Sequestration of CO2 by Phosphatrane Molecules

The stationary points for the reaction between the CO₂ and nine different phosphatranes molecules have been characterized by means of MP2 computational methods. Two minima structures have been located: a pnicogen bonded complex where one of the oxygen atoms of CO₂ acts as electron donor and an adduct that presents a covalent P−C linkage. The corresponding transition state structure linking the two minima has also been characterized. In gas phase, the pnicogen bonded complex is more stable than the corresponding adduct except in one case. In contrast, the inclusion of the solvent effect (toluene and THF), reverts the stability, being in all cases the different adducts more stable than the pnicogen bonded complexes. The electronic properties of the systems have been analysed with the Quantum Theory of Atoms in Molecules (QTAIM) and Electron Density Shift (EDS) methods.     

On exact solutions of a class of fractional Euler–Lagrange equations

In this paper, first a class of fractional differential equations are obtained by using the fractional variational principles. We find a fractional Lagrangian L(x(t), where _a ^c D _t ^α x(t)) and 0<α<1, such that the following is the corresponding Euler–Lagrange

Comparison of various dilutions and solid-phase extraction cleanup on the determination of ephedrine-type alkaloids and internal standard recovery in ephedra botanical raw material and powdered extract

A study was conducted to determine the effect of 3 dilution levels on the precision of the ephedra alkaloid method when used in conjunction with a solid-phase extraction (SPE) column. For the dilutions studied, SPE column cleanup is necessary because it promotes a greater recovery of the internal standard. However, overall, target precision values were not obtained on the test materials. It was determined that the SPE column is not the cause of the lower recovery in the more concentrated solutions. Significant signal suppression of the internal standard occurs in more concentrated solutions within the mass spectrometer. It is hypothesized that this lack of performance on the part of the SPE column may be linked to its inability to fully clean contaminants from the higher concentration solutions and/or a mass spectrometer overload, which resulted in the internal standard not fully correcting for signal suppression in more concentrated solutions. An internal standard is necessary, especially for accuracy, for the determination of all alkaloids, and only dilute solutions can be accurately analyzed. Due to the sensitivity of the mass spectrometer, it is recommended that the determination of ephedrine alkaloids in dietary supplements and botanicals should be studied using a standard graph at a level 10 x less than the current method. It is also recommended that the SPE column used should be evaluated on its need for the sample dilutions made to fit the newly recommended standard graph.     

Dye-assisted chromatographic determination of aliphatic ketones and esters with brilliant green

Determinations of neutral nonchromophoric organic compounds by dye-assisted chromatography are extended to the determination of aliphatic ketones and esters by using reversed-phase conditions and a mobile phase containing Brilliant Green. Detection limits of 6–20 μg were obtained when a mobile phase containing 50% (v/v) methanol/water and 0.00010 M Brilliant Green was used with detection at 575 nm, and 0.5–2 μg with detection in the ultraviolet region. In the absence of dye the detection limits for several solutes were about four times higher than the corresponding values obtained with the dye. The dye was shown to form a dimer having a molar absorptivity two orders of magnitude smaller than that of the monomeric dye. Detection of non-chromophoric compounds is concluded to be due to the desorption of adsorbed dye by the analytes and the shift of the aggregation and hydration equilibria of the dye promoted by the organic solutes. The lowering of the capacity factors is interpreted in terms of the adsorption of dye by the column which reduces the hydrophobicity of the stationary phase.     

Fractional dynamics of populations

Nature often presents complex dynamics, which cannot be explained by means of ordinary models. In this paper, we establish an approach to certain fractional dynamic systems using only deterministic arguments. The behavior of the trajectories of fractional non-linear autonomous systems around the corresponding critical points in the phase space is studied. In this work we arrive to several interesting conclusions; for example, we conclude that the order of fractional derivation is an excellent controller of the velocity how the mentioned trajectories approach to (or away from) the critical point. Such property could contribute to faithfully represent the anomalous reality of the competition among some species (in cellular populations as Cancer or HIV). We use classical models, which describe dynamics of certain populations in competition, to give a justification of the possible interest of the corresponding fractional models in biological areas of research.     

A remark on the optimality of adaptive finite element methods

We show that the standard assumption on the smallness of the marking parameter θ in adaptive finite element methods can be avoided for the proof of the optimality of the algorithm. To this end we propose a new technique based on comparison of the solutions of different finite element spaces obtained by different refinements of a given mesh. We consider conforming and nonconforming low-order finite elements on triangular and tetrahedral meshes.     

Intramolecular Pnicogen Interactions in PHF?(CH2)n?PHF (n=2–6) Systems

A computational study of the intramolecular pnicogen bond in PHF? (CH₂)_n? PHF (n=2–6) systems was carried out. For each compound, two different conformations, (R,R) and (R,S), were considered on the basis of the chirality of the phosphine groups. The characteristics of the closed conformers, in which the pnicogen interaction occurs, were compared with those of the extended conformer. In several cases, the closed conformations are more stable than the extended conformations. The calculated interaction energies of the pnicogen contact, by means of isodesmic reactions, provide values between ?3.4 and ?26.0 kJ mol^?1. Atoms in molecules and electron localization function analysis of the electron density showed that the systems in the closed conformations with short P ??? P distances have a partial covalent character in this interaction. The calculated absolute chemical shieldings of the P atoms showed an exponential relationship with the P ??? P distance. In addition, a search in the Cambridge crystallographic database was carried out to detect those compounds with a potential intramolecular pnicogen bond in the solid phase.     

Polycaprolactone membranes reinforced by toughened sol–gel produced silica networks

The aim of this work is to develop polycaprolactone based porous materials with improved mechanical performance to be used in bone repair. The hybrid membranes consist in a polymeric porous material in which the pore walls are coated by a silica thin layer. Silica coating increases membrane stiffness with respect to pure polymer but in addition filling the pores of the polymer with a silica phase improves bioactivity due to the delivery of silica ions in the neighborhood of the material in vivo. Nevertheless silica network, even that produced by sol–gel, might be too stiff and brittle what is not desirable for its performance as a coating. In this work we produced a toughened silica coating adding chitosan and 3-glycidoxypropyltrimethoxysilane (GPTMS) to the precursor solution looking for having polymer chains linked by covalent bonding to the silica network. Hybrid polymer–silica coating was produced by in situ sol–gel reaction using Tetraethyl orthosilicate (TEOS), GPTMS and chitosan. Chemical reaction between amine groups of chitosan chains and epoxy groups of GPTMS allowed covalent bonding of polymer chains to the silica network. Physical properties of the hybrid membranes were characterized and cell attachment of MC3T3-E1 pre-osteoblastic cells on the surface of these supports was assessed.