Analyse en spectroscopie infrarouge, de la structure des complexes BF3 du méthanol, des méthanols deutériés et de l'acide acétique Comparaison de la liaison hydrogène et de la liaison donneur-accepteur

A study of the infrared spectra led to the conclusion that the 2-1 complexes formed from two molecules of methyl alcohol or acetic acid and one molecule of BF₃ have an open structure. One methyl alcohol molecule is linked by hydrogen bonding to a second molecule which is attached to BF₃. The consequences of the addition of BF₃ to the OH (OD) vibrators are similar to those of the formation of a hydrogen bond: elevation of the wave number of the in-plane bending vibration and lowering of the wave number of the stretching vibration compared with the monomer.     

Étude infrarouge de complexes aldéhyde-trifluorure de bore Rôle des doublets libres de l'oxygène sur la vibration v(CH)ald

The infrared spectra of some aldehyde-BF₃ complexes were measured from 2.5 μ to 19 μ. The intensity and force constant of the v(CH)_ald range is dependent on the lone-pair electrons of the neighbouring oxygen atom. In the BF₃ complexes the intensity of v(CH)_ald is decreased and shifted 150 cm⁻¹ towards higher frequencies, while the band becomes simple. The addition of BF₃ is verified by checking the v(C=O) band, which is shifted 70 cm⁻¹ towards lower frequencies.     

Superparamagnetic poly(methyl methacrylate) nanoparticles surface modified with folic acid presenting cell uptake mediated by endocytosis

The encapsulation of superparamagnetic nanoparticles (MNPs) in polymeric nanoparticles (NPs) with modified surfaces can improve targeted delivery and induce cell death by hyperthermia. The goals of this study were to synthesize and characterize surface modified superparamagnetic poly(methyl methacrylate) with folic acid (FA) prepared by miniemulsion polymerization (MNPsPMMA-FA) and to evaluate their in vitro cytotoxicity and cellular uptake in non-tumor cells, murine fibroblast (L929) cells and tumor cells that overexpressed folate receptor (FR) β, and chronic myeloid leukemia cells in blast crisis (K562). Lastly, hemolysis assays were performed on human red blood cells. MNPsPMMA-FA presented an average mean diameter of 135 nm and a saturation magnetization (Ms) value of 37 emu/g of iron oxide, as well as superparamagnetic behavior. The MNPsPMMA-FA did not present cytotoxicity in L929 and K562 cells. Cellular uptake assays showed a higher uptake of MNPsPMMA-FA than MNPsPMMA in K562 cells when incubated at 37 °C. On the other hand, MNPsPMMA-FA showed a low uptake when endocytosis mechanisms were blocked at low temperature (4 °C), suggesting that the MNPsPMMA-FA uptake was mediated by endocytosis. High concentrations of MNPsPMMA-FA showed hemocompatibility when incubated for 24 h in human red blood cells. Therefore, our results suggest that these carrier systems can be an excellent alternative in targeted drug delivery via FR.     

On-line redox speciation analysis of antimony using l-proline immobilized on controlled pore glass and hydride generation inductively coupled plasma optical emission spectrometry for detection

l-proline was immobilized on controlled pore glass to study the ability of this material for the separation and preconcentration of Sb(III) and Sb(V). The substrate was packed in a minicolumn and incorporated in a flow injection system. The effluents of the on-line solid phase extraction (before and after elution) were directly coupled to the hydride generation inductively coupled plasma optical emission spectrometry system. The effect of pH, sample (and eluent) volume, flow rates of sample loading and elution on separation of Sb(III) e Sb(V) were evaluated. Our experiments demonstrated that Sb(V) was not retained and it was selectively determined during the loading step, while retained Sb(III) was determined after elution. The proposed system was also used for the selective preconcentration of Sb(III). In this case, a preconcentration factor of 11 and a limit of detection of 90 ng L⁻¹ for Sb(III) were achieved when 8 mL of sample were loaded into the column. The speciation analysis of inorganic Sb in river water and effluent samples was performed using the proposed method. The values obtained for total Sb (obtained by sum of Sb(III) and Sb(V)) were in good agreement with expected values. Recoveries of Sb(III) and Sb(V) in the river water Standard Reference Material 1640 (from National Institute of Standard and Technology) and spiked river waters were between 83 and 111%.     

Two-part fractional regression model with conditional FDH responses: an application to Brazilian agriculture

We extend the notion of a two-part fractional regression model with conditional free disposal hull efficiency responses to accommodate two-stage regression analysis. The two-part regression model includes the binomial model with a nonlinear specification for the expected response in (0,1] and is a more general formulation in the context of fractional regressions. We use nonlinear least squares to assess the effect of covariates in the conditional efficiency response. The approach is applied to Brazilian agricultural county data, as reported in the Brazilian agricultural census of 2006. The efficiency measure is output oriented and assumes variable returns to scale. Output is rural gross income and inputs are land expenses, labor expenses and expenses on other technological inputs. The covariates affecting production are credit, technical assistance, a rural development index, income concentration, measured by the Gini index, and regional dummies. Overall Brazilian rural production performance responds positively to all covariates.

     

The Synthesis and Photoisomerization of 5-Methyl-5-Vinyl-1,3-Cyclopentadiene

A versatile scheme for the synthesis of geminally disubstituted cyclopentadienes is used to prepare the title compound 4 . This remarkably stable vinyl-cyclopentadiene, distinguished by its C_s symmetry, undergoes exclusively electrocyclic ring closure upon direct π–π* excitation at 254 nm. The epimeric vinyl-housenes 11 and 12 , which, for geometric reasons, are insensitive to the walk rearrangement, are suggested to be the primary photo-products. One of them, 12 , due to its syn-oriented vinyl group, undergoes spontaneous copy rearrangement to give 2-methylbicyclo[3.2.1]hepta-2,6-diene ( 13 ). The other, 11 , having an anti-oriented vinyl group, can only undergo thermal return to the starting material 4 . Whereas no leakage to a 1,5-vinyl migration is discernible for the S₁ state of 4 , the benzophenone-sensitized photolysis at 350 nm is shown to be governed by this rearrangement. 1-Methyl-5-vinylcyclopenta-1,3-diene ( 14 ), the unstable primary product of the sensitized photoreaction, is trapped by 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione (PTAD).     

Effets de substituant,d'hétéroatome et de solvant sur les cinétiques de décoloration thermique et les spectres d'absorption de photomérocyanines en série spiro[indoline-oxazine]

Substituent, Heteroatom, and Solvent Effects on the Thermal-Bleaching Kinetics and Absorption Spectra of Photomerocyanines Issued from Spiro[indoline-oxazines] Quantitative information useful for the development of new photochromic systems is obtained from the study of heteroatom and substituent effects on the thermal-bleaching kinetics and the absorption spectra of the photomerocyanines issued from spiro[indoline-oxazines]. The effect on photochromic properties of the presence of N-atoms either in the dimethine bridge or in the aromatic rings has been investigated through the comparison of spiro[indoline-naphthopyrans] C with spiro[indoline-naphthoxazines] A and with spiro[indoline-quinolinoxazines] B . Besides the occurrence of biexponential thermal-bleaching kinetics in non-polar solvents is observed: a tentative explanation for this observation is given which involves the formation, in either sequential or parallel steps, of energetically distinct stereoisomers of the opened form.     

Comprehensive two-dimensional liquid chromatography-based quali-quantitative screening of aqueous phases from pyrolysis bio-oils

Pyrolysis processes are an alternative to minimize the environmental problem associated to agrifood industrial wastes. The main product resulting from these processes is a high-value liquid product, called bio-oil. Recently, the use of comprehensive two-dimensional liquid chromatography (LC × LC) has been demonstrated as a useful tool to improve the characterization of the water-soluble phases of bio-oils, considering their complexity and high water content. However, the precise composition of bio-oils from different agrifood byproducts is still unknown. In the present study, the qualitative and quantitative screening of eight aqueous phases from different biomasses, not yet reported in the literature, using LC × LC is presented. The two-dimensional approach was based on the use of two reverse phase separations. An amide column in the first dimension together with a C18 column in the second dimension were employed. Thanks to the use of diode array and mass spectrometry detection, 28 compounds were identified and quantified in the aqueous phase samples with good figures of merit. Samples showed a distinct quali-quantitative composition and a great predominance of compounds belonging to aldehydes, ketones and phenols, most of them with high polarity.     

Analytical characterization of mannosylerythritol lipid biosurfactants produced by biosynthesis based on feedstock sources from the agrofood industry

Mannosylerythritol lipids (MELs) are currently one of the most promising biosurfactants because of their multifunctional applications and good biodegradability. Depending on the yeast strain and the feedstock used for the fermentation process, structural variations in the MELs obtained occur. Therefore, MELs produced by Pseudozyma aphidis DSMZ 70725 with a soybean oil feedstock were characterized by chromatography and mass spectrometry (MS). Column chromatography with silica provided fractionation of the different types of MEL. High-performance liquid chromatography combined with MS was employed for the analysis of the MEL fractions and crude mixtures. A characteristic MS pattern for the MELs was obtained and indications of the presence of new MEL homologues, showing the incorporation of longer and more unsaturated fatty acid chains than previously reported, were given. Gas chromatography?CMS analysis confirmed the presence of such unsaturated fatty acid chains in the MELs, demonstrating the incorporation of fatty acids with lengths ranging from C₈ to C₁₄ and with up to two unsaturations per chain. The incorporation of C₁₆ and C₁₈ fatty acid chains requires further investigation. MS/MS data allowed the unambiguous identification of the fatty acids present in the MELs. The product ion spectra also revealed the presence of a new isomeric class of MELs, bearing an acetyl group on the erythritol moiety.     

Synthesis of Homo- and Heterofunctionalized Glycoclusters and Binding to Pseudomonas aeruginosa Lectins PA-IL and PA-IIL

Homo- and heterofunctionalized glycoclusters with galactose and/or fucose residues targeting both PA-IL and PA-IIL lectins of Pseudomonas aeruginosa were synthesized using "Click" chemistry and DNA chemistry. Their binding to lectins (separately or in a mixture) was studied using a DNA Directed Immobilization carbohydrate microarray. Homoglycoclusters bind selectively to their lectin while the heteroglycocluster binds simultaneously both lectins with a slight lower affinity.