How do parity violating weak nuclear interactions influence rovibrational frequencies in chiral molecules ?

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Gedanken zum Chemieunterricht am Gymnasium aus der Sicht der Hochschule

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Vibrational Predissociation in Hydrogen Bonded Dimers: The Case of (HF)2 and its Isotopomers

We use the dimer (HF???HF) as a model system to understand the dynamics in hydrogen-bonded systems. This particularly simple system has been widely used both in experimental and theoretical studies. Here we focus on the remarkable mode selectivity in vibrational predissociation processes which occur on time scales of picoseconds to nanoseconds. We have performed classical molecular dynamics (MD) calculations on the six-dimensional SO-3 potential energy surface (PES) of (HF)2[1] to estimate absorption spectra and predissociation lifetimes ?PD for various initial vibrational excitations involving HF stretching. Our calculations can qualitatively reproduce the mode selectivity in ?PD observed experimentally: Excitations involving the 'hydrogen-bonded' HF stretching mode give rise to shorter ?PD than those involving the 'free' HF stretching mode. Besides results concerning the HF dimer, this study offers the opportunity to check to what extent classical MD calculations on an accurate and realistic potential are suitable to study dynamical properties in such a molecular system

Ab Initio Study of Some Persistent Nitroxide Radicals

Stable free radicals have a variety of applications. Particularly, the aminoxyl group is frequently used in spin-labeling experiments. Nitroxides may also exhibit intriguing chiral and magnetic properties, and can be of interest for studies of molecular parity violation. We present results for three different groups of persistent nitroxide radicals: i) acyclic: dimethylaminoxyl (Me2NO), bis(trifluoromethyl)aminoxyl (CF3)2NO, and di-tert-butyl nitroxyl [(Me3C)2NO]; ii) cyclic: aziridine-N-oxyl, azetidine-N-oxyl, pyrrolidine-N-oxyl and piperidine-N-oxyl; and iii) imino nitroxides. We used density functional and ab initio (MP2, coupled cluster) methods to obtain insight into the underlying chemistry. The molecular structures, harmonic vibrational frequencies, inversion barriers, and hyperfine coupling constants are reported. The cyclic aziridine-N-oxyl exhibits a considerable inversion barrier of ?hc 3500 cm–1 compared to only ?hc 500 cm–1 for the other examples. Stable imino nitroxides are theoretically characterized for the first time in our work. We discuss the possibilities that some of the chiral derivatives may be dominated by molecular parity violation in their dynamics

The Concept of Law and Models in Chemistry

After a brief introduction to the basic concepts including some questions of language, the first part of this paper provides a brief survey of the historical development of laws and models in Chemistry, in particular atomic and molecular models. In the second part this paper deals with the fundamental role of the observation of symmetry violations in physics and chemistry in understanding the most ‘fundamental laws' and current efforts towards such studies by means of high resolution spectroscopy of molecules. We conclude with a brief discussion of the implications for current unsolved problems in astrophysics and biolog

Investigation of the ν2 + 2ν3 Subband in the Overtone Icosad of 13CH4 by Pulsed Supersonic Jet and Diode Laser Cavity Ring-Down Spectroscopy: Partial Rovibrational Analysis and Nuclear Spin Symmetry Conservation

We have investigated the ν2 + 2ν3 combination band of methane 13CH4 centered at 7493.15918 cm-1 within the icosad of the overtone absorption. The jet-CRD setup combining supersonic jet expansions and cavity ring-down spectroscopy which was already used for the reinvestigation of the same spectral region for the main isotope of methane (12CH4) has been used to record spectra of the Q and R branches at room temperature as well as at very low temperatures (down to 4 K). Based on our previous temperature-dependent investigations and the present results, we provide a careful analysis and the assignment for lines involving angular momentum quantum numbers up to J = 4. The analysis of the relative intensities in spectra taken at various rotational and effective translational temperatures demonstrate conservation of nuclear spin symmetry for 13CH4 under the conditions of a supersonic jet expansion, similar to our previous results regarding 12CH4 and also to further results using other techniques and covering other spectral ranges. This is in agreement with theoretical expectation regarding very slow nuclear spin symmetry relaxation under these conditions in supersonic jet expansions

Playin’ the city : artistic and scientific approaches to playful urban arts

An Theorien und Diskussionen über die Stadt mangelt es nicht, denn Städte dienen uns u.a. als Projektionsfläche zur Auseinandersetzung mit unserer Vergangenheit, der Gegenwart und unserer Zukunft. Diese Ausgabe 1 (2016) der Navigationen untersucht spielerische Formen dieser Auseinandersetzung in und mit der Stadt durch die sogenannten playful urban arts.The city has been discussed and theorized widely, and it continues to serve as a space in which our sense of the present, past, and future is constantly negotiated. This issue 1 (2016) of Navigationen examines new ways of engaging with cities through what are called the playful urban arts. Playful engagements with the urban environment frequently strive to create new ways of imagining and experiencing the city. In and through play, city spaces can become playgrounds that have the potential to transform people’s sense of themselves as human actors in an urban network of spatially bound and socio-economically grounded actions. Emerging from the playin’siegen urban games festival 2015, the essays and panel discussions assembled in this issue provide an interdisciplinary account of the contemporary playful urban arts. Wiht contributions by Miguel Sicart, Andreas Rauscher, Daniel Stein, Judith Ackermann and Martin Reiche, Michael Straeubig and Sebastian Quack, Marianne Halblaub Miranda and Martin Knöll, and Anne Lena Hartman

Arylmethylamino steroids as antiparasitic agents

In search of antiparasitic agents, we here identify arylmethylamino steroids as potent compounds and characterize more than 60 derivatives. The lead compound 1o is fast acting and highly active against intraerythrocytic stages of chloroquine-sensitive and resistant Plasmodium falciparum parasites (IC50 1–5?nM) as well as against gametocytes. In P. berghei-infected mice, oral administration of 1o drastically reduces parasitaemia and cures the animals. Furthermore, 1o efficiently blocks parasite transmission from mice to mosquitoes. The steroid compounds show low cytotoxicity in mammalian cells and do not induce acute toxicity symptoms in mice. Moreover, 1o has a remarkable activity against the blood-feeding trematode parasite Schistosoma mansoni. The steroid and the hydroxyarylmethylamino moieties are essential for antimalarial activity supporting a chelate-based quinone methide mechanism involving metal or haem bioactivation. This study identifies chemical scaffolds that are rapidly internalized into blood-feeding parasites