Elaboración de vídeos y de test de autoevaluación como herramienta docente en una asignatura experimental

Los objetivos generales de la asignatura Experimentación en Química Física son: aprender a organizar un cuaderno de laboratorio, estructurar y analizar la información generada en el laboratorio de forma científicamente correcta, comprender el funcionamiento del instrumental utilizado y comprender y saber manejar los conceptos y cálculos realizados en las prácticas. Para que la evaluación de la asignatura se adaptase a todos los objetivos, se ha incluido recientemente una prueba experimental. Este hecho hacía conveniente proporcionar material nuevo para su preparación. La mayor presencia de las nuevas tecnologías de la información nos ha permitido crear un conjunto de vídeos asequibles a través de internet sobre el funcionamiento de los aparatos del laboratorio y unos test de autoevaluación sobre contenidos y los cálculos. Aunque el porcentaje de utilización en el primer curso de aplicación ha sido escaso, los alumnos señalan la utilidad del material para preparar los exámenes con información adicional a la de guiones y manuales así como la posibilidad que ofrece de detectar errores y ejercitarse en el manejo de conceptos y cálculos.The main aims of the subject Experimentation in Physical Chemistry are: learning to organize a laboratory notebook, structuring and analyzing the information generated in the laboratory in a scientifically correct way, understanding the operation of the instruments used and learning and management of concepts and calculations made during the experimental work. For the evaluation of the subject to arrange to all of the objectives, and experimental probe has been added recently. This fact made convenient to provide new material to facilitate the preparation of the probe. As new technologies are today more feasible we made a group of videos attainable through internet about the way of functioning of the laboratory instruments and six self‐assessment tests about concepts and calculations. During the first year of application a small amount of students used the material, but those who had used it indicated that it was useful to prepare exams due to the additional information provided (more than in manuals and outline of each practice) and because it let them detect misleading ideas and exercise with concepts and calculations

2-(methylamido)pyridine–borane : a tripod κ3N,H,H-ligand in trigonal bipyramidal rhodium(I) and iridium(I) complexes with an asymmetric coordination of its BH3 group

The complexes [M(κ3N,H,H-mapyBH3)(cod)] (M = Rh, Ir; HmapyBH3 = 2-(methylamino)pyridine–borane; cod = 1,5-cyclooctadiene), which contain a novel anionic tripod ligand coordinated to the metal atom through the amido N atom and through two H atoms of the BH3 group, have been prepared by treating the corresponding [M2(μ-Cl)2(cod)2] (M = Rh, Ir) precursor with K[mapyBH3]. X-ray diffraction studies and a theoretical QTAIM analysis of their electron density have confirmed that the metal atoms of both complexes are in a very distorted trigonal bipyramidal coordination environment, in which two equatorial sites are asymmetrically spanned by the H–B–H fragment. While both 3c–2e BH–M interactions are more κ1H (terminal sigma coordination of the B–H bond) than κ2H,B (agostic-type coordination of the B–H bond), one BH–M interaction is more agostic than the other and this difference is more marked in the iridium complex than in the rhodium one. This asymmetry is not evident in solution, where the cod ligand and the BH3 group of these molecules participate in two concurrent dynamic processes of low activation energies (VT-NMR and DFT studies), namely, a rotation of the cod ligand that interchanges its two alkene fragments (through a square pyramidal transition state) and a rotation of the BH3 group about the B–N bond that equilibrates the three B–H bonds (through a square planar transition state). While the cod rotation has similar activation energy in 2 and 3, the barrier to the BH3 group rotation is higher in the iridium complex than in the rhodium one

Experimental and theoretical characterization of the Zn - Zn bond in [Zn2(η5-C5Me5)2]

The existence and characterization of a bond between the Zn atoms in the recently synthesized complex [Zn2(5-C5Me5)2], as well as between Zn and ligand C atoms is firmly based on neutron diffraction and low-temperature X-ray synchrotron diffraction experiments. The multipolar analysis of the experimental electron density and its topological analysis by means of the Atoms in Molecules (AIM) approach reveals details of the Zn - Zn bond, such as its open-shell intermediate character (the results are consistent with a typical metal-metal single bond), as well as many other topological properties of the compound. Experimental results are also compared with theoretical ab initio calculations of the DFT (density functional theory) and MP2 (Mller-Plesset perturbation theory) electron densities, giving a coherent view of the bonding in the complex. For instance, charges calculated from the AIM approach applied to the atomic basin of each Zn atom are, on average, +0.72 e from both the experimental and the theoretical electron density, showing a moderate charge transfer from the metal, confirmed by the calculated topological indexes.Ministerio de Educación y Ciencia MAT2006-0199

Topological analysis of the electron density in the carbonyl complexes M(CO)8 (M = Ca, Sr, Ba)

The quantum theory of atoms in molecules (QTAIM) has been applied to the recently synthesized alkaline-earth cubic Oh-symmetric complexes Ca(CO)8 (1), Sr(CO)8 (2), and Ba(CO)8 (3). Theoretical calculations reveal that M–CO interactions in these complexes can be properly described as highly polar bonds, showing some features traditionally associated with transition-metal bonding, although with noticeable differences, as well. In this sense, δ(M–C) and δ(M···O) delocalization indexes for bonding and nonbonding interactions, electron localization funcion (ELF) analyses, source function (SF) calculations, and the interacting quantum atoms (IQA) approach, among other methodologies, produce results consistent with interactions dominated by electrostatics between the CO ligands and alkaline-earth metals, with an increasing degree of covalency on going from 1 to 3 and without any significant π-back-donation.This work has been supported by the Spanish MINECO project MAT2016-78155-C2-1-R and the Principality of Asturias Grant No. GRUP-IN-14-060.Peer reviewe

Study of the potential of (non-)bakery Saccharomyces cerevisiae strains in bread making and of a yeast strain specific fermentation inhibiting protein in wheat

The production of tasty leavened bread is almost inseparably linked to the presence of Saccharomyces cerevisiae yeast. The main function of yeast during the fermentation phase is the production of CO2, resulting in dough leavening. Besides CO2, the yeast's fermentation metabolism also results in the release of ethanol and other minor constituents, such as glycerol, organic acids and flavor components. These metabolites are known to have a major impact on dough rheology and bread texture, aroma and flavor. The amount and type of metabolites produced by yeast during bread making depend on the ingredients (nutrient availability in flour, salt, etc.), fermentation time and temperature as well as on the pregrowth conditions and genetic background of the yeast strain used. As a consequence of the growing consumer's interest in a wider variety of tasty and healthy food products, industrial and artisanal bakeries are challenged to improve end products. Strategies to do so include changing dough formulations by, for example, addition of enzymes as bread improvers or wheat bran as a source of dietary fiber. Also yeast technology can be used to change bread properties. The Saccharomyces cerevisiae species embraces a lot of different strains, applied in various industrial fermentation processes, offering a large potential for possible application in bread making. Preliminary experiments in our lab showed a very limited fermentation ability of several S. cerevisiae strains in wheat flour dough while studying the impact of strains from diverse industrial categories on dough rheology. As this remarkable observation was left unexplored, the first aim of this doctoral research was to gain insight in this inhibition phenomenon by characterizing it and identifying the inhibition-causing factor(s). The second aim was to evaluate the applicability of (non-bakery) S. cerevisiae strains in bread making. In a first part, the fermentation capacity of a set of 45 S. cerevisiae strains originating from 5 yeast-based industrial categories (bread, beer, bio‑ethanol, sake & spirits and wine) was screened in different fermentation media. In a liquid fermentation medium, with a water activity adjusted to the level in dough, no industrial category differed significantly from the category of bakery strains, suggesting that they all had good fermentation potential. In wheat flour dough, variation in fermentation capacity could be noticed amongst the yeast strains. Most remarkable was the very limited fermentation ability of one fifth of the yeast strains. They produced up to 85% less CO2 than the best bakery strain, clearly demonstrating fermentation inhibition in wheat flour dough. The inhibition-sensitive yeast strains performed significantly better in a gluten‑starch model dough. Replacing the aqueous phase of the model dough by a wheat flour extract induced the same degree of inhibition as did wheat flour dough, allowing to conclude that the water extractable fraction of wheat flour contains a yeast-inhibiting component. In the next part of this PhD work, the yeast inhibition phenomenon was characterized. The representative of the inhibition-sensitive yeast strains showed an inhibited fermentation capacity in the presence of flour from different wheat varieties. Moreover, rye, maize and barley had a similar effect on the yeast's fermentation ability. After further analyses, the inhibition-causing factor turned out to be a water extractable wheat flour protein. Starting from a crude wheat flour extract, the inhibitor was isolated by activity-guided fractionation with cation exchange chromatography and reversed phase-HPLC. Identification of the proteins present in the purest inhibition-active fraction with LC/MS-MS and Edman degradation pointed towards the thaumatin-like protein as the inhibition causing factor. This finding was validated by the fact that the recombinantly expressed target protein also showed fermentation inhibition in representative of the sensitive yeast strains. Based on the differences in sensitivity of S. cerevisiae strains towards the inhibitor, a mode of action comparable with that of thaumatin-like tobacco osmotin was suggested, mainly affecting the permeability of the yeast cell wall. Although the inability of brewer's yeasts to ferment a wheat flour batter was in the early seventies ascribed to purothionins, this was not conform to our results. In the last part, the applicability of a selection of (non-bakery) S. cerevisiae strains in the bread making process was evaluated. After screening 45 yeast strains for their metabolite and aroma profiles, 10 strains (two from each industrial category), including two inhibition-sensitive strains, were selected for further examination of their impact on dough rheology and their influence on final bread aroma and quality characteristics. As was expected based on the variability in fermentation properties, metabolite analysis of these strains during fermentation also showed different profiles. In spite of these differences and of the fact that individual fermentation metabolites have already been shown to impact rheology in yeastless dough, no clear correlations were found between metabolites produced and rheological changes in yeasted dough. The constant change in density through CO2 production was assumed to have the foremost impact on dough properties. Similarly, significantly differing fermentation capacities did not necessarily result in significantly different bread volumes. Furthermore, no clear differences in crumb texture and structure between a control bakery strain and the other inhibition-insensitive yeast strains were observed. The determined variation in fermentation capacity and metabolite production between yeast strains did not seem sufficiently outspoken to result in significant differences in bread volume and texture. All inhibition-insensitive strains in the selection gave rise to breads with similar characteristics to those obtained with the control bakery strain. Aroma profile analysis hinted towards more significant differences between the different strains. The research in this PhD study gave insight in a yeast specific inhibition phenomenon, caused by the thaumatin-like protein during wheat flour dough fermentation. This finding is of clear interest for yeast- and cereal-based fermentation industries, although further work is required on inhibitor quantification and its mode of action. The improvement of existing strains by breeding, the creation of new strains through genetic modification, or genetic modification of wheat to eliminate the harmful component might provide some solutions to enable yeast strains with a beneficial impact on dough and bread quality parameters or with a pleasant volatile compound profile, to be used in the bakery industry.status: publishe

Response to “comment on ‘topological analysis of the electron density in the carbonyl complexes M(CO)8 (M = Ca, Sr, Ba)’”

The Comment by Holzmann et al. does not properly reflect the conclusions of the original article, as shown in the current response. New calculations on the title compounds, as well as on M(CO)2 (M = Ca, Sr, Ba) complexes with both D∞h and C2v symmetry, included in the current response and based not only on the Quantum Theory of Atoms in Molecules but also on the Natural Bond Orbital approach, strengthen the arguments of the original article.This work has been supported by the Spanish MINECO project MAT2016-78155-C2-1-R and the Principality of Asturias grant GRUP-IN-14-060.Peer reviewe

Ag2O versus Cu2O in the Catalytic Isomerization of Coordinated Diaminocarbenes to Formamidines: A Theoretical Study

DFT theoretical calculations for the Ag2O-induced isomerization process of diaminocarbenes to formamidines, coordinated to Mn(I), have been carried out. The reaction mechanism found involves metalation of an N-H residue of the carbene ligand by the catalyst Ag2O and the formation of a key transition state showing a μ-η2:η2 coordination of the formamidinyl ligand between manganese and silver, which allows a translocation process of Mn(I) and silver(I) ions between the carbene carbon atom and the nitrogen atom, before the formation of the formamidine ligand is completed. Calculations carried out using Cu2O as a catalyst instead of Ag2O show a similar reaction mechanism that is thermodynamically possible, but highly unfavorable kinetically and very unlikely to be observed, which fully agrees with experimental results

Una nueva version del programa de refinamiento SHELX Aplicacion a estudios estructurales (por difraccion de rayos X)

Available from Centro de Informacion y Documentacion Cientifica CINDOC. Joaquin Costa, 22. 28002 Madrid. SPAIN / CINDOC - Centro de Informaciòn y Documentaciòn CientìficaSIGLEESSpai

Grand Banc de Terre-Neuve

Hand coloured. Depths shown by soundings. Includes a detailed note on the fisheries in Newfoundland waters, including the seal hunt.CNS map no. 84