Amenability,locally finite spaces,and bi-lipschitz embeddings

We define the isoperimetric constant for any locally finite metric space and we study the property of having isoperimetric constant equal to zero. This property, called Small Neighborhood property, clearly extends amenability to any locally finite space. Therefore, we start making a comparison between this property and other notions of amenability for locally finite metric spaces that have been proposed by Gromov, Lafontaine and Pansu, by Ceccherini-Silberstein, Grigorchuk and de la Harpe and by Block and Weinberger. We discuss possible applications of the property SN in the study of embedding a metric space into another one. In particular, we propose three results: we prove that a certain class of metric graphs that are isometrically embeddable into Hilbert spaces must have the property SN. We also show, by a simple example, that this result is not true replacing property SN with amenability. As a second result, we prove that many spaces with uniform bounded geometry having a bi-lipschitz embedding into Euclidean spaces must have the property SN. Finally, we prove a Bourgain-like theorem for metric trees: a metric tree with uniform bounded geometry and without property SN does not have bi-lipschitz embeddings into finite-dimensional Hilbert spaces.     

Scalar field cosmology in phase space

Using dynamical systems methods, we describe the evolution of a minimally coupled scalar field and a Friedmann-Lemaître-Robertson-Walker universe in the context of general relativity, which is relevant for inflation and late-time quintessence eras. Focussing on the spatially flat case, we examine the geometrical structure of the phase space, locate the equilibrium points of the system (de Sitter spaces with a constant scalar field), study their stability through both a third-order perturbation analysis and Lyapunov functions, and discuss the late-time asymptotics. As we do not specify the scalar field’s origin or its potential, the results are independent of the high-energy model.     

Study of the Effects of Nonlinear Potential Sweeps on Voltammetry

Voltammetric methods use a constant sweep rate during the course of a scan. This paper reports a study of the influence of a nonconstant sweep rate on the voltammetric response. In this approach, either continuously increasing or continuously decreasing potential scan rates can be employed, unlike presently available methods which rely on a constant sweep rate. The voltammetric response of potassium ferrocyanide at a glassy carbon electrode was used as a model system to test the new method. The responses obtained using traditional staircase voltammetry (linear staircase voltammetry) and the new approach (nonlinear staircase voltammetry) were compared by experiment and by simulation. The new approach offers capability for signal enhancement, whereby enhanced current or enhanced peak shape can be obtained by choice of appropriate waveform parameters.     

Straightforward access to oxazaborines, diazaborinones and triazaborines by reactions of β-enaminoamides with 4-methylbenzenediazonium tetraphenylborate

The reaction of substituted β-enaminoamides with 4-methylbenzenediazonium tetraphenylborate in dichloromethane produces besides the primary products of azo coupling reaction at the α-carbon atom of β-enaminoamides, also mixtures of heterocyclic compounds of boron: 1,3,2λ⁴-oxazaborines, 1H-1,3,2λ⁴-diazaborine-4-ones and 4H-1,2,4,3λ⁴-triazaborines. Proportions of the products change depending on the reaction conditions, particularly depending on the presence or absence of base (sodium acetate) in the reaction mixture. The heterocyclic compounds were separated chromatographically and identified by means of X-ray, ¹H, ¹¹B, ¹³C and ¹⁵N NMR spectra and elemental analyses.     

Nucleation, structure and lamellar morphology of isotactic polypropylene filled with polypropylene-grafted multiwalled carbon nanotubes

Polypropylene-based nanocomposites filled with polypropylene-grafted multiwalled carbon nanotubes (PP-g-MWNT) were compared to PP samples filled with pristine MWNT. The effect of such additives on the structure and morphology of the polymer matrix was studied by small angle X-ray scattering (SAXS), wide angle X-ray diffraction (WAXD), polarized light optical microscopy (PLOM) and differential scanning calorimetry (DSC). PP-g-MWNT allowed a more efficient and unhindered crystallization at a lamellar level, while MWNT disrupted the order of lamellar stacks, probably because of their tendency to aggregate. A common trend of tensile properties and lamellar morphology as a function of filler content was noted in the series filled with functionalized carbon nanotubes.     

Preparation and characterization of chloroaluminum phthalocyanine-loaded solid lipid nanoparticles by thermal analysis and powder X-ray diffraction techniques

Solid lipid nanoparticles (SLN) without drug and SLN loaded with chloroaluminum phthalocyanine (AlClPc) were prepared by solvent diffusion method in aqueous system and characterized by thermal analyses and X-ray diffraction (XRD) in this study. Determination of particle size, zeta potential (ZP), and encapsulation efficiency were also evaluated. SLN containing AlClPc of nanometer size with high encapsulation efficiency and ZP were obtained. The results indicated that the size of SLN loaded with AlClPc is larger than that of the inert particle, but ZP is not changed significantly with incorporation of the drug. In differential scanning calorimetry (DSC) curves, it was observed that the melting point of stearic acid (SA) isolated and in SLN occurred at 55 and 64 °C, respectively, suggesting the presence of different polymorphs. DSC also shows that the crystallinity state of SLN was much less than that of SA isolated. The incorporation of drug in SLN may have been favored by this lower crystallinity degree of the samples. XRD techniques corroborated with the thermal analytic techniques, suggesting the polymorphic modifications of stearic acid.     

The Rabe amination after a century: direct addition of N-heterocycles to carbonyl compounds

A catalytic version of the Rabe electrophilic amination is presented. This kind of reaction was originally employed in 1918 in a key step for the conversion of quinotoxine to quinine. Ketones and α-substituted aldehydes give the corresponding α-aminated carbonyl compounds in moderate yield. α,α-Unsubstituted aldehydes give rise to amino ketones via a novel rearrangement.     

Thermal behaviour and electrochemical properties of bis(trifluoromethanesulfonyl)amide and dodecatungstosilicate viologen dimers

We report the synthesis and characterization of dimeric viologen salts (1',1'-(alkane-1,n-diyl)bis(1-ethyl-4,4'-bipyridinium) with n = 4-10) with bis(trifluoromethanesulfonyl)amide (bistriflimide, Tf(2)N(-)) as a counteranion. For n = 4, 5 and 6, and for the nonylviologen cation (1,1'-dinonyl-4,4'-bipyridinium) we also prepared salts with the totally inorganic dodecatungstosilicate anion, SiW(12)O(40)(4-), featuring a poly-charged surface and nanosized dimensions. The materials have been characterized by means of calorimetric techniques, X-ray diffraction and solid state NMR and a comparison is made with analogous monomeric viologen salts exhibiting smectic mesophases. A strong odd-even effect is observed in the melting points and in the thermal behaviour of the bistriflimide dimeric systems, similar to what was reported for dipolar calamitic liquid crystal dimers, although the studied viologen dimers are not mesomorphic. By increasing the size of the counteranion we have observed a destabilization of the crystal phases and of the mesophases in favour of a glassy amorphous state. Implications on the design of novel ionic liquid crystals are discussed. The electrochemical behaviour in solution has been investigated by cyclic voltammetry measurements: interestingly, the odd-even effect is clearly visible also in the redox potentials. The spin-pairing of the viologen radical cations formed at each end of the dimer is responsible for the observed redox trend. Insights on the structure of the spin-paired dimer have been obtained by DFT calculations.     

Mass spectrometic study of speciation in aluminium-fluoroquinolone solutions

Fluoroquinolones (FQLs) are synthetic antibacterial agents containing a 4-oxo-1,4-dihydroquinoline skeleton. When concomintantly administered with other drugs which may contain metal ions, particularly Al(3+) (antacids, phosphate binders, vaccines etc) they may form metal-drug complexes. Pharmacokinetic studies showed that aluminium-quinolone interactions lead to reduced bio- availability and altered activity of the drug with possible development of the toxic effects of aluminum ion. Reliable speciation in Al(3+) - quinolone systems at micromolar concentration level is needed to better understand pharmaco- and toxicokinetics of the FQLs in the presence of Al. In this work, the speciation in solutions containing Al(3+) and FQL family members (fleroxacin, moxifloxacin and ciprofloxacin) was studied by electrospray mass spectrometry (ESI-MS), ESI-MS/MS, and laser desorption ionization (LDI) MS. The dominating species identified in all the three Al(3+)-FQL solutions, at ca 30-50 μmol L(-1) total Al concentration and 2:1 to 1:3 metal-to-ligand ratio in the pH range 3.0- 6.0, were the ions related to the complexes AlL(2+), AlL(2)(+) and AlL(3)(0) (L = ligand in the monodeprotonated form). Mixed protonated and hydroxo complexes were also formed at lower and higher pH values respectively and, as expected, dimeric and polymeric species were not observed in ESI spectra. LDI measurements confirmed the existence of the mononuclear complexes found by ESI, and indicated the formation of polymeric species. The ion [2Al(3+) +5(-)](+) was identified with all three FQLs. This ionic species most probably arises from Al(2)L(2) by clustering with free ligand anions. Comparison of literature potentiometric data with mass spectral data indicated good agreement between speciation schemes. The obtained results suggest the presence of strong interaction between FQLs and Al(3+) which may be important in affecting absorption of these drugs in the gastrointestinal tract.