Polymerization-induced color changes of polydiacetylene-containing liposomes and peptide amphiphile fibers

Polydiacetylenes have received much attention due to their intrinsic optical properties. Their inclination to change color in response to environmental factors has been extensively exploited in the sensing of analytes. In this study we functionalized diacetylene-containing peptide amphiphiles and phospholipids with α-bromo esters so that they could be used as initiators in atom transfer radical polymerization (ATRP) reactions. Subsequently, the supramolecular assemblies formed by these molecules upon their addition to water, namely peptide amphiphile fibers and liposomes, were stabilized by polymerizing the diacetylene moieties present in the molecules. As a result, highly colored, disassembly resistant, macro initiators were created. To investigate whether steric crowding on the surface of these assemblies could influence the color of the polydiacetylenes, we utilized the initiator functionality that had been introduced prior to assembly in ATRP. We found that the chromatic properties of the polydiacetylenes were directly related to the formation of polymer on the surface of peptide amphiphile fibers as well as liposomes. Furthermore, we were able to demonstrate that the progress of this color change could be monitored with UV-visible spectroscopy.     

Make them Blink: Probes for Super‐Resolution Microscopy

In recent years, a number of approaches have emerged that enable far‐field fluorescence imaging beyond the diffraction limit of light, namely super‐resolution microscopy. These techniques are beginning to profoundly alter our abilities to look at biological structures and dynamics and are bound to spread into conventional biological laboratories. Nowadays these approaches can be divided into two categories, one based on targeted switching and readout, and the other based on stochastic switching and readout of the fluorescence information. The main prerequisite for a successful implementation of both categories is the ability to prepare the fluorescent emitters in two distinct states, a bright and a dark state. Herein, we provide an overview of recent developments in super‐resolution microscopy techniques and outline the special requirements for the fluorescent probes used. In combination with the advances in understanding the photophysics and photochemistry of single fluorophores, we demonstrate how essentially any single‐molecule compatible fluorophore can be used for super‐resolution microscopy. We present examples for super‐resolution microscopy with standard organic fluorophores, discuss factors that influence resolution and present approaches for calibration samples for super‐resolution microscopes including AFM‐based single‐molecule assembly and DNA origami.     

Topology optimization methods for guided flow – comparison of optimality criteria vs. phase-field method

Optimization of guided flow problems is an important task for industrial applications especially those with high Reynolds numbers. There exist several optimization methods to increase the energy efficiency of these problems. Different optimization methods are shown bei Klimetzek [1], Hinterberger [2] and Pingen [3]. In recent years the phase-field method has been shown to be an applicable method for different kinds of topology optimization [4, 5]. We present results of topology optimization methods with optimality criterion and by using a phase-field model in the area of guided fluid flow problems. The two methods aim on the same main target reducing the pressure drop between the inlet and outlet of the flow domain. The first method is based on local optimality criterion, preventing the backflow in the flow domain [1, 6, 7]. The second method is based on a phase field model, which describes a minimization problem and uses a specially constructed driving force to minimize the total energy of the system [4, 5]. We investigate the capabilities and limits of both methods and present examples of different resulting geometries. The initial configurations are prepared in a way that the same optimization problem is solved with both methods. We discuss these results regarding the shape of the improved flow geometry. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hardening of smooth pulsed laser deposited PMMA films by heating

Smooth poly(methyl methacrylate) (PMMA) films without any droplets were pulsed laser deposited at a wavelength of 248 nm and a laser fluence of 125 mJ/cm². After deposition at room temperature, the films possess low universal hardness of only 3 N/mm². Thermal treatments up to 200°C, either during deposition or afterwards, lead to film hardening up to values of 200 N/mm². Using a combination of complementary methods, two main mechanisms could be made responsible for this temperature induced hardening effect well above the glass transition temperature of 102°C. The first process is induced by the evaporation of chain fragments and low molecular mass material, which are present in the film due to the ablation process, leading to an increase of the average molecular mass and thus to hardening. The second mechanism can be seen in partial cross-linking of the polymer film as soon as chain scission occurs at higher temperatures and the mobility and reactivity of the polymer material is high enough.     

Differential activation of the lateral premotor cortex during action observation

Background  

Action observation leads to neural activation of the human premotor cortex. This study examined how the level of motor expertise (expert vs. novice) in ballroom dancing and the visual viewpoint (internal vs. external viewpoint) influence this activation within different parts of this area of the brain.