Inclusion Complexes of Chain Molecules with Cycloamyloses III. Molecular Dynamics Simulations of Polyrotaxanes Formed by Poly(propylene glycol) and beta-Cyclodextrins

Molecular dynamics simulations were performed in vacuo on “channel type” polyrotaxanes composed of β-cyclodextrins (βCDs) threaded onto isotactic and syndiotactic poly(propylene glycol) (PPG). In the most stable complex, the βCDs form a close-packed structure from one end of the PPG chain to the other. Non-bonded van der Waals interactions between βCD and PPG are the main source of stabilization of the complex. Head-to-head and tail-to-tail orientation of successive βCDs in the complex is more favorable than a head-to-tail orientation, due to intermolecular hydrogen bonding between head-to-head βCD units. βCDs in polyrotaxanes adopt a more rigid and symmetrical macroring conformation than does an isolated βCD. Formation of the polyrotaxane is accompanied by an increase in the number of trans states at the bonds in the backbone of PPG. For this reason, the PPG chain in the polyrotaxane is much more extended than the unperturbed chain.This work was supported by DGICYT PG94-0364 and by National Science Foundation grant DMR 952327

Experimental study of agglomerated-cork-cored structures subjected to ballistic impacts

The present paper examines the high-velocity impact behaviour of agglomerated cork-cored structures. The ballistic performance was studied by impact-perforation tests. Three different types of specimens were tested: an agglomerated cork, two spaced thin aluminium plates, and a pair of thin aluminium plates separated by an agglomerated-cork core. The behaviour of the agglomerated cork and the effects of the cork core were analysed in terms of the ballistic limit, residual velocity, and energy absorption. The ballistic limit of cork-cored structures increased slightly, whereas the absorbed energy was strongly augmented by the presence of the cork core.The Spanish Ministerio de Educación y Ciencia (Project HP2006-0024) and the Portuguese Ministério da Ciência, Tecnologia e Ensino Superio

Cartographic and geohistoric resources for the inventory of temporary wetlands and mediterranean desections

El presente artículo recopila y examina, desde una vertiente metodológica y geográfica, las fuentes o recursos cartográficos que se han analizado y utilizado para la realización del in-ventario de humedales temporales en el Medio Guadalquivir, y en el seno de nuestro proyecto de investigación. Estudiaremos fundamentalmente las fuentes cartográficas disponibles para el área citada, aunque en gran medida puedan ser extrapolables a la mayor parte de España. Se lleva a cabo una exposición de las líneas de trabajo y de los autores más representativos para el inventario de humedales temporales o desecados, mediante la investigación de la historia de los Archivos, de las Bibliotecas, de los Museos y de los Centros de Documentación convencionales y digitales actuales. En un segundo momento se aborda una propuesta metodológica para la investigación de esta faceta particular, acompañada por un nutrido apéndice en el que se recopilan las fuentes más significativas que venimos utilizando en nuestra investigación.This paper compiles and examines, from a methodological and geographical perspective, the sources or cartographic resources that have been analyzed and used for the realization of the inventory of temporary wetlands in the Middle Guadalquivir, and within our research project. We will study fundamentally the cartographic sources available for the mentioned area, although to a large extent they can be extrapolated to the greater part of Spain. An exposition of the lines of work and of the most representative authors for the inventory of temporary or dried wetlands is carried out, through the investigation of the History of Archives, of Libraries, of Museums and of Conventional Documentation Centers And digital technologies. In a second moment, a methodological proposal for the investigation of this particular facet is approached, accompanied by several appendices in which are collected the most significant sources that we have been using in our investigatio

Aprendiendo reacciones químicas en tiempos de pandemia

Las actividades prácticas son una parte fundamental en la enseñanza de la química. Sin embargo,en un curso como es el último de instituto, no siempre se puede visitar el laboratorio habitualmente. En España, en los cursos 2019-2020 y 2020-21, con la suspensión de las clases presenciales y posterior recomendación de no uso del laboratorio en los institutos, la actividad práctica se ha reducido en su mayor parte. En este artículo se describe una actividad en la que el alumnado preparó y grabó en vídeo actividades experimentales simples sobre reacciones químicas en casa con materiales de uso común, para después visualizarlo y debatirlo entre todos, compartiendo así experiencias prácticas que enriquecieron el contexto formativo de los alumnos en tiempo de pandemia. Hands-on activities are a fundamental part of teaching chemistry. However, in a course like last one of high school, it is not always possible to visit the laboratory on a regular basis. In the 2019-2020 and 2020-21 academic years, with the suspension of face-to-face classes and subsequent recommendation not to use the laboratory in the institutes, practical activity has been reduced for the most part. This article describes an activity in which the students prepared and videotaped experiences on chemical reactions at home with commonly used materials, to later visualize and discuss it among all, thus sharing practical experiences that enriched the educational context of the students in pandemic time. © 2021 Facultad de Quimica, UNAM. All rights reserved

Effects on nodular extracts of Alnus glutinosa (l.) Gaertn. on ammonification, nitrification and CO2 production in different soils

The effect of root nodule extracts from European alder (Alnus glutinosa [L.] Gaertn.) on the rates of amrnonification, nitrification and C02 production was evaluated in three soils of different physico-chemical characteristics. The extracts decreased net ammonification rate (up to a 43% respect to water control), probably because of an increase of immobilization rather than an effect of a speciffc inhibitor. The rate of nitrification was increased by the extracts (up to 40% from water control) because of the ammonium present in the extracts. An increase in C02 production showed that the nodule extracts stimulate microbial activity. This depended not only on the amount of organic matter introduced by the extracts but also to some activator of microflora.Se evalúa el efecto de extractos nodulares del aliso europeo (Alnus glutinosa [L.] Gaertn.) sobre las tasas de amonificación, nitrificación y producción de C02 en tres suelos de características físico-químicas diferentes. Los extractos reducen la tasa de amonificación (un 43% menor que en el control con agua), probablemente debida a un aumento de la inmovilización más que a un inhibidor especifico. La tasa de nitrificación crece por efecto de los extractos (un 40% respecto al control con agua) a consecuencia del amonio presente en éstos. El incremento de la producción de C02 muestra que los extractos estimulan la actividad microbiana. Esto no parece depender sólo del aporte extra de materia orgánica por los extractos, sino por algún activador especifico