A phase field model for martensitic transformations with a temperature-dependent separation potential

Metallic materials often exhibit a complex microstructure with varying material properties in the different phases. Of major importance in mechanical engineering is the evolution of the austenitic and martensitic phases in steel. The martensitic transformation can be induced by heat treatment or by plastic surface deformation at low temperatures. A two dimensional elastic phase field model for martensitic transformations considering several martensitic orientation variants to simulate the phase change at the surface is introduced in [1]. However here, only one martensitic orientation variant is considered for the sake of simplicity. The separation potential is temperature dependent. Therefore, the coefficients of the Landau polynomial are identified by results of molecular dynamics (MD) simulations for pure iron [1]. The resulting separation potential is applied to analyse the mean interface velocity with respect to temperature and load. The interface velocity is computed by use of the dissipative part to the configurational forces balance as suggested in [3]. The model is implemented in the finite element code FEAP using standard 4-node elements with bi-linear shape functions. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tip‐enhanced Raman spectroscopy – an interlaboratory reproducibility and comparison study

Since its first experimental realization, tip‐enhanced Raman spectroscopy (TERS) has emerged as a potentially powerful nanochemical analysis tool. However, questions about the comparability and reproducibility of TERS data have emerged. This interlaboratory comparison study addresses these issues by bringing together different TERS groups to perform TERS measurements on nominally identical samples. Based on the spectra obtained, the absolute and relative peak positions, number of bands, peak intensity ratios, and comparability to reference Raman and surface‐enhanced Raman spectroscopy (SERS) data are discussed. Our general findings are that all research groups obtained similar spectral patterns, irrespective of the setup or tip that was used. The TERS (and SERS) spectra consistently showed fewer bands than the conventional Raman spectrum. When comparing these three methods, the spectral pattern match and substance identification is readily possible. Absolute and relative peak positions of the three major signals of thiophenol scattered by 19 and 9 cm⁻¹, respectively, which can probably be attributed to different spectrometer calibrations. However, within the same group (but between different tips), the signals only scattered by 3 cm⁻¹ on average. This study demonstrated the suitability of TERS as an analytical tool and brings TERS a big step forward to becoming a routine technique. Copyright © 2014 John Wiley & Sons, Ltd.     

The Navier-Stokes equations with particle methods

We consider the initial boundary value problem for the nonstationary Navier-Stokes equations in a bounded three-dimensional domain Ω with a sufficiently smooth boundary ∂Ω. These equations describe the motion of a viscous incompressible fluid contained in Ω for 0 < t < T. They represent a system of nonlinear partial differential equations concerning four unknown functions, i.e. the velocity vector v = (v₁(t, x), v₂(t, x), v₃(t, x)) and the kinematic pressure function p = p(t, x) of the fluid at time t ∈ (0, T) in x ∈ Ω. The purpose of this paper is to construct a Leray-Hopf type weak solution to the nonstationary Navier-Stokes system, which exists globally in time. Our construction is based on a suitable approximation using particle methods for stationary fluid flow. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Semisynthetic Fusicoccane Stabilizes a Protein-Protein Interaction and Enhances the Expression of K+ Channels at the Cell Surface

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Advantages and limitations of a new cationic coating inducing a slow electroosmotic flow for CE-MS peptide analysis: a comparative study with commercial coatings

Capillary coatings are crucial for high-quality separation performance in capillary electrophoresis analysis of proteins or peptides as they prevent analyte adsorption at the capillary wall. These coating materials have to fulfill many requirements such as a good separation performance and ensuring a good repeatability. The number of commercially available coating materials is still limited, especially with regard to the charge density on the coating material and the induced electroosmotic flow (EOF) velocity. In this work, we compare the separation performance of the novel self-made cationic capillary coating OHNOON and two commercially available coating materials, the acrylamide based, neutral LN® and the cationic hexadimethrine bromide (Polybrene), using the same coating procedure for all three coating materials. The coatings are investigated regarding the separation efficiency, analyte resolution, coating stability, and migration time stability in tryptic peptide analysis. Good separation performance was confirmed for all three coating materials: all coatings provided high plate numbers of up to 400,000–500,000 and a repeatability of the EOF and the analyte migration times in the range of 1 % relative standard deviation or below. Our results reveal a moderate EOF velocity for the novel OHNOON coating in comparison to the Polybrene coating. We present a detailed discussion of the impact of this reduced EOF velocity and the separation performance. The results presented here will help to define the necessary properties of coating materials to achieve the best compromise between speed of analysis and resolution for the respective application. We show that our novel OHNOON coating is especially valuable for the analysis of low mobility analytes and for samples with a broad range of analyte mobilities.     

Trans‐Selective Radical Silylzincation of Ynamides

The silylzincation of terminal ynamides is achieved through a radical‐chain process involving (Me₃Si)₃SiH and R₂Zn. A potentially competing polar mechanism is excluded on the basis of diagnostic control experiments. The unique feature of this addition across the CC bond is its trans selectivity. One‐pot electrophilic substitution of the C Zn bond by Cu^I‐mediated C C bond formation and subsequent manipulation of the C Si bond provides a modular access to Z‐α,β‐disubstituted enamides.     

Laminate structures in plastic composite materials with rigid layers

A variational model for composite materials with rigid horizontal layers is introduced within the framework of geometrically nonlinear single-slip plasticity. Considering the orientation of the slip system, we discuss the effective material response in the case of vanishing layer thickness and give explicit examples of possible macroscopic deformations which are realized by simple laminate constructions. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of monodisperse silicon nanocrystals using density gradient ultracentrifugation

We report the preparation of monodisperse silicon nanocrystals (ncSi) by size-separation of polydisperse alkyl-capped ncSi using organic density gradient ultracentrifugation. The ncSi were synthesized by thermal processing of trichlorosilane-derived sol-gel glasses followed by HF etching and surface passivation with alkyl chains and were subsequently fractionated by size using a self-generating density gradient of 40 wt % 2,4,6-tribromotoluene in chlorobenzene. The isolated monodisperse fractions were characterized by photoluminescence spectroscopy and high-angle annular dark-field scanning transmission electron microscopy and determined to have polydispersity index values between 1.04 and 1.06. The ability to isolate monodisperse ncSi will allow for the quantification of the size-dependent structural, optical, electrical, and biological properties of silicon, which will undoubtedly prove useful for tailoring property-specific optoelectronic and biomedical devices.     

Semisynthesis of Biologically Active Glycoforms of the Human Cytokine Interleukin 6

Human interleukin 6 (IL‐6) is a potent cytokine with immunomodulatory properties. As the influence of N‐glycosylation on the in vivo activities of IL‐6 could not be elucidated so far, a semisynthesis of homogeneous glycoforms of IL‐6 was established by sequential native chemical ligation. The four cysteines of IL‐6 are convenient for ligations and require only the short synthetic glycopeptide 43–48. The Cys‐peptide 49–183 could be obtained recombinantly by cleavage of a SUMO tag. The fragment 1–42 was accessible by the simultaneous cleavage of two inteins, leading to the 1–42 thioester with the native N‐terminus. Ligation and refolding studies showed that the inherently labile Asp? Pro bond 139–140 was detrimental for the sequential C‐ to N‐terminal ligation. A reversed ligation sequence using glycopeptide hydrazides gave full‐length IL‐6 glycoproteins, which showed full bioactivity after efficient refolding and purification.     

Structure-Based Evolution of Subtype-Selective Neurotensin Receptor Ligands

Subtype-selective agonists of the neurotensin receptor NTS2 represent a promising option for the treatment of neuropathic pain, as NTS2 is involved in the mediation of μ-opioid-independent anti-nociceptive effects. Based on the crystal structure of the subtype NTS1 and previous structure–activity relationships (SARs) indicating a potential role for the sub-pocket around Tyr11 of NT(8–13) in subtype-specific ligand recognition, we have developed new NTS2-selective ligands. Starting from NT(8–13), we replaced the tyrosine unit by β²-amino acids (type 1), by heterocyclic tyrosine bioisosteres (type 2) and peptoid analogues (type 3). We were able to evolve an asymmetric synthesis of a 5-substituted azaindolylalanine and its application as a bioisostere of tyrosine capable of enhancing NTS2 selectivity. The S-configured test compound 2 a, [(S)-3-(pyrazolo[1,5-a]pyridine-5-yl)-propionyl¹¹]NT(8–13), exhibits substantial NTS2 affinity (4.8 nm) and has a nearly 30-fold NTS2 selectivity over NTS1. The (R)-epimer 2 b showed lower NTS2 affinity but more than 600-fold selectivity over NTS1.