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End date: 2022 × Start date: 2020 × Type: Text × Publisher: London [u.a.] : Royal Society of Chemistry × Subject: chemistry ×

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Now showing 1 - 4 of 4
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    Competition between excited state proton and OH- transport via a short water wire: Solvent effects open the gate
    (London [u.a.] : Royal Society of Chemistry, 2014) Bekçioǧlu, G.; Allolio, C.; Ekimova, M.; Nibbering, E.T.J.; Sebastiani, D.
    We investigate the acid-base proton exchange reaction in a microsolvated bifunctional chromophore by means of quantum chemical calculations. The UV/vis spectroscopy shows that equilibrium of the keto-and enol-forms in the electronic ground state is shifted to the keto conformation in the excited state. A previously unknown mechanism involving a hydroxide ion transport along a short water wire is characterized energetically, which turns out to be competitive with the commonly assumed proton transport. Both mechanisms are shown to have a concerted character, as opposed to a step-wise mechanism. The alternative mechanism of a hydrogen atom transport is critically examined, and evidence for strong solvent dependence is presented. Specifically, we observe electrostatic destabilization of the corresponding πσ* state by the aqueous solvent. As a consequence, no conical intersections are found along the reaction pathway.
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    Time-resolved photoelectron spectroscopy of adenine and adenosine in aqueous solution
    (London [u.a.] : Royal Society of Chemistry, 2013) Buchner, F.; Ritze, H.-H.; Lahl, J.; Lübcke, A.
    Time-resolved photoelectron spectroscopy is applied to study the excited state dynamics of the DNA base adenine and its ribonucleoside adenosine in aqueous solution for pump and probe photon energies in the range between 4.66 eV and 5.21 eV. We follow the evolution of the prepared excited state on the potential energy surface and retrieve lifetimes of the S1 state under different excitation conditions.
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    The influence of the Δk280 mutation and N- or C-terminal extensions on the structure, dynamics, and fibril morphology of the tau R2 repeat
    (London [u.a.] : Royal Society of Chemistry, 2014) Raz, Y.; Adler, J.; Vogel, A.; Scheidt, H.A.; Häupl, T.; Abel, B.; Huster, D.; Miller, Y.
    Tau is a microtubule-associated protein and is involved in microtubule assembly and stabilization. It consists of four repeats that bind to the microtubule. The ΔK280 deletion mutation in the tau R2 repeat region is directly associated with the development of the frontotemporal dementia parkinsonism linked to chromosome 17 (FTDP-17). This deletion mutation is known to accelerate tau R2 repeat aggregation. However, the secondary and the tertiary structures of the self-assembled ΔK280 tau R2 repeat mutant aggregates are still controversial. Moreover, it is unclear whether extensions by one residue in the N- or the C-terminus of this mutant can influence the secondary or the tertiary structure. Herein, we combine solid-state NMR, atomic force microscopy, electron microscopy and all-atom explicit molecular dynamics simulations to investigate the effects of the deletion mutation and the N- and the C-terminal extension of this mutant on the structure. Our main findings show that the deletion mutation induces the formation of small aggregates, such as oligomers, and reduces the formation of fibrils. However, the extensions in the N- or the C-terminus revealed more fibril formation than small aggregates. Further, in the deletion mutation only one structure is preferred, while the N- and the C-terminal extensions strongly lead to polymorphic states. Finally, our broad and combined experimental and computational techniques provide direct structural information regarding ΔK280 tau R2 repeat mutant aggregates and their extensions in the N- and C-terminii by one residue.
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    Cytoskeletal transition in patterned cells correlates with interfacial energy model
    (London [u.a.] : Royal Society of Chemistry, 2014) Müller, A.; Meyer, J.; Paumer, T.; Pompe, T.
    A cell's morphology is intricately regulated by microenvironmental cues and intracellular feedback signals. Besides biochemical factors, cell fate can be influenced by the mechanics and geometry of the surrounding matrix. The latter point was addressed herein, by studying cell adhesion on two-dimensional micropatterns. Endothelial cells were grown on maleic acid copolymer surfaces structured with stripes of fibronectin by microcontact printing. Experiments showed a biphasic behaviour of actin stress fibre spacing in dependence on the stripe width with a critical size of approx. 15 μm. In a concurrent modelling effort, cells on stripes were simulated as droplet-like structures, including variations of interfacial energy, total volume and dimensions of the nucleus. A biphasic behaviour with regard to cell morphology and area was found, triggered by the minimum of interfacial energy, with the phase transition occurring at a critical stripe width close to the critical stripe width found in the cell experiment. The correlation of experiment and simulation suggests a possible mechanism of the cytoskeletal rearrangements based on interfacial energy arguments.