Steady flow of a viscous incompressible fluid in an unbounded «funnel-shaped» domain

In this paper we consider a domain which is tube-like at one exit to infinity and the halfspace at the other side. We prove existence of steady motions for the Navier-Stokes problem and for the case in which the fluid is moving through a porous medium at rest filling . In both cases the proof holds for arbitrary fluxes. We describe the asymptotic behaviour of the solutions in the halfspace for both problems.     

A new pentanuclear cyano-bridged complex [(Fe(II)(tetraazamacrocycle))3{mu-NC-FeIII(CN)5)2]: synthesis, spectroscopic and magnetic characterization

Hexacyanoferrate(III) reacts with [FeII(meso)(CH3CN)2](ClO4)2.2CH3CN (meso=5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) in acetonitrile/water mixture producing the title complex, where three [Fe(meso)]2+ units are connected by two [Fe(CN)6](3-) anions. Molecular modeling (MM+) shows a fairly linear molecule and M?ssbauer data are consistent with two terminal pentacoordinated low spin iron(II)-meso units linked to one hexacoordinated low spin iron(II)-meso through two hexacoordinated low spin iron(III) units. Spectroscopic characterization showed a typical mixed-valence charge transfer band and the degree of electron coupling was calculated to be H(AB)=678 cm(-1). Magnetic properties exhibited an antiferromagnetic exchange interaction between the iron(III) ions with a coupling constant J= -44 cm(-1).     

Photochemical Bromination of 2,5-Dimethylbenzoic Acid as Key Step of an Improved Alkyne-Functionalized Blue Box Synthesis**

Cyclobis(paraquat-p-phenylene), also known as “blue box”, is a highly electron-deficient macrocycle, widely used as a molecular receptor for small electron-rich molecules. Inserting a reactive functional group onto the molecular structure of this cyclophane is paramount for its inclusion into complex architectures. To this aim, including an alkyne moiety would be ideal, because it can participate in click reactions. However, the synthesis of such alkyne-functionalized cyclophane suffers from several drawbacks: the use of toxic and expensive CCl₄, the need for high-pressure reactors, and overall low yield. We have revised the existing synthesis of this cyclophane derivative bearing an alkyne moiety, to overcome all these limitations. In particular, photochemical radical bromination is adopted to obtain a sensitive intermediate. We demonstrated that the synthesized host molecule can be functionalized via click reactions and take part in radical-radical interactions. Our work makes a key functionalized paraquat macrocycle more accessible, facilitating the development of novel redox-responsive systems.     

New sensitive fluorophores for selective DNA detection

4,7-Disubstituted benzothiadiazoles containing 1-arylethynyl and 4-methoxyphenyl groups are selective photoluminescent "light up" probes to duplex DNA with unprecedented sensibility in both spectrophotometric and spectrofluorimetric measurements.     

Electronic interactions and their influence on the conformational stability of trans-2-halocyclopentanol

Conformational preferences and electronic interactions of trans-2-fluorocyclopentanol (1), trans-2-chlorocyclopentanol (2), and trans-2-bromocyclopentanol (3) were analyzed using experimental and theoretical (3)J(HH) coupling constants, theoretical calculations, and natural bond orbital (NBO) analysis. The conformational equilibria of compounds 1-3 can be represented by their diaxial and diequatorial conformers as supported by theoretical calculations. From (3)J(HH) coupling constant values, it can be found that the diequatorial conformer is present in the equilibrium as 55% for compound 1 and as 60% for compounds 2 and 3. This behavior is in agreement with orbital interaction analyses obtained from NBO.     

1,3-Dialkylimidazolium-2-carboxylates as versatile N-heterocyclic carbene-CO2 adducts employed in the synthesis of carboxylates and α-alkylidene cyclic carbonates

1,3-Dialkylimidazolium-2-carboxylate compounds of formulas 1a, 2, and 4 have been synthesized and fully characterized by X-ray spectroscopy quite recently. Up today, these compounds have found some interesting applications as precursors of N-heterocyclic carbenes (NHCs) used as ligands for metal-complexes or in the synthesis of organic compounds and ionic liquids. We have recently reported the use of 1-butyl, 3-methylimidazolium-2-carboxylate and 1,3-dimethylimidazolium-2-carboxylate in a CO₂-transfer reaction to CH₃OH and acetophenone for the synthesis of methylcarbonate and benzoylacetate. The scope of this CO₂-transfer reaction has been expanded to several organic compounds with active hydrogen (acetone, cyclohexanone, and benzylcyanide) for the synthesis of carboxylates of pharmaceutical interest, and to propargyl alcohols for the synthesis of α-alkylidene cyclic carbonates.     

Photoconvertible fluorescent protein EosFP: biophysical properties and cell biology applications

EosFP is a fluorescent protein from the coral Lobophyllia hemprichii that changes its fluorescence emission from green to red upon irradiation with near-UV light. Here we present the spectroscopic properties of wild-type EosFP and a variety of monomeric and dimeric mutants and provide a structural interpretation of its oligomerization and photoconversion, which is based on X-ray structure analysis of the green and red species that we reported recently. Because functional expression of the monomeric EosFP variant is limited to temperatures of 30 degrees C, we have developed a tandem dimer. This construct, in which two EosFP subunits are connected by a flexible 12 amino acid linker, expresses well after fusion with the androgen and endothelin A receptors at 37 degrees C. A variety of applications in cellular imaging, developmental biology and automated high-content screening applications are presented, which demonstrate that EosFP is a powerful tool for in vivo monitoring of cellular processes.     

Synthesis of 1,3-dialkylimidazolium-2-carboxylates by direct carboxylation of 1,3-dialkylimidazolium chlorides with CO2

1,3-Dialkylimidazolium-2-carboxylates 1a and 1b are obtained in good to excellent yield and selectivity by carboxylation of the corresponding 1,3-dialkylimidazolium chloride salts with a CO₂/Na₂CO₃ system at temperatures ranging from 80 to 135 °C. The effect of temperature and reaction time on the yield and the selectivity of the carboxylation products has been studied. Coupling the CO₂-based synthesis of 1,3-dialkylimidazolium-2-carboxylates with the transcarboxylation reaction described earlier [Tommasi, I.; Sorrentino, F.; Tetrahedron Lett., 2005, 46, 2141] allows us to set up a new synthetic procedure for the synthesis of organic carboxylates and alkylcarbonate anions avoiding the use of strong bases.     

Quantitation of glucosamine sulfate in plasma by HPLC-MS/MS after administration of powder for oral solution formulation

A rapid method for the quantification of glucosamine in human plasma using high‐performance liquid chromatography coupled to tandem mass spectrometry was developed and validated. The sample preparation includes a simple deproteinization step, using d ‐[1‐¹³C] glucosamine hydrochloride as an internal standard. Chromatographic separation was performed on an ACE Ciano column using isocratic elution with acetonitrile and aqueous 2 mm ammonium acetate containing 0.025% formic acid (80:20). Selected reaction monitoring was performed using the transitions m/z 180.1 → m/z 72.1 and m/z 181.0 → m/z 74.6 to quantify glucosamine and internal standard, respectively. The method was validated and proved to be linear, accurate and precise over the range 50–5000 ng/mL of glucosamine. Recovery rates higher than 90% were obtained for both glucosamine and internal standard. No matrix effect was detected in the samples. The validated method was successfully applied to a pharmacokinetic study after oral administration of a powder for oral solution formulation containing glucosamine sulfate. Copyright © 2011 John Wiley & Sons, Ltd.     

Distillation of fermented sugarcane juice: fractions characterized by electrospray ionization mass spectrometry and multivariate data treatment

Direct infusion electrospray ionization mass spectrometry in the negative ion mode (ESI(-)-MS) was employed to discriminate among fractions arising from the distillation of fermented sugarcane juice during the production of cacha?a, a typical Brazilian alcoholic beverage. Aliquots were collected in the course of distillation and their ESI(-)-MS shown to be almost indistinguishable by a simple visual inspection. However, when the ESI(-)-MS data were treated by the principal component analysis (PCA) and hierarchical clustering analysis (HCA) statistical methods, four major groups were clearly determined, the so-called head (two distinct clusters), heart and tail fractions. Furthermore, the recognition of diagnostic ions (and their respective intensities) enabled a more confident establishment of the cutoff position (i.e. the initial and final points of each fraction). In conclusion, ESI-MS, in conjunction with PCA or HCA approaches, proved to be a quite efficient method that allowed for a prompt characterization of each fraction derived from the distillation of brewed sugarcane. The results described herein can, therefore, be useful not only to optimize the production of cacha?a but also to improve the quality of the final product.