From micelle supramolecular assemblies in selective solvents to isoporous membranes

The supramolecular assembly of PS-b-P4VP copolymer micelles induced by selective solvent mixtures was used to manufacture isoporous membranes. Micelle order in solution was confirmed by cryo-scanning electron microscopy in casting solutions, leading to ordered pore morphology. When dioxane, a solvent that interacts poorly with the micelle corona, was added to the solution, polymer-polymer segment contact was preferential, increasing the intermicelle contact. Immersion in water gave rise to asymmetric porous membranes with exceptional pore uniformity and high porosity. The introduction of a small number of carbon nanotubes to the casting solution improved the membrane stability and the reversibility of the gate response in the presence of different pH values.     

Evaluation of grinding methods for pellets preparation aiming at the analysis of plant materials by laser induced breakdown spectrometry

It has been demonstrated that laser induced breakdown spectrometry (LIBS) can be used as an alternative method for the determination of macro (P, K, Ca, Mg) and micronutrients (B, Fe, Cu, Mn, Zn) in pellets of plant materials. However, information is required regarding the sample preparation for plant analysis by LIBS. In this work, methods involving cryogenic grinding and planetary ball milling were evaluated for leaves comminution before pellets preparation. The particle sizes were associated to chemical sample properties such as fiber and cellulose contents, as well as to pellets porosity and density. The pellets were ablated at 30 different sites by applying 25 laser pulses per site (Nd:YAG@1064 nm, 5 ns, 10 Hz, 25 J cm⁻²). The plasma emission collected by lenses was directed through an optical fiber towards a high resolution echelle spectrometer equipped with an ICCD. Delay time and integration time gate were fixed at 2.0 and 4.5 μs, respectively. Experiments carried out with pellets of sugarcane, orange tree and soy leaves showed a significant effect of the plant species for choosing the most appropriate grinding conditions. By using ball milling with agate materials, 20 min grinding for orange tree and soy, and 60 min for sugarcane leaves led to particle size distributions generally lower than 75 μm. Cryogenic grinding yielded similar particle size distributions after 10 min for orange tree, 20 min for soy and 30 min for sugarcane leaves. There was up to 50% emission signal enhancement on LIBS measurements for most elements by improving particle size distribution and consequently the pellet porosity.     

Non-oxo vanadium(IV) alkoxide chemistry: solid state structures, aggregation equilibria and thermochromic behaviour in solution

The reversible thermochromic behaviour of homoleptic [{V(OR)(4)}(n)] complexes in solution [R = Pr(i) (product I), Bu(s) (B(s)), Nep (N) and Cy (C)] is accounted for the existence of an aggregation equilibrium involving dimeric and monomeric species in which vanadium(iv) is respectively five- and four-coordinate. Bulky R groups such as Bu(t) and Pe(t) (tert-pentoxide) prevent aggregation and therefore give rise to exclusively mononuclear compounds (B(t) and P(t), respectively) that are not thermochromic. The complexes and their temperature-dependent interconversion were characterised by single crystal X-ray diffractometry, magnetic susceptibility measurements and electronic, FTIR and EPR spectroscopies in a wide temperature range. Equilibrium constants and enthalpy and entropy changes for the dimerization reactions have been determined and compared with literature data.     

Electrokinetic properties of wavellite and its floatability with cationic and anionic collectors

The reverse apatite flotation with fatty acids has been widely used for the reduction of phosphorus content of magmatic origin iron ores. However, the occurrence of phosphorus intensely disseminated as secondary minerals such as wavellite renders the anionic reverse flotation a challenge. Zeta potential measurements and microflotation tests of wavellite with the use of anionic and cationic collectors were carried out in this work. The wavellite's IEP value was achieved at pH 4.5. Below the IEP value, the surface positively charged sites are made up of aluminum ions. The species H(+), Al(OH)(2)(+), Al(OH)(2+), Al(3+), OH(-), H(2)PO(4)(-), HPO(4)(2-), and PO(4)(3-) play a role in the protonation and deprotonation reactions that will determine the wavellite-solution interface properties. The highest values of wavellite's floatability under basic pH conditions were achieved in the presence of cationic collectors (1 × 10(-4) mol L(-1)). The formation of surface complexes and the precipitation of insoluble salt of aluminum onto wavellite surface seems to be the most likely hypothesis for the chemical nature interactions between amines and wavellite. The surface formation of aluminum oleate on the wavellite's surface seems to be the most probable hypothesis for the adsorption mechanism and the resultant high floatability of wavellite between pH 7.5 and pH 10.0 in the presence of sodium oleate (1 × 10(-4) mol L(-1)). The results showed that the cationic reverse flotation of secondary phosphates is a promising route to reduce the phosphorus content of iron ores from deposits that underwent a supergene enrichment process, since wavellite floatability in the alkaline pH range, using amine as collector, was not significantly affected by the presence of corn starch.     

Photochemistry and vibrational spectra of matrix-isolated methyl 4-chloro-5-phenylisoxazole-3-carboxylate

Methyl 4-chloro-5-phenylisoxazole-3-carboxylate (MCPIC) has been synthesized, isolated in low temperature argon and xenon matrices, and studied by FTIR spectroscopy. The characterization of the low energy conformers of MCPIC was made by undertaking a systematic investigation of the DFT(B3LYP)/6-311++G(d,p) potential energy surface of the molecule. The theoretical calculations predicted the existence of three low energy conformers. Two of them (I and II) were observed experimentally in the cryogenic matrices. The third one (III) was found to be converted into conformer II during deposition of the matrices, a result that is in agreement with the predicted low III → II energy barrier (<0.3 kJ mol(-1)). In situ UV irradiation (λ > 235 nm) of matrix-isolated MCPIC yielded as final photoproduct the corresponding oxazole (methyl 4-chloro-5-phenyl-1,3-oxazole-2-carboxylate). Identification of the azirine and nitrile-ylide intermediates in the spectra of the irradiated matrices confirmed their mechanistic relevance in the isoxazole → oxazole photoisomerization.     

Calorimetric aspects of adsorption of pesticides 2,4-<Emphasis Type="SmallCaps">d</Emphasis>, diuron and atrazine on a magadiite surface

H-magadiite was applied to remove the pesticides 2,4-d, diuron, and atrazine from water. The H-magadiite containing herbicides adsorbed were investigated by FTIR, DRX, N₂ adsorption and desorption isotherms, and surface area. Calorimetric studies were carried out to determine the heat of interaction between pesticides and magadiite. It was possible to ride the cycle of interaction of magadiite–pesticide for a better understanding of the process involved. From the results of the thermal effect of the interaction of magadiite–pesticide, the thermochemical parameters can be determined by using the relationship between the data obtained from adsorption and calorimetry results. The interaction of pesticide–magadiite follows the sequence of adsorption: diuron > atrazine > 2,4-d. The ΔH values for the interactions were determined to be −20.62 ± 1.08, −24.04 ± 0.86–26.34 ± 0.93 kJ mol⁻¹ for 2,4-d, diuron and atrazine, respectively. All the interactions were spontaneous, enthalpically and entropically favored demonstrating the effectiveness and efficiency of the method.     

Thermal studies on solid 1,4-bis(3-carboxy-3-oxo-prop-1-enyl) benzene of lighter trivalent lanthanides

Solid-state compounds of general formula Ln₂L₃·nH₂O, where L represents 1,4-bis(3-carboxy-3-oxo-prop-1-enyl)benzene and Ln = La, Ce, Pr, Nd, Sm, were synthesized. Complexometric titrations with EDTA, thermogravimetry (TG), differential thermal analysis (DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, elemental analysis and infrared spectroscopy have been employed to characterize and to study the thermal behavior of these compounds in dynamic air atmosphere. The results led to information about the composition, dehydration, crystallinity, and thermal decomposition of the synthesized compounds.     

Environmental effects on vibrational properties of carotenoids: experiments and calculations on peridinin

Carotenoids are employed in light-harvesting complexes of dinoflagellates with the two-fold aim to extend the spectral range of the antenna and to protect it from radiation damage. We have studied the effect of the environment on the vibrational properties of the carotenoid peridinin in different solvents by means of vibrational spectroscopies and QM/MM molecular dynamics simulations. Three prototypical solvents were considered: cyclohexane (an apolar/aprotic solvent), deuterated acetonitrile (a polar/aprotic solvent) and methanol (a polar/protic solvent). Thanks to effective normal mode analysis, we were able to assign the experimental Raman and IR bands and to clarify the effect of the solvent on band shifts. In the 1500-1650 cm(-1) region, seven vibrational modes of the polyene chain were identified and assigned to specific molecular vibrations. In the 1700-1800 cm(-1) region a strong progressive down-shift of the lactonic carbonyl frequency is observed passing from cyclohexane to methanol solutions. This has been rationalized here in terms of solvent polarity and solute-solvent hydrogen bond interactions. On the basis of our data we propose a classification of non-equivalent peridinins in the Peridinin-Chlorophyll-Proteins, light-harvesting complexes of dinoflagellates.     

Electron transfer processes in potassium collisions with 5-fluorouracil and 5-chlorouracil

Electron transfer to uracil (U), 5-chlorouracil (5-ClU) and 5-fluorouracil (5-FU) yielding anion formation has been investigated in 30-100 eV potassium-molecule collisions. The rich fragmentation patterns of all three molecules suggest that electron transfer in collisions with electronegative neutrals may cause efficient damage to RNA. The main ring fragment anion in all the mass spectra was NCO(-) while the production of X(-) (X = F, Cl) was a strong decomposition of the halouracil temporary negative ions. Cl(-) was the most intense fragment anion in the 5-chlorouracil measurements, whereas NCO(-) production dominated in the U and 5-FU data. Arguments based on energetics and vibrational dynamics have been proposed to explain these differences. Electronic coupling between dipole- and valence-bound states may play a particularly important role in the fragmentation pathways of the 5-ClU parent anion. The stabilizing influence of the potassium cation following electron transfer (ionic scattering) on the observed fragmentation patterns is discussed, notably in the context of comparisons with free electron attachment processes.