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Göttingen, Germany

News Article | November 25, 2015
Site: http://www.forbes.com/energy/feed2/

Starfire Energy is picking up where the Kaiser Wilhelm Institute for Physical Chemistry left off.

News Article
Site: http://phys.org/chemistry-news/

What exactly are the processes when x-ray photons damage biomolecules with a metal centre? This question has been investigated by a team of scientists at the Institute for Physical Chemistry of Heidelberg University. Using the methods of quantum chemistry, they examined the underlying electronic processes caused by x-ray absorption. It turned out that the metal centre plays a key role in destroying a biomolecule. The research results of Vasili Stumpf, Dr. Kirill Gokhberg and Prof. Dr. Lorenz S. Cederbaum have appeared in Nature Chemistry. Radiation damage, arising from the interaction of high-energy x-rays with biological material, is a phenomenon widely known in science. It occurs, for example, when substrates – such as proteins – are analysed using x-ray light in order to determine their electronic structure or the spatial order of atoms. According to Prof. Cederbaum, this damage is most visible in the direct neighbourhood of metal centres, which are essential for the stability and biological function of biomolecules. The Heidelberg researchers investigated the related processes of electronic decay using computer-aided methods from quantum chemistry. They focused on processes occurring when radiation is absorbed through the metal centre of a biomolecule. As a model system they used a microcluster. That is a chemical system in which water molecules are arranged around a metal centre, in this case the positive doubly charged magnesium ion. Prof. Cederbaum explains that the metal centre initially loses several electrons through absorbing the radiation. That produces a highly charged, high-energy metal ion, which then returns to its original state through a cascade of electronic decay steps. In some of them the energy is transferred from the metal centre to the neighbouring molecules – a process known as interatomic Coulombic decay (ICD). In others, electrons from the neighbouring molecules are transferred to the metal ion in the so called electron transfer mediated decay (ETMD). According to Prof. Cederbaum, the two processes are ultrafast and take place on a scale of femtoseconds – the thousand millionth part of a micro-second. So they leave very little time for determination of the accurate molecular structure. In the course of the decay cascade, several neighbouring molecules emit slow electrons, both through the ICD and the ETMD processes. The molecules therefore charge positively, which leads to an explosion of the microcluster. In a bigger system, e.g. a protein with a metal centre, the positively charged neighbouring molecules and the slow electrons would react with the biomolecule and do more secondary damage, Prof. Cederbaum adds. The metal centre works like a lens that focuses the energy of the x-ray light onto its immediate environment. The result is a massive alteration of the surrounding chemical structure on a fast time scale. "We assume that the mechanism we have identified plays an important role when it comes to radiation damage in biological building-blocks with metal atoms – notably proteins and DNA," says Prof. Cederbaum. He hopes that these findings will contribute to decoding the complicated processes caused by radiation in living organisms. Explore further: How do free electrons originate? More information: V. Stumpf et al. The role of metal ions in X-ray-induced photochemistry, Nature Chemistry (2016). DOI: 10.1038/nchem.2429

Mattner C.,Institute for Physical Chemistry | Roling B.,University of Marburg | Heuer A.,Institute for Physical Chemistry
Solid State Ionics | Year: 2014

For a single-particle hopping model of arbitrary dimension we determine analytically the linear and nonlinear parts of the response to a periodic external field. Despite its simplicity the model contains the effects of localized double-well potential dynamics as well as long-range transport, i.e. reflecting key elements of the dynamics in truly disordered systems. The model parameters reflect typical symmetries between adjacent sites as well as the degree of barrier disorder. It is shown that in the 1D case the dc-limit of the nonlinear conductivity behaves differently than that in higher dimensions. Only for low dimensions the nonlinear conductivity displays a minimum. The scaling of this minimum with system parameters is derived. It is shown that for a broad range of frequencies the nonlinear conductivity can be expressed as a superposition of one contribution related to the linear conductivity, and another one related to the nonlinearity in a double-well potential. The present results are also discussed in the context of recent measurements of the non-linear conductivity for inorganic ion conductors as well as ionic liquids. © 2014 Elsevier B.V. Source

Pandey S.K.,CSIR - National Chemical Laboratory | Jogdand G.F.,CSIR - National Chemical Laboratory | Oliveira J.C.A.,Institute for Physical Chemistry | Mata R.A.,Institute for Physical Chemistry | And 2 more authors.
Chemistry - A European Journal | Year: 2011

The synthesis of homochiral homo-oligomers of cis- and trans-3- aminotetrahydrofuran-2-carboxylic acids (parent cis- and trans-furanoid-β- amino acids, referred to as "cis-/trans-FAA") has been carried out to understand their secondary structures and their dependence on the ring heteroatom. The oligomers of two diastereomers have been shown to have a distinct left-handed helicity. The cis-FAA homo-oligomers show a 14-helix structure, in contrast to the homo-oligomers of cis-ACPC, which adopt a sheet like structure. The trans-FAA homo-oligomers were found to adopt a 12-helix structure, the same trend found in trans-ACPC homo-oligomers. With the help of ab initio calculations, the structural features of cis-ACPC and cis-FAA hexamers were compared. We believe that the more compact packing of the cis-FAA hexapeptide should be due to a more favorable interaction between the ring and the backbone amide hydrogen. It's the heteroatom that counts: trans-Furanoid-β-amino acid (FAA) homo-oligomers adopt a 12-helix structure similar to that of trans-ACPC (2-aminocyclopentane carboxylic acid) oligomers. However, cis-FAA oligomers seem to adopt 14-helix solution structures, which is in contrast to cis-ACPC oligomers, for which a sheetlike structure has been observed. Calculations reveal that this preference in cis-FAAs is due to a more favorable contact between the backbone and the ring (see scheme). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Heine J.,Battery Research Center | Rodehorst U.,Battery Research Center | Qi X.,Battery Research Center | Badillo J.P.,Battery Research Center | And 6 more authors.
Electrochimica Acta | Year: 2014

Binder formulations based on N-methylpyrrolidone/polyvinylidene fluoride (NMP/PVdF) or water/carboxymethyl cellulose (H2O/CMC) are state of the art in the fabrication of anodes for lithium-ion battery (LIB) applications. However, in combination with metallic lithium these materials tend to degrade. Therefore, for the production and operation of anodes employing metallic lithium particles another binder system, which is flexible, chemically and electrochemically inert, inexpensive, commercially available and, especially for industrial applications, usable within a broad temperature range, is needed. Polyisobutylene (PIB) is able to fulfil these criteria. The advantages of this binder are its inert structure and its solubility in alkanes (e.g. heptane), which are inert against lithium metal, as well. In this work we will introduce heptane/PIB as a binder formulation for the preparation of electrodes from coated lithium powder (CLiP) particles. We demonstrate that CLiP electrodes fabricated with this binder system exhibit better electrochemical performance than electrodes made with NMP/PVdF or tetrahydrofuran (THF)/PVdF formulations. Furthermore, CLiP immersed in heptane/PIB show also better thermal stability compared to CLiP immersed in NMP/PVdF and THF/PVdF. © 2014 Elsevier Ltd. Source

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