Visible Studies Research Articles

Spectral, thermal, electrochemical, biological and DFT studies on nanocrystalline Co(II), Ni(II), Cu(II) and Zn(II) complexes with a tridentate ONO donor Schiff base ligand

Co(II), Ni(II), Cu(II) and Zn(II) Schiff base complexes derived from 3-hydrazinoquionoxaline-2-one and 1,2-diphenylethane-1,2-dione were synthesized. The compounds were characterized by elemental analyses, molar conductance, magnetic susceptibility measurements, FTIR, UV–vis, 1H NMR, 13C NMR, ESR, and mass spectral studies. Thermal studies of the ligand and its metal complexes were also carried out to determine their thermal stability. Octahedral geometry has been assigned for Co(II), Ni(II), and Zn(II) complexes, while Cu(II) complex has distorted octahedral geometry. Powder XRD study was carried out to determine the grain size of ligand and its metal complexes. The electrochemical behavior of the synthesized compounds was investigated by cyclic voltammetry. For all complexes, a 2 : 1 ligand-to-metal ratio is observed. The ligand and its metal complexes were screened for their activity against bacterial species such as E. coli, P. aeruginosa, and S. aureus and fungal species such as A. niger, C. albicans, and A. flavus by disk diffusion method. The DNA-binding of the ligand and its metal complexes were investigated by electronic absorption titration and viscosity measurement studies. Agarose gel electrophoresis was employed to determine the DNA-cleavage activity of the synthesized compounds. Density functional theory was used to optimize the structure of the ligand and its Zn(II) complex.

Formation of polymeric assemblies of six-coordinate metal complexes with mixed bridges of dicarboxylato-azido moieties

New biscarboxylato zwitterionic ligands, namely bis(N-carboxylatoethyl)-4,4′-dipyridinum) L1 and bis(N-carboxylatopropyl)-)-4,4′-dipyridinum) L2, were synthesized from the reaction of 4,4′-dipyridine with 3-bromopropanoic acid and 4-bromobutanoic acid, respectively. The reaction of these ligands and the azido coligand with some metal ions resulted in the formation of polymeric complexes of general formulae [Cr2(Ln)(N3)4]Cl2·H2O and [M2(Ln)(N3)4] xH2O, where (M=Mn (II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II); n=1, 2; x=1, 1, 1, 1, 0, 1, and 1, respectively.) The oxygens of the carboxylato group are coordinated to the metal ion in a bidentate fashion. The mode of bonding and overall geometry of the complexes were determined through IR, UV–VIS, NMR and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, chloride content and conductance. These studies revealed the formation of polymeric assemblies of six-coordinate complexes with distorted octahedral geometries a...

Synthesis, characterization, photoluminescent properties and supramolecular aggregations in diimine chelated cadmium dihalides

A series of 12 new cadmium compounds, [Cd(X2)(L)] (4, 10), [Cd(X2)(L)(DMSO)] (9), [Cd(X2)(L)]2 (1–3, 5, 7, 8, 11, and 12), and [Cd(Cl2)2(L)]n (6) where X = chloride, bromide, and iodide, and diimine L = (E)-N-(pyridin-2-ylmethylidene)arylamine, were synthesized and characterized by elemental analyses. The spectroscopic properties were investigated by IR, UV–Vis, fluorescence, and 1H NMR studies. The solid-state structures of the 12 reaction products were studied by X-ray crystallography. A majority of the structures are binuclear with five-coordinate cadmium centers: dimerization occurs through μ2-bridging of the respective halides; the second halide is bound terminally. In the case of X = Br and I, dimerization is circumvented when L carries an additional donor capable of coordinating cadmium (4, 10) or when the additional donor is provided by coordinating solvent (9). A similar situation pertains in the CdCl2 analog (7). In the case where L strongly coordinates with cadmium, i.e. (6), an edge-shared polymeric chain and octahedrally coordinated cadmium are found as a result of μ2-bridging of both chloro ligands. An interesting feature of the crystal packing is the observation of rare C–Hπ interactions where the π-system is a chelate ring or a Cd2Br2 unit.

Synthesis, Characterisation and Capacitive Behaviour of Poly(3,4-ethylenedioxythiophene)-Copper Oxide Nanocomposites

Nano particles of Copper oxide and Poly(3,4-ethylenedioxythiophene)-Copper oxide nanocomposite were prepared by chemical oxidation method. The formed metal oxide nanoparticle and polymer metal oxide nanocomposites were characterized by UV–VIS, XRD, SEM and EIS studies. The UV-VIS studies of nanoparticles and nanocomposites exhibited four peaks, two peaks are sharp and centered at 280nm and 360 nm while the other two were broaden waves obtained at 780nm and 985nm. SEM image of copper oxide nanoparticles and nanocomposite exhibits sponge-like morphologies, in addition to nanospheres, nanowires, and nanotube shapes. The grain size of the metal oxide nanoparticle and polymer metaloxide nanocomposites was calculated using Scherrer’s formula. Electrochemical impedance spectroscopy (EIS) studies revealed the high conductivity nature due to the increased surface area of the nanocomposites.

Synthesis, Characterization, and Antibacterial Activities of Organotin(IV) Complexes with 2‐Acetylpyridine‐N(4)‐cyclohexylthiosemicarbazone (HAPCT)

ABSTRACTThe reaction of 2‐acetylpyridine‐N(4)‐cyclohexylthiosemicarbazone [(HAPCT), (1)] ligand with organotin(IV) chloride(s) afforded the five new organotin(IV) complexes: [MeSnCl2(APCT)] (2), [BuSnCl2(APCT)] (3), [PhSnCl2(APCT)] (4), [Me2SnCl(APCT)] (5), and [Ph2SnCl(APCT)] (6). The ligand (1) and its organotin(IV) complexes (2–6) have been synthesized and characterized by CHN analyses, molar conductivity, UV–vis, FT IR, 1H, 13C, and 119Sn NMR spectral studies. The single crystal X‐ray diffraction studies indicated that [PhSnCl2(APCT)] (4) is six coordinated and strongly adopts a distorted octahedral configuration with the coordination through pyridine‐N, azomethine‐N, and thiolato‐S atoms of the ligand. The compound crystallizes into a monoclinic lattice with the space group P21/n. The ligand (1) and its organotin(IV) complexes (2–6) were assayed for in vitro antibacterial activity against Staphylococcus aureus, Escherichia coli, Enterobacter aerogenes, and Salmonella typhi. The screening results have shown that the organotin(IV) complexes (2–6) have better antibacterial activity than the free ligand. Furthermore, it has been shown that the diphenyltin(IV) derivative (6) exhibits significantly better activities than the other organotin(IV) derivatives (2–5). © 2012 Wiley Periodicals, Inc. Heteroatom Chem 24:43–52, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.21061

Anion binding to a tetracopper resorcinarene-based complex

UV–vis and electron paramagnetic resonance (EPR) spectroscopic studies have been carried out on the multinuclear copper(II) complex Cu4BpaRes. The copper atoms are in a tetragonal distorted geometry with nitrogens from bispicolylamine (Bpa) coordinating in the equatorial plane and water molecules or anions completing four coordination sites. The interaction of anions with this polynuclear copper complex in aqueous solution supports the formation of different complex species, which depend on the type and the concentration of the anions. In the presence of excess anions, frozen solution EPR parameters show the formation of species in which the in-plane coordination is characterised by the presence of three nitrogen atoms coming from the ligand and a donor atom from the specific anion. For the bidentate anion ligands and especially for malonate, UV–vis titrations indicate the formation of a 1:4 (Cu4BpaRes:anion) species. EPR experiments support the formation of such a species and indicate that the four copper centres are equivalent and reach penta-coordination via the coordination of both oxygens from the bidentate ligand.

Synthesis and Characterization of Thermally Stable and Biologically Active Metal-Based Schiff Base Polymer

Schiff base was prepared via condensation of ethanedihydrazide with 2-hydroxy benzaldehyde and further this monomeric Schiff base polymerize with formaldehyde and barbituric acid and form polymeric Schiff base (PLSB) ligand. The ligand and its polymer metal complexes were characterized by using elemental analysis, IR, UV–VIS, 1HNMR, magnetic susceptibility and thermogravimetric studies. On basis of elemental analysis and spectral studies, six coordinated geometry was assigned for Mn(II), Co(II) and Ni(II) complexes and four coordinated for Cu(II) and Zn(II) complexes. PLSB act as a tetradentate and coordinate through the azomethine nitrogen and phenolic oxygen. The thermal behavior of these polymer metal complexes showed that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The (PLSB) ligands and its polymer metal complexes were screened against bacterial species Escherichia coli, Staphylococcus aureus, Bacillus subtilis and fungal species Aspergillus flavus, Candida albicans, A. niger. The activity data show that the metal complexes were more potent than the parent Schiff bases.

Pyrene-based simple new hetero bis amide pyridinium salt for selective sensing of benzoate and hydrogen sulphate

A new pyrene-based hetero bis amide pyridinium salt 1 has been designed and synthesised. The hetero bis amide salt 1 selectively recognises benzoate over a range of aliphatic monocarboxylates in CHCl3 containing 2% CH3CN by showing concomitant increase in emission of pyrene. The flexible cleft of 1 also showed selective sensing of tetrahedral-shaped ion over ion. The recognition property of 1 was evaluated by 1H NMR, UV–vis and fluorescence studies.

DDA-Based Simulation of UV–vis Extinction Spectra of Ag Nanorods Synthesized Through Seed-Mediated Growth Process

Present investigation demonstrates a very simple seed-mediated route for the synthesis of silver nanorods in aqueous solution. Central to the concept of seed-mediated growth of nanoparticles is that small nanoparticle seeds serve as nucleation centres to grow nanoparticles to a desired size and shape. Hydroxypropyl methyl cellulose (HPMC) has been used as soft template for one-dimensional growth of silver particles. Morphological, structural and spectral changes that are associated with the seed-mediated growth of the nanoparticles in presence of HPMC are characterized using UV–vis and HR-TEM spectroscopic study. Simulation of UV–vis extinction spectra of our synthesized silver nanorods has been carried out using discrete dipole approximation methodology. The broad red-shifted longitudinal extinction band of green-coloured silver sol has been explained, due to the presence of silver nanorods of different aspect ratios.

Cyclopentadienyl Chromium β-Diketiminate Complexes: Initiators, Ligand Steric Effects, and Deactivation Processes in the Controlled Radical Polymerization of Vinyl Acetate

The new compounds CpCr(nacnacAr,Ar′) with nacnacAr,Ar′ = Ar−N---C(Me)---CHC(Me)---N−Ar′ (Ar = Ar′ = C6H2Me3-2,4,6 or mes, 2; C6H3Et2-2,6 or dep, 3; Ar = C6H3Me2-2,6 or xyl and Ar′ = C6H3iPr2-2,6 or dipp, 4) have been synthesized and used in polymerization experiments in addition to the previously known analogues with Ar = Ar′ = xyl, 1, or dipp, 5. The compounds were used as moderators for the polymerization of vinyl acetate (VAc) initiated by V-70, according to an OMRP mechanism. The alkylchromium(III) thermal initiator CpCr(nacnacxyl,xyl)(CH2CMe3) (8) was synthesized from CpCr(nacnacxyl,xyl)(OTs) (7) and Mg(CH2CMe3)2(dioxane), while 7 was obtained from CpCr(nacnacxyl,xyl)Cl (6) and AgOTs. The polymerizations carried out with (1−5)/V-70/VAc at elevated temperatures yielded rapid deactivation, suggestive of irreversible radical trapping. On the other hand, room-temperature polymerizations carried out with 6/VAc proceeded, albeit slowly, to greater conversions. A labilizing effect of the Ar/Ar′ steric bulk is suggested by QM/MM calculations of CrIII−C BDE for models of the OMRP dormant species with 1, 5, and the parent system where Ar = Ar′ = Ph. Thermal deactivation of the nacnacxyl,xyl system has been evidenced, with formation of the acetate complex CpCr(nacnacxyl,xyl)(OAc), 9, as confirmed by an UV−vis study and by independent synthesis. This product is proposed to form by β-acetate transfer from the growing radical chain, triggered by a head−head monomer insertion. Compounds 2, 3, 6, 7, 8, and 9 have been structurally characterized by X-ray diffraction methods.

Synthesis, spectral characterization and antimicrobial activity of macrocyclic Schiff-base copper(II) complexes containing polycrystalline nanosized grains

Schiff-base copper(II) complexes were prepared using macrocyclic ligands, synthesized by condensation of diethylmalonate with Schiff bases derived from o-phenylenediamine and Knoevenagel condensed β-ketoanilides (obtained by the condensation of acetoacetanilide and substituted benzaldehydes). The ligands and their copper complexes were characterized by microanalytical, mass, UV–Vis, IR, 1H-NMR, ESR and CV studies, as well as conductivity data. Microanalytical, mass and magnetic moment analyses are consistent with formation of monomeric [CuL]Cl2. Spectral studies indicate square-planar geometry around copper. The smaller grain sizes found from XRD data suggest that these complexes are polycrystalline with nanosized grains. The SEM images of [CuL1]Cl2 have leaf-like morphology. The in vitro biological screening of the investigated compounds against the bacteria Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Pseudomonas aeruginosa and Staphylococcus aureus and fungi Aspergillus niger, Rhizopus stolonifer, Aspergillus flavus, Rhizoctonia bataicola and Candida albicans were tested by the well diffusion method to assess growth inhibition. A comparative study of MIC values of the Schiff-base ligands and their complexes indicate that the complexes exhibit higher antimicrobial activity than the free ligands.

Synthesis of porphyrin end-capped water-soluble poly(phenylene ethynylene) and study of its optical properties

A novel Porphyrin End-Capped poly(phenylene ethynylene) (P-PPE) was synthesized by palladium-catalyzed cross-coupling reaction. Porphyrin was successfully introduced to the polymer backbone, which was confirmed by 1H NMR, UV–Vis and Fluorescence spectroscopy. The degree of polymerization of P-PPE was characterized by both 1H NMR and GPC analysis. UV–Vis absorption and fluorescence studies in organic solvent indicate that there is significant energy transfer between the PPE backbone and the terminal porphyrin end group, and the PPE backbone works as an antenna transferring photo energy to ZnTPP terminal. The aggregation state of P-PPE in water was also investigated by UV–Vis and fluorescence studies.

Synthesis and characterization of metal complexes of 3-( N -phenyl)-thiourea-pentanone-2

Copper and cobalt complexes derived from 3-(N-phenyl)-thiourea-pentanone-2 were characterized by elemental, XRD, FTIR, UV–Vis, SEM and 1H NMR spectroanalytical studies. The X-ray diffraction studies indicate that 3-(N-phenyl)-thiourea-pentanone-2 and complexes with copper and cobalt are crystalline in nature with simple cubic lattice structure. IR spectroscopic data were used to assign characteristic vibrational frequencies of groups present in these compounds. Scanning electron micrograms were used to assign morphology and particle size.

Complexation of α, ω-dicarboxylates by 3,3′-bis(5-phenyl-1,4-dioxo-2,3,5-triaza)-2,2′-bipyridine

A new bipyridine derivative has been synthesized and characterized. The UV spectra of the prepared ligand are strongly dependent on the solvent, probably due to the different conformations present in each solvent. The ability of this ligand to act as chemosensor for α,ω-dicarboxylates has been evaluated by UV–vis and fluorescence studies. The stoichiometry of the formed complexes was always 1:2. The rigidity induced by the complexation gives rise to an enhancement of the fluorescence emission when DMSO was used.

Computational and Experimental Evidence for the Structural Preference of Phenolic C-8 Purine Adducts

The structural and spectral properties of (ortho and para) C8-aryl-purine adducts formed from carbon attachment by phenolic toxins were investigated through DFT calculations and UV-vis absorbance and emission studies. The global minima of both the deoxyadenosine (dA) and deoxyguanosine (dG) adducts adopted a syn conformation about the glycosidic bond due to the presence of an O5'-H...N3 hydrogen bond, where the anti minima are 20-30 kJ mol-1 higher in energy. While the nucleobase adducts are planar, the presence of the deoxyribose sugar induces a twist about the carbon-carbon bond connecting the phenol and nucleobase rings. ortho-Phenolic adducts are less twisted than the corresponding para adducts due to stabilization provided by an intramolecular O-H...N7 bond. Solvation calculations, in combination with UV-vis studies, demonstrate that the structural preference is solvent dependent, where solvents with hydrogen-bonding abilities disrupt the intramolecular O-H...N7 hydrogen bond such that a greater degree of twist is observed, and less polar solvents stabilize the planar structure. Indeed, the ratio of twisted to planar conformers is estimated to be as large as 50:50 in some aprotic solvents. Thus, the combined experimental and computational approach has provided a greater understanding of the structure of the ortho- and para-dA and dG C-bonded phenoxyl adducts as the first step to understanding the biological consequences of this form of DNA damage.

Visible Colorimetric Sensor for Fluoride Ion Based on o-Phenylenediamine

A new chromogenic receptor based on 1,2-phenylene derivative containing thiourea moieties is synthesized and examined for its anion binding ability by UV–Vis and 1H NMR studies. The results show that the receptor has selective colorimetric sensing of fluoride over all other anions like chloride, bromide, iodide, nitrate, hydrogen sulphate and acetate.

The Synthesis of Ester and Ketone Derivatives of Azocalix[4]arene Containing Chromogenic Groups

Azocalix[4]arenes were prepared by linking 4-ethylaniline, 4-n-butylaniline, 4-acetamide aniline and 2-aminothiazol to calix[4]arene through a diazo-coupling reaction. A new family of azocalix[4]arenes, L1–L12, have been prepared by the incorporation of acetyl, benzoyl, and methyl ketone units to azocalix[4]arene. Characterization of the synthesized compounds was carried using elemental analyses, UV–Vis, IR and 1H NMR spectroscopic studies.

UV–vis, IR and 1H NMR spectroscopic studies of some mono- and bis-azo-compounds based on 2,7-dihydroxynaphthalene and aniline derivatives

The absorption spectra of mono- and bis-azo-derivatives obtained by coupling the diazonium salts of aromatic amines and 2,7-dihydroxynaphthalene have been studied in six organic solvents. The different absorption bands have been assigned and the effect of solvents on the charge transfer band is also discussed. The diagnostic IR spectral bands and 1H NMR signals are assigned and discussed in relation to molecular structure. Also, semi-empirical molecular orbital calculations using the atom superposition and electron delocalization molecular orbital (ASED-MO) theory have been performed to investigate the molecular and electronic structures of these compounds. According to these calculations, an intramolecular hydrogen bonding is essential for stabilization of such molecules.

Intermolecular π-to-π Bonding between Stacked Aromatic Dyads. Experimental and Theoretical Binding Energies and Near-IR Optical Transitions for Phenalenyl Radical/Radical versus Radical/Cation Dimerizations

The high symmetry and stability of phenalenyl systems, both as the planar pi-radical (P*) and as the pi-cation (P+), are desirable characteristics of prototypical aromatic donor/acceptor pairs that encourage their use as (binary) models for the study of intermolecular interactions extant in stacked molecular arrays. Thus, quantitative ESR spectroscopy of the paramagnetic P* identifies its spontaneous self-association to the diamagnetic P2, previously characterized as the stacked pi-dimer by X-ray crystallography. Likewise, the rapid cross-association of P* with the closed-shell P+ leads to the stacked pi-dimer cation P2*+ with the "doubled" ESR spectrum diagnostic of complete (odd) electron delocalization. These pi-associations are confirmed by UV-vis studies that reveal diagnostic near-IR bands of both P2 and P2*+-strongly reminiscent of intermolecular charge-transfer absorptions in related aromatic (donor/acceptor) pi-associations. Ab initio molecular-orbital calculations for the pi-dimer P2 predict a binding energy of DeltaED = -11 kcal mol(-1), which is in accord with the experimental enthalpy change of DeltaHD = -9.5 kcal mol(-1) in dichloromethane solution. Most importantly, the calculations reproduce the intermonomer spacings and reveal the delicate interplay of attractive covalent and dispersion forces, balanced against the repulsions between filled orbitals. For comparison, the binding energy in the structurally related cationic pi-pimer P2*+ is calculated to be significantly larger with DeltaEP approximately -20 kcal mol(-1) (gas phase), owing to favorable electrostatic interactions not present in the neutral pi-dimer (which outweigh the partial loss of covalent interactions). As a result, our theoretical formulation can correctly account for the experimental enthalpy change in solution of DeltaHP = -6.5 kcal mol(-1) by the inclusion of differential ionic solvation in the formation of the pi-pimer.

Mass and Energy Transport in Conjugated Polymer Langmuir−Blodgett Films: Conductivity, Fluorescence, and UV−Vis Studies

We have investigated a model thin film sensory system in which analytes diffuse into multilayers of a fluorescent conjugated polymer. The film thickness is precisely controlled by depositing discrete monolayers by the Langmuir−Blodgett technique. The effects of analyte mass transport and energy migration on the photophysical properties of the films were investigated by conducting UV−vis, fluorescence, and electrical conductivity measurements. Thin films show different properties when compared to relatively thick films due to prevailing surface phenomena. The diffusion constant of the analyte through the films is estimated to be ∼7 × 10-14 cm2/s from an analysis of a phenomenological model. A bilayer LB film exposed to the analyte implies higher sensitivity in fluorescence quenching compared to a solution system due to a fast interpolymer energy migration in the condensed phase. However, as the number of layer increases, the efficiency of fluorescence quenching decreases. The difference between a sensory s...