On/off photoswitching of the electropolymerizability of terthiophenes

In this contribution the polymerization of terthiophene, to form an alkene bridged alpha,alpha-coupled sexithiophene polymer, is controlled by light; i.e. the electropolymerizability of the monomer 1F is switched off and on with UV and visible light, respectively. The system comprises of both bis-terthiophene and photochromic dithienylethene units. The presence of a light-switchable unit allows on-off switching of the electropolymerization of the monomer with light. Furthermore the incorporation of the dithienylethene in the polymer backbone increases dramatically the homogenity of the polymer formed (i.e., only sexithiophene units are formed). The derived films are robust and fully retain electrochromic behavior as has been demonstrated through cyclic voltammetry while spatial control (patterning) is readily achieved by applying simple optical masking techniques.     

Artificial cilia for active micro-fluidic mixing

In lab-on-chip devices, on which complete (bio-)chemical analysis laboratories are miniaturized and integrated, it is essential to manipulate fluids in sub-millimetre channels and sub-microlitre chambers. A special challenge in these small micro-fluidic systems is to create good mixing flows, since it is almost impossible to generate turbulence. We propose an active micro-fluidic mixing concept inspired by nature, namely by micro-organisms that swim through a liquid by oscillating microscopic hairs, cilia, that cover their surface. We have fabricated artificial cilia consisting of electro-statically actuated polymer structures, and have integrated these in a micro-fluidic channel. Flow visualization experiments show that the cilia can generate substantial fluid velocities, up to 0.6 mm s(-1). In addition, very efficient mixing is obtained using specially designed geometrical cilia configurations in a micro-channel. Since the artificial cilia can be actively controlled using electrical signals, they have exciting applications in micro-fluidic devices.     

Photoresponsive dithienylethene-urea-based organogels with "reversed" behavior

Dithienylperhydrocyclopentene-bisurea-based low molecular weight gelators are described that function as photoresponsive organogels that show a remarkable gel-to-liquid transition upon irradiation. The two series of derivatives, with and without alkyl spacers between the urea hydrogen bonding groups and the photochromic unit, show different gelation behavior. Upon UV irradiation of the gels, a gel liquified at only 1.4% conversion of the photochromic unit. Transmission electron microscopy (TEM) shows that the gel fibres consist of thin ribbons. Semi-empirical (PM3) calculations indicate that the hydrogen bonding between the open-ring isomer (o) molecules is weak, and that formation of the closed-ring isomer (c) destabilises the hydrogen bonding further. The results indicate that a small amount of the closed-ring isomer will disrupt the intermolecular hydrogen-bonding, leading to disintegration of the gel fibre ribbons and hence reversible liquification.     

Rapid free energy calculation of peptide self-assembly by REMD umbrella sampling

We extend umbrella sampling with replica exchange steps to calculate free energies that are important in the self-assembly of peptides. This leads to a more than 10-fold speed up over conventional umbrella sampling, thereby providing a practical method to calculate these free-energy differences. This approach can also observe first-order phase transitions and pinpoint the location of the concomitant boundary. When conformational changes are involved, this method can handle peptides up to approximately 7 residues, providing a rapid and accurate assessment of the thermodynamic properties of model systems, and can thus be used to answer fundamental questions about peptide self-assembly. When no major conformational changes are involved, we expect the size limit to be equal to that of standard molecular dynamics.     

Comparative performance evaluation under uncertainty

In this article CCPR, a multidimensional framework for comparative performance evaluation is proposed, which is elaborated and illustrated through a real-life case. A particular feature of the approach is that it takes account of and corrects for the influence of risks, which are beyond the control of the decision maker. Here risk is seen as a multidimensional measure; it is expressed by means of sensitivities to unexpected changes of a multitude of risk factors. Furthermore, the approach corrects for differences in characteristics between the firms that are being compared. Some characteristics are fixed and thus uncontrollable for the decision maker, whereas others may be changed and controlled by the decision maker. The approach also answers whether the changes in firm characteristics made by management have been appropriate or not.     

Development and validation of automated SPE-HPLC-MS/MS methods for the quantification of asenapine, a new antipsychotic agent, and its two major metabolites in human urine

To support the evaluation of the pharmacokinetic parameters of asenapine (ASE) in urine, we developed and validated online solid‐phase extraction high‐performance liquid chromatography methods with tandem mass spectrometry detection (SPE‐LC‐MS/MS) for the quantification of ASE and two of its major metabolites, N‐desmethylasenapine (DMA) and asenapine‐N⁺‐glucuronide (ASG). The linearity in human urine was found acceptable for quantification in a concentration range of 0.500–100 ng/mL for ASE and DMA and 10.0–3000 ng/mL for ASG, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Hydroxide-ion binding to nonionic interfaces in aqueous solution

The mechanism of hydroxide ion binding to nonionic surfaces is explored by variation of the properties of the water-aggregate interface and by variation of the type of the aggregate.     

Diastereoselective cyclization of a dithienylethene switch through single crystal confinement

Upon UV irradiation of the hydrogen-bond confined crystal state of a dithienylhexafluorocyclopentene with (R)-N-phenylethylamide substituents, the photochemical cyclization reaction proceeds diastereoselectively to form the coloured, closed-ring isomer with 97% de.     

Simplifying the setup for vacuum‐outlet GC: Using a restriction inside the injection port

The application of vacuum GC has several advantages over pressurized GC. One of the key characteristics is that the optimal gas velocity is very high. Combined with short capillary columns of wide internal diameter, this results in short analysis times using standard GC‐MS equipment. To make vacuum GC possible using a GC‐MS system, a restriction must be positioned at the injection side of the column. This restriction is usually made of deactivated 0.1 mm i.d. fused‐silica tubing which is coupled to the analytical column. Such restrictions will work, but practical challenges are found in coupling, reducing dead volume and robustness. A new way of making restrictions is by incorporating the restriction into the injection port. Using well‐defined short pieces of fused silica with internal diameter of 0.025 mm, one can make a restriction using a Press‐Tight® type connector, and position this inside the injection port. By doing this, the restriction is very short and at high temperature all the time. Activity plays a minimal role, and also leaks will not be an issue as the coupling is in 100% inert gas. Data obtained using this concept is promising as vacuum GC becomes easier and more robust.     

Room-temperature laser emission of ZnO nanowires explained by many-body theory

Are excitons involved in lasing in ZnO nanowires or not? Our recently developed and experimentally tested quantum many-body theory sheds new light on this question. We measured the laser thresholds and Fabry-Pérot laser modes for three radically different excitation schemes. The thresholds, photon energies, and mode spacings can all be explained by our theory, without invoking enhanced light-matter interaction, as is needed in an earlier excitonic model. Our conclusion is that lasing in ZnO nanowires at room temperature is not of excitonic nature, as is often thought, but instead is electron-hole plasma lasing.