Modelos estructurales de cristales quirales de C10H12N2

[ES] En este trabajo se han estudiado diferentes modelos estructurales de cristales de 2-propil-1H-Benzimidazol (C10H12N2) con el fin de dar una explicación al origen estructural de la quiralidad en este compuesto orgánico. Inicialmente, se piensa que pueda deberse al ordenamiento helicoidal de las cadenas moleculares polares. Se ha partido de resultados experimentales realizados anteriormente mediante técnicas de dicroísmo circular vibracional (VCD), los cuales no revelan la configuración quiral del compuesto 2-propil-1H-Benzimidazol. Por ello, se intenta dar una explicación desde el punto de vista estructural usando la técnica de difracción de rayos-X. Sin embargo, se han observado que existen diferentes configuraciones, llamadas diastereómeros, las cuales se ajustan igual de bien a los resultados obtenidos experimentalmente. Debido a este hecho, y a que los tres diastereómeros poseen diferente energía de cohesión, se ha calculado el diagrama de difracción de neutrones para determinar si, mediante esta última técnica, se podrían diferenciar las estructuras. No obstante, tampoco se observan diferencias apreciables entre las tres configuraciones. Por este motivo, se ha intentado buscar una relación entre los tres diastereómeros basada en las simetrías del grupo espacial al que pertenecen, el grupo ��212121, y al normalizador de dicho grupo. Se ha comprobado que las tres configuraciones a las que se hacía referencia llamándolas diastereómeros son, en realidad, descripciones equivalentes de la misma estructura. De esta manera, se han podido justificar los resultados obtenidos mediante las otras técnicas y se deduce que las energías de cohesión calculadas previamente a este trabajo no son correctas, error principal que ha llevado a realizar todos los modelos estructurales posteriores. Por último, se concluye que el ordenamiento helicoidal de las cadenas polares es el responsable de la existencia de quiralidad en este compuesto y que, aunque posea dos formas enantioméricas, solo cristaliza en una de ellas, como mostraban los experimentos de VCD

Diseño de medios quirales basados en estructuras individuales bidimensionales

In this paper, we present a new way of constructing chiral media, in 8.2-12.4 GHz band, starting from achiral individual metallic elements (right angle). We showed that an appropriate distribution of such inclusions in a dielectric host responds in a manner consistent to that obtained with other media constructed using chiral metal inclusions. Appropriately modifying the size and spatial distribution of right angles is possible to model the response of these media. The media manufactured by the inclusion of right angles can be fabricated using technology printed circuit board (PCB).Ingeniería, Industria y Construcció

Caracterización de medios quirales utilizando ondas con polarización circular

The characterization of metamaterials is usually carried out by illuminating a sample with a linearly polarized plane electromagnetic wave. In points far from the sample, sensors are introduced to measure the transverse components of the field, before and after the sample, in order to compute the reflection and transmission coefficients related with the coand cross-polar field components. Based on this information, retrieval algorithms allow parameters like rotation angle, effective chirality, refraction index, etc., to be calculated. Here we obtain information only on the transmission signals under illumination with plane circularly polarized waves, from which chirality and the rotation angle due to the electromagnetic activity of the material can be directly calculated. The method, which allows a simpler characterization of the metamaterial slab under study, is applied to the study of simulated chiral metamaterials composed of a dielectric slab substrate with a periodic array of metallic inclusions. The findings are contrasted with the experimental results obtained with linear polarization irradiation.Ingeniería, Industria y Construcció

Diseño de medios quirales basados en la distribución ordenada de manivelas

In this communication, the experimental results obtained from the measurements of evenly distributed metallic cranks on a dielectric plate substrate is presented. The effect we have analyzed is the rotation of the polarization plane of an electromagnetic wave, both in free space and inside a circular waveguide. It is shown that the rotation of the polarization plane by some distributions of cranks, with specific symmetry properties, can be explicitly ascribed to a chirality effect.Ingeniería, Industria y Construcció

Caracterización experimental de medios quirales basados en inclusiones periódicas. El resonador de cuatro manivelas

The periodical distribution of elements forming a bi- or three-dimensional periodical lattice has provided a fundamental tool to develop new materials with exotic and, sometimes, amazing electromagnetic properties. Here we have analyzed the effects related to the electromagnetic activity produced by a 2D array of four crank resonators (4CR), which is composed by same handeness cranks in a packed configuration forming a parallelepiped. The sample has been built using printed circuit technology and the unit cell was designed to fit its electromagnetic response into the X band frequency range. Using a free-wave system and the corresponding reciprocal algorithms, we have characterized the material and determined the rotation angle, refraction index and chirality parameter.Ingeniería, Industria y Construcció

Síntesis estereoselectiva de nuevos inhibidores de la agregación plaquetaria

Chirality is a feature instrinsically linked to life. For this reason, the use of stereochemically pure compounds presents numerous advantages compared to the use of racemates in pharmaceutical industry. Therefore, the present work is a part of a broader project aimed to the development of new strategies for the design and the stereoselective synthesis of chiral compounds with biological activity. In particular, we focus on the enantioselective synthesis of a new family of 4-aminocroman-2-one derivatives as antiplatelet drugs and their phosphorated analogous. These compounds constitute the basic structure of a family of inhibitors of platelet aggregation, modulator of thrombus formation, whose synthesis in optically pure form has not been developed so far. Our methodology is based on the efficiency of the tert-butylsulfinylsulfinil group as chiral inductor in nucleophilic additions to chiral N-sulfinylimines. On the one hand, the addition of the ethyl acetate anion allows the preparation of the corresponding optically pure 2-aminocromanones. On the other hand, the addition of the methyl phenylphosphinate carbanion leads to the corresponding phosphinyl bioisosteres. In both cases, the addition takes place stereoselectively and it allows, for the first time, the preparation of a diverse array of enantiopure 4-amino-croman-2-one derivatives, allowing the study of the activity of both enantiomers separately. To sum up, we have developed a new, general, easy, effective and modular methodology for the stereoselective synthesis of both enantiomers of a wide range o β-amino esters, which constitute a new family of pharmacologically relevant compoundsUniversidad de Sevilla. Grado en Farmaci

Metamateriales Quirales Basados en Manivelas de Cinco Segmentos

A new structure formed by five segments cranks is here presented. By using numerical simulations, we show that a material composed by a 2D periodical distribution of a unit cell based on such structures is able to produce electromagnetic rotatory dispersion and circular dichroism. The symmetry requirements on the unit cell are analyzed in order to obtain a material with homogeneous and isotropic behavior for normal incidence. The material can exhibit several resonant frequencies, where the rotation angle reaches a peak of ±90º and the transmitted wave changes from linear to elliptical polarization.Ingeniería, Industria y Construcció

Actividad electromagnética de medios quirales basados en manivelas

Materials with electromagnetic activity are usually made by spreading helices inclusions into a host medium. In previous work, a new manufacturing technique based on the inclusion of few three segment wire hooks (cranks) was presented and the rotation of the polarisation angle in circular waveguide discussed. Here we present that the random inclusion of many cranks into a host medium produces electromagnetically active materials. Based on a free-wave experimental system, we have found that the transmitted wave through the material is rotated with respect to the incident one. First results seem to be in agreement with the typical behaviour of chiral media at the resonant frequency.Ingeniería, Industria y Construcció

Algoritmo para la caracterización univoca de metamateriales basados en inclusiones quirales

Electromagnetic characterization is perfomed from the reflection and transmission coefficients by making use of retrieval algorithms. However, it is known the existence of uncertainties in the determination of these electromagnetic parameters. Here, we present a new algorithm that uses some techniques in order to avoid these uncertainities, some based on continuity conditions of physical magnitudes and some others based on causality relations, that is, exploiting Kramers-Kronig relations.Ingeniería, Industria y Construcció