Interrupted coarse-grained theory of quasi-conitinuum photoexcitation

We propose a theory of quasi-continuum phenomena in unimolecular photoreactions. The theory is simple enough not to require computer implementation but is able to reproduce analytically and semi-quantitatively the results of full computer simulations.     

Some analytical results forABC,ABCD, andXBCD coupled spin 1/2 systems. I

By choosing a suitable linear combination of the constants of the motion , it is shown that the calculation of the density matrix(t) can be simplified by subdividing the Hamiltonian into . In particular, this technique can be used to obtain closed form solutions for the eigenfunctions and eigenvalues of spin 1/2ABC andXBCD spin systems, evolving in the presence of Zeeman offsets, scalar coupling and dipolar interactions. In general, the eigenvalues and eigenvalues of are very transparent, while those of require more effort. Nevertheless, simplifications can be made. Firstly, the effective size of the Hamiltonian matrix which needs to be considered, is reduced fromN ×N to at least (N – 2) × (N – 2), while forXBC ... systems it is reduced to (N – 4) × (N – 4). Secondly, the highest rank and highest/lowest order tensor operators available to the spin ensemble are constants of the motion under . Finally, by exploiting the fact that is a good quantum number, it is possible to block-diagonalize the matrix into no more than 3 × 3 matrices.     

Thin-layer spectroelectrochemical kinetic study of viologen cation radicals reacting at hydrogen-evolving gold and nickel electrodes

The kinetics of viologen cation radicals reacting at hydrogen-evolving gold and nickel electrodes in pH 6–8 electrolytes have been investigated. Visible absorption spectroscopy was used to follow the course of the reaction in an optically transparent thin-layer electrochemical cell under quasi-steady-state conditions. The spectroelectrochemical data were analyzed using classical kinetics and yielded zero-order behavior with respect to the viologen cation radical. For methyl viologen cation radical at gold, a formal zero-order rate constant evaluated at zero hydrogen overpotential was found to be 1.0 × 10^?13 mol s^?1 cm^?2. At nickel the comparable rate constant was nearly two orders of magnitude larger than at gold. Increasing pH from 6 to 8 at gold electrodes shifted both the hydrogen evolution and the methyl viologen cation radical reaction 60–70 mV/pH unit in a negative direction. The diquat cation radical behaved in a similar manner. The proposed mechanism involves a fast, non-rate-limiting, chemical reaction between the viologen cation radical and adsorbed hydrogen atom(s). Results are interpreted in terms of previous proposed hydrogen evolution reaction mechanisms.     

A new rearranged dolabellane diterpene from the soft coral Clavularia inflata

A new dolabellane type diterpene 1 has been isolated through its acetate 1a. The structure of 1a was elucidated by extensive 1D and 2D NMR spectroscopy and confirmed by mass spectrometry. The structure of 1 was deduced by comparison of its NMR spectral data with those of 1a, while its relative stereochemistry was deduced by NOESY. The absolute stereochemistry of C-7 was determined by analyses of 1 separately esterified with R and S O-mandelic acids.     

A prototype industrial sensing system for phosphorus based on micro system technology

Progress in the development of a miniaturised microfluidic instrument for monitoring phosphorus in natural waters and wastewater is presented. The yellow colorimetric method for phosphate analysis has been transferred to a microfluidic chip configuration This simple method employs one reagent mixed in a 1:1 ratio with a sample to produce a yellow colour absorbing strongly below 400 nm. A stopped flow approach is used which, together with the very rapid kinetics and simple reagent stream, enables a very uncomplicated microfluidic manifold design to be adopted. The working wavelength is 380 nm to coincide with the peak output of a recently developed UV-LED narrow bandwidth light source. The limit of detection for the yellow method is 0.2 ppm with a dynamic linear range from 0-50 ppm possible. The reaction time at room temperature is less than 3 min, which means that up to 20 samples per hour can be analysed.     

Kohlenwasserstoffe

Ohne Zusammenfassung     

Towards autonomous environmental monitoring systems

The concept of micro total analysis systems (muTAS) or Lab-on-a-chip is based on the twin strategies of integration and miniaturisation that have been so successful in the electronics industry. This paper will look at the materials issues, particularly with respect to the new polymeric materials that are becoming available, and strategies for integrating optical (colorimetric) detection. The influence of breakthroughs in apparently unrelated areas on the range of chemistries that can be applied will be illustrated. For environmental monitoring, the further integration of wireless communications with micro-dimensioned analytical instruments and sensors will become the ultimate driving force. The emergence of these compact, self-sustaining, networked instruments will have enormous impact on all field-based environmental measurements.     

Inhibition of UVA-induced c-Jun N-terminal kinase activity results in caspase-dependent apoptosis in human keratinocytes

Inhibition of c-Jun N-terminal kinase (JNK) with the pharmacologic inhibitor SP600125 in UVA-irradiated HaCaT cells and human primary keratinocytes resulted in dramatic phenotypic changes indicative of cell death. These phenotypic changes correlated with caspase 8, 9 and 3 activations as well as cleavage of the caspase substrate polyADP-ribose polymerase (PARP). Morphologic analysis and analysis of sub-G0 DNA content confirmed apoptotic cell death in these keratinocytes after combination treatment. Addition of the general caspase inhibitor zVAD-fmk to combination-treated HaCaT cells was able to completely block caspase activation, PARP cleavage, the increase in sub-G0 DNA content and the classic morphologic features of apoptosis, indicating that this combination treatment resulted in caspase-dependent apoptotic cell death. zVAD-fmk treatment of primary keratinocytes was able to completely inhibit caspase activation and PARP cleavage, reduce morphologic apoptosis at lower concentrations of SP600125 and decrease the sub-G(0) DNA content detected after UVA + SP600125 treatment. However, cell death and a significant amount of debris was still detected after caspase inhibitor treatment, particularly with 125 nM SP600125. At subconfluent conditions and low passage, primary keratinocytes were more sensitive to UVA irradiation alone than HaCaT cells. In conclusion, we have observed that inhibition of UVA-induced JNK activity with the pharmacologic inhibitor SP600125 resulted in caspase-dependent apoptotic cell death in both the immortalized keratinocyte cell line HaCaT and primary keratinocytes. However, the increased sensitivity of primary keratinocytes to experimental stress may have also resulted in direct cellular injury and caspase-independent cell death.