Charge transfer complexes of some anilides with nitrobenzene derivatives as pi-electron acceptors

The charge transfer complexes formed between some anilides and pi-electron acceptors [picric acid, 2,4-dinitrophenol, 3,5-dinitrobenzoic aicd, 3,5-dinitrosalicylic acid and m-dinitrobenzene] are synthesized and characterized. Spectral characteristics and stability of the complexes are investigated and discussed in terms of donor molecular structure, pi-acceptor electron affinity, and solvent polarity. It is deduced that the complexes are mainly of the n-pi* and pi-pi* type where the ground state wave function can be described primarily by the non-bonding structure. The optimum conditions favouring the formation of the coloured complexes are extensively studied for the microdetermina-tion of anilides derivatives in pharmaceutical drugs using nitrobenzene as acceptor; the molecular structure was found to be 1:1 (D:A). Beer's law is obeyed up to 23.0, 18.60 and 16.0 micrograms ml-1 for p(OH), p-(OCH3), and p-N(CH3)2, respectively.     

Spectrophotometric microdetermination of phenylephrine hydrochloride in pure and in pharmaceutical formulations using haematoxylin

A simple, rapid, selective and sensitive method for the micro amount determination of phenylephrine hydrochloride either in pure form (raw material) or in pharmaceutical formulations is described. The method is based on the development of violet colour charge transfer complex with haematoxylin in alkaline medium with 10 min after heating at 65 °C. The wavelength and maximum absorption range was found in the range from 640 to 620 nm. Molar absorptivity and Sandell sensitivity were found to be 2.38 × 10⁴ L mol^− 1 cm^− 1 and 8.6 ng cm^− 2 respectively. A linear correlation was found between absorbance (at the λ_max) and concentration. The resulting colour is stable for more than 10 h. Results of the analyses of pure drug and dosage forms by the proposed method are in good agreement with those of the official BP 1998 procedure.     

Dielectric relaxation spectroscopy of heteronuclear cobalt(II)-copper(II) complex of 1-phenyl-3-methyl-5-pyrazolone

A bright green CoCu(PMP)(OH)2(H2O)2 complex was synthesized. Its structure was elucidated and characterized by different spectroscopic techniques. Both cobalt and copper atoms attain tetrahedral geometry. The complex was investigated by the dielectric relaxation spectroscopy. The dielectric parameters are discussed in terms of temperature and frequency changes. The conductivity of the complex decreased as the temperature increased in the temperature range 30-100 degrees C, while above this temperature range stepwise increase in the conductivity was observed.     

Electronic structure of the LPE grown semiconductor,p-ZnSnAs2, explored by newly-observed laser-excited photoluminescence

Radiative recombination phenomena are reported for the first time for ZnSnAs₂. The specimens are of (112) growth on (111) GaAs and (004) growth on (100) GaAs, the substrates bring semi-insulating. Measurements of photoluminescence (PL) band widths, band energies, and intensities at several excitation power density levels and several temperatures between 5 and 200 K lead to a donor-acceptor pairing assignment for the ca. 0.6 eV PL bands. The agreement between the calculated activation energy within the effective mass approximation and that observed experimentally is consistent with the identification of a shallow acceptor center at 25 ± 5 meV in both (112) and (004) ZnSnAs₂. The data also indicate that the ZnSnAs₂ has a deep donor center in each of the directional growth types. Finally, (112) ZnSnAs₂ on (111) GaAs was found to grow more homogeneously than (004) on (100) GaAs.     

Two novel long-chain alkanoic acid esters of lupeol from alecrim-propolis

Two new long-chain alkanoic acid esters of lupeol were isolated together with known triterpenoids, alpha-amyrin, beta-amyrin, cycloartenol, lanosta-7,24-diene-3beta-ol and lupeol from Alecrim-propolis collected in Brazil. The structures were characterized by spectroscopic means.     

Statistical analysis of HDPE fatigue lifetime

Fatigue lifetime of HDPE structures such as pipes is recognized to show a large scatter. This study aims to compare different statistical methods and distributions, in order to give convenient modeling of tensile and fatigue test results of commercially available polyethylene compression molded sheets. The median rank, the maximum likelihood and the Kolmogorov-Smirnov fitting are compared for the estimation of Weibull parameters. The choice of the best distribution to fit fatigue lifetime is discussed on the basis of the goodness-of-fit results. It is found that whether the three-parameter distributions of Weibull and lognormal types are suitable for lifetime prediction, the two-parameter Weibull is more conservative for probabilistic fatigue design.     

Colorimetric Estimation of Melatonin in Pharmaceutical Formulations

 Three simple and sensitive colorimetric methods (A–C) for the determination of melatonin in bulk samples and in pharmaceutical formulations are described. They are based on the formation of coloured species by reaction of ninhydrin with the drug (method A, λ_max 397 nm) by oxidation of the indol moiety in melatonin with potassium persulphate (method B, λ_max 450 nm) or by reduction of osmium (VIII) (method C, λ_max 516 nm). Regression analysis of Beer-Lambert plots showed good correlations in concentration ranges between 0.8–14.2, 70.0–140.0 and 2.0–40.0 μg/mL for methods A, B and C, respectively. The molar absorptivity, Sandell sensitivity and detection limit were calculated. For more accurate analysis, Ringbom optimum concentration ranges were calculated. The validity of the proposed methods was tested by analysing pharmaceutical formulations containing melatonin. The relative standard deviations were ≤ 0.95% with recoveries 99.0–101.33%. Received October 20, 1999. Revision February 10, 1999.     

Characterization of modified styrene-co-2-acrylamido-2-methylpropane sulfonic acid magnetite nanoparticles

This work provides an insight into the effect of incorporating of magnetite nanoparticles on the rheology of fluids. In this respect, polymer-stabilized magnetite nanoparticles were obtained using sodium salt of poly (2-acrylamido-2-methylpropanesulfonate (PAMPS-Na). Monodisperse polymer coated magnetite nanoparticles Fe₃O₄/poly(styrene-AMPS) copolymer nanoparticles with diameters of 50–300 nm were prepared by radical polymerization in the presence of a ferrofluid coated with PAMPS-Na. The magnetic nanoparticles were easily separated in a magnetic field. The structure of the obtained magnetic nanoparticles was characterized by Fourier transform infrared spectroscopy (FTIR). The morphology and size of the magnetic nanoparticles were determined by transmission electron microscopy (TEM). FTIR and TEM revealed that the Fe₃O₄ nanoparticles were incorporated into the shells of poly(styrene-AMPS). Aqueous dispersed solutions of a charged hydrophobically modified Fe₃O₄/poly(styrene-AMPS) copolymer nanoparticles exhibit high viscosities even at low polymer concentrations (0.1 wt %), which is an interesting feature in connection with enhanced oil recovery. Effects of temperature and addition of sodium chloride on the viscosity properties of a semidilute dispersed solution of Fe₃O₄/poly(styrene-AMPS) copolymer nanoparticles are examined. The results indicated that Fe₃O₄/poly(styrene-AMPS) copolymer nanoparticles disclose strong interactions between magnetite and coated polymers of both PAMPS-Na and styrene-AMPS copolymers.     

The role of Fe–X···X–Fe contacts in the crystal structures of [(2-iodopyridinium)2FeX4]X (X = Cl, Br)

The analogy of chloride–chloride contacts in compounds containing Fe–Cl1···Cl2–Fe synthons with well-studied organic C–Cl1···Cl2–C interactions has been investigated. The crystal structures of the two tetrahaloferrate(III) salts, [(2-iodopyridinium)₂FeX₄]X (X = Cl, Br) have been determined. Analysis of these two isomorphous structures and related published structures shows that the arrangement of Fe–Cl1···Cl2–Fe synthons is similar to that of C–Cl1···Cl2–C with the Fe–Cl1···Cl2 and Cl1···Cl2–Fe angles being ~150°. While inter-chlorine distances are less than the sum of van der Waals radii in C–Cl1···Cl2–C units, they are equal to, or longer, than the sum of van der Waals radii in the corresponding Fe–Cl1···Cl2–Fe contacts. This might indicate that the arrangement of Fe–Cl1···Cl2–Fe synthons occurs predominately to reduce repulsive forces rather than as a result of attractive forces. However, it is observed that the halide–halide distance in [(2-iodopyridinium)₂FeBr₄]Br is shorter than in the isostructural chloride species, which can be explained by the fact that bromine is softer than chlorine. Several intermolecular forces unite the cations and anions within the crystalline lattice of [(2-iodopyridinium)₂FeX₄]X including N–H···X^?, C–I···X–Fe, N(π)···X–Fe, N(π)···I–C, and Fe–X1···X2–Fe contacts. The calculated electron density and electrostatic potential of the [FeX₄]^? anions and the organic iodopyridinium cations was used to describe the arrangement of these synthons and the hierarchy of the strengths of the respective contacts.     

Facile Syntheses of Some Thieno[2,3-d] Pyrimidine Derivatives

In one-pot synthesis 2-arylidene-5,6,7,8-tetrahydrothiazolo[3,2-a] cyclopenteno-thieno[2,3-d] pyrimidine-3,5-diones (3) were prepared via the reaction of a ternary mixture of 2-thioxo-1,3,4,5,6,7-hexahydr cyclopentinothieno [2,3-d]-4-one (2), chloroacetic acid and a proper aldehyde. Compound 2 reacted with 3-chloropent-2, 4-dione in ethanolic potassium hydroxide yielding the S-acetyl acetone derivative 5f . The latter compound reacted with hydrazine hydrate and phenyl hydrazine yielded the 2-pyrazolthio derivative 10a, b. Compound 5f also underwent cyclization on heating with acetic acid—pyridine solution to give 11. The 2-methylthio derivative 5a, when treated with hydrogen peroxide gave the corresponding oxidized product 9.