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Graphene on Rh(111): STM and AFM studies  [PDF]
E. N. Voloshina,Yu. S. Dedkov,S. Torbruegge,A. Thissen,M. Fonin
Physics , 2012, DOI: 10.1063/1.4729549
Abstract: The electronic and crystallographic structure of the graphene/Rh(111) moir\'e lattice is studied via combination of density-functional theory calculations and scanning tunneling and atomic force microscopy (STM and AFM). Whereas the principal contrast between hills and valleys observed in STM does not depend on the sign of applied bias voltage, the contrast in atomically resolved AFM images strongly depends on the frequency shift of the oscillating AFM tip. The obtained results demonstrate the perspectives of application atomic force microscopy/spectroscopy for the probing of the chemical contrast at the surface.
Misfolding and Amyloid Aggregation of Apomyoglobin  [PDF]
Clara Iannuzzi,Rosa Maritato,Gaetano Irace,Ivana Sirangelo
International Journal of Molecular Sciences , 2013, DOI: 10.3390/ijms140714287
Abstract: Apomyoglobin is an excellent example of a monomeric all α-helical globular protein whose folding pathway has been extensively studied and well characterized. Structural perturbation induced by denaturants or high temperature as well as amino acid substitution have been described to induce misfolding and, in some cases, aggregation. In this article, we review the molecular mechanism of the aggregation process through which a misfolded form of a mutated apomyoglobin aggregates at physiological pH and room temperature forming an amyloid fibril. The results are compared with data showing that either amyloid or aggregate formation occurs under particular denaturing conditions or upon cleavage of the residues corresponding to the C-terminal helix of apomyoglobin. The results are discussed in terms of the sequence regions that are more important than others in determining the amyloid aggregation process.
科学通报 , 1994,
Abstract: 扫描隧道显微镜(STM)和原子力显微镜(AFM)是Binnig等人于80年代研制成功的新型表面分析仪器.它们具有原子级高分辨率,能够用于实时地观察原子在物质表面的排列状态和与表面电子行为有关的物理、化学性质.将STM和AFM用于煤的研究,迄今为止尚未见报道.煤的主体由复杂的高分子化合物组成,结构极不均一.通过成像技术,在无降解的前提
煤结构的STM和AFM研究  [PDF]
科学通报 , 1994,
Abstract: 扫描隧道显微镜(STM)和原子力显微镜(AFM)是Binnig等人于80年代研制成功的新型表面分析仪器.它们具有原子级高分辨率,能够用于实时地观察原子在物质表面的排列状态和与表面电子行为有关的物理、化学性质.将STM和AFM用于煤的研究,迄今为止尚未见报道.煤的主体由复杂的高分子化合物组成,结构极不均一.通过成像技术,在无降解的前提
The effect of interstitial clusters and vacancies on the STM image of graphite  [PDF]
Arkady V. Krasheninnikov,Vladimir F. Elesin
Physics , 1999, DOI: 10.1016/S0039-6028(00)00088-1
Abstract: Making use of the tight-binding Green's function technique, we have calculated the STM images of graphite with surface and sub-surface defects, while taking into account the relaxation of the lattice due to defects. We have demonstrated that two different physical mechanisms may result in the formation of hillocks in the STM images: buckling of the graphite surface due to interstitials between the uppermost graphite layers and the enhancement of the electron density of states close to the Fermi energy on the carbon atoms in the vicinity of vacancies. Our results indicate that small hillocks may originate both from the interstitial clusters and from the vacancies. By contrast, however, large hillocks in excess of 10 \AA~ in diameter can be caused only by interstitial clusters.
STM, SECPM, AFM and Electrochemistry on Single Crystalline Surfaces  [PDF]
Holger Wolfschmidt,Claudia Baier,Stefan Gsell,Martin Fischer,Matthias Schreck,Ulrich Stimming
Materials , 2010, DOI: 10.3390/ma3084196
Abstract: Scanning probe microscopy (SPM) techniques have had a great impact on research fields of surface science and nanotechnology during the last decades. They are used to investigate surfaces with scanning ranges between several 100 mm down to atomic resolution. Depending on experimental conditions, and the interaction forces between probe and sample, different SPM techniques allow mapping of different surface properties. In this work, scanning tunneling microscopy (STM) in air and under electrochemical conditions (EC-STM), atomic force microscopy (AFM) in air and scanning electrochemical potential microscopy (SECPM) under electrochemical conditions, were used to study different single crystalline surfaces in electrochemistry. Especially SECPM offers potentially new insights into the solid-liquid interface by providing the possibility to image the potential distribution of the surface, with a resolution that is comparable to STM. In electrocatalysis, nanostructured catalysts supported on different electrode materials often show behavior different from their bulk electrodes. This was experimentally and theoretically shown for several combinations and recently on Pt on Au(111) towards fuel cell relevant reactions. For these investigations single crystals often provide accurate and well defined reference and support systems. We will show heteroepitaxially grown Ru, Ir and Rh single crystalline surface films and bulk Au single crystals with different orientations under electrochemical conditions. Image studies from all three different SPM methods will be presented and compared to electrochemical data obtained by cyclic voltammetry in acidic media. The quality of the single crystalline supports will be verified by the SPM images and the cyclic voltammograms. Furthermore, an outlook will be presented on how such supports can be used in electrocatalytic studies.
The mechanism of high-resolution STM/AFM imaging with functionalized tips  [PDF]
Prokop Hapala,Georgy Kichin,Christian Wagner,F. Stefan Tautz,Ruslan Temirov,Pavel Jelinek
Physics , 2014, DOI: 10.1103/PhysRevB.90.085421
Abstract: High resolution Atomic Force Microscopy (AFM) and Scanning Tunnelling Microscopy (STM) imaging with functionalized tips is well established, but a detailed understanding of the imaging mechanism is still missing. We present a numerical STM/AFM model, which takes into account the relaxation of the probe due to the tip-sample interaction. We demonstrate that the model is able to reproduce very well not only the experimental intra- and intermolecular contrasts, but also their evolution upon tip approach. At close distances, the simulations unveil a significant probe particle relaxation towards local minima of the interaction potential. This effect is responsible for the sharp sub-molecular resolution observed in AFM/STM experiments. In addition, we demonstrate that sharp apparent intermolecular bonds should not be interpreted as true hydrogen bonds, in the sense of representing areas of increased electron density. Instead they represent the ridge between two minima of the potential energy landscape due to neighbouring atoms.
A Role for Amyloid in Cell Aggregation and Biofilm Formation  [PDF]
Melissa C. Garcia,Janis T. Lee,Caleen B. Ramsook,David Alsteens,Yves F. Dufrêne,Peter N. Lipke
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0017632
Abstract: Cell adhesion molecules in Saccharomyces cerevisiae and Candida albicans contain amyloid-forming sequences that are highly conserved. We have now used site-specific mutagenesis and specific peptide perturbants to explore amyloid-dependent activity in the Candida albicans adhesin Als5p. A V326N substitution in the amyloid-forming region conserved secondary structure and ligand binding, but abrogated formation of amyloid fibrils in soluble Als5p and reduced cell surface thioflavin T fluorescence. When displayed on the cell surface, Als5p with this substitution prevented formation of adhesion nanodomains and formation of large cellular aggregates and model biofilms. In addition, amyloid nanodomains were regulated by exogenous peptides. An amyloid-forming homologous peptide rescued aggregation and biofilm activity of Als5pV326N cells, and V326N substitution peptide inhibited aggregation and biofilm activity in Als5pWT cells. Therefore, specific site mutation, inhibition by anti-amyloid peturbants, and sequence-specificity of pro-amyloid and anti-amyloid peptides showed that amyloid formation is essential for nanodomain formation and activation.
Inhibition of Alzheimer amyloid β aggregation by polyvalent trehalose
Yoshiko Miura et al
Science and Technology of Advanced Materials , 2008,
Abstract: A glycopolymer carrying trehalose was found to suppress the formation of amyloid fibrils from the amyloid β peptide (1–42) (Aβ), as evaluated by thioflavin T assay and atomic force microscopy. Glycopolymers carrying sugar alcohols also changed the aggregation properties of Aβ, and the inhibitory effect depended on the type of sugar and alkyl side chain. Neutralization activity was confirmed by in vitro assay using HeLa cells. The glycopolymer carrying trehalose strongly inhibited amyloid formation and neutralized cytotoxicity.
Effective screen for amyloid β aggregation inhibitor using amyloid β-conjugated gold nanoparticles
Sun-Ho Han, Yu Jin Chang, Eun Sun Jung, et al
International Journal of Nanomedicine , 2011, DOI: http://dx.doi.org/10.2147/IJN.S15278
Abstract: tive screen for amyloid β aggregation inhibitor using amyloid β-conjugated gold nanoparticles Original Research (5286) Total Article Views Authors: Sun-Ho Han, Yu Jin Chang, Eun Sun Jung, et al Published Date December 2010 Volume 2011:6 Pages 1 - 12 DOI: http://dx.doi.org/10.2147/IJN.S15278 Sun-Ho Han1, Yu Jin Chang1, Eun Sun Jung1, Jong-Won Kim2, Duk Lyul Na3, Inhee Mook-Jung1 1Department of Biochemistry and Biomedical Sciences, Seoul National University, College of Medicine, Jongro-gu, Seoul, Korea; 2Department of Laboratory Medicine and Genetics, Samsung Medical Center, Sungkyunkwan University, School of Medicine, Kangnam-Ku, Seoul, Korea; 3Department of Neurology, Samsung Medical Center, Sungkyunkwan University, School of Medicine, Kangnam-Ku, Seoul, Korea Abstract: The abnormal aggregation of amyloid β (Aβ) and its subsequent intra- and extracellular accumulation constitute the disease-causing cascade of Alzheimer's disease (AD). The detection of Aβ aggregates and senile plaque formation, however, is nearly impossible during early pathogenesis, and the absence of a convenient screen to validate the activity of Aβ aggregation regulators impedes the development of promising drug targets and diagnostic biomarkers for AD. Here, we conjugated amyloid β42 (Aβ42) peptide to gold nanoparticles (AuNPs) to visualize Aβ42 aggregation via Aβ42 aggregation-induced AuNP precipitation. AuNP–Aβ42 precipitate was quantified by optical density measurements of supernatants and thioflavin T binding assay. Transmission electron microscopy (TEM) analysis also showed reduced interparticle distance of AuNPs and confirmed the Aβ42 aggregation-induced AuNP precipitation. Transthyretin, a widely known Aβ aggregation inhibitor, limited AuNP–Aβ42 precipitation by preventing Aβ42 aggregation. Finally, according to TEM analysis, Aβ42-conjugated AuNPs treated with blood-driven serum revealed the differentiated aggregation patterns between normal and AD. These findings may open a scientific breakthrough in finding a possible diagnostic and prognostic tool for neurodegenerative diseases involving abnormal protein aggregation as their key pathogenesis processes.
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