Combinación de radicales metilo y la descomposición del etano del vibracionalmente excitado

(1) A 94,5° C los radicales se produjeron por fotólisis de la metil isopropil cetona y a 146,5°C por pirólisis de di t-butil peróxido en presencia de isobutiraldehido. El cociente X (ecuación (1)) se determinó a distintas presiones, encontrándose que para presiones mayores que 10 torr, X era independiente de la misma, y su valor a ambas temperaturas es 4,0 ± 0,2 de acuerdo con lo encontrado por otros investigadores. Al disminuir la presión se encontró que X aumentaba. Esto está de acuerdo con lo esperado, dado que k1 debe disminuir al disminuir la presión total en el sistema. Se determinaron curvas completas para esta dependencia con la presión a ambas temperaturas. b)Teórico Las experiencias anteriores se realizaron con el fin de aclarar en lo posible el confuso panorama presentado por los resultados experimentales obtenidos tanto para la reacción (1) como para su inversa (la descomposición unimolecular de la molécula de etano). El objetivo final de esta tesis era seleccionar los datos más representativos del sistema y tratar una interpretación teórica de los mismos. Esto se logró aplicando la Teoría de Reacciones Unimoleculares en la versión cuántica de Marcus. El problema consistía en encontrar un modelo de complejo activado que reprodujese los resultados experimentales desde temperatura ambiente hasta 700°C. Esta coincidencia se pudo obtener en base a un modelo propuesto por Laidler para la pirólisis del etano a altas temperaturas, ligeramente modificado. Con este modelo se calcularon las curvas de dependencia con la presión en todo el rango de temperaturas, encontrándose una razonable concordancia con nuestros resultados y los provenientes de pirólisis del etano.Fil: Previtali, Carlos Mario. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Simple procedures for analyzing and purifying methylene green

Methylene green is a versatile dye that can be used in a wide range of technical applications, most of which require the dye to be pure. Because commercial lots of methylene green are known to be heterogeneous, we report a thin layer chromatographic method for checking purity. We also describe a simple and effective flash chromatographic purification procedure for subsequent purification. The identity and purity of the dye can be checked easily using UV-visible absorption spectrum measurements or by more sophisticated procedures if necessary. © 2012 The Biological Stain Commission.Fil: Glusko, Carlos Abel. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Previtali, Carlos Mario. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Chesta, Carlos Alberto. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Montejano, Hernan Alfredo. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentin

Quenching of the triplet state of safranine-O by aliphatic amines in AOT reverse micelles studied by transient absorption spectroscopy

The photophysics of Safranine-O (3,6-diamino-2,7-dimethyl-5 phenyl phenazinium chloride) (SfH+Cl-) was investigated in reverse micelles (RMs) of AOT  (sodium bis(2-ethylhexyl) sulfosuccinate) with special emphasis on the triplet state processes. The excited singlet state properties were measured by absorption and fluorescence spectroscopy. Steady state anisotropy was also measured as a function of the water content. All the measurements indicate that the dye is localized in the interface, sensing a medium of polarity similar to EtOH:water (3:1) mixtures. The triplet is formed in its monoprotonated form, independently of the pH of the water used to prepare the RMs. The  maximum of the T-T absorption spectrum in RMs confirms this conclusion. The triplet lifetime is much longer in AOT RMs than in homogeneous organic solvents. The intersystem crossing quantum yields are similar to those in organic solvents. A remarkable difference is observed in the quenching by aliphatic amines, while the quenching by the hydrophobic tributylamine is similar to that in methanol, the hydro-soluble triethanolamine is one order of magnitude more effective in RMs than in homogeneous solution. In the latter case  the quenching process is interpreted by a very fast intramicellar quenching, the overall kinetics being controlled by the exchange of amine molecules between RMs. Semireduced dye is formed in the quenching process in RMs in the di-protonated state with a comparable quantum yield to the monoprotonated state formed in homogeneous solvents. The results point to the advantage of the reverse micellar system for the generation of active radicals for the initiation of vinyl polymerization, since a much lower concentration of amine can be employed with similar quantum yields.Fil: Porcal, Gabriela Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Chesta, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Biasutti, Maria Alicia. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Previtali, Carlos Mario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin

Dihydroquinidine versus disopyramide: Efficacy in patients with chronic stable ventricular ectopy

Dihydroquinidine (DQ) is contained in substantial amounts in quinidine salts, but its direct antiarrhythmic action has not been studied. The efficacy of oral DQ (300 mg t. i. d.) compared to disopyramide (D) (200 mg t.i.d.) was thus investigated using a double-blind crossover placebo-controlled protocol in 12 patients, aged 13 to 67 years, with chronic stable high frequency premature ventricular beats (PVB), defined as greater than 100 PVB/h during 48-72-h control Holter monitoring. The protocol included three 72-h treatment periods: DQ, D, and placebo at random. On days 2 and 3 of each period a 24-h Holter recording was carried out; drug blood levels were determined at peak (days 2 and 3) and trough time (day 3). No significant difference in the mean PVB/h was found between control (735 +/- 400) and placebo periods (564 +/- 388), or between the two Holter recordings of each period. Compared to placebo both DQ (106 +/- 113, p less than 0.005) and D (240 +/- 263, p less than 0.05) reduced the mean PVB/h, but the decrease was significantly higher with DQ (78 versus 53%, p less than 0.02). Nine patients (75%) on DQ and 5 (42%) on D had a greater than 70% decrease in mean PVB/h; complex PVBs were abolished in 3 of 6 patients on both treatments. On day 3, DQ plasma levels were 1.31 +/- 0.44 (peak) and 0.92 +/- 0.45 (trough) mg/l; D plasma levels were 2.88 +/- 0.64 (peak) and 2.02 +/- 0.31 (trough) mg/l; no significant difference was found between day 2 and day 3 samples.(ABSTRACT TRUNCATED AT 250 WORDS

Photophysics and photochemistry of porphyrin core PAMAM dendrimers. Excited states interaction with quinones

Quenching of excited states of the meso-substituted tetraphenyl porphyrins with PAMAM branches, and one with PAMAM generation 1 peripherally-modified with thiazole groups by p-benzoquinones, were studied in DMF solution. Fluorescence lifetime measurements evidence a static component in the quenching process. The dynamic quenching rate constants were close to the diffusional limit except for the case of duroquinone. Apparent association constants of the porphyrin compounds with the quinones were determined by comparison of static and dynamic measurements of fluorescence quenching. The ground state interaction is very weak with the exception of tetrachlorobenzoquinone. The triplet state decay kinetics and the transient absorption spectra in the presence of the quinones were determined by laser flash photolysis. Triplet quenching rate constants were lower than those of singlet quenching. An electron transfer mechanism was proposed to explain the results. The long-time transient absorption spectra were assigned to the radical cation of the dyes. Relative radical yields were determined and a dependence on the side chains and the quencher was observed.Fil: Militello, María Paula. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Hernández Ramírez, Raquel E.. Tecnológico de Estudios Superiores de Coacalco; MéxicoFil: Lijanova, Irina Victorovna. Instituto Politécnico Nacional; MéxicoFil: Montejano, Hernan Alfredo. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Previtali, Carlos Mario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentin

Dobutamine stress echocardiography for assessing the role of dynamic intraventricular obstruction in left ventricular ballooning syndrome

<p>Abstract</p> <p>Background</p> <p>Dynamic intraventricular obstruction has been observed in patients with left ventricular ballooning syndrome (LVBS) and has been hypothesized as a possible mechanism of the syndrome. The aim of this study was to assess the prevalence and significance of dynamic intraventricular obstruction in patients with LVBS.</p> <p>Methods and Results</p> <p>Dobutamine stress echocardiography was carried out in 22 patients with LVBS (82% apical), all women, aged 68 ± 9 years. At baseline 1 patient had a > 30 mmHg LV gradient; during stress a LV gradient > 30 mm Hg developed in 6/21 patients (28%) and was caused by systolic anterior motion of the mitral valve in the 3 patients with severe gradient (mean 116 ± 29 mmHg), who developed mitral regurgitation and impaired apical wall motion and by obstruction at mid-ventricular level in the other 3 with a moderate gradient (mean 46 ± 16 mmHg). Compared with patients without obstruction those with obstruction had a greater mean septal thickness (11.6 ± .6 vs 9.8. ± 3, p < .01), a higher prevalence of septal hypertrophy (71% vs 7%, p < .005) and a higher peak wall motion score index (1.62 ± .4 vs 1.08 ± .4, p < .01).</p> <p>Conclusion</p> <p>Spontaneous or dobutamine-induced dynamic LV obstruction is documented in 32% of patients with LVBS, is correlated with the presence of septal hypertrophy and may play a role in the development of LVBS in this subset of patients. In those without septal hypertrophy a dynamic obstruction is rarely induced with dobutamine and is unlikely to be a major pathogenetic factor of the syndrome.</p