Aggregation and fibrillization of human islet amyloid polypeptide (hIAPP) plays an important role in the development of type 2 diabetes mellitus. Understanding the interaction of hIAPP with interfaces such as cell membranes at a molecular level therefore represents an important step toward new therapies. Here, we investigate the fibrillization of hIAPP at different self-assembled alkanethiol monolayers (SAMs) by quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM), and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). We find that hydrophobic interactions with the CH-terminated SAM tend to retard hIAPP fibrillization compared to the carboxylic acid-terminated SAM where attractive electrostatic interactions lead to the formation of a three-dimensional network of interwoven fibrils. At the hydroxyl- and amino-terminated SAMs, fibrillization appears to be governed by hydrogen bonding between the peptide and the terminating groups which may even overcome electrostatic repulsion. These results thus provide fundamental insights into the molecular mechanisms governing amyloid assembly at interfaces.

The assembly of peptides and proteins into nanoscale amyloid fibrils via formation of intermolecular β-sheets not only plays an important role in the development of degenerative diseases but also represents a promising approach for the synthesis of functional nanomaterials. In many biological and technological settings, peptide assembly occurs in the presence of organic and inorganic interfaces with different physicochemical properties. In an attempt to dissect the relative contributions of the different molecular interactions governing amyloid assembly at interfaces, we here present a systematic study of the effects of terminal modifications on the adsorption and assembly of the human islet amyloid polypeptide fragment hIAPP(20–29) at organic self-assembled monolayers (SAMs) presenting different functional groups (cationic, anionic, polar, or hydrophobic). Using a selection of complementary in situ and ex situ analytical techniques, we find that even this well-defined and comparatively simple model system is governed by a rather complex interplay of electrostatic interactions, hydrophobic interactions, and hydrogen bonding, resulting in a plethora of observations and dependencies, some of which are rather counterintuitive. In particular, our results demonstrate that terminal modifications can have tremendous effects on peptide adsorption and assembly dynamics, as well as aggregate morphology and molecular structure. The effects exerted by the terminal modifications can furthermore be modulated in nontrivial ways by the physicochemical properties of the SAM surface. Therefore, terminal modifications are an important factor to consider when conducting and comparing peptide adsorption and aggregation studies and may represent an additional parameter for guiding the assembly of peptide-based nanomaterials.

No abstract

The cold pressure welding of metals is a joining by forming technique capable of joining both similar and dissimilar metals in their solid state. In this article collective research on the cold pressure welding of metals with the aim of increasing both the overall weld strength and the weld-ability is presented. The application of innovative strategies based on electrochemical methods for an optimized conditioning of metal surfaces is investigated. The results account for a noticeable increase in the weld strength of steel-aluminum joints after a surface activation consisting of either an electrochemical roughening or electrodeposition of a bifunctional organosilane thin film. In addition to the surface activation process regimes for the preand post-welding heat treatment is investigated. Both weld strength and weld ability are improved due to heat treatments of steel sheets with various coatings and uncoated aluminium. The cold pressure welding is hereby done by incremental rolling, a new design process that allows for the manufacture of linear and curved joints between sheet metal blanks. Keywords: Electrochemical added joining of plates (ECUF) / incremental rolling / bonding agent / organosilane / heat treatment / intermetallic phases Das Kaltpressschweißen von Metallen ist ein Verfahren des Umformtechnischen Fügens mit besonders interessanten Möglichkeiten für Multi-Material-Verbindungen aus artfremden Metallen. Dieser Artikel beschreibt Untersuchungsergebnisse zum Kaltpressschweißen von artgleichen und artfremden Metallen mit dem Ziel die Verbindungsfestigkeit zu erhöhen und die erforderlichen Prozesskräfte zu reduzieren. Untersucht werden dazu Methoden der elektrochemischen Oberflächenaktivierung, der Wärmebehandlung der Fügepartner vor und nach dem Kaltpress-schweißen, sowie ein neuer Umformprozess zur flexibleren Herstellung der Fügeverbindungen, dem inkrementellen Walzen. Es wird gezeigt, dass die Verbindungsfestigkeit durch eine werkstoffspezifische Vorbehandlung mit elektrochemischen Methoden deutlich ansteigt. Darüber hinaus werden die Auswirkungen von Wärme-vor-und nachbehandlungen der Fügepartner untersucht und in den Untersuchungen an beschichteten Stählen und einer unbeschichtete Aluminiumlegierung gezeigt, dass eine gezielte Wärmebehandlung zu festeren Verbindungen führt oder diese erst ermöglicht. Mit dem inkrementellen Walzen wird dabei ein Umformprozess untersucht, der die Herstellung von linienförmigen Verbindungen zwischen artgleichen und artfremden Blechplatinen ermöglicht. Schlüsselwörter: Elektrochemisch unterstützes Fügen blechförmiger Werkstoffe (ECUF) / inkrementelles Walzen / Haftvermittler / Silane / Wärmebehandlung / intermetallische Phasen Joining of blanks by cold pressure welding Materialwiss. Werkstofftech.

No abstract