La investigación activa como herramienta para mejorar la enseñanza de la química : nuevos enfoques

In many European countries, chemistry education faces a number of important recurrent difficulties. For example, at the secondary school level, students' interest in chemistry is decreasing and teachers complain that repeated explanation and demonstration are not very effective, which frustrates them. At university level, lecture courses and laboratory courses are often disconnected and many student experiments are considered as boring «cookbook» problems. These and other recurrent difficulties have evoked the need to improve the quality of chemistry education at both levels. In this article, the contribution of educational research to an improvement of chemistry education is discussed. This research is considered as a tool for analysing teaching and learning problems, for elucidating backgrounds of these difficulties and for developing and evaluating new approaches in chemistry education. Special attention is focused on two promising new research approaches. First, a new research instrument is presented: protocols of discussions during real classroom and laboratory sessions. Second, a new research design is presented: the developmental research approach. Both research approaches can contribute to the improvement of chemistry classroom/laboratory practices and chemistry teacher training

NMR solvent shifts of acetonitrile from frozen density embedding calculations

We present a density functional theory (DFT) study of solvent effects on nuclear magnetic shielding parameters. As a test example we have focused on the sensitive nitrogen shift of acetonitrile immersed in a selected set of solvents, namely water, chloroform, and cyclohexane. To include the effect of the solvent environment in an accurate and efficient manner, we employed the frozen-density embedding (FDE) scheme. We have included up to 500 solvent molecules in the NMR computations and obtained the cluster geometries from a large set of conformations generated with molecular dynamics. For small solute - solvent clusters comparison of the FDE results with conventional supermolecular DFT calculations shows close agreement. For the large solute - solvent clusters the solvent shift values are compared with experimental data and with values obtained using continuum solvent models. For the water → cyclohexane shift the obtained value is in very good agreement with experiments. For the water → chloroform NMR solvent shift the classical force field used in the molecular dynamics simulations is found to introduce an error. This error can be largely avoided by using geometries taken from Car - Parrinello molecular dynamics simulations. © 2008 American Chemical Society

Recent progress in adaptive multiscale molecular dynamics simulations of soft matter

Understanding mesoscopic phenomena in terms of the fundamental motions of atoms and electrons poses a severe challenge for molecular simulation. This challenge is being met by multiscale modeling techniques that aim to bridge between the microscopic and mesoscopic time and length scales. In such techniques different levels of theory are combined to describe a system at a number of scales or resolutions. Here we review recent advancements in adaptive hybrid simulations, in which the different levels are used in separate spatial domains and matter can diffuse from one region to another with an accompanying resolution change. We discuss what it means to simulate such a system, and how to enact the resolution changes. We show how to construct efficient adaptive hybrid quantum mechanics/molecular mechanics (QM/MM) and atomistic/coarse grain (AA/CG) molecular dynamics methods that use an intermediate healing region to smoothly couple the regions together. This coupling is formulated to use only the native forces inherent to each region. The total energy is conserved through the use of auxiliary bookkeeping terms. Error control, and the choice of time step and healing region width, is obtained by careful analysis of the energy flow between the different representations. We emphasize the CG → AA reverse mapping problem and show how this problem is resolved through the use of rigid atomistic fragments located within each CG particle whose orientation is preconditioned for a possible resolution change through a rotational dynamics scheme. These advancements are shown to enable the adaptive hybrid multiscale molecular dynamics simulation of macromolecular soft matter systems

Vinylphosphirane-phospholene rearrangements: Pericyclic [1,3]-sigmatropic shifts or not ?

The conversion of "free" and Cr(CO

The effects of Aluminum Oxide and Manganese Iron Oxide nanoparticles on the extraction of motor oil from Bucephala albeola feathers

As the industrial revolution increased demands and sales, petroleum has risen to be the largest import. There is an increase in the amount of oil and petroleum being spilled and they are proving to be hazardous to the wildlife, including a variety of bird species. The purpose of this experiment was to find a more effective way to extract oil from Bucephala albeola feathers than the current method, which is not efficient. It was hypothesised that if Aluminum Oxide and Manganese Iron Oxide nanoparticles were used to extract oil, then the Manganese Iron Oxide nanoparticles more effective than the Aluminum Oxide nanoparticles at removing oil from the Bucephala albeola feathers. Twenty feathers had motor oil applied to them, and half were treated with Aluminum Oxide nanoparticles and the others with Manganese Iron Oxide nanoparticles. They were then massed before and after the extraction process. A two sample t-test (t(9)=5.53,p\u3c0.001) determined that there was a significant difference between the two treatments. The Aluminum Oxide nanoparticles had an average difference of 0.220 grams after the extraction while the average difference for Manganese Iron Oxide was 0.0255 grams. In conclusion, the treatment consisting of the Aluminum Oxide nanoparticles was more efficient at removing the oil

Proton Transfer in Aqueous Solution: Exploring the Boundaries of Adaptive QM/MM

In this chapter, we review the current state-of-the-art in quantum mechanical/molecular mechanical (QM/MM) simulations of reactions in aqueous solutions, and we discuss how proton transfer poses new challenges for its successful application. In the QM/MM description of an aqueous reaction, solvent molecules in the QM region are diffusive and need to be either constrained within the region, or their description (QM versus MM) needs to be updated as they diffuse away. The latter approach is known as adaptive QM/MM. We review several constrained and adaptive QM/MM methods, and classify them in a consistent manner. Most of the adaptive methods employ a transition region, where every solvent molecule can continuously change character (from QM to MM, and vice versa), temporarily becoming partially QM and partially MM. Where a conventional QM/MM scheme partitions a system into a set of QM and a set of MM atoms, an adaptive method employs multiple QM/MM partitions, to describe the fractional QM character. We distinguish two classes of adaptive methods: Discontinuous and continuous. The former methods use at most two QM/MM partitions, and cannot completely avoid discontinuities in the energy and the forces. The more recent continuous adaptive methods employ a larger number of QM/MM partitions for a given configuration. Comparing the performance of the methods for the description of solution chemistry, we find that in certain cases the low-cost constrained methods are sufficiently accurate. For more demanding purposes, the continuous adaptive schemes provide a good balance between dynamical and structural accuracy. Finally, we challenge the adaptive approach by applying it to the difficult topic of proton transfer and diffusion. We present new results, using a well-behaved continuous adaptive method (DAS) to describe an alkaline aqueous solution of methanol. Comparison with fully QM and fully MM simulations shows that the main discrepancies are rooted in the presence of a QM/MM boundary, and not in the adaptive scheme. An anomalous confinement of the hydroxide ion to the QM part of the system stems from the mismatch between QM and MM potentials, which affects the free diffusion of the ion. We also observe an increased water density inside the QM region, which originates from the different chemical potentials of the QM and MM water molecules. The high density results in locally enhanced proton transfer rates

PyADF - A scripting framework for multiscale quantum chemistry

Applications of quantum chemistry have evolved from single or a few calculations to more complicated workflows, in which a series of interrelated computational tasks is performed. In particular multiscale simulations, which combine different levels of accuracy, typically require a large number of individual calculations that depend on each other. Consequently, there is a need to automate such workflows. For this purpose we have developed PYADF, a scripting framework for quantum chemistry. PYADF handles all steps necessary in a typical workflow in quantum chemistry and is easily extensible due to its object-oriented implementation in the Python programming language. We give an overview of the capabilities of PYADF and illustrate its usefulness in quantum-chemical multiscale simulations with a number of examples taken from recent applications. © 2011 Wiley Periodicals, Inc