Haloacetylated enol ethers. 7 . Synthesis of 3-aryl-5-trihalomethylisoxazoles and 3-aryl-5-hydroxy-5-trihalomethyl-4,5-dihydroisoxazoles

β-Aryl-β-methoxyvinyl trihalomethyl ketones 1a-g, 2a-g [aryl = p-YC₆H₄ where Y= H, Me, OMe, F, Cl, Br, NO₂] are cyclocondensed with hydroxylamine hydrochloride to afford the 3-aryl-5-hydroxy-5-trihalomethyl-4,5-dihydroisoxazoles 3a-g, 4a-f in good yield. The dehydratation of compounds 3a-g with concentrated sulfuric acid, led the corresponding 3-aryl-5-trichloromethylisoxazoles 5a-g . An alternative one-pot procedure yields 3-aryl-5-trihalomethylisoxazoles 5,6a-g directly by cyclocondesation of 1,2a-g with hydroxylamine hydrochloride in the presence of an excess of concentrated hydrochloric acid.     

Oxazolidine copper complexes: Synthesis,characterization and superoxide dismutase activity of copper(II) complexes with oxazolidine ligands derived from hydroxyquinoline carboxaldehyde

This work describes the synthesis of copper(II) complexes, their identification using spectroscopic and electrochemical methods, structural characterization with X‐ray diffraction and density functional theory calculations (DFT), as well as their catalytic activity mimicking that of superoxide dismutase. Structural analysis revealed the formation of complexes with cyclization of ligands L1 and L2 with the formation of a heterocycle, 1,3‐oxazolidine. The DFT calculations confirmed this trend by stabilizing with lower energy. In addition, evaluations of mimetic enzymatic activity of complexes C1, C2, C3 and C4 revealed promising IC₅₀ values compared to other results seen in the literature (IC₅₀ = 0.22, 0.328, 0.55 and 0.92). Also, calf thymus DNA interactive experiments using UV–visible spectroscopy were conducted in the presence of the copper(II) complexes.     

A numerical study on heat transfer of a ferrofluid flow in a square cavity under simultaneous gravitational and magnetic convection

Theoretical and Computational Fluid Dynamics - Thermomagnetic convection is based on the use of external magnetic fields to better control heat transfer fluxes in ferrofluids, finding important...     

Tunable second harmonic generation by phase-modulated ultrashort laser pulses

We report on the generation of tunable light around 400?nm by frequency-doubling ultrashort laser pulses whose spectral phase is modulated by a sum of sinusoidal functions. The linewidth of the ultraviolet band produced is narrower than 1?nm, in contrast to the 12?nm linewidth of the non-modulated incident spectrum. The influence of pixellation of the liquid crystal spatial light modulator on the efficiency of the phase-modulated second harmonic generation is discussed.     

Synthesis of alexine-like compounds from chiral five-membered endocyclic enecarbamates

Stereoselective syntheses of enantiomerically enriched trihydroxy pyrrolizidine and indolizidines were accomplished from a common chiral endocyclic enecarbamate. The synthetic strategy features an efficient [2+2] cycloaddition of ketenes to the endocyclic enecarbamate and a highly regioselective Baeyer-Villiger oxidation of the intermediate azabicyclic-cyclobutanones. These new heterocycles are compounds structurally related to the alexines.     

Rhodium-catalyzed intramolecular formation of N-sulfamoyl 2,3-aziridino-γ-lactones and their use for the enantiospecific synthesis of α,β-diamino acid derivatives

4-Hydroxymethylbutenolide 4 was transformed into its sulfamoyl derivative 5, which upon treatment with iodosobenzene diacetate and magnesium oxide in the presence of a rhodium catalyst afforded the product of intramolecular aziridination 6. Reaction of 6 with primary or secondary amines in DMA led to regioselective opening of the aziridine ring at C2 to give the corresponding bicyclic derivatives 7a-7g in good to excellent yields. Methanolysis of the lactone ring of the N-benzyl-N-methyl derivative 7c followed by protection of the resulting secondary hydroxy group and treatment of the product with Boc anhydride provided the activated cyclic sulfamates 13 and 14. The latter then reacted with a second nucleophile (azide or thiophenol) to give the corresponding difunctionalized α,β-diamino methyl esters 15-18, 20.     

High enzymatic activity preservation with carbon nanotubes incorporated in urease-lipid hybrid Langmuir-Blodgett films

The search for optimized architectures, such as thin films, for the production of biosensors has been challenged in recent decades, and thus, the understanding of molecular interactions that occur at interfaces is essential to improve the construction of nanostructured devices. In this study, we investigated the possibility of using carbon nanotubes in hybrid Langmuir-Blodgett (LB) films of lipids and urease to improve the catalytic performance of the immobilized enzyme. The molecular interactions were first investigated at the air-water interface with the enzyme adsorbed from the aqueous subphase onto Langmuir monolayers of dimyristoylphosphatidic acid (DMPA). The transfer to solid supports as LB films and the subsequent incorporation of carbon nanotubes in the hybrid film permitted us to evaluate how these nanomaterials changed the physical properties of the ultrathin film. Colorimetric measurments indicated that the presence of nanotubes preserved and enhanced the enzyme activity of the film, even after 1 month. These results show that the use of such hybrid films is promising for the development of biosensors with an optimized performance.     

Synthesis,characterization and thermal behavior on solid tartrates of light trivalent lanthanides

Solid state Ln–L compounds, where Ln stands for light trivalent lanthanides (L–Gd) and L is tartrate, have been synthesized. Thermogravimetry and differential thermal analysis (TG/DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, elemental analysis and complexometry were used to characterize and to study the thermal behaviour of these compounds. The results led to information about the composition, dehydration and thermal decomposition of the isolated compounds.     

Molecular conformation of the racemic indan derivative (±)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxamide

This paper presents the structural characterization of the indan derivative (±)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxamide, which was unambiguously determined by X-ray diffraction (XRD) to be a racemate (R/S: 50/50) crystallizing in an achiral crystal structure (P2₁/c, a = 9.3180(1) Å, b = 7.9070(2) Å, c = 19.7550(4) Å, β = 103.250(1)°, V = 1416.75(5) Å³ and Z = 4). The diastereomers are related by the inversion symmetry and linked by H bond forming a dimer. The crystal packing is stabilized by hydrogen bonds, including the classical one responsible for the formation of centrosymmetric dimers, and non-classical ones involving C–H···O and C–H···π-aryl interactions. The intra and intermolecular geometry of the title compound is compared to the (±)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxylic acid one, which also present an achiral crystal structure from racemates (R/S: 50/50). The two indan derivatives crystallize in a very similar unit cell.