Structural and Mössbauer characterization of the ball milled Fex(Cr2O3)1−x system

The Fe_x(Cr₂O₃)_1?x system, with 0.10 ≤ X ≤ 0.80, was mechanically processed for 24 h in a high-energy ball-mill. In order to examine the possible formation of iron–chromium oxides and alloys, the milled samples were, later, thermally annealed in inert (argon) and reducing (hydrogen) atmospheres. The as-milled and annealed products were characterized by X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy and magnetization. The as-milled samples showed the formation of an Fe_1+YCr_2?YO_4?δ nanostructured and disordered spinel phase, the α₁-Fe(Cr) and α₂-Cr(Fe) solid solutions and the presence of non-exhausted precursors. For the samples annealed in inert atmosphere, the chromite (FeCr₂O₄) formation and the recrystallization of the precursors were verified. The hydrogen treated samples revealed the reduction of the spinel phase, with the phase separation of the chromia phase and retention of the Fe–Cr solid solutions. All the samples, either as-milled or annealed, presented the magnetization versus applied field curves typical for superparamagnetic systems.     

Ionization energies of hypervalent Li2F,Li2Cl and Na2Cl molecules obtained by surface ionization electron impact neutralization mass spectrometry

Ionization energies of hypervalent Li(2)F, Li(2)Cl and Na(2)Cl molecules detected by surface ionization electron impact neutralization mass spectrometry are reported. The ionization energies were 3.78 +/- 0.2 eV for Li(2)F, 4.93 +/- 0.2 eV for Li(2)Cl, and 4.21 +/- 0.2 eV for Na(2)Cl. The ionization energies (IE) agree with theoretical ionization energies calculated by ab initio methods, supporting the theoretical prediction that Li(2)F has a hyperlithiated configuration in which the odd electron delocalizes over the two lithiums and with photoionization measurement. The first ionization energy of Na(2)Cl was experimentally confirmed earlier and for Li(2)Cl as well.8 We have developed and used this new approach for the problem--in the present work ions were first formed by surface ionization, followed by electron attachment (neutralization).     

Stability of nanodispersions: a model for kinetics of aggregation of nanoparticles

In the course of aggregation of very small colloid particles (nanoparticles) the overlap of the diffuse layers is practically complete, so that one cannot apply the common DLVO theory. Since nanopoarticles are small compared to the extent of the diffuse layer, the process is considered in the same way as for two interacting ions. Therefore, the Br?nsted concept based on the Transition State Theory was applied. The charge of interacting nanoparticles was calculated by means of the Surface Complexation Model and decrease of effective charge of particles was also taken into account. Numerical simulations were performed using the parameters for hematite and rutile colloid systems. The effect of pH and electrolyte concentration on the stability coefficient of nanosystems was found to be more pronounced but similar to that for regular colloidal systems. The effect markedly depends on the nature of the solid which is characterized by equilibrium constants of surface reactions responsible for surface charge, i.e., by the point of zero charge, while the specificity of counterions is described by their association affinity, i.e., by surface association equilibrium constants. The most pronounced is the particle size effect. It was shown that extremely small particles cannot be stabilized by an electrostatic repulsion barrier. Additionally, at the same mass concentration, nanoparticles aggregate more rapidly than ordinary colloidal particles due to thier higher number concentration.     

X-ray structural analysis and antitumor activity of new salicylic acid derivatives

Tetrakis-, tris-, bis-, and mono salicylic acid derivatives 1–4 were synthesized by reaction of methyl 2-hydroxy benzoate (methyl salicylate) with 2,2-bis (hydroxymethyl) propane-1,3-diol (pentaerythritol) in the presence of sodium. Yields of different salicyloyloxy derivatives were changed by varying the molar ratios of reactants. For compounds 2 and 3, X-ray structure analysis was performed, as well as molecular energy minimization, to define their conformation in terms of their energy minima. Comparison of crystal and energy minimized structures for these two compounds (2 and 3) revealed that the intramolecular hydrogen bonds play an important role, stabilizing conformation of the most part of the molecule. The antioxidant activity and cytotoxicity of the synthesized derivatives were evaluated in a series of in vitro tests, as well as 17β-hydroxysteroid dehydrogenase type 2 inhibition potency. Tetrakis salicyloyloxy derivative 1 expressed the highest antioxidant potency, tris salicyloyloxy derivative 2 was the best inhibitor of 17βHSD2 enzyme, while bis salicyloyloxy derivative 3 showed strong cytotoxicity against prostate and breast cancer cells with no cytotoxicity against healthy cells.     

Preparation of 4(5)-vinylimidazole-co-acrylic acid copolymer and thermal performances related to applicability as PEM fuel cells

A series of acrylic acid and 4(5)-vinylimidazole copolymers for a non-hydrous proton transferring membrane used in polymer electrolyte membrane for fuel cell (PEMFC) are reported. The feed ratio of each monomer results in the variation of copolymer as evaluated by Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (¹H-NMR). Differential scanning calorimeter and thermal gravimetric analyzer confirm the thermal properties of copolymer films with T_g at 105-177 °C and T_d above 230 °C. The simultaneous analysis of wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) suggests the thermal performance about the decrease in domain size as a consequence of the loss of moisture content in the membrane and the increase in domain size as a consequence of chain mobility after T_g. The proton conductivities under anhydrous condition of the copolymer membranes are in the range of 10⁻² S/cm even up to 120 °C.     

Influence of temperature on performance of an anaerobic sequencing biofilm batch reactor with circulation applied to treatment of low-strength wastewater

The effect of temperature on the performance of an anaerobic sequencing biofilm batch reactor (ASBBR) with liquid-phase recirculation was assessed. Assays were performed using a recirculation velocity of 0.20 cm/s, 8-h cycles, and an average treated synthetic wastewater volume of 2 L/cycle with a concentration of 500 mg of Chemical Oxygen Demand (COD)/L. Operation temperatures were 15, 20, 25, 30, and 35°C. At 25, 30, and 35°C, organic matter removal efficiencies for filtered samples ranged from 81 to 83%. At lower temperatures, namely 15 and 20°C, removal efficiency decreased significantly to 61 and 65%, respectively. A first-order model could be fitted to the experimental concentration profile values. The first-order kinetic parameter value of this model varied from 0.46 to 0.81 h¹ considering the lowest and highest temperature studied. Moreover, analysis of the removal profile values allowed fitting of an Arrhenius-type equation with an activation energy of 5715 cal/mol.     

Spectroscopic Studies of water-soluble porphyrins with protein encapsulated in bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles: aggregation versus complexation

We have investigated the interaction of two water-soluble free-base porphyrins (negatively charged meso-tetrakis(p-sulfonatophenyl)porphyrin sodium salt (TSPP) and positively charged meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMpyP)) with two drug-carrier proteins (human serum albumin (HSA) and beta-lactoglobulin (betaLG)) in bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane/water reverse micelles (RM) by using steady-state and transient-state fluorescence spectroscopy. TSPP exhibited a complex pattern of aggregation on varying the RM size and pH in the absence of the protein: at low omega0 (the ratio of water concentration to AOT concentration, the emission of H-aggregates prevails under acidic or neutral "pH(ext)" conditions. Upon formation of the water-pool, J-aggregates and monomeric diacid species dominate at low "pH(ext)" but only monomer is detected at neutral "pH(ext)". The aggregation number increases with omega0 and the presence of the protein does not seem to contribute to further growth of the aggregate. The presence of protein leads to H-deaggregation but promotes J-aggregation up to a certain protein/porphyrin ratio above which, complexation with the monomer bound to a hydrophobic site of the protein prevails. The effective complex binding constants are smaller than in free aqueous solution; this indicates a weaker binding in these RM probably due to some conformational changes imposed by encapsulation. Only a weak quenching of TMpyP fluorescence is detected due to the presence of protein in contrast to the negative porphyrin.     

Normal- and Reversed-Phase Behaviour of 16,17-Secoestrone Derivatives on Cyanopropyl-Bonded Silica Gel

The retention behaviour of a number of 16,17-secoestrone derivatives has been studied by LC and HPTLC on a polar cyanopropyl-bonded stationary phase using non-aqueous and aqueous-organic mobile phases. The retention behaviour has been discussed in terms of nature of the solute, eluent and stationary phase. The correlation between retention constants of 16,17-secoestrone derivatives obtained from reversed-phases and commercially available ACD log P software (Advanced Chemistry, Toronto, Canada) has also been examined.