse from that at higher pH. To explore the roles of Asp-97 and Glu-108 in the proposed pumping with variable vectoriality, we compared the photocycles of D97N and E108Q mutants, and the effects of azide on the photocycle of the E108Q mutant, at low and high pH. Unlike at high pH, at a pH low enough to protonate Asp-97 neither the mutations nor the effects of azide revealed evidence for the participation of the acidic residues in proton transfer, and as in the photocycle of the wild-type protein, no intermediate with unprotonated Schiff base accumulated. In view of these f...
TL;DR: In this paper, vanadium(V) compounds were characterized (IR, UV/Vis, and 51V NMR spectroscopy, and in selected examples by X-ray diffraction analysis) and were applied as oxidation catalysts for the stereoselective synthesis of functionalized tetrahydrofurans.
TL;DR: Several new hexa-coordinated ruthenium(II) complexes of the type [Ru(CS)(Cl)(Py)(PPh3)(L)], [Ru (CS)(CL)(Bipy)(L)] and [Ru[Cl)(Phen)(Pph3]-L] have been synthesized as discussed by the authors, where Py = pyridine, Bipy = 2,2′-bipyridyl, Phen = 1,10−phenanthroline, L = monobasic bidentate Schiff base viz sal
Abstract: Several new hexa‐coordinated ruthenium(II) complexes of the type [Ru(CS)(Cl)(Py)(PPh3)(L)], [Ru(CS)(Cl)(Bipy)(L)] and [Ru(Cl)(Phen)(PPh3)(L)], (where Py = pyridine, Bipy = 2,2′‐bipyridyl, Phen = 1,10‐phenanthroline, L = monobasic bidentate Schiff base viz salicylaldehydemethylamine (HSalmet), salicylaldehydecyclohexylamine (HSalchx) and salicylaldehyde‐2‐aminopyridine (HSalampy)) have been synthesized All of the new complexes have been characterised on the basis of analytical and spectral data These new complexes showed a reasonable amount of antifungal activity
TL;DR: In this article, the mononuclear copper(II) complexes, [CuL1]-ClO4] (1) with unsymmetrical quadridentate Schiff base ligands derived from the 1:1:1 condensation of 2,4-pentanedione, pyridine-2-carboxaldehyde and 1,2-ethanediamine (HL1) or 1,3-propanediamine(HL2) have been prepared and characterised.