Impact of vibrational entropy on the stability of unsolvated peptide helices with increasing length

Helices are a key folding motif in protein structure. The question which factors determine helix stability for a given polypeptide or protein is an ongoing challenge. Here we use van der Waals corrected density-functional theory to address a part of this question in a bottom-up approach. We show how intrinsic helical structure is stabilized with length and temperature for a series of experimentally well studied unsolvated alanine based polypeptides, Ac-Alan-LysH+. By exploring extensively the conformational space of these molecules, we find that helices emerge as the preferred structure in the length range n=4-8 not just due to enthalpic factors (hydrogen bonds and their cooperativity, van der Waals dispersion interactions, electrostatics), but importantly also by a vibrational entropic stabilization over competing conformers at room temperature. The stabilization is shown to be due to softer low-frequency vibrational modes in helical conformers than in more compact ones. This observation is corroborated by including anharmonic effects explicitly through \emph{ab initio} molecular dynamics, and generalized by testing different terminations and considering larger helical peptide models

Bausteine eines bundesstaatlichen Haushaltsnotlagenregimes : zugleich ein Beitrag zur Governance der Finanzbeziehungen im Bundesstaat

Immer mehr Länder blicken auf eine desolate Finanzsituation und steuern auf eine Haushaltsnotlage zu. Vor dem Bundesverfassungsgericht sind derzeit zwei Klagen zu dieser Thematik anhängig. Die Regelung eines Haushaltsnotlagenregimes ist also dringend geboten. Der Beitrag zeigt diese Regelungsbedürftigkeit auf und beschäftigt sich mit der Frage, wie ein solches Haushaltsnotlagenregime rechtlich ausgestaltet sein könnte. Aus governancetheoretischer Perspektive wird dabei zunächst die besondere Bedeutung der Finanzverfassung im föderalistischen System beleuchtet und insbesondere die Regelungsebene zwischen der Verfassung und dem einfachen Gesetz in den Blick genommen. Als Regelungsform in dieser Zwischenebene wird der Erlass eines Haushaltsnotlagen-Grundsätzegesetzes vorgeschlagen, das drei zentrale Aspekte zu behandeln hätte: die Prävention und die Feststellung einer Haushaltsnotlage sowie die Haushaltssanierung. Für den eigentlichen Sanierungsvorgang bedarf es des Abschlusses eines Sanierungsvertrags, mit dessen konkreter Ausgestaltung Bedenken gegen Souveränitätsverluste begegnet werden kann

Modulation of the Work Function by the Atomic Structure of Strong Organic Electron Acceptors on H-Si(111)

Advances in hybrid organic/inorganic architectures for optoelectronics can be achieved by understanding how the atomic and electronic degrees of freedom cooperate or compete to yield the desired functional properties. Here we show how work-function changes are modulated by the structure of the organic components in model hybrid systems. We consider two cyano-quinodimethane derivatives (F4-TCNQ and F6-TCNNQ), which are strong electron-acceptor molecules, adsorbed on H-Si(111). From systematic structure searches employing range-separated hybrid HSE06 functional including many body van der Waals contributions, we predict that despite their similar composition, these molecules adsorb with significantly different densely-packed geometries in the first layer, due to strong intermolecular interaction. F6-TCNNQ shows a much stronger intralayer interaction (primarily due to van der Waals contributions) than F4-TCNQ in multilayered structures. The densely-packed geometries induce a large interface-charge rearrangement that result in a work-function increase of 1.11 and 1.76 eV for F4-TCNQ and F6-TCNNQ, respectively. Nuclear fluctuations at room temperature produce a wide distribution of work-function values, well modeled by a normal distribution with {\sigma}=0.17 eV. We corroborate our findings with experimental evidence of pronounced island formation for F6-TCNNQ on H-Si(111) and with the agreement of trends between predicted and measured work-function changes

Exploring the effects of seismicity on landslides and catchment sediment yield: An Italian case study

Recent studies showed that contemporary average catchment sediment yields (SY, [t km− 2 y− 1]) at regional and continental scales are often strongly correlated to spatial patterns of seismic activity. Nonetheless, we currently have little insights into the mechanisms that explain these correlations. We investigated how spatial patterns of SY in Italy are linked to patterns of seismic activity. For a dataset of 103 Italian catchments with average SY measured over a period of years to decades, we extracted tectonic and none-tectonic variables that potentially explain observed differences in SY. These include proxies for vertical uplift rates and cumulative seismic moments (CSM) associated with historic earthquakes of different ranges of magnitude. Results showed that also across Italy, SY is significantly correlated to seismicity. However, SY showed much stronger correlations with proxies of seismicity relating to small but frequent earthquakes (2 ≤ Mw < 4) than with proxies relating to tectonic uplift or large, potentially landslide-triggering earthquakes (Mw ≥ 4). Analyses of a dataset of about 500,000 landslides across Italy showed very comparable trends: spatial patterns of landslides within similar lithological units generally show a significant positive correlation with CSM of weak but frequent seismicity and generally not with CSM of large earthquakes. These results suggest that, on a decadal time scale and at a regional/continental spatial scale, frequent but relatively weak seismicity may exert a more important geomorphic impact than large earthquake events or tectonic uplift. © 2016 Elsevier B.V