Stop-and-go kinetics in amyloid fibrillation

Many human diseases are associated with protein aggregation and fibrillation. Using glucagon as a model system for protein fibrillation we show that fibrils grow in an intermittent fashion, with periods of growth followed by long pauses. Remarkably, even if the intrinsic transition rates vary considerably in each experiment, the probability of being in the growing (stopping) state is very close to 1/4 (3/4), suggesting the presence of 4 independent conformations of the fibril tip. We discuss this possibility in terms of existing structural knowledge

Density-functional theory applied to Rh(111) and CO/Rh(111) systems: Geometries, energies, and chemical shifts

We present extensive density-functional theory (DFT) based calculations of the clean Rh(111) surface and of CO/Rh(111) overlayer systems. We study both ground-state structural properties and core-level shifts from differences in total energies at different coverages and adsorption sites. Most results are obtained using using norm-conserving or ultrasoft pseudopotentials. The overall reliability of the pseudopotential method is analyzed theoretically, and computationally by way of all-electron calculations. In general, core corrections are required in order to correctly simulate all-electron total energies, although the corrections are rather small for the systems considered here. Overall there is a very good agreement both between the pseudopotential and all-electron results as well as with high-resolution experimental spectra. The obtained agreement between theoretical and experimental core-level energies, however, requires that the correct geometrical parameters are used. For instance, inclusion of bucklings of the first Rh layer in the (2x2)-1CO and (root3x3)R30degrees-1CO overlayers is essential. For the overlayers studied here, different competing adsorption sites give almost the same frozen-lattice adsorption energies. However, the C 1s binding energy shows large differences between CO adsorbed in different sites. Thus calculations of the C 1s shifts allow us to predict the adsorption sites despite the small differences in ground-state energies. We also analyze sources of the shifts in terms of differences in Hartree potential and relaxation at different sites. As the DFT core eigenvalue lies above rather than below the core excitation energy some care is required in order to properly identify a relaxation energy in a DFT framework. In order to clarify the question we relate the DFT approach for core energies to approaches based on self-energies or the Hartree-Fock approximation

Identification of Step Atoms by High Resolution Core Level Spectroscopy

Vicinal Rh(111) surfaces are studied with high resolution core level photoemission. We demonstrate the possibility to distinguish between the different kinds of surface atoms on these surfaces by virtue of their 3d core level binding energies. In particular, the low coordinated step atoms are found to exhibit a clear fingerprint in Rh 3d spectra. We demonstrate how this may be used to show that initial oxygen adsorption occurs on the steps and not on the terraces of the vicinal surfaces

Density of configurational states from first-principles calculations: The phase diagram of Al-Na surface alloys

The structural phases of AlxNa1-x surface alloys have been investigated theoretically and experimentally. We describe the system using a lattice gas Hamiltonian, determined from density functional theory together with Monte Carlo (MC) calculations. The obtained phase diagram reproduces the experiment on a quantitative level. From calculation of the (configurational) density of states by recently introduced Wang-Landau MC algorithm, we derive thermodynamic quantities such as free energy and entropy which are not directly accessible from conventional MC simulations. We accurately reproduce the stoichiometry, as well as the temperature at which an order-disorder phase transition occurs, and demonstrate the crucial role, and magnitude of the configurational entropy

The Rh(100)-(3 × 1)-2O structure.

The O adsorption on Rh(100) has been studied using high resolution core level spectroscopy, low energy electron diffraction and scanning tunnelling microscopy. In addition to the well known (2 × 2), (2 × 2)-pg and c(8 × 2) structures at coverages of 0.25, 0.5 and 1.75 ML respectively, an intermediate (3 × 1) structure with a coverage of 2/3 ML is identified

Interface composition of InAs nanowires with Al2O2 and HfO2 thin films

Abstract in Undetermined Vertical InAs nanowires (NWs) wrapped by a thin high-kappa dielectric layer may be a key to the next generation of high-speed metal-oxide-semiconductor devices. Here, we have investigated the structure and chemical composition of the interface between InAs NWs and 2 nm thick Al(2)O(3) and HfO(2) films. The native oxide on the NWs is significantly reduced upon high-kappa deposition, although less effective than for corresponding planar samples, resulting in a 0.8 nm thick interface layer with an In-/As-oxide composition of about 0.7/0.3. The exact oxide reduction and composition including As-suboxides and the role of the NW geometry are discussed in detail

Structure and formation of the Al(100)-(root 5 x root 5) R27 degrees-Na phase: a LEED, DFT and HRCLS study

Adsorption of 0.2 ML Na on Al(1 0 0) at room temperature yields a disordered Al(1 0 0)-(1 x 1)-Na phase, which transforms reversibly to a well-ordered Al(1 0 0)-(root5 x root5)R27degrees-Na phase on cooling below 250 K. Based on low energy electron diffraction (LEED) and high resolution core-level spectroscopy (HRCLS) measurements, and on ab initio calculations, it is concluded that the structure of the Al(1 0 0)-(root5 x root5-)R27degrees-Na phase consists of Na atoms occupying substitutional sites. The structural parameters obtained from LEED and density functional theory analyses are in quantitative agreement. Adsorption of 0.2 ML Na at 100 K yields an Al(1 0 0)-c(2 x 2)-Na island structure, which transforms irreversibly into the (root5 x root5)R27degrees-Na structure by annealing above 190 K. The nature of the reversible and irreversible phase transformations to the (root5 x root5)R27degrees structure is investigated by HRCLS and LEED. (C) 2002 Elsevier Science B.V. All rights reserved