On the asymptotics of solutions of the Lane-Emden problem for the p-Laplacian

In this paper we consider the Lane–Emden problem adapted for the p-Laplacian

Quantum Refinement Does Not Support Dinuclear Copper Sites in Crystal Structures of Particulate Methane Monooxygenase

Particulate methane monooxygenase (pMMO) is one of the few enzymes that can activate methane. The metal content of this enzyme has been highly controversial, with suggestions of a dinuclear Fe site or mono‐, di‐, or trinuclear Cu sites. Crystal structures have shown a mono‐ or dinuclear Cu site, but the resolution was low and the geometry of the dinuclear site unusual. We have employed quantum refinement (crystallographic refinement enhanced with quantum‐mechanical calculations) to improve the structure of the active site. We compared a number of different mono‐ and dinuclear geometries, in some cases enhanced with more protein ligands or one or two water molecules, to determine which structure fits two sets of crystallographic raw data best. In all cases, the best results were obtained with mononuclear Cu sites, occasionally with an extra water molecule. Thus, we conclude that there is no crystallographic support for a dinuclear Cu site in pMMO.     

Calibration graphs in isotope dilution mass spectrometry

Isotope-based quantitation is routinely employed in chemical measurements. Whereas most analysts seek for methods with linear theoretical response functions, a unique feature that distinguishes isotope dilution from many other analytical methods is the inherent possibility for a nonlinear theoretical response curve. Most implementations of isotope dilution calibration today either eliminate the nonlinearity by employing internal standards with markedly different molecular weight or they employ empirical polynomial fits. Here we show that the exact curvature of any isotope dilution curve can be obtained from three-parameter rational function, y = f(q) = (a₀ + a₁q)/(1 + a₂q), known as the Padé[1,1] approximant. The use of this function allows eliminating an unnecessary source of error in isotope dilution analysis when faced with nonlinear calibration curves. In addition, fitting with Padé model can be done using linear least squares.     

Positively charged biopolymeric nanoparticles for the inhibition of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> biofilms

Currently, many microbial infections have the potential to become lethal owing to the development of antimicrobial resistance by means of different mechanisms and mainly on the basis of the fact that many drugs are unable to reach therapeutic levels in the target sites. This requires the use of high doses and frequent administrations, causing adverse side effects or in some cases toxicity. The use of nanoparticle systems could help overcome such problems and increase drug efficacy. In the present study, we developed a new drug delivery system based on the use of biopolymeric nanovectors loaded with tobramycin (Tb), which is the standard antibiotic for the treatment of Cystic Fibrosis-associated P. aeruginosa lung infections. Tb-loaded biopolymeric nanoparticles composed by dextran sulfate (DS) and chitosan (CS) were prepared by ionotropic gelation. We optimized drug entrapment in DS/CS nanoparticles, obtaining particles of 170 nm and with a drug loading of 400 µg Tb/mg of nanoparticles. In accord with in vitro release experiments, such preparations were able to release approximately 25 % of their cargo in 60 h. In vitro, the antimicrobial efficacy of the drug delivery system on P. aeruginosa biofilm was tested and compared to the effects of free drug revealing that this formulation can reduce the viability of P. aeruginosa biofilms for 48 h with a single-dose administration.     

Photo‐Assisted Immobilized Fenton Degradation up to pH 8 of Azo Dye Orange II Mediated by Fe3+/Nafion/Glass Fibers

Fe³⁺ Ions have been immobilized into very thin Nafion films cast onto a glass‐fiber mat immersed in an alcoholic solution of Nafion oligomers. This immobilized Fenton catalyst was used to abate/mineralize the azo dye Orange II, taken as a model organic compound. The abatement of Orange II on the Fe³⁺/Nafion/glass fibers was observed to proceed within the same time period as when Nafion alone was used to immobilize the Fe³⁺ ions during the photo‐Fenton reaction. The amount of Nafion in the Nafion Fe³⁺/Nafion/glass fibers was ca. 15 times less per unit surface area compared to Fe³⁺‐exchanged on conventional Nafion membranes used to immobilize Fe³⁺ ions. Orange II solutions under visible‐light irradiation in the presence of H₂O₂ were mineralized up to pH 8 with a kinetics comparable to that found during the degradation runs at pH 3. Repetitive mineralization cycles mediated by the Fe³⁺/Nafion/glass fibers under visible light did not show any decrease in the activity of the immobilized catalysts. A reaction mechanism consistent with the experimental data is suggested. The morphology of the Fe³⁺/Nafion/glass fibers was characterized by scanning electron microscopy (SEM) showing thin Nafion films cast deposited on the glass fibers. Transmission‐electron‐microscopy (TEM) micrographs reveal Fe³⁺‐oxy‐hydroxide particles of 3 – 6 nm before and after repetitive Orange II photodegradation. X‐Ray photoelectron spectroscopy (XPS) provided the evidence for the existence of Fe clusters on the topmost layer of the catalyst mainly as Fe^III. The improvements brought by the glass fibers are a) the use of low quantities of expensive Nafion supported on glass mats to achieve dye degradation rates comparable to Nafion alone and b) Fenton‐mediated degradation of azo dyes at pH 8 without the costly initial acidification usually needed for this type of treatment.     

Relations linéaires enthalpies-entropies complexation de l'argent par des pyridines substituées

Thermodynamic quantities of silver complexation with a series of eight substituted (ethyl, propyl, amino, halogeno) pyridines are determined at 25°C, in an aqueous medium containing 0.5M KNO₃ to assure constant ionic strength.The discussion takes into account results of 21 systems, obtained under the same experimental conditions.Basicity-stability parallelism is discussed on the basis of thermodynamic arguments. The extension to complexation of the Hepler substituents theory is tried.     

Thermodynamique des complexes metalliques ternaires des amino acides: Etude du systeme Ni(II)—Glycine—DL-α-alanine

Standard enthalpies and entropies of formation for binary and ternary Ni(II) complexes with glycine and DL-α-alanine were calorimetrically determined at 25°C in aqueous solution (I = 1 M NaClO₄). The evolution of these values from binary to ternary complexes is discussed on the basis of the stabilization characterizing the stability constants of the ternary species which have been previously calculated under the same experimental conditions.     

Étude thermodynamique de la complexation de l'argent par la pipérazine et quelques-uns de ses derives en milieu eau—ethanol

The stability constants of the complexes of Ag⁺ ion with piperazine and its 2-methyl-, 2-methyl-1-m-tolyl-, 2-methyl-1-p-tolyl- and 1-(p-methoxyphenyl)-2-methyl-derivatives are obtained at 25°C in water—ethanol (52%, w/w) solvent and KNO₃ 0.1 M ionic strength, by means of corresponding metal-complex electrodes.The enthalpies of formation are determined by direct calorimetry, in the same conditions of temperature and medium.The comparison of the thermodynamic functions ΔG_n°, ΔH_n°, ΔS_n° allows a discussion about the ability of each amine to coordinate, in terms of nature and position of the entering group.     

Insertion of tear proteins into a meibomian lipids film

The eyelid meibomian gland secretions form the outer layer of the tear film. That layer functions as a lubricant during a blink, and as a barrier against intrusion of foreign bodies. The lipid film is also exposed to proteins present in the aqueous phase that may adsorb there, and thus form an integral part of the surface of the tear film, or possibly, cause disruption to the outermost layer. Therefore, the adsorption of tear proteins to the meibomian lipid layer was object of the present investigation. A model tear was set up coating a pendant drop of saline with a film of meibomian lipids and measuring variations of the interfacial pressure after the injection of tear proteins into the aqueous subphase at their physiological concentration. All tear proteins adsorbed at the interface causing the initial surface pressure to increase. For each protein, a limiting surface pressure at which a given protein was no longer able to insert into the lipid layer was found. Among the proteins tested, lipocalin was the most surface active one and inserted into the lipid layer in the whole range of surface pressure exerted by the meibomian lipid mixture. Lactoferrin, lysozyme and IgA also interacted with the lipids whereas albumin interacted more weakly. The timescale of the protein insertion into the lipid layer was of the order of 10(2) s. It was hypothesized that protein adsorption at the interface could be associated with structural changes. Indeed, the enzymatic activity of lysozyme was maintained in the presence of an outermost meibomian lipid layer that prevented its denaturation while exposure at the air/aqueous interface induced significant lysozime degradation. meibomian lipid composition is therefore functional to maintain tear proteins activity.     

Quantitative analysis of DHEA and androsterone in female urine: investigating the effects of menstrual cycle, oral contraception and training on exercise-induced changes in young women

Dehydroepiandrosterone (DHEA) and its metabolite androsterone (A) are natural steroids secreted in high quantities in human body. To assess the influence of oral contraceptives, menstrual cycle phase, and also physical exercise (acute and chronic such as training) on these metabolites excretions, a collection of 28 female urine specimens was organized. A three-extraction-step method was developed, and the analyses were performed by gas chromatography–mass spectrometry using deuterated 19-noretiocholanolone as the internal standard. Sample hydration state was found to be of great importance for kinetic studies, as it directly influenced the concentrations. No influence of menstrual cycle and training was found for androsterone and DHEA. However, oral contraceptive intake lowered DHEA excretion in urine and A seems to be slightly affected by exercise.