Syntheses and Biological Activity of the HDAC Class I Inhibitor Largazole

Histone deacetylase inhibitors are an emerging class of antiproliferative agents that have the potential to combat cancer on an epigenetic level. The recently reported marine natural product largazole has been recently isolated in trace amounts from cyanobacteria and displays a very potent and selective antiproliferative activity towards a number of cell lines. Several lines of evidence suggested it might act as a histone deacetylase inhibitor. These compelling properties have generated considerable interest in the synthetic community which resulted in several total syntheses of largazole. The present review offers a brief overview of the synthetic routes and some early structure–activity relationships

Der Mensch in der Logistik: Planer, Operateur und Problemlöser

Innerhalb des Sonderforschungsbereiches 559 analysiert das Teilprojekt M14 "Der Mensch in der Logistik", wie die Rolle des Menschen als Planer, Operateur und Problemlöser in großen Netzen der Logistik entwickelt werden kann. Das zentrale Ziel unseres Beitrags ist es, Anschlussmöglichkeiten der techniksoziologischen Analyse an das Kuhnsche Prozesskettenparadigma darzustellen. Dazu werden zunächst techniksoziologische Grundannahmen unter besonderer Berücksichtigung des soziotechnischen Systemansatz und Steuerungsmöglichkeiten komplexer Systeme resümiert (Kapitel 1) und sozialwissenschaftliche Befunde zur Rolle des Menschen in soziotechnischen System diskutiert (Kapitel 2). Fragen der Gestaltung logistischer Systeme stehen im Mittelpunkt von drei Fallstudien (Kapitel 4 bis 6), die logistische Prozesse der maritimen Containerlogistik, der Luftfracht und des Straßengüterverkehrs betreffen. Abschließend diskutieren wir, welche spezifischen Kompetenzen den Menschen befähigen, die logistischen Prozesse zu gestalten und unvorhersehbare Situationen zu bewältigen

Complex THz and DC inverse spin Hall effect in YIG/Cu1−x_{1-x}Irx_{x} bilayers across a wide concentration range

We measure the inverse spin Hall effect of Cu$_{1-x}$Ir$_{x}$ thin films on yttrium iron garnet over a wide range of Ir concentrations ($0.05 \leqslant x \leqslant 0.7$). Spin currents are triggered through the spin Seebeck effect, either by a DC temperature gradient or by ultrafast optical heating of the metal layer. The spin Hall current is detected by, respectively, electrical contacts or measurement of the emitted THz radiation. With both approaches, we reveal the same Ir concentration dependence that follows a novel complex, non-monotonous behavior as compared to previous studies. For small Ir concentrations a signal minimum is observed, while a pronounced maximum appears near the equiatomic composition. We identify this behavior as originating from the interplay of different spin Hall mechanisms as well as a concentration-dependent variation of the integrated spin current density in Cu$_{1-x}$Ir$_{x}$. The coinciding results obtained for DC and ultrafast stimuli show that the studied material allows for efficient spin-to-charge conversion even on ultrafast timescales, thus enabling a transfer of established spintronic measurement schemes into the terahertz regime.Comment: 12 pages, 4 figure

Charge Carrier Mobility in Organic Mixed Ionic–Electronic Conductors by the Electrolyte-Gated van der Pauw Method

Organic mixed ionic–electronic conductors (OMIECs) combine electronic semiconductor functionality with ionic conductivity, biocompatibility, and electrochemical stability in water and are currently investigated as the active material in devices for bioelectronics, neuromorphic computing, as well as energy conversion and storage. Operation speed of such devices depends on fast electronic transport in OMIECs. However, due to contact resistance problems, reliable measurements of electronic mobility are difficult to achieve in this class of materials. To address the problem, the electrolyte-gated van der Pauw (EgVDP) method is introduced for the simple and accurate determination of the electrical characteristics of OMIEC thin films, independent of contact effects. The technique is applied to the most widespread OMIEC blend, poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonic acid) (PEDOT:PSS). By comparing with organic electrochemical transistor (OECT) measurements, it is found that gate voltage dependent contact resistance effects lead to systematic errors in OECT based transport characterization. These observations confirm that a contact-independent technique is crucial for the proper characterization of OMIECs, and the EgVDP method reveals to be a simple, elegant, but effective technique for this scope

In Situ Force Microscopy to Investigate Fracture in Stretchable Electronics: Insights on Local Surface Mechanics and Conductivity

Stretchable conductors are of crucial relevance for emerging technologies such as wearable electronics, low-invasive bioelectronic implants, or soft actuators for robotics. A critical issue for their development regards the understanding of defect formation and fracture of conducting pathways during stress−strain cycles. Here we present a combination of atomic force microscopy (AFM) methods that provides multichannel images of surface morphology, conductivity, and elastic modulus during sample deformation. To develop the method, we investigate in detail the mechanical interactions between the AFM tip and a stretched, free-standing thin film sample. Our findings reveal the conditions to avoid artifacts related to sample bending modes or resonant excitations. As an example, we analyze strain effects in thin gold films deposited on a soft silicone substrate. Our technique allows one to observe the details of microcrack opening during tensile strain and their impact on local current transport and surface mechanics. We find that although the film fractures into separate fragments, at higher strain a current transport is sustained by a tunneling mechanism. The microscopic observation of local defect formation and their correlation to local conductivity will provide insight into the design of more robust and fatigue resistant stretchable conductors

Quantifying nanoscale charge density features of contact-charged surfaces with an FEM/KPFM-hybrid approach

Kelvin probe force microscopy (KPFM) is a powerful tool for studying contact electrification at the nanoscale, but converting KPFM voltage maps to charge density maps is non-trivial due to long-range forces and complex system geometry. Here we present a strategy using finite element method (FEM) simulations to determine the Green's function of the KPFM probe/insulator/ground system, which allows us to quantitatively extract surface charge. Testing our approach with synthetic data, we find that accounting for the AFM tip, cone and cantilever are necessary to recover a known input, and that commonly applied heuristics and approximations lead to gross miscalculation. Applying it to experimental data, we demonstrate its capacity to extract realistic surface charge densities and fine details from contact charged surfaces. Our method gives a straightforward recipe to convert qualitative KPFM voltage data into quantitative charge data over a range of experimental conditions, enabling quantitative contact electrification experiments at the nanoscale

AC amplification gain in organic electrochemical transistors for impedance-based single cell sensors

Research on electrolyte-gated and organic electrochemical transistor (OECT) architectures is motivated by the prospect of a highly biocompatible interface capable of amplifying bioelectronic signals at the site of detection. Despite many demonstrations in these directions, a quantitative model for OECTs as impedance biosensors is still lacking. We overcome this issue by introducing a model experiment where we simulate the detection of a single cell by the impedance sensing of a dielectric microparticle. The highly reproducible experiment allows us to study the impact of transistor geometry and operation conditions on device sensitivity. With the data we rationalize a mathematical model that provides clear guidelines for the optimization of OECTs as single cell sensors, and we verify the quantitative predictions in an in-vitro experiment. In the optimized geometry, the OECT-based impedance sensor allows to record single cell adhesion and detachment transients, showing a maximum gain of 20.2±0.9 dB with respect to a single electrode-based impedance sensor

Direct X-ray photoconversion in flexible organic thin film devices operated below 1 v

The application of organic electronic materials for the detection of ionizing radiations is very appealing thanks to their mechanical flexibility, low-cost and simple processing in comparison to their inorganic counterpart. In this work we investigate the direct X-ray photoconversion process in organic thin film photoconductors. The devices are realized by drop casting solution-processed bis-(triisopropylsilylethynyl)pentacene (TIPS-pentacene) onto flexible plastic substrates patterned with metal electrodes; they exhibit a strong sensitivity to X-rays despite the low X-ray photon absorption typical of low-Z organic materials. We propose a model, based on the accumulation of photogenerated charges and photoconductive gain, able to describe the magnitude as well as the dynamics of the X-ray-induced photocurrent. This finding allows us to fabricate and test a flexible 2 × 2 pixelated X-ray detector operating at 0.2 V, with gain and sensitivity up to 4.7 × 10^4 and 77,000 nC mGy ^(-1) cm^(-3), respectively

Accurate determination of band tail properties in amorphous semiconductor thin film with Kelvin Probe Force Microscopy

Amorphous oxide semiconductors are receiving significant attention due to their relevance for large area electronics. Their disordered microscopic structure causes the formation of band tails in the density of states (DOS) that strongly affect charge transport properties. Bandtail properties are crucial to understand for optimizing thin film device performance. Among the available techniques to measure the DOS, KPFM is exceptional as it enables precise local electronic investigations combined with microscopic imaging. However, a model to interpret KPFM spectroscopy data on amorphous semiconductors of finite thickness is lacking. To address this issue, we provide an analytical solution to the Poisson's equation for a metal-insulator-semiconductor (MIS) junction interacting with the AFM tip. The solution enables us to fit experimental data for semiconductors with finite thickness and obtain the DOS parameters, such as band tail width (E_t), doping density (N_D), and flat band potential. To demonstrate our method, we perform KPFM experiments on Indium-Gallium-Zinc Oxide (IGZO) thin film transistors (IGZO-TFTs). DOS parameters compare well to values obtained with photocurrent spectroscopy. We demonstrate the potentials of the developed method by investigating the impact of ionizing radiation on DOS parameters and TFT performance. Our results provide clear evidence that the observed shift in threshold voltage is caused by static charge in the gate dielectric leading to a shift in flat band potential. Band-tails and doping density are not affected by the radiation. The developed methodology can be easily translated to different semiconductor materials and paves the way towards quantitative microscopic mapping of local DOS parameters in thin film devices