Chemistry

Abstract The influence of dissolved substances on the temperature of the maximum density of water has been studied in relation to their effect on water structure as they can change the equilibrium between structured and unstructured species of water. However, most work has been performed using salts and the studies with small organic solutes such as amides are scarce. In this work, the effect of acetamide, propionamide and butyramide on the temperature of maximum density of water was determined from density measurements using a magnetic float densimeter. Densities of aqueous solutions were measured within the temperature range from T = (275.65–278.65) K at intervals of 0.50 K in the concentration range between (0.10000 and 0.80000) mol·kg−1. The temperature of maximum density was determined from the experimental results. The effect of the three amides is to decrease the temperature of maximum density of water and the change does not follow the Despretz equation. The results are discussed in terms of solute-water interactions and the disrupting effect of amides on water structure.

Hierarchical ZSM-5 zeolites were prepared by alkali treatment (desilication) at two temperatures, two reaction times, and two NaOH concentrations. A 2 factorial design was used to study the effect of these variables on the crystallinity, microporosity, and mesoporosity of the zeolite due to the desilication treatment. The factorial design analysis showed that the temperature, reaction time and NaOH concentration and the second order interaction between temperature and time have statistically significant effect on the micropore volume. On mesopore volumes (Vmeso) and areas (Smeso), the reaction time and NaOH concentration factors have statistically significant effects. In the case of mesopore volumes, the second order reaction time and NaOH concentration interaction factor are also significant. On the other hand, only the alkali concentration affected, negatively, the relative crystallinity. Two hierarchical ZSM-5 zeolites with the highest relative crystallinity and mesoporosity were...

New macrocyclic compounds having two benzoxazine subunits joined by two ethylene bridges have been prepared by Mannich condensation of the appropriate 4-hydroxyphenylethylamine with an excess of formaldehyde. This is a general method for synthesising a new family of heterocyclophanes.

Durante el estudio de la potencial actividad toxica del extracto alcoholico de ios tallos de la especie nativa Berberis glauca (HBK) (Berberidaceae). se realizaron bioensayos con larvas del crustaceo Artemia salina, y de los insectos Musca domestica (Diptera) y Spodoptera sunia (Lepidoptera). La fraccion alcaloidal soluble en CHCl, obtenida por extraccion acido-base del extracto etanolico mostro notable accion antialimentaria frente a larvas de 3° y 4° estadio de la polilla S. sunia. La separacion cromatografica guiada por bioensayos permitio aislar y purificar de la fraccion de mayor actividad varios alcaloides benciltctrahidroisoquinolinicos. Por metodos espectroscopicos se identificaron berbamina, isotalicberina. O- metilisotalicberina y 7- 0-demetilisotalicberina. Este es el primer reporte sobre la presencia de bases dimericas bisbenciltetrahidroisoquinolinicas (bbi) en especies de Berberis colombianas. Ademas se detecto la presencia de una base dimerica novedosa de PM 712 cuya ...

Se aislaron triterpenos de los frutos de tres especies de Clusia (familia Guttiferae). En C.multlflora y C. grandiflora se encontraron eufenol, epimero en C-20 del tirucallol, y 3 ceto eufano antes no reportados para este genero. Tambien se encontro isocariofileno en C. grandiflora.

RESUMEN El fraccionamiento guiado por bioensayos, frente a larvas del crustáceo Artemia salina y del insecto Culex quinquefasciatus, del extracto alcaloidal de tallos de Berberis tabiensis (Berberidaceae) condujo al aislamiento de un nuevo alcaloide del tipo aporfina-bencilisoquinolina oxidado (tabienina A). El análisis estructural se realizó por medio de métodos químicos y espectroscópicos.

The species Chelananthus alatus is an herbaceous plant with known ethno botanical and medicinal properties used in control of fever, especially those produced by malaria. From dried leaves (1.11 Kg), the crude alcoholic extract was fractionated by liquid-liquid partition with different polarity solvents. From the sec-butyl alcohol soluble fraction, by successive application of chromatographic methods, four compounds type iridoid were isolated and identified by spectroscopic techniques. Compound 1 is a new secoiridoid which was identified as sweroside 7-isobutyryloxy, and it is reported here for the first time in the Gentianaceae family; the other secoiridoids which were isolated are known as vogeloside (2), dihydro-chelonanthoside (3) and sweroside (4); vogeloside was identified for the first time in this plant (C. alatus). From the isopropyl acetate extract, in conjunction with the sweroside 7-isobutyryloxy (1), chelonanthoside (5) and sweroside (4), were identified, along with the sweroside 7-isovaleryloxy-(6) as a new side chain isomeric ester of dihydrochelonanthoside (3). This work presents the spectroscopic analysis of the new structures and some bioactivity data.

De ios extractos de los frutos de C. saruliensis, C. minor y C. criuva y de las raíces de C. eugenioides, se separaron por Cromatografía de Columna, unas fracciones oleosas incoloras, constituidas en gran mayoría por hidrocarburos sesquiterpénicos y derivados oxigenados de éstos. La identificación de los compuestos se efectuó por Cromatografía de Gases y Espectrometría de Masas.

realizó un experimento con el objeto de evaluar la actividad insecticida de extractos etanólicos de las plantas Berberis samacana, Berberis saboyana, Nycandria physa/oides, Eucaliptus g/obu/us y Sa/picroa difussa, cuando son usados en concentraciones de 100, 1.000 Y 10.000 ppm, con el fin de determinar efectos favorables o desfavorables para el desarrollo de Tecia so/anivora (Lepidoptera: Gelechiidae). Se usó un Diseño Completamernte al Azar, tomando como unidad experimental 500 gramos de papa criolla So/anum phureja, a los cuales se aplicaron los tratamientos, consistentes en sumergir los tubérculos en los extractos por un tiempo de 5 minutos e infestando cada unidad con 15 larvas de primer instar, luego de comprobada la evaporación del solvente.

Se aislaron triterpenos de los frutos de tres espedes de Clusia (familia Guttiferae). En C. multlflora y C. grandiflora se encontraron eufd, eplmero en C-20 del tirucalld, y 3 ceto eufano antes no reportados para este género. Tamt>ién se encontró isocarioflleno en C. grandiflora.

Durante el estudio de la potencial actividad toxica del extracto alcoholico de ios tallos de la especie nativa Berberis glauca (HBK) (Berberidaceae). se realizaron bioensayos con larvas del crustaceo Artemia salina, y de los insectos Musca domestica (Diptera) y Spodoptera sunia (Lepidoptera). La fraccion alcaloidal soluble en CHCl, obtenida por extraccion acido-base del extracto etanolico mostro notable accion antialimentaria frente a larvas de 3° y 4° estadio de la polilla S. sunia. La separacion cromatografica guiada por bioensayos permitio aislar y purificar de la fraccion de mayor actividad varios alcaloides benciltctrahidroisoquinolinicos. Por metodos espectroscopicos se identificaron berbamina, isotalicberina. O- metilisotalicberina y 7- 0-demetilisotalicberina. Este es el primer reporte sobre la presencia de bases dimericas bisbenciltetrahidroisoquinolinicas (bbi) en especies de Berberis colombianas. Ademas se detecto la presencia de una base dimerica novedosa de PM 712 cuya ...

It is generally accepted that filtering microRNA (miRNA) target predictions by conservation or by accessibility can reduce the false discovery rate. However, these two strategies are usually not exploited in a combined and flexible manner. Here, we introduce PACCMIT, a flexible method that filters miRNA binding sites by their conservation, accessibility, or both. The improvement in performance obtained with each of these three filters is demonstrated on the prediction of targets for both i) highly and ii) weakly conserved miRNAs, i.e., in two scenarios in which the miRNA-target interactions are subjected to different evolutionary pressures. We show that in the first scenario conservation is a better filter than accessibility (as both sensitivity and precision are higher among the top predictions) and that the combined filter improves performance of PACCMIT even further. In the second scenario, on the other hand, the accessibility filter performs better than both the conservation and combined filters, suggesting that the site conservation is not equally effective in rejecting false positive predictions for all miRNAs. Regarding the quality of the ranking criterion proposed by Robins and Press and used in PACCMIT, it is shown that top ranking interactions correspond to more downregulated proteins than do the lower ranking interactions. Comparison with several other target prediction algorithms shows that the ranking of predictions provided by PACCMIT is at least as good as the ranking generated by other conservation-based methods and considerably better than the energy-based ranking used in other accessibility-based methods.