Poly-Sarcosine and Poly(ethylene-glycol) interactions with proteins investigated using molecular dynamics simulations

Nanoparticles coated with hydrophilic polymers often show a reduction in unspecific interactions with the biological environment, which improves their biocompatibility. The molecular determinants of this reduction are not very well understood yet, and their knowledge may help improving nanoparticle design. Here we address, using molecular dynamics simulations, the interactions of human serum albumin, the most abundant serum protein, with two promising hydrophilic polymers used for the coating of therapeutic nanoparticles, poly(ethylene-glycol) and poly-sarcosine. By simulating the protein immersed in a polymer-water mixture, we show that the two polymers have a very similar affinity for the protein surface, both in terms of the amount of polymer adsorbed and also in terms of the type of amino acids mainly involved in the interactions. We further analyze the kinetics of adsorption and how it affects the polymer conformations. Minor differences between the polymers are observed in the thickness of the adsorption layer, that are related to the different degree of flexibility of the two molecules. In comparison poly-alanine, an isomer of poly-sarcosine known to self-aggregate and induce protein aggregation, shows a significantly larger affinity for the protein surface than PEG and PSar, which we show to be related not to a different patterns of interactions with the protein surface, but to the different way the polymer interacts with water

Disorder control in crystalline GeSb2Te4 and its impact on characteristic length scales

Crystalline GeSb2Te4 (GST) is remarkable material, as it allows to continuously tune the electrical resistance by orders of magnitude without involving a phase transition or stoichiometric changes, just by altering the short-range order. While well-ordered specimen are metallic, increasing amounts of disorder can eventually lead to an insulating state with vanishing conductivity in the 0K limit, but a similar number of charge carriers. These observations make disordered GST one of the most promising candidates for the realization of a true Anderson insulator. While so far the low-temperature properties have mostly been studied in films of small grain size, here a sputter-deposition process is employed that enables preparation of a large variety of these GST states including metallic and truly insulating ones. By growing films of GST on mica substrates, biaxially textured samples with huge grain sizes are obtained. A series of these samples is employed for transport measurements, as their electron mean free path can be altered by a factor of 20. Yet, the mean free path always remains more than an order of magnitude smaller than the lateral grain size. This proves unequivocally that grain boundaries play a negligible role for electron scattering, while intragrain scattering, presumably by disordered vacancies, dominates. Most importantly, these findings underline that the Anderson insulating state as well as the system's evolution towards metallic conductivity are indeed intrinsic properties of the material

Erfolgsfaktoren des Softwarepricing - eine Benchmarkingstudie unter deutschen Softwareherstellern

Vor einigen Monaten wurde der deutsche So ftwarehersteller SAP mit einer unangenehmen Nachricht konfrontiert. Die Deutschsprachige SAP-Anwendergruppe (DSAG) trat an die Konzernleitung heran und bemängelte das aktuelle Preissystem für SAP BusinessObjects-Produkte (BO). Die Anschaffung der Software sei wegen hoher Anfangsinvestitionen und mangelnder Kostentransparenz für viele – vor allem mittelständische – Unternehmen weniger interessant. Die tatsächlichen Preise für einzelne Unternehmen sind aufgrund komplexer Preismodelle und verschiedener Rabatte, welche zudem kombiniert werden können, nur mit viel Aufwand zu errechnen. SAP nahm diese Kritik auf und hat beim Preismodell nachgebessert. Das Preismodell wurde durch die Einführung eines BO-Sta rterpakets zu einem Festpreis deutlich übersichtlicher. Aufwendige Rechnungen entfallen somit vollständig. Für Kunden, denen das Paket nicht ausreicht, wird optional ein Upgrade auf ein umfangreiches Business-Intelligence-Paket angeboten (vgl. Schulze 2009). Das Beispiel zeigt, wie wichtig und vor allem topaktuell das Thema Preismanagement in der Softwarebranche ist. Daher haben wir uns im Rahmen einer empirischen Studie intensiv mit dem Thema Softwarepricing beschäftigt. Ziel der Studie war es, durch ein Benchmarking unter deutschen Softwareherstellern Erfolgsfaktoren für Preismanagement in der Softwarebranche zu identifizieren