Francisco López

Effect of low oral doses of disopyramide and amiodarone on ventricular and atrial arrhythmias of chagasic patients with advanced myocardial damage

Low-dose (7 mg/kg per day) disopyramide administration to arrhythmic chagasic patients decreased the frequency of ventricular extrasystoles in 4 of 17 patients (24%) and suppressed most complex ventricular arrhythmias in 12 of 15 patients (80%). This assessment was made from 72-h continuous Holter monitoring recorded during the course of this double blind, placebo-controlled randomized crossover study. Seven patients (41%) complained of anticholinergic side effects, but no contractile or conduction system depression was seen. Amiodarone (200 mg) given on a single blind, placebo-controlled basis to 9 of these patients reduced the frequency of ventricular extrasystoles in 6 of 9 patients (67%) and suppressed complex ventricular ectopy in 6 of 7 patients (85%). One patient was unable to tolerate this drug (11%). Both drugs seemed less effective in controlling supraventricular arrhythmias, although disopyramide eliminated paroxysms of supraventricular tachycardia in 9 of 13 (69%) and amiodarone in all 6 patients with this arrhythmia. Amiodarone appears to be a better antiarrhythmic drug for chagasic patients, due to its greater effectiveness and lower incidence of side effects.

Epichlorohydrin polymerization using diphenylzinc-cocatalyst systems in benzene solution

SummaryVarious diphenylzinc-cocatalyst systems were used as initiators of epichlorohydrin polymerization in benzene solution. Water, acetone, butanone, acetophenone and cyclopentanone were employed as cocatalyst but in the most of the cases diphenylzinc alone produced the better conversion to polymer. GPC results suggest the presence of more than one active species for the polymerization initiated by those systems. For diphenylzinc alone as initiator the reaction at 120°C is first order with respect to monomer with kp=1.21x10 -5L mol-1sec-1.

Some aspects on the polymerization of ethylene oxide initiated by diphenylzinc-butanone and diphenylzinc-cyclohexanone systems

SummaryThe diphenylzinc-butanone and diphenylzinc-cyclohexanone systems were used as catalyst for ethylene oxide polymerization in benzene solution at 60°C. The catalytic activity of both systems is influenced by the molar ratio of ketone to diphenylzinc. Regardless of the molar ratio employed, the diphenylzinc-cyclohexanone combination was more active in the polymerization than diphenylzinc-butanone system. GPC results strongly suggest the presence of more than one active species for these systems.

Propylene oxide polymerization using the diphenylzinc-acetone system in benzene at 60°C

SummaryThe diphenylzinc-acetone system was used as catalyst for propylene oxide polymerization in benzene solution at 60°C. This system as well as the diphenylzinc-water system is greatly influenced by the molar ratio of acetone to diphenylzinc and the maximum catalyst activity was found for a ratio of unity. GPC results strongly suggest the presence of more than one active species for the system.13CNMR analysis indicates that the resulting poly(propylene oxide) has a head-to-tail arrangement. This system was not an effective catalyst for the styrene oxide polymerization.

Propylene oxide polymerization by diphenylzinc-ketone systems at 60°

Abstract Propylene oxide (PO) was polymerized by some diphenylzinc-ketone systems. Cocatalytic effects of nine ketones were examined. The systems are greatly influenced by the nature of the ketone and by the molar ratio of ketone to diphenylzinc. Methyl and cyclic ketones were the most effective as cocatalyst and the maximum catalyst activity was found, in most cases, for a molar ratio of unity. The difference in cocatalyst activities for methyl ketones is attributed to electronic effects, while steric hindrance is not relevant. Similar effects were found for PO polymerization initiated by diphenylzinc in combination with cyclic and with non-halogenated methyl ketones. However the activity of the diphenylzinc-diethyl ketone system increases with increase of the molar ratio. The diphenylzinc-benzophenone system shows a small dependence on the molar ratio. The activity of the diphenylzinc-acetylacetone decreases with increase of the molar ratio showing maximum conversion to polymer when no ketone was added. Polymerization of ethylene oxide by some of these systems showed behaviour similar to that found for PO.

Electrochemically controlled molecular weight of polystyrene production

SummaryIt is well known that physical properties such as mechanical and thermal characteristics of a polymer are highly dependent on its molecular weight and molecular weight distribution (MWD). This feature encourages our interest for finding suitable conditions that allow us to control the molecular weight of the formed polymer, by controlling the experimental parameters. We are reporting some results about the electropolymerization of styrene in tetrahydrofuran with tetrabutylammonium tetrafluoroborate and sodium tetraphenylboron as supporting electrolytes. From the electrolyses using tetrabutylammonium tetrafluoroborate two molecular weight distribution curves, showing weight average molecular weight values (

Epoxide polymerization, 6. Structure of poly(propylene oxide) prepared with diphenylzinc/water as initiating system

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Caracterización de 129 mujeres con cáncer de cuello uterino en el IAHULA, Mérida. Venezuela

) of 3.6×105–1.7×106 for the first and 5×103 for the second one were observed. When using sodium tetraphenylboron a unique distribution curve was displayed suggesting that the weight average molecular weight of the polystyrene, increases by increasing the current density; the observed MWD being rather low.