Sobre nuevas reacciones microquímicas de la piperacina y del licetol y su aplicación microanalitica

Resumen El A. estudia un nuevo reactivo, el iodo bismutato de potasio, que mediante su aplicación da lugar a nuevas reaociones microcristalinas, que sirven para caracterizar y diferenciar a la piperacina y del licetol. Del estudio microanalítico realizado y de las técnicas aconsejadas deduce que se puede investigar ambas sustancias en mezclas de cualquier proporción, por poseer cada complejo integrado, formas cristalinas, cromatismo y sensibilidades diferentes. Analiza Iuego, otras nuevas reacciones microquímicas que sirven también como elementos de juicio en la caracterización de las sustancias estudiadas. Se acompañan fotomicrografïas de los cristales obtenidos.

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Summary The use of potassium iodobismuthate led to new microanalytical precipitation reactions which are suited to the characterization and differentiation of piperazine and -dimethylpiperazine. The studies and proposed procedure show that both materials can be detected in any mixture no matter what their proportions since the compounds formed differ with respect to crystal form, color, and detection sensitivity. Other microchemical reactions were studied, which likewise are suitable for characterizing these compounds. Photographs of the crystals are included.

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Zusammenfassung Die Anwendung von Kaliumjodbismutat führte zu neuen mikroanalytischen Kristallfällungsreaktionen, die sich zur Charakterisierung und Unterscheidung von Piperazin und -Dimethylpiperazin eignen. Aus den durchgeführten Untersuchungen und der vorgeschlagenen Arbeitsweise geht hervor, daß beide Substanzen in beliebigen Mischungsverhältnissen nachweisbar sind, da sich die hergestellten Verbindungen hinsichtlich Kristallform, Farbe und Nachweisempfindlichkeit unterscheiden. Es wurden auch andere mikrochemische Reaktionen geprüft, die sich gleichfalls zur Charakterisierung der beiden Substanzen eignen. Abbildungen der erhaltenen Kristalle werden beigebracht.

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Résumé L'emploi de l'iodobismuthate de potassium a conduit à de nouvelles réactions microanalytiques de précipitation cristalline qui sont appropriées à la caractérisation et à la différenciation de la piperazine et de l' -diméthylpiperazine. Les recherches effectuées et l'application du mode opératoire recommandé par les auteurs montrent que les deux substances sont identifiables dans leurs mélanges quelles que soient leurs proportions relatives; leurs combinaisons avec le réactif se différencient en effet par leurs formes cristallines et leurs couleurs ainsi que par la sensibilité d'identification. Quelques autres réactions microchimiques ont été également éprouvées avec le même succès pour la caractérisation des deux substances. Les cristaux obtenus sont reproduits sur les figures de la communication.

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Al Señor Dr.Hans Lieb, Profesor de Universidad, con motivo de su 70⁰ aniversario.     

Multibeam second-harmonic generation by spatiotemporal shaping of femtosecond pulses

We present a technique for efficient generation of the second-harmonic signal at several points of a nonlinear crystal simultaneously. Multispot operation is performed by using a diffractive optical element that splits the near-infrared light of a mode-locked Ti:sapphire laser into an arbitrary array of beams that are transformed into an array of foci at the nonlinear crystal. We show that, for pulse temporal durations under 100 fs, spatiotemporal shaping of the pulse is mandatory to overcome chromatic dispersion effects that spread both in space and time the foci showing a reduced peak intensity that prevents nonlinear phenomena. We experimentally demonstrate arbitrary irradiance patterns for the second-harmonic signal consisting of more than 100 spots with a multipass amplifier delivering 28 fs, 0.8 mJ pulses at 1 kHz repetition rate.     

Rheo-PIV of a yield-stress fluid in a capillary with slip at the wall

An analysis of the yielding and flow behavior of a model yield-stress fluid, 0.2 wt% Carbopol gel, in a capillary with slip at the wall has been carried out in the present work. For this, a study of the flow kinematics in a capillary rheometer was performed with a two-dimensional particle image velocimetry (PIV) system. Besides, a stress-controlled rotational rheometer with a vane rotor was used as an independent way to measure the yield stress. The results in this work show that in the limit of resolution of the PIV technique, the flow behavior agrees with the existence of a yield stress, but there is a smooth solid?Cliquid transition in the capillary flow curve, which complicates the determination of the yield stress from rheometrical data. This complication, however, is overcome by using the solely velocity profiles and the measured wall shear stresses, from which the yield-stress value is reliably determined. The main details of the kinematics in the presence of slip were all captured during the experiments, namely, a purely plug flow before yielding, the solid?Cliquid transition, as well as the behavior under flow, respectively. Finally, it was found that the slip velocity increases in a power-law way with the shear stress.     

A survey on multi-objective evolutionary algorithms for many-objective problems

Multi-objective evolutionary algorithms (MOEAs) are well-suited for solving several complex multi-objective problems with two or three objectives. However, as the number of conflicting objectives increases, the performance of most MOEAs is severely deteriorated. How to improve MOEAs’ performance when solving many-objective problems, i.e. problems with four or more conflicting objectives, is an important issue since a large number of this type of problems exists in science and engineering; thus, several researchers have proposed different alternatives. This paper presents a review of the use of MOEAs in many-objective problems describing the evolution of the field, the methods that were developed, as well as the main findings and open questions that need to be answered in order to continue shaping the field.     

The hydrothermal synthesis of tetragonal tungsten bronze-based catalysts for the selective oxidation of hydrocarbons

Mixed metal oxides with tetragonal tungsten bronze (TTB) structure, showing high activity and selectivity for the gas phase partial oxidation of olefins, have been prepared by hydrothermal synthesis from Keggin-type heteropolyacids.     

Synthetic studies on neoclerodane diterpenes from Salvia splendens: oxidative modifications of ring A

Salvinorin A (1), a neoclerodane diterpene from the hallucinogenic mint Salvia divinorum, is the only known naturally occurring non-nitrogenous and specific κ-opioid agonist. Some oxidative modifications of the A ring in the congeners of 1 isolated from Salvia splendens salviarin, splenolide B, splendidin, and in the non-natural 8-epi-salviarin gave new derivatives, some of which were tested as agonists at opioid receptors. However, none of these compounds was active. The presence of the C-18, C-19 lactone could be at the origin of the observed lack of binding affinity.     

ESR, electrochemical, molecular modeling and biological evaluation of 4-substituted and 1,4-disubstituted 7-nitroquinoxalin-2-ones as potential anti-Trypanosoma cruzi agents

Electrochemical and ESR studies were carried out in this work with the aim of characterizing the reduction mechanisms of 4-substituted and 1,4-disubstituted 7-nitroquinoxalin-2-ones by means of cyclic voltammetry in DMSO as aprotic solvent. Two reduction mechanisms were found for these compounds: the first, for compounds bearing a labile hydrogen by following a self-protonation mechanism (ECE steps), and the second, for compounds without labile hydrogen, based on a purely electrochemical reduction mechanism (typical of nitroheterocycles). The electrochemical results were corroborated using ESR spectroscopy allowing us to propose the hyperfine splitting pattern of the nitro-radical, which was later corroborated by the ESR simulation spectra. All these compounds were assayed as growth inhibitors against Trypanosoma cruzi: first, on the non-proliferative (and infective) form of the parasite (trypomastigote stage), and then, the ones that displayed activity, were assayed on the non-infective form (epimastigote stage). Thus, we found four new compounds highly active against T. cruzi. Finally, molecular modeling studies suggest the inhibition of the trypanothione reductase like one of the possible mechanisms involved in the trypanocidal action.