The mechanism of intramolecular energy transfer in terminally substituted polyene molecules

Absorption, fluorescence and excitation spectra of different terminally substituted polyenes have been recorded in the UV-Vis region. The observed intramolecular unidirectional energy transfer from a donor substituent to an acceptor at the other end of the chain is influenced but not inhibited by incorporation of a spacer into the polyene chain. In molecules without a spacer, internal conversion within the supermolecule can explain the observed transfer of energy. In molecules with a spacer interrupting the polyene chain the observed intramolecular energy transfer can be explained in terms of Förster transfer

Role of heat accumulation in the multi-shot damage of silicon irradiated with femtosecond XUV pulses at a 1 MHz repetition rate

The role played by heat accumulation in multi-shot damage of silicon was studied. Bulk silicon samples were exposed to intense XUV monochromatic radiation of a 13.5 nm wavelength in a series of 400 femtosecond pulses, repeated with a 1 MHz rate (pulse trains) at the FLASH facility in Hamburg. The observed surface morphological and structural modifications are formed as a result of sample surface melting. Modifications are threshold dependent on the mean fluence of the incident pulse train, with all threshold values in the range of approximately 36-40 mJ/cm². Experimental data is supported by a theoretical model described by the heat diffusion equation. The threshold for reaching the melting temperature (45 mJ/cm²) and liquid state (54 mJ/cm²), estimated from this model, is in accordance with experimental values within measurement error. The model indicates a significant role of heat accumulation in surface modification processes

Lowest excited singlet states of α-9-anthrylpolyenes

Properties of the electronically excited states of α-9-anthrylpolyenes are studied in n-hexane solutions by using optical absorption, emission and fluorescence excitation spectroscopy. The absorption spectra reveal a complex structure with contributions of both anthracene and polyene type bands but also of bands with mixed anthracence/polyene character. Small amounts of remaining impurities are chemically not separable but can be detected via fluorescence measurements. By computer-aided decomposition of spectra measured under variable selective excitation the actual, clearly chain-length dependent, fluorescences could be obtained

Release of nitric oxide from endothelial cells stimulated by YC-1, an activator of soluble guanylyl cyclase

1. In this study we examined the endothelium-dependent effect of YC-1–a benzyl indazole derivative which directly activates soluble guanylyl cyclase (sGC)–on vascular relaxation and nitric oxide (NO) and guanosine-3′,5′-cyclic monophosphate (cyclic GMP) in endothelial cells. 2. In preconstricted rat aortic rings with intact endothelium, YC-1 produced a concentration-dependent relaxation. However, the concentration response curve was shifted rightward to higher concentrations of YC-1, when (i) the aortas were pre-treated with L-N(G)-nitroarginine methylester (L-NAME) or (ii) the endothelium was removed. 3. Incubation of bovine aortic endothelial cells (BAEC) with YC-1 produced a concentration-dependent NO synthesis and release as assessed using a porphyrinic microsensor. Pre-incubating cells with L-NAME or with 8-bromo-cyclic GMP decreased this effect indicating that the YC-1 stimulation of NO synthesis is due to an activation of nitric oxide synthase, but not to an elevation of cyclic GMP. No direct effect of YC-1 on recombinant endothelial constitutive NO synthase activity was observed. 4. The YC-1 stimulated NO release was reduced by 90%, when extracellular free calcium was diminished. 5. In human umbilical vein endothelial cells (HUVEC), YC-1 stimulated intracellular cyclic GMP production in a concentration- and time-dependent manner. Stimulation of cyclic GMP was greater with a maximum concentration of YC-1 compared to calcium ionophore A23187. Similar effects were observed in BAEC and rat microvascular coronary endothelial cells (RMCEC). 6. When HUVEC and RMCEC were pre-treated with L-N(G)-nitroarginine (L-NOARG), the maximum YC-1 stimulated cyclic GMP increase was reduced by ⩾50%. 7. These results indicate, that beside being a direct activator of sGC, YC-1 stimulates a NO-synthesis and release in endothelial cells which is independent of elevation of cyclic GMP but strictly dependent on extracellular calcium. The underlying mechanism needs to be determined further