Risselada H.J.,Max Planck Institute for Biophysical Chemistry |
Risselada H.J.,Leibniz Institute of Surface Modification |
Bubnis G.,Max Planck Institute for Biophysical Chemistry |
Grubmuller H.,Max Planck Institute for Biophysical Chemistry
Proceedings of the National Academy of Sciences of the United States of America | Year: 2014
Over the past 20 years, it has been widely accepted that membrane fusion proceeds via a hemifusion step before opening of the productive fusion pore. An initial hourglass-shaped lipid structure, the fusion stalk, is formed between the adjacent membrane leaflets (cis leaflets). It remains controversial if and howfusion proteins drive the subsequent transition (expansion) of the stalk into a fusion pore. Here, we propose a comprehensive and consistent thermodynamic understanding in terms of the underlying free-energy landscape of stalk expansion. We illustrate how the underlying free energy landscape of stalk expansion and the concomitant pathway is altered by subtle differences in membrane environment, such as leaflet composition, asymmetry, and flexibility. Nonleaky stalk expansion (stalk widening) requires the formation of a critical trans-leaflet contact. The fusion machinery can mechanically enforce trans-leaflet contact formation either by directly enforcing the trans-leaflets in close proximity, or by (electrostatically) condensing the area of the cis leaflets. The rate of these fast fusion reactionsmay not be primarily limited by the energetics but by the forces that the fusion proteins are able to exert.
Agency: European Commission | Branch: FP7 | Program: CP | Phase: FoF-ICT-2013.7.2 | Award Amount: 14.01M | Year: 2013
During more than 50 years of the laser existence, they have been proved as the unique tool for diverse material processing application. New application ideas, coming from universities and research institutions, are usually implemented by spin-off companies with limited resources for market penetration. Research laboratories are using universal laser tools, while effective and low-cost production requires adaptation of the processes and equipment during the technology assessment by the end-user.\nThe APPOLO project seeks to establish and coordinate connections between the end-users, which have demand on laser technologies for (micro)fabrication, knowledge accumulated in the application laboratories of the research institutes, as well as universities and the laser equipment manufacturers (preferable SMEs) of novel lasers, beam control and guiding, etc. The goal is to facilitate faster validation of the process feasibility and adaptation of the equipment for manufacturing, as well as assessment of the selected production processes. The core of the consortium comprises laser application laboratories around Europe which are connected into a virtual hub to accumulate knowledge and infrastructure and promote the easy-to-access environment for the development and validation of laser-based technologies. All the partners have chosen a few directions for the assessment of novel laser technologies: in ultra-short pulse laser scribing for monolithic interconnections in thin film CIGS solar cells - from lasers to pilot lines; use of the lasers and intelligent scanning in smart surface texturing for automotive and printing/decoration industries and for 3D flexible electronics.\nImplementation of the APPOLO project will help the partners from European photonics industry to preserve their competitiveness and penetrate new niches on the global market. The equipment builders for automotive, photovoltaics, electronics and printing industries will benefit from faster integration of innovative technologies which will provide the new-quality consumer products, including low-cost and high-efficiency solar cells, comfortable interior and functionality of cars, smart sensors for environmental monitoring and more.
Reichelt S.,Leibniz Institute of Surface Modification
Refrigeration Science and Technology | Year: 2016
Polymeric cryogels represent a relatively new class of porous monolithic scaffolds. These sponge-like materials are characterized by an interconnected network of pores with diameters ranging from 10-200 μm. Due to their unique properties they are particularly suitable for biological application. The matrices presented in this paper are synthesized at sub-zero temperatures from gel-forming precursors by free radical polymerization. Thereby, the pores are shaped by ice-crystals. The main fields of application are in biotechnology, biomedicine, and tissue engineering. At the Leibniz Institute of Surface Modification a novel strategy to generate macroporous (biocompatible) cryogels was developed. The reaction is started by electrons of a high energy accelerator. No additional initiators are required. This short perspective highlights our recent achievements in the field of E-beam (electron beam) synthesis of macroporous cryogels. © 2016, International Institute of Refrigeration. All rights reserved.
Agency: European Commission | Branch: FP7 | Program: CP-IP | Phase: NMP.2013.4.0-1 | Award Amount: 12.40M | Year: 2013
GLADIATOR (Graphene Layers: Production, Characterization and Integration) will enable the scalable production of cheaper, higher quality and larger area graphene sheets. The project will achieve this by optimizing the performance of CVD graphene (using doping), by increasing the throughput and size of CVD batch reactors, and by improving the process by which graphene is transferred for the CVD catalysts to the application substrate. GLADIATOR directly targets the gobal market for transparent electrodes (estimated to be worth over 11,000 million USD in 2016) and will demonstrate that the performance and price of indium tin oxide can be matched by graphene (transparency > 90%, sheet resistance < 10 Ohm/sq, cost < 30 Eur/ square meter). The new production technologies will be demonstrated by making ultraviolet organic photodiodes (possible application as fire sensors) and large area flexible OLEDs. CVD graphene production will be optimized using new diagnostic and process control instrumentation based on Raman spectroscopy and spectrometric ellipsometry; the quality of graphene layers post-transfer will be assured using new non-contact in-line eddy current measurements and THz imaging. CVD production costs per unit area will be reduced not only by the process parameter optimization, but also by developing methods to re-use the catalysts and by increasing the size of the reactor chamber. The process safety will be addressed, too. A critical issue for graphene, especially as a transparent electrode, is how to achieve homogenous large area coverage. GLADIATOR will extend the size of graphene layers beyond that of the CVD tools by implementing a novel patchwork process using a transfer process with high yields and negligible impact upon the properties of the graphene. Transfer processes will be developed for rigid and flexible substrates appropriate for organic large area electronics (OLAE), and substrate and barrier properties will be optimized for use with graphene.
Abel B.,Leibniz Institute of Surface Modification |
Abel B.,Wilhelm Ostwald Institute for Physical and Theoretical Chemistry
Annual Review of Physical Chemistry | Year: 2013
Charged particles such as hydrated ions and transient hydrated electrons, the simplest anionic reducing agents in water, and the special hydronium and hydroxide ions at water interfaces play an important role in many fields of science, such as atmospheric chemistry, radiation chemistry, and biology, as well as biochemistry. This article focuses on these species near hydrophobic interfaces of water, such as the air or vacuum interface of water or water protein/membrane interfaces. Ions at interfaces as well as solvated electrons have been reviewed frequently during the past decade. Although all species have been known for some time with seemingly familiar features, recently the picture in all cases became increasingly diffuse rather than clearer. The current account gives a critical state-of-the art overview of what is known and what remains to be understood and investigated about hydrated interfacial ions and electrons. © 2013 by Annual Reviews. All rights reserved.
Sivis M.,University of Gottingen |
Duwe M.,University of Gottingen |
Abel B.,Leibniz Institute of Surface Modification |
Ropers C.,University of Gottingen
Nature Physics | Year: 2013
Strong-field phenomena in optical nanostructures have enabled the integration of nanophotonics, plasmonics and attosecond spectroscopy. For example, tremendous excitement was sparked by reports of nanostructure-enhanced high-harmonic generation. However, there is growing tension between the great promise held by extreme-ultraviolet and attosecond-pulse generation on the nanoscale, and the lack of successful implementations. Here, we address this problem in a study of highly nonlinear optical processes in gas-exposed bow-tie nanoantennas. We find multiphoton- and strong-field-induced atomic excitation and ionization resulting in extreme-ultraviolet fluorescence, as well as third- and fifth-harmonic generation intrinsic to the nanostructures. Identifying the intensity-dependent spectral fingerprint of atomic fluorescence, we gauge local plasmonic fields. Whereas intensities sufficient for high-harmonic generation are indeed achieved in the near-field, the nanoscopic volume is found to prohibit an efficient conversion. Our results illustrate opportunities and challenges in highly nonlinear plasmonics and its extension to the extreme ultraviolet. © 2013 Macmillan Publishers Limited. All rights reserved.
Pawar G.M.,Leibniz Institute of Surface Modification |
Buchmeiser M.R.,Leibniz Institute of Surface Modification |
Buchmeiser M.R.,University of Stuttgart
Advanced Synthesis and Catalysis | Year: 2010
The synthesis of a resin-supported, carbon dioxide-protected N-heterocyclic carbene (NHC) and its use in organocatalysis and organometallic catalysis are described. The resin-bound carbon dioxide-protected NHC-based catalyst was prepared via ring-opening metathesis copolymerization of l,4,4a,5,8,8a- hexahydro-l,4,5,8-exo,endo-dimethanonaphthalene (DMNH6) with 3-(bicyclo[2.2.1]hept-5en-2-ylmethyl)-l-(2-propyl)-3,4,5,6-tetranydropyrimidin- l-ium-2-carboxylate (M1), using the well-defined Schrock catalyst Mo[N-2,6-(2-Pr)2-QH3] (CHCMe2Ph)(OCMe 3)2 and was used for a series of organocatalytic reactions, i.e., for the trimerization reaction of isocyanates, as well as for the cyanosilylation of carbonyl compounds. In the latter reaction, turn-over numbers (TON) up to 5000 were achieved. In addition, the polymer-supported, carbon dioxideprotected N-heterocyclic carbene served as an excellent progenitor for various polymer-supported metal complexes. It was loaded with a series of rhodium(I), iridium(I), and palladium(II) precursors and the resuiting Rh-, Ir-, and Pd-loaded resins were successfully used in the polymerization of phenylacetylene, in the hydrogen transfer reaction to benzaldehyde, as well as in Heck-type coupling reactions. In the latter reaction, TONs up to 100,000 were achieved. M1, as a non-supported analogue of poly-Ml-6-DMNH6, as well as the complexes PdCl2[1,3-bis(2-Pr)tetrahydropyrimidin-2-ylidene] 2 (Pd-I) and IrBr[1-(norborn-5ene-2-ylmetnyl)-3-(2-Pr)-3,4,5,6- tetrahydropyrimidin2-ylidine](COD) (Ir-1) were used as homogeneous analogues and their reactivity in the above-mentioned reactions was compared with that of the supported catalytic systems. In all reactions investigated, the TONs achieved with the supported systems were very similar to the ones obtained with the unsupported, homogeneous ones, the turn-over frequencies (TOFs), however, were lower by up to a factor of three. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA,.
Scherzer T.,Leibniz Institute of Surface Modification
Macromolecular Chemistry and Physics | Year: 2012
Acrylates and methacrylates are photopolymerized without photoinitiator by exposure to 172 nm radiation. The kinetics of the polymerization is studied using real-time Fourier-transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. It is shown that layers with a thickness of ≈500 nm can be polymerized very rapidly. The effect of structure, viscosity, functionality, and absorption of the acrylates as well as the influence of temperature and oxygen concentration on the reactivity are studied. A strong conversion gradient is observed in layers up to ≈2 μm thickness, which reflects the intensity gradient within the layer. However, the penetration of the polymerization into the layer exceeds the initial penetration depth of the VUV radiation, which indicates strong bleaching of the acrylates during irradiation. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Risselada H.J.,Leibniz Institute of Surface Modification
Structure | Year: 2015
In this issue of Structure, Reddy and colleagues combined various experimental data to build a realistic near-atomic model of the complete lipidic influenza A virion. Here, we illustrate the advances made by this pioneering simulation study and discuss ongoing challenges. ©2015 Elsevier Ltd. All rights reserved.
Naumov S.,Leibniz Institute of Surface Modification |
Buchmeiser M.R.,University of Stuttgart
Organometallics | Year: 2012
The experimentally observed high α-addition selectivity of 1,6-heptadiynes to modified Grubbs-Hoveyda initiators was elucidated with quantum chemical calculations. For these purposes, the two possible pathways of initiation in the Ru alkylidene triggered cyclopolymerization (CP) of 1,6-heptadiynes, resulting in either five-membered (α insertion) or six-membered (β insertion) repeat units, were treated as a multistep process. The first reaction cascade entails the activation of the precatalyst RuX 2(IMesH 2)(CH-2-(2-PrO-C 6H 4)) (1: X = F, Cl, Br, I, CF 3COO; IMesH 2 = 1,3- dimesitylimidazolin-2-ylidene), reaction with a 1,6-heptadiyne (π-1 complex formation), and further transformation into the first metallacyclobutene (MCB-1) followed by ring opening. The second reaction cascade entails again the formation of a π complex (π-2) through binding of the second alkyne moiety of the 1,6-heptadiyne and further transformation into MCB-2 followed by ring opening of MCB-2. The energies of the transition structures for both MCB-1 and MCB-2 formation (TS-1 and TS-2), which are considered the rate-determining steps in CP, are systematically lower for an α insertion of a monomer than for a β insertion. In addition, the geometrical parameters of the most stable structure of the βπ-2 complex are systematically less favorable for MCB-2 formation than in the case of an απ-2 complex, resulting in very high activation energies for βMCB-2 formation. Finally, the formation of βMCB-2 needs an additional step: namely, the endergonic formation of the intermediate βMCB-2. Since a halogen exchange to pseudohalides in Grubbs-Hoveyda initiators is required to turn them into active initiators in CP, the effect of electronegativity (EN) of the X ligands on the stability of the π-1 complex was calculated for X = I, Br, Cl, CF 3COO, F. There, an increase in EN results in lower energies for the α-insertion-derived π-1 complexes. For α insertion, the barriers to the MCB-1 intermediate formation, i.e. the energies of the transition states (TS-1(α)) for MCB-1 formation, decrease in the order I > Br > Cl > CF 3COO < F. All findings are consistent with the experimentally observed preference for α insertion in the cyclopolymerization of 1,6-heptadiynes with modified Grubbs-Hoveyda initiators and with the necessity for using pseudohalide variations of the Grubbs-Hoveyda initiator. © 2012 American Chemical Society.