Vol. 115 No. 5 (2019)

This article describes the nature and electronic properties of kékulé diradicals from two main perspectives: i) the diradical as the result of the sequential rupture of a chemical bond; and ii) the connection between the diradical character and the singlet-triple (observable magnitud) gap by means of two mechano-quantum parameters, U ( related with the electronic repulsion) and tab (due to the electronic delocalization). The relevance of these diradicals is addressed in the context of other diradicals, such as non-kékulé and antiaromatic dira- dicals. 7 families of oligomers are presented all of them sharing quinoidal core which promotes the formation of the diradical by recovery of aromaticity. The paper closes with the explanation of the recent interest of these broken molecules in the field of organic electronics.

Resumen: Prácticamente todos los elementos de la tabla periódica tienen al menos un isótopo natural activo en RMN. Aunque todos se rigen por los mismos fundamentos, la accesibilidad de la información de RMN está condicionada por las propiedades de cada núcleo. En este artículo se analizan esos condicionantes como punto de partida para mostrar la amplitud de aplicaciones asociadas al recorrido multinuclear de esta técnica espectroscópica a través de la tabla periódica sobre la base de una selección de ejemplos representativos en disolución.
Palabras clave: Tabla periódica, RMN, multinuclear, detección inversa, cuadrupolar.
Abstract: Almost all the elements in the periodic table have at least one natural isotope active in NMR. Although the same principles apply to all of them, accessing to the NMR information greatly depends on the properties of each nucleus. This article describes these issues as the starting point to show the breath of applications derived from the multinuclear approach of this spectroscopic technique across the periodic table based on representative selected examples in solution.
Keywords: Periodic table, NMR, multinuclear, inverse detection, quadrupolar.

Tropane core is found in many natural compounds as Solanaceae alkaloids, atropine or scopolamine. In relation with this skeleton, nor-tropane core appears in calystegines, which are polyhydroxylated alkaloids isolated from rhizomes of plants as Calystegia sepium or Convolvulus arvensis. These compounds show an important glucosidase-inhibitory activity, inhibiting β-glucosidase and α-galactosidase among others. These enzymes are altered in diverse metabolic pathologies as the Gaucher’s disease. Synthesis of oxygenated analogues of these compounds are arising due to these pharmacological properties. In this review, 2-oxa- and 6-oxa-nortropanes last related researches are shown.

Keywords: Tropanes, calystegines, oxa-nortropanes, alkaloids, glycosidases.

Resumen: La biomasa lignocelulósica es una materia prima renovable que ayudará a reducir la dependencia de las materias primas fósiles. Para poder aprovechar la biomasa es necesario aplicar procesos biológicos y termoquímicos para acceder a sus componentes principales. A partir de los componentes principales se pueden producir moléculas plataforma que sirven como materia prima para obtener productos químicos de interés industrial. La presente contribución expone las posibilidades de la biomasa lignocelulósica como materia prima para producir combustibles y productos químicos. Se pretende que el artículo sirva como un documento introductorio para el estudio de procesos para la transformación de la biomasa.
Palabras clave: biorefinería, celulosa, hemicelulosa, lignina, moléculas plataforma.
Abstract: Lignocellulosic biomass is a renewable raw material that will help to reduce dependence on fossil raw materials. In order to take advantage of the biomass it is necessary to apply biological and thermochemical processes to access its main components. From the main components, platform molecules can be produced which serve as raw material to obtain chemical products of industrial interest. This contribution presents the possibilities of lignocellulosic biomass as a raw material to produce fuels and chemical products. The paper is intended to serve as an introductory document for the study of processes for the transformation of biomass.
Keywords: biorefinery, cellulose, hemicellulose, lignin, platform chemicals.

This article presents a project that comprises a series of inquiries of such ingenious everyday items as the match. Each proposed issue is linked to a chemical substance and/or a process required to enable a match to provide fire instantly.

Keywords: matches, phosphorus, sulphur dioxide

It is usually said in Spanish that “para gustos, colores” (in English: one man’s meat is another man’s poison). This adage highlights metaphorically that the perception of colours is in our mind. Such colours, which have inspired so many artists and have a great influence in our mood, have their roots in how the brain responds to the stimuli that are produced when incoming light reacts with the several types of photoreceptor cells in the eye. On the other hand, light interacts with a given object in a specific way which depends on its chemical composition, and the perceived colour may also change under different lighting conditions. After analysing all these variables, it would be clear that the colour of things is not as straightforward as it might appear “at first glance”.

Keywords: Colour, spectroscopy, quantum mechanics, interaction of radiation with matter, physiology

Quantitative chemistry experiments, with low-cost materials, for Non-Compulsory Secondary Education students. One of the reasons that explain why there is not enough practice for non-compulsory secondary education students is the low provision of laboratory material public high schools. To try to relieve this problem, there have been and there are many attempts to use homemade, recycled or acquired materials through the internet, trying to bring experimental work to students. However, most of these proposals focus on the qualitative aspects of physical-chemical phenomena. In this article we make a proposal, which goes further, with concrete examples of quantitative experiments, using low-cost materials, in which students must take measurements, interpret data and use simple software programs to analyze the results obtained and present their findings or conclusions.

Keywords: Teaching chemistry, Quantitative experiments, Low-cost materials

We use a seasonal fruit (quince), and we study the chemistry of one of its carbohydrates (pectins), to explain the procedures, techniques and technologies necessary to obtain a natural product, healthy and easy to keep in a simple, safe, economical and reproducible way (quince jelly). The acidic properties of lemon juice and the hygroscopic properties of sucrose will favor the interchain interactions and the gelation of pectin. The inversion reaction of sucrose will be decisive to improve the palatability of the final product obtained. The substances responsible for the colour and fragrancy characteristic will appear during the caramelization process of the fructose generated.

Keywords: Quince, pectins, high methoxyl, gelation, inversion of sucrose

Resumen: En el CXXV aniversario del nacimiento de Miguel A. Catalán Sañudo, que coincide con el centenario de la publicación de su primer libro y del inicio de su estancia como becario en Inglaterra, en los laboratorios del Imperial College (1919-1921), recordaremos la figura de este ilustre químico. Fue uno de los protagonistas de la “Edad de Plata” de la Ciencia Española, al convertir la espectroscopia en el instrumento más avanzado para la investigación de la estructura de la materia, de aquel momento. También concibió una original tabla periódica de los elementos.
Palabras clave: Miguel A. Catalán, “Edad de Plata” de la Ciencia en España, Estructura Atómica, Modelo atómico.
Abstract: On the CXXV anniversary of the birth of Miguel A. Catalán Sañudo, on the centenary of the publication of his first book and the beginning of his stay as a fellow in England, in the laboratories of Imperial College (1919-1921), we will remember the figure of this illustrious chemist. He was one of the protagonists of the “Silver Age” of Spanish Science, by turning spectroscopy into the most advanced instrument for the investigation of the structure of matter, at that time. He also conceived a periodic table of the elements.
Keywords: Miguel A. Catalán, “Silver Age” of Spanish Science, Atomic Structure, Atomic Model.