Measurements of the refractive indices and refractive index increment of a synthetic PMMA solutions at 488 nm

We describe a Mach–Zehnder interferometer (MZI) method for measuring the refractive index (RI) of polymethyl-methacrylate (PMMA) solution in both acetone and methyl-ethyl-ketone (MEK). The measurements are made as a function of concentration values 4, 8, 12, 16 and 20 g/l at a wavelength of 488 nm with a high degree of accuracy tends to 1.4×10⁻⁵. The refractive index increments (RIIs) dn/dc of PMMA in both investigated solvents are determined too. In addition, the RIIs Δn as a function of concentration and the RIIs at zero concentration (dn/dc)_c=0 are determined for both solvents accurately. The PMMA solutions in acetone and MEK solvents are chosen for laser light scattering investigations.     

Synthesis and characterization of nickel(II) complexes with symmetrical tetradentate N2O2 naphthaldimine ligands. Their application as catalysts for the hydrogenation of cyclohexene

Ni acetate reacts with naphthaldimines containing the N2O2 donor group to yield two types of complex. The first, of molecular formula NiL (L=naphthaldimine), is free of the anions in which the ligand behaves as a dibasic tetradentate towards one Ni ion. These complexes are all diamagnetic, having square planar geometry. In the second type, the ligand behaves either as a monobasic acid towards the Ni ion or as a neutral molecule. These complexes are paramagnetic and exhibit a tetrahedral configuration around the central metal ion. The metal chelates were characterized by elemental analyses (t.g.a. and d.t.a.), and by i.r. and u.v.–vis. spectroscopy. Magnetic moments were also measured. A series of NiII–Schiff base complexes were tested for their catalytic activity in the hydrogenation of cyclohexene with molecular H2. The effects of the bridge length, amounts of solvent and cosolvent were studied. The use of H2O as a cosolvent greatly increases the yield of the reaction product. The hydrogenation product yield is linearly related to the dielectric constant of the medium.     

The Polarographic Behaviour of Some Arylidene Benzoic Hydrazide Derivatives and Substituent Effect

The polarographic reduction of some arylidene derivatives of benzoic hydrazide are investigated at the DME. The polarograms in solutions of pH≤8 consist of a single wave corresponding to 4 electrons in acid media and 2 electrons in alkaline ones. The wave splite into two daughter waves in media of pH≥10, the more negative wave increases in height at the expense of ihe original one with rise of pH. The reduction waves are essentially diffusion controlled with one proton and two electrons in the rate determining step. The electrode reaction is discussed and the important kinetic parameters are determined.     

UV/Vis, IR and 1H NMR spectrophotometric studies of some bisazo-dianil compounds based on bis-(hydroxy, formyl) phenylazo phenylene and anthranilic acid

The electronic absorption spectra of some bisazo-dianils are studied in organic solvents of different polarity and in buffer solutions of varied pH. The different absorption bands are assigned to the corresponding electronic transitions, the solvent effect on the CT band energy is also discussed. The spectral study in buffer solutions is utilized for the determination of the pKa of the phenolic OH-groups. The important bands in the IR spectra as well as the signals of the 1H NMR spectra are assigned and discussed in relation to molecular structure. The fluorescence spectra of the compounds are recorded. The fluorescence quantum yield and pK in the ground and excited states are determined.     

Spectral and photophysical studies of inclusion complexes of 2-amino-4,6-dimethyl pyrimidine with beta-cyclodextrin

The interaction of 2-amino-4,6-dimethyl pyrimidine (ADMP) with beta-cyclodextrin (beta-CD) has been studied by means of UV absorption, steady state and time resolved fluorescence techniques. Spectral characteristics, bandwidths and photophysical parameters indicating that ADMP experience two different environments in aqueous solutions: bulk water and 1:1 (ADMP:beta-CD) inclusion complexation. The size restriction of the upper rim of beta-CD partially include ADMP and prevent the possibility of formation of 1:2 complex. The effective polarity of the cyclodextrin cavity experienced by the induced ADMP is equivalent with the polarity of an 80:20 methanol-water mixture.     

Mononuclear and Binuclear Fe(III), Co(II), Ni(II), and Cu(II) Complexes of 3,4′-Dihydroxyazobenzene-3′,4-dicarboxylic Acid and 3-Carboxy-4-hydroxyphenylazo-3-carboxy-4-hydroxynaphthalene

Fe(III), Co(II), Ni(II), and Cu(II) complexes of the title azodyes have been synthesized and characterized by elemental analysis, molar conductance, TGA, DTA, magnetic susceptibility measurements, IR, electronic and ESR spectral studies. The spectral studies suggest an octahedral geometry for Fe(III) and Co(II) complexes but a square planar geometry for Ni(II) and Cu(II) complexes. The kinetics of the catalysed oxidation of N,N,N,N-tetramethyl-p-phenylenediamine dihydrochloride (TMPPD) with mononuclear and binuclear copper complexes were studied to check the activity of these copper complexes in oxidizing organic amines. The electrochemical behaviour of the metal complexes was studied using DC polarography and cyclic voltammetry. Antimicrobial activity of the azo compounds and its complexes have been tested against different microorganisms.     

Nanoporous metal organic framework materials for hydrogen storage

Hydrogen is expected to play an important role in future transportation as a promising alternative clean energy source to carbon-based fuels.One of the key challenges to commercialize hydrogen energy is to develop appropriate onboard hydrogen storage systems,capable of charging and discharging large quantities of hydrogen with fast enough kinetics to meet commercial requirements.Metal organic framework (MOF) is a new type of inorganic and organic hybrid nanoporous particulate materials.Its diverse networks can enhance hydrogen storage through tuning the structure and property of MOFs.The MOF materials so far developed adsorb hydrogen through weak disperston interactions,which allow significant quantity of hydrogen to be stored at cryogenic temperatures with fast kinetics.Novel MOFs are being developed to strengthen the interactions between hydrogen and MOFs in order to store hydrogen under ambient conditions.This review surveys the development of such candidate materials,their performance and future research needs.     

π-π* Molecular charge transfer complexes of antipyrineSchiff bases with 1,4-benzoquinone derivatives as π-acceptors

Summary Spectrophotometric studies of compounds formed by several substituted antipyrineSchiff bases as electron donors with 2,3-dichloro-5,6-dicyano-benzoquinone, chloranilic acid, and chloranil as electron acceptors have given results that are consistent with 1:1 charge transfer complexes. Transition energies, oscillator strengths, and dipole moments of the complexes as well as the effect of solvent upon their stability are discussed. Also their free energies and absorption cross sections have been determined.

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Charge-transfer-KomplexeSchiffscher Basen vom Antipyrintyp mit 1,4-Benzochinon-Akzeptoren

Zusammenfassung Spektrophotometrische Untersuchungen von ausSchiffschen Basen des Antipyrintyps als Elektronendonatoren und 2,3-Dichlor-5,6-dicyanobenzochinon, Chloranilsäure und Chloranil als Elektronenakzeptoren gebildeten Verbindungen zeigen die Entstehung vonCharge-transfer-Komplexen der Stöchiometrie 1:1. Neben der Berechnung von freien Energien und Absorptionsquerschnitten werden Übergangsenergien, Oszillatorstärken, Dipolmomente und der Einfluß des Lösungsmittels auf die Stabilität der Komplexe diskutiert.

     

Voltammetric, Potentiometric and Spectrophotometric Studies of Some Hydrazones and Their Metal Complexes in Ethanolic-Aqueous Buffered Solutions

Summary. The electrochemical behavior of some hydrazones derived from 6-chloro-2-hydrazinopyridine in the Britton-Robinson universal buffer of pH 2–11 containing 35% ethanol was investigated at the mercury electrode using dc-polarography, controlled-potential coulometry, and cyclic voltammetry techniques. The examined hydrazones were reduced in solutions of pH < 9 in a single 4-electron diffusion-controlled irreversible step corresponding to both the saturation of –N=C< double bond and cleavage of the –HN–NH– single bond of the hydrazone molecule via the consumption of two electrons for each center. Whereas the starting compound, 6-chloro-2-hydrazinopyridine, was reduced in a single 2-electron diffusion-controlled irreversible step corresponding to cleavage of its –NH–NH₂ single bond. The mechanistic pathway of the electrode reaction of the studied compounds was elucidated and discussed. The pK_a values of the examined hydrazones and the stoichiometry of their complexes in solution with some transition metal ions were determined spectrophotometrically. The dissociation constants and the thermodynamic parameters of the investigated hydrazones, and the stability constants of their metal complexes in solution were determined potentiometrically.