Thursday, October 23, 2014

 

 



Soy un nuevo usuario

Olvidé mi contraseña

Entrada usuarios

Lógica Matemáticas Astronomía y Astrofísica Física Química Ciencias de la Vida
Ciencias de la Tierra y Espacio Ciencias Agrarias Ciencias Médicas Ciencias Tecnológicas Antropología Demografía
Ciencias Económicas Geografía Historia Ciencias Jurídicas y Derecho Lingüística Pedagogía
Ciencia Política Psicología Artes y Letras Sociología Ética Filosofía
 

rss_1.0 Clasificación por Disciplina

Nomenclatura Unesco > (23) Química

Mostrando recursos 201 - 220 de 41,369

201. Zn(II), Cd(II) and Cu(II) separation through organic–inorganic Hybrid Membranes containing di-(2-ethylhexyl) phosphoric acid or di-(2-ethylhexyl) dithiophosphoric acid as a carrier - Resina Gallego, Montserrat; Macanàs de Benito, Jorge; de Gyves Marciniak, Josefina; Muñoz Tapia, Maria
A membrane process for metal recovery from aqueous solutions was studied. Metal ions diffused from the feed solution to the stripping phase through an Hybrid Membrane containing di-(2-ethylhexyl) phosphoric acid (D2EHPA) and/or di-(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA) as a carrier. Such membranes were prepared by a sol–gel route including cellulose triacetate and polysiloxanes. Transport behaviour was evaluated for both carriers under similar experimental conditions. The transport experiments reported here concerned transport at different cycles and selectivity towards different metal ions. Using D2EHPA the membrane provided a selective transport of zinc to the stripping compartment of the membrane cell, while copper and...

202. Electrophoresis and stability of nano-colloids: History, theory and experimental examples - Felix, C.; Yaroshchuk, Andriy; Pasupathi, S.; Pollet, B. G.; Bondarenko, M.P.; Kovalchuk, V.I.; Zholkovskij, Emiliy K.
The paper contains an extended historical overview of research activities focused on determining interfacial potential and charge of dispersed particles from electrophoretic and coagulation dynamic measurements. Particular attention is paid to nano-suspensions for which application of Standard Electrokinetic Model (SEM) to analysis of experimental data encounters difficulties, especially, when the solutions contain more than two ions, the particle charge depends on the solution composition and zeta-potentials are high. Detailed statements of Standard Electrokinetic and DLVO Models are given in the forms that are capable of addressing electrophoresis and interaction of particles for arbitrary ratios of the particle to Debye radius,...

203. Electrocatalytic production of hydrogen boosted by organic pollutants and visible light - Soler Turu, Lluis; Macanàs de Benito, Jorge; Muñoz Tapia, Maria; Casado Giménez, Juan
A new method to produce high-purity hydrogen using photoelectrocatalytic reactions is studied. This integrated process uses solar energy and the Gibbs free energy of oxidation of organic wastes to help reducing the energy consumption of water electrolysis. The method diminishes the thermodynamic potential to 0.77 V and practical voltages to ca. 1.2 V, due to an electrocatalytic reaction in the presence of iron ions. The anolyte is illuminated, and separated from the catholyte by a proton exchange membrane. The process oxidizes water pollutants and avoids the anodic corrosion of a stainless steel anode, but not every sacrificial substance has a...

204. Estudio comparativo de la composición química de los aceites esenciales de aloysia triphylla l´her britton cultivada en diferentes regiones de colombia. - Stashenko, Elena; Martínez, Jairo René; Durán G., Diego Camilo; Díaz, Olga Liliana
Essential oils were obtained with microwave-assisted hydrodistillation from Aloysia triphylla plants collected at three stages of development in three different regions of Colombia. Their composition was determined by GC-MS (EI, 70 eV). The main component in all oils was citral (32-41%). The highest oil yield was obtained from plants collected in Bolívar, Santander (0.88%). Plants with 2 months of development and before flowering, showed the largest content of metabolites of interest

205. Determinación mediante hs-spme/gc-ms, de la composición química de la fragancia y el absoluto de las flores de posoqueria latifolia. - Martínez Morales, Jairo; Stashenko, Elena; Ariza, Oscar Augusto; Rueda Parra, Elkin Darío; Archila, Johanna Andrea
The chemical compositions of the absolute and the fragrance of the flowers of Posoqueria latifolia were determined by GC-MS (EI, 70 eV) . The fragrance was sampled in vivo by means of HS-SPME. The compounds found in the fragrance were (Z)-3-hexenyl acetate (80.7%) and hexyl acetate (5.8%). The absolute was obtained from the concrete of the flowers by means of ethanolic extraction at 38 ºC. The main compounds found in the absolute were 1-pentacosane (26.2%), benzyl salicylate (7.4%), tricosane (5.9), linolenic acid (4.8%), pentacosane (4.5%), benzyl benzoate (3.3%) and eugenol (2.8%).

206. Estudio quimico y obtencion de principios activos de la especie rollinia pittieri (annonaceae) del alto sinu. - Torres, Omar; Angulo Ortiz, Alberto; Santafe Patiño, Gilmar; Saez Vega, Jairo; Alberto Rojano, Benjamín; Villa, Hiltony; Montaño, Mary; Galeano, Paula
From the etanolic extract of the leaves, bark and wood of the Rollinia Pittieri ( Annonaceae) were isolated and identified five alkaloids with aporphine nucleus: Anonaine 1, Nornuciferine 2, O-methilmoschatoline 3, Isomoschatoline 4 and Liriodenine 5; two flavoniods: 5,7,3´,4´-tetrahidroxi-3- O-rhamnosil-2-phenilcromone 6, 5,7,4´-tetrahidroxi-3-O-rhamnosil-2- phenilcromone 7. All compounds were identified by spectroscopic methods (IR, UV MS, 1H NMR and 13C NMR,), including 2D techniques and by comparison with dates reported spectroscopic in the literature. The compound 7 showed a significant activity catcher of free radicals according to the DPPH, ABTS and Enzimatic Generation of Superoxid Anion essays.

207. Tamizaje fitoquimico y actividad antioxidante de extractos acuoso y orgánicos de justicia pectoralis jacq. (amansa toros) y de volátiles y no volátiles de lippia alba mill. (pronto alivio) cultivadas en diferentes pisos térmicos.
El uso de Justicia pectoralis Jacq. y Lippia alba Mill en la cultura popular colombiana en el tratamiento de diferentes enfermedades y su escaso conocimiento y aplicabilidad en la región tolimense, motivó el estudio de estas especies vegetales a fin de determinar el efecto del cambio altitudinal en la actividad antioxidante de los extractos acuoso y orgánicos de J. pectoralis y de los volátiles y no volátiles de L. alba. Las diferencias de altitud no modifican la proporción relativa de los constituyentes químicos, lo que a su vez no influye en la actividad antioxidante de estas especies.

208. Azafluorenonas en corteza de oxandra longipetala r. e. fr. (annonaceae). - Angulo Ortiz, Alberto; Cuca Suarez, Luis E.; Santafe Patiño, Gilmar; Torres, Omar
El estudio químico del extracto de alcaloides totales, realizado por el método clásico, de la corteza de Oxandra longipetala R. E. Fr., colectada en el departamento de Córdoba, Colombia, permitió el aislamiento e identificación de cuatro alcaloides de tipo azafluorenona: ursulina, isoursulina, O-metilmacondina y macondina, junto con las oxoaporfinas lysicamina, O-metilmoschatolina, y liriodenina. Las estructuras fueron elucidadas por métodos espectroscópicos (UV, IR, RMN-1H, RMN-13C, experimentos 2D, espectrometría de masas) y por comparación con datos de la literatura.

209. Estudio de la composición química y la actividad biológica de los aceites esenciales de diez plantas aromáticas colombianas. - Martínez, Jairo René; Stashenko, Elena; Castañeda, Martha I.; Muñoz, Amner
En este estudio se determinó la composición química de los aceites esenciales (AEs) de las hojas de 10 plantas aromáticas colombianas. Los AEs se aislaron empleando la técnica de hidrodestilación asistida por la radiación de microondas (MWHD) y la identificación de los componentes de los AEs se realizó mediante el análisis por cromatografía de gases � espectrometría de masas (GC-MS), utilizando dos columnas (DB-5 y DB-Wax). La identificación de los compuestos se basó en los índices de Kovàts y en la comparación de los espectros de masas con los de las bases de datos QuadLib2004, NIST 2002, Wiley 138k.

210. Composición química del aceite esencial de hojas y tallos de bursera graveolens (burseraceae) de colombia. - Leyva, Miguel Antonio; Martínez, Jairo René; Stashenko, Elena
The essential oils of leaves and stems of Bursera graveolens (Burseraceae family), were obtained using microwave-assisted hydrodistillation (MWHD) and analyzed by gas chromatography-mass spectrometry (EI, 70 eV). The main components found in the oil of leaves were: limonene (48.3%), caryophyllene oxide (13.6%) and trans-caryophyllene (8.1%). The essential oil of stems showed a higher content of limonene (42.1%), myrcene (19.8%) and menthofuran (14.7). The components Z-b-ocymene (14.3%) and menthofuran present in the oil of stems, were not found in the essential oil of leaves.

211. Química y actividad biologica de chromolaena perglabra. - Rodriguez, Oscar E.; Torrenegra G., Rubén D.
Esta investigación se encaminó a determinar los metabolitos secundarios presentes en hojas y tallos de la especie: Chromolaena perglabra (B. L. Robinson) King & H. Rob., colectada en Tinjacá (Boyacá � Colombia). Se estableció la actividad antiprotozoaria (leishmaniosis y chagas.) y toxicidad. Los resultados de este trabajo suministraron herramientas para validar el uso de esta especie considerada maleza. Se encontró actividad significativa in Vitro contra agentes causantes de chagas y leishmaniosis en algunos extractos y fracciones. Se identificaron esteroides y flavonoides; se estableció de manera preliminar la toxicidad para reconocer parte de los riesgos inherentes a su uso.

212. Química y actividades antioxidante y bactericida del extracto etanólico del hongo ganoderma lucidum. - Angulo Ortiz, Alberto; Santafe Patiño, Gilmar; Zuluaga Vega, Juan; Pérez C., Carlos; Torres, Omar
The ethanolic extract of the fungi Ganoderma lucidum was analyzed by HRGCMS identifying 14 compounds highlighting 4,4-dimethyl-ergosta-7-en-3â-ol (4), 4-methyl-2-nitropentan-1-ol (5), 1-nitrododeca-2,10-dien-6-ino (6), 4-methylergosta- 5,7,9,14,22,24-hexen-3-ol (13) y 4-methyl-23-isopropyl-ergosta- 5,7,9,14,22,24-hexen-3-ol (14). Information about these compounds was not found in the bibliography, therefore, these can be considered as new chemical compounds. The bactericide assay showed negative results. The antioxidant activity was carried out by DPPH and ABTS methods finding values of EC50 = 48.7 ppm and 15.5 ppm in the EtOAc subextract and 80.7 ppm y 19.2 ppm in the CH2Cl2 subextract, respectively.

213. Estudio quimico preliminar de los fenoles y polifenoles de dos accesiones de calliandra calothyrsus (mimosaceae). - Moreno M., Bárbara; Quevedo, Rodolfo; Sánchez, Angélica; Carulla F., Juan E.
Chemical composition and relative amounts of phenolic compounds and condensed tannins in two accessions of the forage tree Calliandra calothyrsus were evaluated. Chromatographic and spectroscopic techniques were used to find clear differences between the samples. Among mayor low mass compounds the isoflavones: genistein, prunetin and 7-O-glucosylgenistein were found. Furthermore catechins, quercetin, miricetin and their dihydroderivatives, EGC and EGCG were identified. By Maldi-tof and ESI methods, until pentamers of different phenolic units, according the Krueger�s rule, were detected.

214. Evaluacion quimica del extracto total etanolico de las hojas y corteza fresca de muntingia calabura (elaeocarpaceae). - Marquez Vizcaino, Rita Luz; Mendoza Mendoza, Danys; Parejo Alcocer, Maria Stella; Hernández S., Rosario; Martinez Gonzalez, Alex; Vanegas Contreras, Ana Milena
The phytochemical screening of the ethanolic extract of the fresh leaves showed the presence of alkaloids, flavonoids, phenolic compounds and terpens. In the fresh bark, it was showed the absence of alkaloids as well as the presence of tannins and saponins.

215. Comparación de la composición química y de la actividad biológica de los aceites esenciales de lippia alba (mill.) n.e.br., obtenidos variando las condiciones de extracción y secado. - Martínez, Jairo René; Durán G., Diego Camilo; Gómez, Germán Augusto; Olivero Verbel, Jesús
A comparison was made between the chemical composition and biological activity of Lippia alba essential oils, obtained by microwave-assisted hydrodistillation, MWHD under different extraction times and plant drying (in the shade) levels. The essential oils were analyzed by GC-MS. Although the oils were qualitatively similar, quantitative differences in the composition and significant oil yield differences were observed. The oil with the highest yield (2.2 % w/w) and limonene and carvone content was obtained after 45 min extraction from plant material dried for 4 days. The highest toxicity against Artemia franciscana was shown by the oil obtained after 60 min extraction from plant material dried for 3 days.

216. Determinación de la composición química y actividad antioxidante in vitro del aceite esencial de piper auritum kunth (piperaceae) difundida en la costa colombiana. - Martínez, Jairo René; Stashenko, Elena; Leyva, Miguel Antonio; Garcia Rios, Alejandro
The essential oil of leaves and inflorescences of Pipper auritum, was obtained by microwave-assisted hydrodistillation (MWHD) and analyzed by means of high resolution gas chromatography coupled to mass spectrometry (HRGC-MS). The extraction yield was 2,3% (leaves) and 2,4% (inflorescences). The main components were safrol (94,0% in leaves and 90,3% in inflorescences) and myristycin, (3,2% in leaves and 5,8% in inflorescences). The antioxidant activity of the oil was evaluated and compared with that of vitamin E.

217. Estudio comparativo de la composición química de aceites esenciales de lippia alba provenientes de diferentes regiones de colombia, y efecto del tiempo de destilación sobre la composición del aceite. - Martínez, Jairo René; Stashenko, Elena; Monsalve, Luz Adriana; Durán G., Diego Camilo
Microwave-assisted hydrodistilation (MWHD) was used to obtain the essential oils of Lippia alba plants collected in 16 Colombian locations. The composition of these oils was determined by GC-MS, based on chromatographic and spectroscopic criteria. The effects of leaf ripeness, distillation time, and the manufacturing material of the stills (copper and steel stainless) on chemical composition and extraction yield were evaluated.

218. Analogías y modelización en la enseñanza del cambio químico - Aragón, M.M; Oliva, J.M; Navarrete, A.

219. Hormigones de alta resistencia con fibras de poliolefina - Castillo Ventura, Julio
El hormigón constituye la base del desarrollo moderno de la humanidad, gracias a este material homogéneo compuesto de materiales heterogéneos hoy en día podemos disfrutar de las maravillosas construcciones hechas por el hombre a lo largo de la historia. Este material ha experimentado mejoras en los últimos años, las cuales han contribuido con el fortalecimiento de sus propiedades físicas y químicas, lo que lo ha convertido en el material más utilizado en la construcción. El hormigón de alta resistencia es una de las mejoras que ha experimentado el hormigón convencional. Este material ha hecho posible la construcción de estructuras cada...

220. O ensino e a aprendizagem da Química e da Bioquímica no ensino superior apoiado nas novas tecnologias da informação e da comunicação - Belo, João Luís de Morais de Oliveira
Actualmente com o desenvolvimento das novas Tecnologias da Informação e Comunicação (TIC) abriram-se novos caminhos para o ensino das Ciências, permitindo desenvolver novas técnicas de ensino bem como melhorar as antigas. Com vista a permitir um melhor ensino e aprendizagem da Química e da Bioquímica, pretende-se recorrer às novas TIC como suporte às aulas “tradicionais”. Com este trabalho pretende-se conseguir uma melhor transmissão de conhecimentos, bem como uma melhor avaliação dos mesmos, apoiando-nos nas tecnologias e aplicações emergente, tais como os “Campus Virtuais”, os programas de ensino e avaliação on-line (E-learning), os quadros interactivos, cuja utilização não fica restrita à sala de aula nem ao horário da unidade curricular. São...

 

Busque un recurso