Field-Desorption Mass Spectra of Fern Phloroglucinols Containing Three to Six Ring Constituents

It has been previously shown that the structural analysis of the title compounds by electron-impact ionization (EI)mass spectrometry is complicated by extensive, if not complete, thermal rottlerone-type rearrangement and/or fragmentation reactions. The use of a ‘softer’ ionization technique such as field desorption (FD) is, therefore, required in order that these compounds may be characterized in terms of their molecular size and composition. In this report, the FD mass spectra of typical representatives of this class of compounds are described along with the attempted suppression of undesirable thermal reactions by the optimization of the emitter temperatures.     

Search for cold nuclear fusion in palladium-deuteride

We searched for protons generated in cold D fusion reactions in Pd cathodes doped electrolytically with D. The applied experimental technique allowed the detection of proton production rates exceeding 0.074 s^–1 per cm³ cathode material (or 3.1·10^–24 s^–1 per D pair). Our results do not confirm fusion rates such like those recently reported.     

A new rotating-disk sorptive extraction mode,with a copolymer of divinylbenzene and N-vinylpyrrolidone trapped in the cavity of the disk,used for determination of florfenicol residues in porcine plasma

A novel extraction approach was developed based on rotating-disk sorptive extraction (RDSE). In this approach the rotating-disk extraction device consists of a Teflon disk, with a cavity that is loaded with a commercial sorbent phase selected according to the polarity of the analyte. To avoid leakage of the sorbent, the cavity is covered with a fiberglass filter and sealed with a Teflon ring. The proposed novel analytical RDSE technique was used in this study to determine florfenicol levels in plasma as a model analyte, or sample system, to describe the pharmacokinetics of a veterinary formulation. The sorbent used for this application was the copolymer of divinylbenzene and N-vinylpyrrolidone (Oasis HLB), which was selected because the florfenicol molecule contains both hydrophilic and lipophilic moieties. After the extraction, final determination of the analyte was performed by HPLC–DAD. Calibration plots and other analytical features were obtained after 90 min of extraction. The calibration plot was linear over the interval 0.4–16 μg mL^?1 (n?=?6), with R ²?=?0.9999. Recovery and repeatability were determined using a blank plasma sample spiked with 4.8 μg mL^?1 florfenicol. A recovery of 91.5 %, with a relative standard deviation (RSD) of 8.8 %, was obtained when the extraction was evaluated using six different rotating-disk devices. Precision was also assessed, using the same disk (containing the same sorbent phase) for eight aliquots of the same sample. The RSD under these conditions was 10.2 %, clearly indicating that the sorptive phase could possibly be re-used. Accordingly, RDSE is a suitable sample preparation alternative to liquid–liquid extraction (LLE), solid-phase extraction (SPE), and stir-bar sorptive extraction (SBSE).     

An optimised small-molecule stabiliser of the 14-3-3-PMA2 protein-protein interaction

Modulation of protein-protein interactions (PPIs) is a highly demanding, but also a very promising approach in chemical biology and targeted drug discovery. In contrast to inhibiting PPIs with small, chemically tractable molecules, stabilisation of these interactions can only be achieved with complex natural products, like rapamycin, FK506, taxol, forskolin, brefeldin and fusicoccin. Fusicoccin stabilises the activatory complex of the plant H(+)-ATPase PMA2 and 14-3-3 proteins. Recently, we have shown that the stabilising effect of fusicoccin could be mimicked by a trisubstituted pyrrolinone (pyrrolidone1, 1). Here, we report the synthesis, functional activity and crystal structure of derivatives of 1 that stabilise the 14-3-3-PMA2 complex. With a limited compound collection three modifications that are important for activity enhancement could be determined: 1) conversion of the pyrrolinone scaffold into a pyrazole, 2) introduction of a tetrazole moiety to the phenyl ring that contacts PMA2, and 3) addition of a bromine to the phenyl ring that exclusively contacts the 14-3-3 protein. The crystal structure of a pyrazole derivative of 1 in complex with 14-3-3 and PMA2 revealed that the more rigid core of this molecule positions the stabiliser deeper into the rim of the interface, enlarging especially the contact surface to PMA2. Combination of the aforementioned features gave rise to a molecule (37) that displays a threefold increase in stabilising the 14-3-3-PMA2 complex over 1. Compound 37 and the other active derivatives show no effect on two other important 14-3-3 protein-protein interactions, that is, with CRaf and p53. This is the first study that describes the successful optimisation of a PPI stabiliser identified by screening.     

Hexagonal AlN films grown on nominal and off-axis Si(0 0 1) substrates

Nucleation and growth of wurtzite AlN layers on nominal and off-axis Si(0 0 1) substrates by plasma-assisted molecular beam epitaxy is reported. The nucleation and the growth dynamics have been studied in situ by reflection high-energy electron diffraction. For the films grown on the nominal Si(0 0 1) surface, cross-sectional transmission electron microscopy and X-ray diffraction investigations revealed a two-domain film structure (AlN¹ and AlN²) with an epitaxial orientation relationship of [0 0 0 1]_AlN || [0 0 1]_Si and AlN¹ || AlN² || [1 1 0]_Si. The epitaxial growth of single crystalline wurtzite AlN thin films has been achieved on off-axis Si(0 0 1) substrates with an epitaxial orientation relationship of [0 0 0 1]_AlN parallel to the surface normal and 0 1 1 0_AlN || [1 1 0]_Si.     

Zeta-potential measurements of OTS-covered silica samples

We have carried out zeta-potential measurements on two different OTS (octadecyl-trichlorosilane)-covered silicas (fused silica, quartz 0001) prepared under identical conditions. Streaming current measurements on the fused silica supported OTS sample indicate a well reproducible IEP of 3.5. The major part of the study focused on the quartz 0001 supported sample with an IEP lower than that of the fused silica support and in agreement with that found in a spectroscopic study. The IEP in water (on addition of HCl) was found at around pH 3, and appeared to shift to lower values in three subsequent measurements. A final measurement after a separate series in KCl media gave the same IEP as obtained in the very first measurement, suggesting that the experiments did not significantly change the interfacial properties despite a large number of experiments. In one series of measurements care was taken to exclude any cations other than protons from the measurements, such that protons are the only counter-ions to the negative net charge. While our IEPs with the quartz support agree well with recent estimates from sum frequency generation (SFG) investigations, none of the zeta-potential vs pH curves would mimic a pattern experimentally observed in the amplitude of the “ice-like” water band between pH 3.5 and 5 in that SFG study. Furthermore, our results do not indicate any significant chloride-ion adsorption in KCl systems, but instead the shift of the IEP with increasing KCl to higher pH values rather indicates specific effects of potassium ions. Under conditions more relevant to the spectroscopic study (i.e. in absence of potassium) no specific pattern reminiscent of the SFG results was found. When tested it was found that surface conductivity was negligible.     

Transport properties of a lateral semiconductor quantum dot defined by a single connected metallic front-gate

We present studies on the electric transport in a lateral GaAs/AlGaAs quantum dot defined by a patterned single connected metallic front-gate. This gate design allows to easily couple a large number of quantum dots and therefore holds high potential in the design of new materials with tailor-made band structures based on quantum dot superlattices of controlled shape. Clear Coulomb diamond structures and well pronounced tunneling peaks observed in experiment indicate that single-electron control has been achieved. However, the dependence on electron density in the heterostructure embedding the dot, which is controlled by an additional back-gate, reveals that transport characteristics are strongly influenced supposedly by potential fluctuations in the dot and lead regions.