Synthesis and properties of a new member of the calixnaphthalene family: a C(2)-symmetrical endo-calix[4]naphthalene

The synthesis of a new endo-calix[4]naphthalene is described. The reaction sequence involves the cyclocondensation of a key bisnaphthylmethane intermediate (8) with formaldehyde. This key intermediate (8) is formed using a modified Suzuki-Miyaura Pd-catalyzed cross-coupling reaction between bromomethylnaphthyl (6) and naphthylboronic acid (7), both of which can be derived from 2-hydroxynaphthoic acid.     

Electrospun poly(lactic acid) nanofibers loaded with silver sulfadiazine/[Mg–Al]‐layered double hydroxide as an antimicrobial wound dressing

Poly(lactic acid) (PLA) is a versatile, bioabsorbable, and biodegradable polymer with excellent biocompatibility and ability to incorporate a great variety of active agents. Silver sulfadiazine (SDZ) is an antibiotic used to control bacterial infection in external wounds. Aiming to combine the properties of PLA and SDZ, hydrotalcite ([Mg–Al]‐LDH) was used as a host matrix to obtain an antimicrobial system efficient in delivering SDZ from electrospun PLA scaffolds intended for wound skin healing. The structural reconstruction method was successfully applied to intercalate silver sulfadiazine in the [Mg–Al]‐LDH, as evidenced by X‐ray diffraction and thermogravimetric analyses. Observations by scanning electron microscopy revealed a good distribution of SDZ‐[Mg–Al]‐LDH within the PLA scaffold. Kinetics studies revealed a slow release of SDZ from the PLA scaffold due to the intercalation in the [Mg–Al]‐LDH. In vitro antimicrobial tests indicated a significant inhibitory effect of SDZ‐[Mg–Al]‐LDH against Escherichia coli and Staphylococcus aureus. This antibacterial activity was sustained in the 2.5‐wt% SDZ‐[Mg–Al]‐LDH–loaded PLA nanofibers, which also displayed excellent biocompatibility towards human cells. The multifunctionality of the PLA/SDZ‐[Mg–Al]‐LDH scaffold reported here is of great significance for various transdermal applications.     

Stereoselective synthesis of trifluoromethyl-substituted 1,2-diamines by aza-Michael reaction with trans-3,3,3-trifluoro-1-nitropropene

Aza-Michael addition of optically pure 4-phenyl-2-oxazolidinone to 3,3,3-trifluoro-1-nitropropene proceeds smoothly at low temperature with a high yield. Diastereoselectivity of the addition depends on the base used and lithiated species proved to be highly efficient affording 92% de. Optically pure 1,2-diamino-3,3,3-trifluoropropane is prepared in 58% yield from the aza-Michael addition product through a three-step procedure.     

Characterization of Biocatalysts Prepared with Thermomyces lanuginosus Lipase and Different Silica Precursors,Dried using Aerogel and Xerogel Techniques

The use of lipases in industrial processes can result in products with high levels of purity and at the same time reduce pollutant generation and improve both selectivity and yields. In this work, lipase from Thermomyces lanuginosus was immobilized using two different techniques. The first involves the hydrolysis/polycondensation of a silica precursor (tetramethoxysilane (TMOS)) at neutral pH and ambient temperature, and the second one uses tetraethoxysilane (TEOS) as the silica precursor, involving the hydrolysis and polycondensation of the alkoxide in appropriate solvents. After immobilization, the enzymatic preparations were dried using the aerogel and xerogel techniques and then characterized in terms of their hydrolytic activities using a titrimetric method with olive oil and by the formation of 2-phenylethyl acetate in a transesterification reaction. The morphological properties of the materials were characterized using scanning electron microscopy, measurements of the surface area and pore size and volume, thermogravimetric analysis, and exploratory differential calorimetry. The results of the work indicate that the use of different silica precursors (TEOS or TMOS) and different drying techniques (aerogel or xerogel) can significantly affect the properties of the resulting biocatalyst. Drying with supercritical CO₂ provided higher enzymatic activities and pore sizes and was therefore preferable to drying, using the xerogel technique. Thermogravimetric analysis and differential scanning calorimetry analyses revealed differences in behavior between the two biocatalyst preparations due to the compounds present.     

Analysis of β-agonists by HPLC/ESI-MS(n) in horse doping control

A sensitive method using LC/ESI-MS(n) has been developed on a quadrupole linear ion trap mass analyser for the detection of nine β(2) agonists (cimaterol, clenbuterol, fenoterol, formoterol, mabuterol, terbutaline, ractopamine, salbutamol and salmeterol) in horse urine. The method consists of solid-phase extraction on CSDAU cartridges before analysis by LC/ESI-MS(n) . The efficiency of extraction combined with the sensitivity and the selectivity of MS(n) allowed the detection of these compounds at pg/mL levels. Administration studies of fenoterol and formoterol are reported and show their possible detection after inhalation. The method is applicable for screening and confirmatory analysis.     

Synthesis and clathrates of oligomeric 2-O-naphthoide macrocycles

New macrocyclic O-naphthoides 4-6 were synthesized from dehydration reactions of 3-hydroxy- and 7-tert-butyl-3-hydroxy-2-naphthoic acids, respectively. Their X-ray structures were determined and their clathrate inclusion properties were investigated. Hexamer 6 formed an inclusion clathrate with four chloroform molecules. The trimer 5, by analogy with tri-o-thymotide, was studied for its potential optical resolution effects.     

Influence of pH on the incorporation and growth of Pb<Subscript>2</Subscript>CrO<Subscript>5</Subscript> crystallites in silica matrix

Pb₂CrO₅ nanoparticles were embedded in an amorphous SiO₂ matrix by the sol–gel process. The pH and heat treatment effects were evaluated in terms of structural, microstructural and optical properties from Pb₂CrO₅/SiO₂ compounds. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), energy dispersive spectroscopy (EDS), and diffuse reflectance techniques were employed. Kubelka–Munk theory was used to calculate diffuse reflectance spectra that were compared to the experimental results. Finally, colorimetric coordinates of the Pb₂CrO₅/SiO₂ compounds were shown and discussed. In general, an acid pH initially dissolves Pb₂CrO₅ nanoparticles and following heat treatment at 600 °C crystallized into PbCrO₄ composition with grain size around 6 nm in SiO₂ matrix. No Pb₂CrO₅ solubilization was observed for basic pH. These nanoparticles were incorporated in silica matrix showing a variety of color ranging from yellow to orange.     

Coupling versus surface-etching reactions of alkyl halides on GaAs(100): I. CF3CH2I reactions

We report the rich surface chemistry exhibited by the reactions of 1,1,1-trifluoroethyl iodide (CF3CH2I) adsorbed onto gallium-rich GaAs(100)-(4 x 1), studied by temperature-programmed desorption (TPD) and low-energy electron diffraction (LEED) studies and X-ray photoelectron spectroscopy (XPS). CF3CH2I adsorbs molecularly at 150 K but dissociates, below room temperature, to form a chemisorbed monolayer of CF3CH2 and I species. Recombinative desorption of molecular CF3CH2I competes with the further reactions of the CF3CH2 and I chemisorbed species. The CF3CH2 species can either undergo beta-fluoride elimination to yield gaseous CF2=CH2 or it can undergo self-coupling to form the corresponding higher alkane, CF3CH2CH2CF3. A second coupling product, CF3CH2CH=CF2, is also evolved, and it is postulated that migratory insertion of the liberated CF2=CH2 into the surface-carbon bond of the chemisorbed CF3CH2 is responsible for its formation. The iodines, formed by C-I scission in the chemisorbed CF3CH2I, and the fluorines, derived from beta-fluoride elimination in CF3CH2, react with the surface gallium dimers, and Ga-As back-bonds to generate five etch products (GaF, AsF, GaI, AsI, and As2) that desorb in the temperature range of 420 to >600 K. XPS data reveal that the surface stoichiometry remains constant throughout the entire annealing temperature range because of the desorption of both gallium- and arsenic-containing etch products, which occur sequentially. In this article, plausible mechanisms by which all products form and the binding sites of these reactions in the (4 x 1) reconstruction are discussed. Factors that control the rate constants of etch product versus hydrocarbon product formation and in particular how they impact on the respective desorption temperatures will be discussed.     

Chromatographic separation simulation of metal‐chelating peptides from surface plasmon resonance binding parameters

Some metal‐chelating peptides have antioxidant properties, with potential nutrition, health, and cosmetics applications. This study aimed to simulate their separation on immobilized metal ion affinity chromatography from their affinity constant for immobilized metal ion determined in surface plasmon resonance, both technics are based on peptide‐metal ion interactions. In our approach, first, the affinity constant of synthetic peptides was determined by surface plasmon resonance and used as input data to numerically simulate the chromatographic separation with a transport‐dispersive model based on Langmuir adsorption isotherm. Then, chromatographic separation was applied on the same peptides to determine their retention time and compare this experimental t_R with the simulated t_R obtained from simulation from surface plasmon resonance data. For the investigated peptides, the relative values of t_R were comparable. Hence, our study demonstrated the pertinence of such numerical simulation correlating immobilized metal ion affinity chromatography and surface plasmon resonance.