Vapour pressures,enthalpies and entropies of sublimation of <Emphasis Type="Italic">para</Emphasis> substituted benzoic acids

The vapour pressures of six para-substituted benzoic acids were measured using the Knudsen effusion method within the pressure range (0.1–1 Pa) in the following temperature intervals: 4-hydroxybenzoic acid (365.09–387.28) K; 4-cyanobenzoic acid (355.14–373.28) K; 4-(methylamino)benzoic acid (359.12–381.29) K; 4-(dimethylamino)benzoic acid (369.29–391.01) K; 4-(acetylamino)benzoic acid (423.10–443.12) K; 4-acetoxybenzoic acid (351.28–373.27) K. From the temperature dependence of the vapour pressure, the standard molar enthalpy, entropy and Gibbs energy of sublimation, at the temperature 298.15 K, were derived for each of the studied compounds using estimated values of the heat capacity differences between the gaseous and the crystalline phases. Equations for estimating the vapour pressure of para substituted benzoic acids at the temperature of 298.15 K are proposed.     

Antiproliferative activity, antioxidant capacity and tannin content in plants of semi-arid northeastern Brazil

The objective of this study was to evaluate antiproliferative activity, antioxidant capacity and tannin content in plants from semi-arid northeastern Brazil (Caatinga). For this study, we selected 14 species and we assayed the methanol extracts for antiproliferative activity against the HEp-2 (laryngeal cancer) and NCI-H292 (lung cancer) cell lines using the (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazole) (MTT) method. In addition, the antioxidant activity was evaluated with the DPPH (2,2-diphenyl-2-picrylhydrazyl) assay, and the tannin content was determined by the radial diffusion method. Plants with better antioxidant activity (expressed in a dose able to decrease the initial DPPH concentration by 50%, or IC50) and with higher levels of tannins were: Poincianella pyramidalis (42.95±1.77 μg/mL IC50 and 8.17±0.64 tannin content), Jatropha mollissima (54.09±4.36μg/mL IC50 and 2.35±0.08 tannin content) and Anadenanthera colubrina (73.24±1.47 μg/mL IC50 and 4.41±0.47 tannin content). Plants with enhanced antiproliferative activity (% living cells) were Annona muricata (24.94±0.74 in NCI-H292), Lantana camara (25.8±0.19 in NCI-H292), Handroanthus impetiginosus (41.8±0.47 in NCI-H292) and Mentzelia aspera (45.61±1.94 in HEp-2). For species with better antioxidant and antiproliferative activities, we suggest future in vitro and in vivo comparative studies with other pharmacological models, and to start a process of purification and identification of the possible molecule(s) responsible for the observed pharmacological activity. We believe that the flora of Brazilian semi-arid areas can be a valuable source of plants rich in tannins, cytotoxic compounds and antioxidant agents.     

Compatibility studies between nebicapone,a novel COMT inhibitor,and excipients using stepwise isothermal high sensitivity DSC method

Study of excipients incompatibility with drugs in an early phase of pharmaceutical development is still a persistent difficulty within the pharmaceutical industry. We examine here the compatibility between an experimental drug (nebicapone) and common excipients using differential scanning calorimetry (DSC), high sensitivity DSC (HSDSC) and a conventional heat stress test. The results obtained indicate that nebicapone may be compatible with lactose monohydrate and sodium croscarmellose but is incompatible with magnesium stearate. This study concludes that HSDSC, in stepwise isothermal mode, may be used as a potential tool for detecting excipient incompatibilities.     

Ethylbenzene to chemicals: Catalytic conversion of ethylbenzene into styrene over metal-containing MCM-41

Isomorphously substituted (MeDM) and impregnated metal-containing MCM-41 (MeO_x/IM) catalysts, in which Me = Co, Cu, Cr, Fe or Ni, have been prepared. Structural and textural characterizations of the catalysts were performed by means of X-ray diffraction (XRD), chemical analysis, Raman spectroscopy, electron paramagnetic resonance (EPR), N₂ adsorption isotherms and temperature programmed reduction (TPR). Cu²⁺, Co²⁺, and Cr⁴⁺/Cr³⁺ species were found over the catalysts as cations incorporated in the MCM-41 structure (MeDM) or highly dispersed oxides on the surface (MeO_x/IM). The MeDM catalysts exhibited a good performance in the dehydrogenation of ethylbenzene with CO₂. However, MeO_x/IM catalysts had a low performance in styrene production (activity less than 15 × 10^?3 mmol h^?1 and selectivity for styrene less than 80%) due to the high reducibility of the metals species. However, Ni²⁺ or Fe³⁺ coordinated with the MCM-41 framework, as well as NiO_x and Fe₂O₃ extra-framework species, is continuously oxidized by the CO₂ to maintain the active sites for dehydrogenating ethylbenzene. Deactivation studies on the FeDM sample showed that Fe³⁺ species produced active sp² carbon compounds, which are removed by CO₂; the referred sample is catalytically selective for styrene and stable over 24 h of reaction. In contrast, highly active Ni²⁺ and Ni⁰ species produced a large amount of polyaromatic carbonaceous deposits from styrene, as identified by TPO, TG and Raman spectroscopy. An acid–base mechanism is proposed to operate to adsorb ethylbenzene and abstract the β-hydrogen. CO₂ plays a role in furnishing the lattice oxygen to maintain the Fe³⁺ active sites in the dehydrogenation of ethylbenzene to form styrene.     

Study of the Light‐Induced Spin Crossover Process of the [FeII(bpy)3]2+ Complex

Ab initio calculations have been performed on [Fe^II(bpy)₃]²⁺ (bpy=bipyridine) to establish the variation of the energy of the electronic states relevant to light‐induced excited‐state spin trapping as a function of the Fe? ligand distance. Light‐induced spin crossover takes place after excitation into the singlet metal‐to‐ligand charge‐transfer (MLCT) band. We found that the corresponding electronic states have their energy minimum in the same region as the low‐spin (LS) state and that the energy dependence of the triplet MLCT states are nearly identical to the ¹MLCT states. The high‐spin (HS) state is found to cross the MLCT band near the equilibrium geometry of the MLCT states. These findings give additional support to the hypothesis of a fast singlet–triplet interconversion in the MLCT manifold, followed by a ³MLCT–HS (⁵T₂) conversion accompanied by an elongation of the Fe? N distance.     

Synthesis and Study of the Photophysical Properties of a New Eu<Superscript>3+</Superscript> Complex with 3-Hydroxypicolinamide

This work reports on the synthesis and characterization of a new complex of Eu³⁺ with the 3-hydroxypicolinamide ligand (Hhpa). Here we present an approach for obtaining bis[2-carbamoyl(κO)pyridin-3-olato(κO’)] lanthanide complexes, which were characterized through elemental analysis, thermal analysis, infrared and photoluminescence spectroscopies (emission, excitation, luminescence lifetimes, quantum efficiencies, Judd-Ofelt parameters and quantum yields). Although hpa can act as a bidentate ligand in different conformations, the results attest for the occurrence of a unique coordination site of low symmetry for the Eu³⁺ ions, in which two anionic hpa ligands coordinate the cations through an O/O chelating system. The phosphorescence of the synthesized gadolinium complex provides the energy of the triplet state, which is determined to be at 20,830 cm^-1 over the ground state. This makes the Hhpa ligand very adequate for sensitizing the Eu³⁺ luminescence, which leads to a very efficient antenna effect and opens a wide range of applications for the complex in light emitting organic-inorganic devices.     

Quantum readout and fast initialization of nuclear spin qubits with electric currents

Nuclear spin qubits have the longest coherence times in the solid state, but their quantum readout and initialization is a great challenge. We present a theory for the interaction of an electric current with the nuclear spins of donor impurities in semiconductors. The theory yields a sensitivity criterion for quantum detection of nuclear spin states using electrically detected magnetic resonance, as well as an all-electrical method for fast nuclear spin qubit initialization.     

Free-standing urethane/urea elastomer films undoped and doped with ferro-nano-particles

We report on an experimental study of the structures presented by urethane/urea elastomeric films without and with ferromagnetic nanoparticles incorporated. The study is made by using the X-ray diffraction, nuclear magnetic resonance (NMR), optical, atomic and magnetic force (MFM) microscopy techniques, and mechanical assays. The structure of the elastomeric matrix is characterized by a distance of 0.46nm between neighboring molecular segments, almost independent on the stretching applied. The shear casting performed in order to obtain the elastomeric films tends to orient the molecules parallel to the flow direction thus introducing anisotropy in the molecular network which is reflected on the values obtained for the orientational order parameter and its increase for the stretched films. In the case of nanoparticles-doped samples, the structure remains nearly unchanged although the local order parameter is clearly larger for the undoped films. NMR experiments evidence modifications in the molecular network local ordering. Micrometer size clusters were observed by MFM for even small concentration of magnetic particles.     

EELS characterization of radiolytic products in frozen samples

Electron energy loss spectroscopy (EELS) was used to obtain information about the radiation chemistry of frozen aqueous specimens in the electron microscope by observing the hydrogen and oxygen K-edges. Measurements on frozen solutions of 30% hydrogen peroxide revealed the presence of molecular oxygen identified by a distinct 531-eV peak at the O K-edge even for electron doses below 100 e/nm2. The molecular oxygen content of irradiated H?O? solution was determined by least squares fitting of O K-edge reference spectra from water and gas-phase oxygen. It was found that the fraction of molecular oxygen to water oxygen was in the range 0.03-0.05. EELS from pure frozen water showed no features attributable to molecular oxygen or molecular hydrogen (K edge at ~13 eV) even at high electron doses above 10? e/nm2. Spectra from frozen sucrose and protein solutions and their mixtures, however, did show evolution of a molecular hydrogen peak at ~13 eV for doses above 10? e/nm2, consistent with previous measurements and indicative of hydrogen bubble formation. Molecular oxygen was not observed in any of the frozen solutions of organic compounds indicating that oxygen is not a major product of free radical decay, in contrast to molecular hydrogen formation.