RESUMEN
ZnO particles were synthetized by the sol-gel method and subsequent heat treatment of 400, 500 and 600 °C was applied. The nano ZnO particles were incorporated to the unsaturated polyester resin by solution blending at 0.05 wt % concentration. X-ray diffraction detected the formation of a wurtzite-like structure. Viscoelastic behavior of neat polyester and nanocomposites revealed the nano ZnO particles does not promote better mechanical properties because of a weak interaction and the glass transition temperature of the polyester was favored by the presence of a higher quantity of nano-size ZnO particles. Thermogravimetric analysis at 5, 10 and 20 °C/min allowed determining the degradation kinetic parameters based on the Friedman and Kissinger models for neat polyester and nanocomposites. Heating rates promoted an increase in the temperature degradation and the addition of ZnO particles promoted a catalyst effect that reduce the amount of thermal energy needed to start the thermal degradation.
RESUMEN
15alpha-Hydroxy-21-keto-pristimerine (1), a new nortriterpene quinone methide was isolated from the root bark of Maytenus catingarum along with other well-known related compounds, including pristimerine (2), tingenone, and 20alpha-hydroxy-tingenone. The structure of 1 was determined by means of 1H and 13C NMR spectroscopy, including homonuclear and heteronuclear correlations. Compound 1 showed antibiotic activity against Gram-positive bacteria.
Asunto(s)
Antibacterianos/aislamiento & purificación , Rosales/química , Antibacterianos/farmacología , Candida albicans/efectos de los fármacos , Bacterias Gramnegativas/efectos de los fármacos , Bacterias Grampositivas/efectos de los fármacos , Espectroscopía de Resonancia Magnética , Pruebas de Sensibilidad Microbiana , Noresteroides/aislamiento & purificación , Noresteroides/farmacología , Raíces de Plantas/química , Espectrofotometría Infrarroja , Espectrofotometría UltravioletaRESUMEN
Contamination studies by ochratoxin A on pork kidney and chicken liver has been carried out in Catalonia (Spain). 73% of the pork kidney samples analyzed did not contain an amount of ochratoxin A over our detection limit (0.5 ng/g) whereas only 7% had contamination higher than 1 ng/g. None of the chicken samples analyzed were contaminated by this toxin above the detection limit. All contamination levels found are below the maximum levels accepted by several countries for this kind of material. A confirmative test is necessary before discarding false positive samples.