Synthesis and spectroscopic studies of new Schiff bases

Five novel Schiff bases have been prepared from o-formylphenoxyacetic acid and a series of aminothiazoles to form a number of potentially biologically active compounds. The structures of these Schiff bases have been characterized using IR and (1)H-and (13)C-NMR spectroscopy.     

Synthesis,characterization and electrochemical studies of ruthenium(III) heterocyclic Schiff bases

A series of hexacoordinated Ru^III–PPh₃ complexes of general formula [RuCl(PPh₃)L] (L = tetradentate Schiff bases derived from the condensation of 2-furaldehyde or thiophene-2-carboxyaldehyde with alkyl and aryl diamines have been synthesized. The complexes were characterized by elemental analyses, spectroscopic and cyclic voltammetric studies. All of the complexes were paramagnetic. Coordination of the Schiff base appears to occur through the two nitrogen and two heterocyclic oxygen/sulphur atoms.     

Synthesis,characterization, DNA binding,photo-induced DNA cleavage,and antimicrobial activity of metal complexes of a Schiff base derived from bis(3-aminophenyl)malonamide

The peptide linkage Schiff base (H₂L) and its complexes have been synthesized and fully characterized by elemental analysis, UV–Vis, FTIR, ¹H-NMR, ¹³C-NMR, EPR, and FAB-mass spectra. The stoichiometry of the complexes is [ML] (where M = Cu(II), Co(II), Ni(II), Zn(II), and VO(IV)). All the complexes exhibit square-planar geometry except the vanadyl complex which has square-pyramidal geometry. Interactions of the complexes and free ligand with double-stranded calf thymus DNA (CT-DNA) are studied by UV-spectrophotometric, electrochemical, and viscosity measurements. The data suggest that all the complexes form adducts with DNA and distort the double helix by changing the base stacking. Vanadyl complex forms a weaker adduct to CT-DNA than other complexes, probably due to the square-pyramidal geometry. CT-DNA induces extensive distortion in the planarity of vanadyl complex as EPR spectral calculations reveal. The intrinsic binding constants (K _b) of [ZnL], [CuL], [CoL], and [NiL] are 1.1 × 10⁵, 1.4 × 10⁵, 0.8 × 10⁵, and 0.6 × 10⁵ M^?1, respectively. Photo-induced DNA cleavage indicates that all complexes cleave DNA effectively. Control DNA cleavage experiments using pUC19 supercoiled (SC) DNA and minor groove binder distamycin suggest major groove binding for the synthesized complexes. The antimicrobial results indicate that the complexes inhibit the growth of bacteria and fungi more than the free ligand.     

Synthesis,antimicrobial and antioxidant activity of bis sulfonamide/carbamate derivatives of bis-(4-aminophenyl) methane

A series of new bis sulfonamide/carbamate derivatives of bis-(4-aminophenyl)methane 3 ( a–d )/ 5 ( a–f ) were synthesized from bis-(4-aminophenyl)methane ( 1 ) using various pharmacologically active sulfonyl chlorides 2 ( a–d ) and carbonochloridates 4 ( a–f ) in high yields. The structures of all the newly synthesized compounds were characterized by the Infrared spectroscopy, NMR (¹H and ¹³C), mass, and elemental analyses. Further, all the synthesized compounds were tested for the antioxidant activity by using 2, 2-diphenyl-1-picrylhydrazyl, NO, and H₂O₂ scavenging methods and antimicrobial activity. Most of the compounds exhibited good antioxidant and antimicrobial activities.     

Synthesis and spectroscopic studies on organotin derivatives of biologically active Schiff bases

Some five- and six-coordinated di- and tri-n-butyl tin(IV) complexes of the type Bu₂SnL, Bu₂SnL₂ and Bu₃SnL (where L is the anion of a monofunctional bidentate or bifunctional tridentate Schiff base) have been synthesized and characterised on the basis of microanalyses, molecular weight determinations, IR, NMR (¹H, ¹³C, ¹¹⁹Sn) and ¹¹⁹Sn Mössbauer spectroscopy. These complexes are highly active towards bacteria.     

Synthesis of coordination compounds of dibutyltin(IV) with Schiff bases having nitrogen donor atoms

The new dibutyltin(IV) complexes of Schiff bases is designed & synthesis from the interaction between various substituted amines and aromatic aldehyde with general formula Bu₂Sn(L^1-7)₂Cl₂. Where L¹: (E)-4-chloro-N-(thiophen-2-ylmethylene) aniline; L²: (E)-2-chloro-N-(3,4,5-trimethoxybenzylidene) aniline; L³: (E)-N-((1H-indol-3-yl) methylene)-4-chloro-2-nitroaniline; L⁴: (E)-4-nitro-N-(3,4,5-trimethoxybenzylidene) aniline; L⁵: (E)-N-(3,4,5-trimethoxybenzylidene) aniline; L⁶: (E)-4-nitro-N-(thiophen-3-ylmethylene) aniline; L⁷: (E)-4-chloro-2-nitro-N-(pyridin-3-ylmethylene) aniline. Analytical and spectroscopic methods, such as molar conductance measurement, UV–Vis, IR, NMR, and DFT studies, have been used to describe newly synthesised compounds. The DFT studies have also provided confirmation regarding the complexes' geometry. The results of the Tauc equation indicate that the fundamental band gap of the compound [Bu₂Sn(L⁵)₂Cl₂] is 2.670 eV, which is in agreement with the findings of DFT studies, which indicate that the band gap is 2.657 eV. The bactericidal effects of Schiff bases and their dibutyltin(IV) complexes were tested. The antibacterial activity of organotin(IV) complexes is enhanced in comparison to that of the free ligands.     

Synthesis and spectroscopic and electrochemical studies of chitosan Schiff base derivatives

Schiff derivatives were prepared by the reactions of salicylaldehyde and its derivatives (5-chloro, 5-methoxy, 5-fluoro, 5-methyl, 5-nitro) with the amino group of chitosan. The Schiff bases were studied by Fourier IR spectroscopy and by UV-visible spectroscopy. The cyclic voltammograms of the Schiff bases were analyzed and compared to those of chitosan and salicylaldehyde. The formal potential of the chitosan Schiff base derivative correlates with the Hammett parameters. The oxidation potential increases and the optical density decreases with enhancement of the electron-acceptor properties of the functional group R in the m-position to the -N=CH-group. Chitosan (Chi) is a polysaccharide whose chains consist of recurrent units of acetamido-2-deoxy-D-glucode linked by the 1,4-β-glycoside bond. This polysaccharide was widely studied as drug carrier [1, 2], because it is nontoxic, biodegradable, and well biocompatible [3].     

UV-vis, IR and (1)H NMR spectroscopic studies of some Schiff bases derivatives of 4-aminoantipyrine

Five Schiff bases derived from 4-aminoantipyrine and benzaldehyde derivatives (I) are prepared and their UV-vis, IR, (1)H NMR and fluorescence spectra are investigated and discussed. The electronic absorption spectra of the hydroxy 4-aminoantipyrine Schiff bases Ib and Ie as well as the fluorescence spectra of Ie are studied in the organic solvents of different polarity. The UV-vis absorption spectra of 4-aminoantipyrine Schiff bases Ib, Id and Ie are investigated in aqueous buffer solutions of varying pH and utilized for the determination of pK(a) and DeltaG of the ionization process. The reactions of the hydroxy compounds Ib and Ie with Ni(II) and Cu(II) ions are also studied. The results of spectral studies are supported by some molecular orbital calculations using an atom superposition and electron delocalization molecular orbital theory for a compound Ib.     

Syntheses, magnetic and spectral studies on polystyrene supported coordination compounds of bidentate and tetradentate Schiff bases

The reaction of aminomethylated polystyrene (PSCH₂-NH₂) and 2-hydroxyacetanilide in DMF results in the formation of polystyrene-anchored monobasic bidentate Schiff base, PSCH₂-LH (I). On the other hand, the reaction of chloromethylated polystyrene (PSCH₂-Cl), 3-formylsalicylic acid, ethylenediamine and acetylacetone in DMF in presence of ethyl acetate (EA) and triethylamine (TEA) produces another polystyrene-anchored dibasic tetradentate Schiff base, PSCH₂-L′H₂ (II). BothI andII react with a number of di-, tri-and hexavalent metal ions like Co, Ni, Cu, Zn and Cd to form polystyreneanchored coordination compounds, and these have been characterized and discussed.     

Synthesis and spectroscopic studies of new organotin(IV) complexes with tridentate N- and O-donor Schiff bases

The Schiff bases H₂L¹ and H₂L² have been prepared by the reaction of 2-amino-4-chlorophenol with pyrrole-2-carbaldehyde and 2-hydroxy-1-naphtaldehyde, respectively, and HL³ from reaction of 2-(aminomethyl)pyridine with 2-hydroxy-1-naphtaldehyde. Organotin complexes [SnPh₂(L¹)] (1), [SnPh₂(L²)] (2), [SnMe₂(L²)] (3) and [SnPhCl₂(L³)] (4) were synthesized from reaction of SnPh₂Cl₂ and SnMe₂Cl₂ with these Schiff bases. The synthesized complexes have been investigated by elemental analysis and FT-IR, ¹H NMR and ¹¹⁹Sn NMR spectroscopy. In complexes the Schiff bases are completely deprotonated and coordinated to tin as tridentate ligands via phenolic oxygen, pyrrolic, and imine nitrogens in 1, two phenolic oxygens and imine nitrogen in 2 and 3, and phenolic oxygen, imine and pyridine nitrogens in 4. The coordination number of tin in 1, 2, and 3 is five and in 4 is six.     

Synthesis,characterization and microbiocidal studies of novel ionic liquid tagged Schiff bases

The synthesis of novel imidazolium ionic liquid, tagged Schiff, has been described. The synthesis was achieved in three steps from 2,4-dihydroxybenzaldehyde by selective alkylation with 1,3-dibromopropane, followed by reaction with 1-methylimidazole and Schiff base formation with aromatic amines. The compounds were evaluated for antibacterial and antifungal activities. The ionic liquid tagged Schiff base 4a showed the inhibition of both Gram positive and Gram negative bacteria. It also showed broad spectrum antifungal activity against all four tested fungi; however, 4f showed highest antifungal activity against A. niger.     

Synthesis, spectroscopic characterization and comparative DNA binding studies of Schiff base complexes derived from L-leucine and glyoxal

The mononuclear Schiff base complexes of the type, [ML(CH₃OH)₂] [M = Co(II), Ni(II), Cu(II) and Zn(II)] have been synthesized by template condensation of l-leucine and glyoxal. The complexes have been characterized on the basis of the results of the elemental analysis, molar conductance, magnetic susceptibility measurements and spectroscopic studies viz, FT-IR, Mass, ¹H NMR and ¹³C NMR spectra. The UV–vis and magnetic moment data revealed an octahedral geometry around Co(II), Ni(II) ion with distortion around Cu(II) ion complex confirmed by EPR data. The conductivity data show a non-electrolytic nature of the complexes. Absorption and fluorescence spectroscopic studies support that all the complexes exhibit a significant binding to calf thymus DNA.     

Synthesis,spectroscopic and electrochemical studies of mixed ligand ruthenium(II) chiral Schiff base complexes with nitrogen donors

Summary Mixed ligand complexes (1)-(18) of composition [RuL-(PPh₃)Y] and [RuL(PPh₃)(H₂O)Y]^- (L = chiral Schiff bases derived from l-alanine, l-valine, l-serine, l-cystein, l-arginine or l-aspartic acid with salicylaldehyde; Y = azide, 2,2-bipyridyl or 1,10-phenanthroline) have been prepared and characterized by microanalysis, spectroscopy and polarography. The conformational aspects regarding the relationship of the asymmetric carbon atom to the nitrogen donors around the Ru^II are discussed. All complexes showed quasi-reversible c.v. behaviour and the redox potentials of the Ru^II/Ru^I couple lie in the -0.31 to-0.16 V range.     

Diorganotin(IV) complexes of biologically potent 4(3H)-quinazolinone derived Schiff bases: synthesis, spectroscopic characterization, DNA interaction studies and antimicrobial activity

Four Schiff base ligands and their corresponding organotin(IV) complexes have been synthesized and characterized by elemental analyses, IR, (1)H NMR, MS and thermal studies. The Schiff bases are obtained by the condensation of 3-amino-2-methyl-4(3H)-quinazolinone with different substituted aldehydes. The elemental analysis data suggest the stoichiometry to be 1:1 ratio formation. Infrared spectral data agreed with the coordination to the central metal ion through imine nitrogen, lactam oxygen and deprotonated phenolic oxygen atoms. All the synthesized compounds have been evaluated for antimicrobial activity against selected species of microorganisms. In addition, DNA binding/cleavage capacity of the compounds was analyzed by absorption spectroscopy, viscosity measurements and gel electrophoresis methods.     

Synthesis, characterization, and spectroscopic investigation of benzoxazole conjugated Schiff bases

Two Schiff bases were synthesized by reaction of 2-(4'-aminophenyl)benzoxazole derivatives with 4-N,N-diethylaminobenzaldehyde. UV-visible (UV-vis) and steady-state fluorescence in solution were applied in order to characterize its photophysical behavior. The Schiff bases present absorption in the UV region with fluorescence emission in the blue-green region, with a large Stokes' shift. The UV-vis data indicates that each dye behaves as two different chromophores in solution in the ground state. The fluorescence emission spectra of the dye 5a show that an intramolecular proton transfer (ESIPT) mechanism takes place in the excited state, whereas a twisted internal charge transfer (TICT) state is observed for the dye 5b. Theoretical calculations were performed in order to study the conformation and polarity of the molecules at their ground and excited electronic states. Using density functional theory (DFT) methods at theoretical levels BLYP/Aug-SV(P) for geometry optimizations and B3LYP/6-311++G(2d,p) for single-point energy evaluations, the calculations indicate that the lowest energy conformations are in all cases nonplanar and that the dipole moments of the excited state relaxed structures are much larger than those of the ground state structures, which corroborates the experimental UV-vis absorption results.     

Convenient Synthesis of 2,7-Diamino-9,9- bis(4-aminophenyl)fluorene

For the synthesis of 2,7-diamino-9,9-bis(4-aminophenyl)fluorene 2 , first 2,7-dinitro-9,9-bis(4-aminophenyl)fluorene 1 was synthesized by the reaction of 2,7-dinitro-9-fluorenone with aniline and aniline hydrochloride. 2 was obtained by the reduction of 1 with hydrazine hydrate and 10% palladium on carbon.     

Synthesis, crystal structures, DNA binding and cleavage studies of two oxovanadium(IV) complexes of 1,10-phenanthroline and Schiff bases derived from tryptophan

Two new V(IV) complexes, [VO(Naph?Ctrp)(phen)]·CH₃OH (1) and [VO(o-Van?Ctrp)(phen)]·CH₃OH·H₂O (2) (Naph?CTrp?=?Schiff base derived from 2-hydroxy-1-naphthaldehyde and l-tryptophan, o-Van?Ctrp?=?Schiff base derived from o-vanillin and l-tryptophan, phen?=?1,10-phenanthroline), have been synthesized and characterized by physicochemical methods. The V(IV) atoms in both complexes are six-coordinated in a distorted octahedral environment. In the crystals of complex 1, the C?CH···?? and ?ШC?? stacking interactions form a 1D chain structure, whereas for complex 2, hydrogen bonds connect the molecular units into a 2D plane structure. The DNA binding properties and cleavage efficiencies of the complexes have been investigated by spectroscopic methods, viscosity measurements and agarose gel electrophoresis. The results suggest that both complexes can bind to CT-DNA in an intercalative mode and can also cleave pBR322 DNA.     

Synthesis,crystal structure,spectroscopic, and biological studies on Cu(II) complexes of N,O donor dimethyl isoxazole Schiff bases

Cu(II) complexes with Schiff bases DMIIMP, DMIIMBD, DMIIMBP, DMIIMCP, DMIIMMP, and DMIIMNP (see Introduction for definitions) are derived from condensation of 3,4-dimethyl 5-amino-isoxazole with salicylaldehyde and substituted salicylaldehydes. The newly synthesized ligands were characterized by IR, UV-Vis, ¹H NMR, ¹³C NMR, mass spectra, and elemental analysis. The Cu(II) complexes were characterized by IR, UV-Vis, ESR, elemental analysis, magnetic moments, thermogram, DTA, and single crystal analysis. The complexes have general formula [M(L)₂]. The Schiff bases are bidentate coordinating through the azomethine nitrogen and phenolic oxygen of salicylaldehydes. Based on the analytical and spectral data, four-coordinate geometry is assigned for all the complexes. ESR and single crystal analysis suggests square planar geometry for all complexes. [Cu(DMIIMP)₂] crystallizes in the orthorhombic system. Antimicrobial studies of Schiff bases and their metal complexes show significant activity with the metal complexes showing more activity than corresponding Schiff bases. Cytotoxicity of the copper complexes on human cervical carcinoma cells (HeLa) was measured using the Methyl Thiazole Tetrazolium assay.