Photodissociation of small carbonaceous molecules of astrophysical interest

Astronomical observations have shown that small carbonaceous molecules can persist in interstellar clouds exposed to intense ultraviolet radiation. Current astrochemical models lack quantitative information on photodissociation rates in order to interpret these data. We here present ab initio multi-reference configuration-interaction calculations of the vertical excitation energies, transition dipole moments and oscillator strengths for a number of astrophysically relevant molecules: C3, C4, C2H, l- and c-C3H, l- and c-C3H2, HC3H, l-C4H and l-C5H. Highly excited states up to the 9'th root of each symmetry are computed, and several new states with large oscillator strengths are found below the ionization potentials. These data are used to calculate upper limits on photodissociation rates in the unattenuated interstellar radiation field by assuming that all absorptions above the dissociation limit lead to dissociation.Comment: Full tables, rates and cross sections are posted at http://www.strw.leidenuniv.nl/~ewine/phot

Function of the Diiron Cluster of Escherichia coli Class Ia Ribonucleotide Reductase in Proton-Coupled Electron Transfer

The class Ia ribonucleotide reductase (RNR) from Escherichia coli employs a free-radical mechanism, which involves bidirectional translocation of a radical equivalent or “hole” over a distance of ~35 Å from the stable diferric/tyrosyl-radical (Y[subscript 122]•) cofactor in the β subunit to cysteine 439 (C[subscript 439]) in the active site of the α subunit. This long-range, intersubunit electron transfer occurs by a multistep “hopping” mechanism via formation of transient amino acid radicals along a specific pathway and is thought to be conformationally gated and coupled to local proton transfers. Whereas constituent amino acids of the hopping pathway have been identified, details of the proton-transfer steps and conformational gating within the β sununit have remained obscure; specific proton couples have been proposed, but no direct evidence has been provided. In the key first step, the reduction of Y[subscript 122]• by the first residue in the hopping pathway, a water ligand to Fe[subscript 1] of the diferric cluster was suggested to donate a proton to yield the neutral Y[subscript 122]. Here we show that forward radical translocation is associated with perturbation of the Mössbauer spectrum of the diferric cluster, especially the quadrupole doublet associated with Fe[subscript 1]. Density functional theory (DFT) calculations verify the consistency of the experimentally observed perturbation with that expected for deprotonation of the Fe[subscript 1]-coordinated water ligand. The results thus provide the first evidence that the diiron cluster of this prototypical class Ia RNR functions not only in its well-known role as generator of the enzyme’s essential Y[subscript 122]•, but also directly in catalysis.National Institutes of Health (U.S.) (GM-29595

On Predicting Mössbauer Parameters of Iron-Containing Molecules with Density-Functional Theory

The performance of six frequently used density functional theory (DFT) methods (RPBE, OLYP, TPSS, B3LYP, B3LYP*, and TPSSh) in the prediction of Mössbauer isomer shifts(δ) and quadrupole splittings (ΔEQ) is studied for an extended and diverse set of Fe complexes. In addition to the influence of the applied density functional and the type of the basis set, the effect of the environment of the molecule, approximated with the conducting-like screening solvation model (COSMO) on the computed Mössbauer parameters, is also investigated. For the isomer shifts the COSMO-B3LYP method is found to provide accurate δ values for all 66 investigated complexes, with a mean absolute error (MAE) of 0.05 mm s–1 and a maximum deviation of 0.12 mm s–1. Obtaining accurate ΔEQ values presents a bigger challenge; however, with the selection of an appropriate DFT method, a reasonable agreement can be achieved between experiment and theory. Identifying the various chemical classes of compounds that need different treatment allowed us to construct a recipe for ΔEQ calculations; the application of this approach yields a MAE of 0.12 mm s–1 (7% error) and a maximum deviation of 0.55 mm s–1 (17% error). This accuracy should be sufficient for most chemical problems that concern Fe complexes. Furthermore, the reliability of the DFT approach is verified by extending the investigation to chemically relevant case studies which include geometric isomerism, phase transitions induced by variations of the electronic structure (e.g., spin crossover and inversion of the orbital ground state), and the description of electronically degenerate triplet and quintet states. Finally, the immense and often unexploited potential of utilizing the sign of the ΔEQ in characterizing distortions or in identifying the appropriate electronic state at the assignment of the spectral lines is also shown

Ethischer Konsens und Rechtsbewusstsein im nachmetaphysischen Kontext | Humanökologische Voraussetzungen aus sozialwissenschaftlicher und theologisch-ethischer Perspektive

Ethics and legal design currently seem to be involved in a “vortex of temporality” (Jürgen Habermas), which, according to the understanding of many, integrates them into a modern way of life. Examples are the protection of life (Embryo Protection Act and abortion, reinterpretation of Article 1 of the Basic Law in the Maunz/Dürig commentary by Herdegen), the promotion of plural family forms and sexual relationship worlds (“marriage for all“, life stage partnership), assisted dying (judgment of the Federal Constitutional Court on assisted suicide). Apparently, it is always about the dismantling of traditional taboos and the establishment of legal regulations that are intended to correspond to a new ethical consciousness and plural ideological worlds.The discussion in ethics theory and legal theory in this situation has agreed on a model of the gravitational fields of liberal self-execution, in which cultural development in ethics and law should find its moral support and at the same time its legal ethical dynamics. According to this understanding, a basic consensus is maintained in the execution of liberal debates (also on moral and legal questions). It is articulated in human rights principles, which themselves must be discussed again in open conversation in their meaning, but which at the same time bring themselves to the fore as irrefutable exactly in this social process.Theological ethics maintains a certain distance from this interpretation. The understanding of freedom must then be structured for the lifestyle of society in such a way that the one-sidedness of individualism and abstract overemphasis, even exaggeration, is avoided. The aim is to integrate social integration, reference to natural framework conditions and realistic border awareness in ethics and law. Moral theology can be based in this on the further development of social science

Structural characteristics of redox-active pyridine-1,6-diimine complexes: Electronic structures and ligand oxidation levels

N-aryl and N-alkyl substituted pyridine-2,6-diimines (pdi) are useful tridentate ligands that are redoxactive and can coordinate to main group elements, transition metal ions, lanthanides and actinides. The neutral (pdi)(0) ligand can accept up to four electrons generating a monoanion (pdi(center dot))(1-) pi-radical, singlet or triplet dianion (pdi)(2-) or (pdi(center dot center dot))(2-), a trianionic pi-radical (pdi(center dot))(3-), and a singlet tetraanion (pdi)(4-). Upon this stepwise reduction the four C-N bond distances (C-py-N-py and C-imine-N-imine 1 increase and at the same time the two C-py-C-imine bond distances decrease. We show here that the single structural parameter Delta = [(d2 + d2')/2 - (d1 + d1' + d3 + d3')/4] varies in a linear fashion with increasing reduction of the (pdi(0))-ligand. Delta represents therefore a powerful structural parameter for the determination of the oxidation level of this ligand in a given complex provided the central metal ion does not exhibit significant pi-backdonation effects (M -> pdi(0)) as found in compounds with a neutral ligand and where M is a 2nd or 3rd row transition metal ion with d(n) configuration and n >= 6. (C) 2018 Elsevier B.V. All rights reserved