The low-density/high-density liquid phase transition for model globular proteins

The effect of molecule size (excluded volume) and the range of interaction on the surface tension, phase diagram and nucleation properties of a model globular protein is investigated using a combinations of Monte Carlo simulations and finite temperature classical Density Functional Theory calculations. We use a parametrized potential that can vary smoothly from the standard Lennard-Jones interaction characteristic of simple fluids, to the ten Wolde-Frenkel model for the effective interaction of globular proteins in solution. We find that the large excluded volume characteristic of large macromolecules such as proteins is the dominant effect in determining the liquid-vapor surface tension and nucleation properties. The variation of the range of the potential only appears important in the case of small excluded volumes such as for simple fluids. The DFT calculations are then used to study homogeneous nucleation of the high-density phase from the low-density phase including the nucleation barriers, nucleation pathways and the rate. It is found that the nucleation barriers are typically only a few $k_{B}T$ and that the nucleation rates substantially higher than would be predicted by Classical Nucleation Theory.Comment: To appear in Langmui

Assembling Carbon Nanotube Architectures

Well-defined multiwalled carbon nanotube structures are generated on stainless steel AISI 304 (EN AW 1.4301) by chemical vapor deposition. Pulsed laser-induced dewetting (PLiD) of the surface, by 532 nm nanosecond laser pulses, is utilized for the preparation of metal oxide nanoparticle fields with a defined particle number per area. The reduction of the precursor particles is achieved in an Ar/H2 (10% H2) atmosphere at 750 °C, thereby generating catalytic nanoparticles (c-NPs) for carbon nanotube (CNT) growth. Ethylene is used as a precursor gas for CNT growth. CNT lengths and morphology are directly related to the c-NP aerial density, which is dependent on the number of dewetting cycles during the PLiD process. Within a narrow window of c-NP per area, vertically aligned carbon nanotubes of great lengths are obtained. For more intense laser treatments, three-dimensional dewetting occurs and results in the formation of cauliflower-like structures. The laser process enables the creation of all kinds of CNT morphologies nearby on the microscale

Noncovalent Functionalization of Carbon Substrates with Hydrogels Improves Structural Analysis of Vitrified Proteins by Electron Cryo-Microscopy

In electron cryo-microscopy, structure determination of protein molecules is frequently hampered by adsorption of the particles to the support film material, typically amorphous carbon. Here, we report that pyrene derivatives with one or two polyglycerol (PG) side chains bind to the amorphous carbon films, forming a biorepulsive hydrogel layer so that the number of protein particles in the vitreous ice drastically increases. This approach could be extended by adding a hydrogel-functionalized carbon nanotube network (HyCaNet, the hydrogel again being formed from the PG-pyrene derivatives), which stabilized the protein-containing thin ice films during imaging with the electron beam. The stabilization resulted in reduced particle motion by up to 70%. These substrates were instrumental for determining the structure of a large membrane protein complex

Smart Molecular Nanosheets for Advanced Preparation of Biological Samples in Electron Cryo-Microscopy

Transmission electron cryo-microscopy (cryoEM) of vitrified biological specimens is a powerful tool for structural biology. Current preparation of vitrified biological samples starts off with sample isolation and purification, followed by the fixation in a freestanding layer of amorphous ice. Here, we demonstrate that ultrathin (∼10 nm) smart molecular nanosheets having specific biorecognition sites embedded in a biorepulsive layer covalently bound to a mechanically stable carbon nanomembrane allow for a much simpler isolation and structural analysis. We characterize in detail the engineering of these nanosheets and their biorecognition properties employing complementary methods such as X-ray photoelectron and infrared spectroscopy, atomic force microscopy as well as surface plasmon resonance measurements. The desired functionality of the developed nanosheets is demonstrated by in situ selection of a His-tagged protein from a mixture and its subsequent structural analysis by cryoEM

Unpacking the notion of prototype archetypes in the early phase of an innovation process

International audienceThe literature on new product development examines a variety of roles that prototypes can play based on the phase of the design process when they are used, but the characteristics of these prototypes that correspond to the expected outcomes, especially in the early phase of the design process, are understudied. We address this gap by studying the characteristics of the prototypes used in the design process (especially during the early phase) that correspond to their roles. Based on an analysis of six cases of prototypes that are used early on in the design process, we characterize three different archetypes of artefacts: stimulators, demonstrators, and validators, and we emphasize the coherence between the role they play in the design process and the characteristics that enable these roles. Specifying the roles of these artefacts should contribute to addressing the two flaws that are generally encountered during prototyping: overdesigning and overtrusting the prototypes

Structural Investigation of 1,1 '-Biphenyl-4-thiol Self-Assembled Monolayers on Au(111) by Scanning Tunneling Microscopy and Low-Energy Electron Diffraction

Matei D, Muzik H, Gölzhäuser A, Turchanin A. Structural Investigation of 1,1 '-Biphenyl-4-thiol Self-Assembled Monolayers on Au(111) by Scanning Tunneling Microscopy and Low-Energy Electron Diffraction. Langmuir. 2012;28(39):13905-13911.Self-assembled monolayers (SAMs) of 1,1'-biphenyl-4-thiol (H-(C6H4)(2)-SH) on Au(111) were prepared from solution or via vapor deposition in ultrahigh vacuum and characterized by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and X-ray photoelectron spectroscopy (XPS). In contrast to the typically observed for densely packed alkane-thiol SAMs on Au(111) (root 3 x root 3)R30 degrees structure, the densely packed aromatic biphenylthiol SAMs prepared by both methods exhibit an unusual hexagonal (2 x 2) structure. Upon annealing at 100 degrees C, this structure evolves into the (2 x 7 root 3) structure resulting in the formation of highly ordered pinstripes oriented along the directions. Lower density SAMs, prepared by vapor deposition in vacuum, show mixed structures comprising the hexagonal (2 x 2) structure and two rectangular arrangements with the unit cells of (3 root 3 x 9) and (2 root 3 x 8). An extinction of the (3 root 3 x 9) structure in the favor of the (2 root 3 x 8) structure is observed upon annealing at temperatures of similar to 100 degrees C