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Contreras-Carballada P.,University of Amsterdam | Edafe F.,University of Fribourg | Tichelaar F.D.,Kavli Institute of Nanoscience | Belser P.,University of Fribourg | And 2 more authors.
Journal of Physical Chemistry Letters | Year: 2011

The combination of platinum nanoparticles with a tripodal osmium complex that anchors to the metal surface leads, under visible light irradiation, to the formation of solvated electrons. The formation kinetics is limited by the detachment of the electron from the platinum surface into the solution, the particle showing a type of capacitor behavior. © 2011 American Chemical Society.

Weyher J.L.,Polish Academy of Sciences | Tichelaar F.D.,Kavli Institute of Nanoscience | Van Dorp D.H.,University Utrecht | Kelly J.J.,University Utrecht | Khachapuridze A.,Polish Academy of Sciences
Journal of Crystal Growth | Year: 2010

A recently developed photoetching system for n-type GaN, a KOH solution containing the strong oxidizing agent potassium peroxydisulphate (K 2S2O8), was studied in detail. By careful selection of the etching parameters, such as the ratio of components and the hydrodynamics, two distinct modes were defined: defect-selective etching (denoted by KSO-D) and polishing (KSO-P). Both photoetching methods can be used under open-circuit (electroless) conditions. Well-defined dislocation-related etch whiskers are formed during KSO-D etching. All types of dislocations are revealed, and this was confirmed by cross-sectional TEM examination of the etched samples. Extended electrically active defects are also clearly revealed. The known relationship between etch rate and carrier concentration for photoetching of GaN in KOH solutions was confirmed for KSO-D etch using Raman measurements. It is shown that during KSO-P etching diffusion is the rate-limiting step, i.e. this etch is suitable for polishing of GaN. Some constraints of the KSO etching system for GaN are discussed and peculiar etch features, so far not understood, are described. © 2010 Elsevier B.V. All rights reserved.

Mejia J.,University of Namur | Tichelaar F.,Kavli Institute of Nanoscience | Saout C.,University of Namur | Toussaint O.,University of Namur | And 4 more authors.
Journal of Nanoparticle Research | Year: 2011

Multi-walled carbon nanotubes (MWC NTs) were dispersed in water and in a Pluronic F108 solution by four different dispersion methods (stirring, bath sonication, stirring followed by bath sonication, and sonication probe). The effect of the dispersion methods were evaluated in terms of the particle size distribution, the agglomerates size, and the exfoliated fraction produced, as well as in terms of the surface and bulk chemical composition. Energy dispersive X-ray, X-ray photoelectron spectroscopy, and centrifugal liquid sedimentation techniques were used to characterize pristine MWCNTs and their dispersion. It is shown that, irrespective of the dispersion methods used, the MWCNTs are strongly wrapped with the biocompatible surfactant Pluronic F108, thereby modifying the external surface of the MWCNTs. Some shortening of MWCNTs and more wrapping are also observed when sonication methods are used. These observations raise questions as to the validity of results obtained in toxicology tests, in vitro and in vivo, were such methods of dispersion procedures are used. © Springer Science+Business Media B.V. 2010.

Ali M.,Stanford University | Lipfert J.,Kavli Institute of Nanoscience | Seifert S.,Argonne National Laboratory | Herschlag D.,Stanford University | Doniach S.,Stanford University
Journal of Molecular Biology | Year: 2010

Riboswitches are elements of mRNA that regulate gene expression by undergoing structural changes upon binding of small ligands. Although the structures of several riboswitches have been solved with their ligands bound, the ligand-free states of only a few riboswitches have been characterized. The ligand-free state is as important for the functionality of the riboswitch as the ligand-bound form, but the ligand-free state is often a partially folded structure of the RNA, with conformational heterogeneity that makes it particularly challenging to study. Here, we present models of the ligand-free state of a thiamine pyrophosphate riboswitch that are derived from a combination of complementary experimental and computational modeling approaches. We obtain a global picture of the molecule using small-angle X-ray scattering data and use an RNA structure modeling software, MC-Sym, to fit local structural details to these data on an atomic scale. We have used two different approaches to obtaining these models. Our first approach develops a model of the RNA from the structures of its constituent junction fragments in isolation. The second approach treats the RNA as a single entity, without bias from the structure of its individual constituents. We find that both approaches give similar models for the ligand-free form, but the ligand-bound models differ for the two approaches, and only the models from the second approach agree with the ligand-bound structure known previously from X-ray crystallography. Our models provide a picture of the conformational changes that may occur in the riboswitch upon binding of its ligand. Our results also demonstrate the power of combining experimental small-angle X-ray scattering data with theoretical structure prediction tools in the determination of RNA structures beyond riboswitches. © 2009 Elsevier Ltd. All rights reserved.

News Article | January 22, 2016
Site: phys.org

By blowing extremely small bubbles, researchers from the Kavli Institute of Nanoscience at Delft University of Technology (TU Delft) have found an efficient way of producing so-called liposomes – very small bubble-like structures often used to deliver medicine, but also key to generating artificial cells. The scientists publish their findings in the online edition of Nature Communications on Friday 22 January.

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