Purple membranes from Halobacterium salinarum as building blocks for nanobiotechnology: The importance of mechanical and thermal properties for matrix and surface applications

Bacteriorhodopsin (BR) is a light-driven proton pump and the key protein in halobacterial photosynthesis. In its native host, the archaeon Halobacterium salinarum, BR trimers arrange into a 2-D crystalline lattice, the so-called purple membranes (PMs) which comprise BR and lipids only. Along with the PM assembly BR is astonishingly stable against thermal and chemical stress which makes it an excellent candidate for a variety of technical applications. Many technical applications involve immobilization of PM in a matrix or at a surface. Sugar glasses are frequently used matrixes for the stabilization of biomolecules against thermal stress as well as dehydration. In the following work temperature-dependent interactions between PM and sugar glasses were analyzed. Above T > 60°C a blue membrane is formed the so-called sugar-induced membrane (SIBM). This thermochromism was explained by a model which is based on the release of divalent cations from PM and the chelating properties of carbohydrates. Due to their high mass adsorption is an appropriate method for the immobilization of PMs at surfaces. In this work self-assembled monolayers (SAMs) of alkanethiols on gold were used and analyzed for this purpose. To fabricate selective adsorption sites the alkanethiol-SAMs have to be structured. An appropriate procedure for the patterning of alkanethiol-SAMs has been developed which has been named “submerged laser ablation” (SLAB). Knowledge about the mechanical properties of freely suspended membranes is essential for nanobiotechnological applications of PM. In each PM thousands of BR molecules are arranged in a unidirectional manner and are strongly coupled due to the crystalline assembly. Therefore, collective conformational changes of single BRs should influence the topology of freely suspended PMs. In this work it was demonstrated by direct imaging of freely suspended native PMs via cryogenic high-resolution scanning electron microscopy (cryo-SEM) that the flat disk-like shape of PM changes dramatically as soon as most of the BRs are in the M2 state which is characterized by wedge-shaped BRs due to collective opening of the cytoplasmatic half-channels. Light- as well as pH-induced shape changes are easily observed with mutated BRs which accumulate wedge-shaped BR molecules. These results open the way for further nanobiotechnological applications of PM, i. e. as supramolecular actuator

Directed deposition of silicon nanowires using neopentasilane as precursor and gold as catalyst

In this work the applicability of neopentasilane (Si(SiH3)4) as a precursor for the formation of silicon nanowires by using gold nanoparticles as a catalyst has been explored. The growth proceeds via the formation of liquid gold/silicon alloy droplets, which excrete the silicon nanowires upon continued decomposition of the precursor. This mechanism determines the diameter of the Si nanowires. Different sources for the gold nanoparticles have been tested: the spontaneous dewetting of gold films, thermally annealed gold films, deposition of preformed gold nanoparticles, and the use of “liquid bright gold”, a material historically used for the gilding of porcelain and glass. The latter does not only form gold nanoparticles when deposited as a thin film and thermally annealed, but can also be patterned by using UV irradiation, providing access to laterally structured layers of silicon nanowires

Energy-filtered transmission electron microscopy of biological samples on highly transparent carbon nanomembranes

Ultrathin carbon nanomembranes (CNM) comprising crosslinked biphenyl precursors have been tested as support films for energy-filtered transmission electron microscopy (EFTEM) of biological specimens. Due to their high transparency CNM are ideal substrates for electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) of stained and unstained biological samples. Virtually background-free elemental maps of tobacco mosaic virus (TMV) and ferritin have been obtained from samples supported by ~ 1 nm thin CNM. Furthermore, we have tested conductive carbon nanomembranes (cCNM) comprising nanocrystalline graphene, obtained by thermal treatment of CNM, as supports for cryoEM of ice-embedded biological samples. We imaged ice-embedded TMV on cCNM and compared the results with images of ice-embedded TMV on conventional carbon film (CC), thus analyzing the gain in contrast for TMV on cCNM in a quantitative manner. In addition we have developed a method for the preparation of vitrified specimens, suspended over the holes of a conventional holey carbon film, while backed by ultrathin cCNM

UNIVERSIDAD Y ATENCIÓN A LOS DICENTES PORTADORA DE NECESIDADES ESPECIALES.

La pesquisa fue constituída por empleados administrativos de una Universidad del Sur de Brasil, que tratan de manera directa con todos los alumnos de la Universidad y que, escogidos aleatoriamente en un universo de personas, fueron invitados a participar de este estudio. Los datos fueron conseguidosen el local de trabajo de los empleados, para el cual se solicitó correspondiente autorización de la Pró-Rectoria de Enseñanza de la Universidad, bien como de las personas , que fueron esclarecidos sobre los objetivos de la encuesta. Se usó un guía de entrevista con preguntas abiertas, algunas de ellas referidas a situaciones que se viven en el atendimiento a los alumnos PNE, con la idea de verificar las estratégias que generalmente los empleados utilizan en el atendimiento. Las encuestas fueron grabadas (con permiso de las personas) y escritas. Los datos fueron analisados de forma cualitativa, utilizando para tanto Análisis de Contenido, a partir de la metodologia propuesta por BARDIN (1988)

Retrato incompleto de Eudinyr Fraga

Retrato incompleto de Eudinyr Frag

Single-walled carbon nanotubes and nanocrystalline graphene reduce beam-induced movements in high-resolution electron cryo-microscopy of ice-embedded biological samples

For single particle electron cryo-microscopy (cryoEM), contrast loss due to beam-induced charging and specimen movement is a serious problem, as the thin films of vitreous ice spanning the holes of a holey carbon film are particularly susceptible to beam-induced movement. We demonstrate that the problem is at least partially solved by carbon nanotechnology. Doping ice-embedded samples with single-walled carbon nanotubes (SWNT) in aqueous suspension or adding nanocrystalline graphene supports, obtained by thermal conversion of cross-linked self-assembled biphenyl precursors, significantly reduces contrast loss in high-resolution cryoEM due to the excellent electrical and mechanical properties of SWNTs and graphene

The Knowledge Handling Notation: building an interface to enable design conversation diagnosis

Abstract: With the development of the Knowledge Handling Notation (KHN) we were able to provide a model for a notation that captures modes of knowledge handling and visualizes its dynamics in design conversations. The KHN functions as an interface between transcript and pattern analysis for researchers or coaches who aim at diagnosing knowledge handling in conversational interactions in general, and design reviews in particular. We applied the notation to different design review sessions and iterated on the coding, which is presented in a coding manual. A visualization of the coding shows the dynamics of the conversational interaction. We developed the Knowledge Handling Notation (KHN) by integrating Nonaka’s concept of externalization and combination, enriched with sub-categories that account for transitions between those activities. In that, KHN maps out design conversations focused on the dynamics of knowledge handling and thereby serve as an orientation system for knowledge handling interactions in the context of design conversations

The application of Graphene as a sample support in Transmission Electron Microscopy

Transmission electron microscopy has witnessed rampant development and surging point resolution over the past few years. The improved imaging performance of modern electron microscopes shifts the bottleneck for image contrast and resolution to sample preparation. Hence, it is increasingly being realized that the full potential of electron microscopy will only be realized with the optimization of current sample preparation techniques. Perhaps the most recognized issues are background signal and noise contributed by sample supports, sample charging and instability. Graphene provides supports of single atom thickness, extreme physical stability, periodic structure, and ballistic electrical conductivity. As an increasing number of applications adapting graphene to their benefit emerge, we discuss the unique capabilities afforded by the use of graphene as a sample support for electron microscopy.Comment: Review, to appear in solid state communication

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