Design and Synthesis of 3‐Aryl‐5‐Alicylic‐[1,2,4]‐oxadiazoles as Novel Platelet Aggregation Inhibitors

A series of 4‐[2‐(alicyclic‐[1,2,4]oxadiazol‐3‐yl)phenoxy]‐butyric acids were synthesized from N‐hydroxy‐2‐isopropoxy benzamidine in 4 steps with good yields. These [1,2,4]oxadiazoles are novel platelet aggregation inhibitors preventing human platelet aggregation induced by thromboxane derivative U44,619 and adenosine diphosphate. A structure‐activity‐relationship study revealed that the potency for these 5‐oxadiazoles increases with the increase in the ring size of the alicylic rings. Derivative 8f may be useful as a template for the design of more potent anti‐platelet agents.     

Synthesis of highly oriented TiNx coatings by free-electron laser processing of titanium in nitrogen gas

Titanium substrates were irradiated in pure nitrogen gas by means of a free-electron laser. The treatment resulted in the formation of δ-TiN_x coatings, with surface stoichiometry x≈1 and thickness of about 15 μm. Under specific experimental conditions the nitride phase had a remarkable crystallographic texture with the δ-TiN_x(200) planes parallel to the irradiated surface, and well aligned dendrites growing normal to the surface. The mechanism of the dendritic alignment and the origin of the texture correlate with the existence of a solidification front starting at the surface, which is very peculiar for laser surface treatments. This phenomenon is explained with the help of numerical simulations. PACS 61.80.Ba; 81.15.Fg; 81.65.Lp     

Synthesis and optical and electrochemical properties of copolymers consisting of 9,9‐dihexylfluorene and aromatic triazole chromophores

Aromatic triazole chromophores were incorporated into polyfluorene in an attempt to increase electron affinity, to promote emission efficiency, and to diminish excimer formation. Poly(9,9‐dihexylfluorene) ( P1 ) and new copolymers with aromatic triazoles ( P2 – P4 ) were prepared by Suzuki coupling polymerization. In P2 , the aromatic triazole (3.8 mol %) was attached exclusively as terminal groups, whereas P3 and P4 were main‐chain copolymers containing 3.9 and 10.3 mol % aromatic triazole chromophores, respectively. The copolymers were soluble in common organic solvents and showed high decomposition temperatures (437–458 °C). The twisted structure between the triazole and fluorene increased the emission efficiency and effectively prevented excimer formation in P2 – P4 . After the introduction of the triazole units, the absorption spectra showed a blueshift (from 388 to 381 nm in chloroform) due to confined conjugation, but the photoluminescence spectra remained almost the same (417–418 nm); this was attributed to oligofluorene segments. No emission of triazole fluorophores was observed because of efficient energy transfer from the triazole to oligofluorene segments. However, incomplete energy transfer was observed in CH₃COOH. The optical stability upon thermal annealing was also improved by the incorporation of aromatic triazole segments. From cyclic voltammetry results, P2 – P4 , containing triazole groups, showed greater electron affinity (lowest unoccupied molecular orbital level = ?2.67 to ?2.71 eV) than P1 (?2.52 eV). Electroluminescence devices of P1 – P4 all exhibited excimer emissions (483–521 nm), which could also be diminished by the introduction of aromatic triazole chromophores. © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 136–146, 2007     

Optical and electrochemical properties of copoly(aryl ether)s consisting of alternate 2,5‐distyrylbenzene and electron‐transporting oxadiazole or triazole derivatives

New copoly(aryl ether) P1 consisting of alternate electron‐transporting 2‐(3‐(trifluoromethyl)phenyl)‐5‐(4‐(5‐(3‐(trifluoromethyl)phenyl)‐1,3,4‐oxadiazol‐2‐yl)‐2,5‐bis(hexyloxy)phenyl)‐1,3,4‐oxadiazole and hole‐transporting 2,5‐distyrylbenzene (DSB) was synthesized via nucleophilic substitution polymerization. We investigated the optical and electrochemical properties of alternate copoly(aryl ether)s P1 – P6 , which contain the same hole‐transporting DSB segments, but with different electron transporting segments. The effect of trifluoromethyl groups in electron transporting segments is also discussed. Referencing to the spectra of their model compounds M1 – M4 , the emissions of P1 – P3 are dominated exclusively by the hole‐transporting fluorophores with longer emissive wavelength about 452–453 nm via efficient excitation energy transfer. Furthermore, P1 – P3 also exhibit unique variations in energy transfer in acidic media and solvatochromism in organic solvents. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of P1 – P4 , estimated from electrochemical data, are ?5.12, ?5.15, ?5.18, ?5.00 eV and ?2.93, ?3.39, ?3.49, ?2.76 eV, respectively. The electron and hole affinity of P1 – P6 can be enhanced simultaneously by introducing isolated hole‐ and electron‐transporting segments in backbone. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5083–5096, 2005     

Das Atomgewicht des Palladiums

Ohne Zusammenfassung     

Stimulated desorption from CO chemisorbed on Cr(110)

Electron stimulated desorption (ESD) experiments using a time-of-flight pulse counting method are reported for molecular CO chemisorbed on the Cr(110) surface at 90 K. Consistent with previous qualitative observations, negligible CO⁺ and O⁺ desorption signals were measured from the ₁CO overlayer which saturates at 1/4 monolayer. For θ_CO > 0.25, a terminally-bonded (₂CO) binding mode is populated in addition to the existing ∝₁CO binding mode and the ion yield increases sharply. For ₂CO, both O⁺ and CO⁺ ions are observed; the CO⁺ ions desorb with characteristically lower kinetic energies than O⁺ ions. Near saturation coverages of CO(ads), an observed decrease in the O⁺ yield is attributed to adsorbate-adsorbate interactions which reduce the ion desorption probability, as seen in ESD studies of terminally-bonded CO on other metals. These results are considered in the context of two possible models proposed for the ₁CO binding state and related ESD observations for CO chemisorbed on Fe(001) and potassium-promoted Ru(001).     

Nuclear energy conversion with stacks of graphene nanocapacitors

The efficiency of conventional techniques used to harvest energy in nuclear reactors lies around 35%. This limit exists, because the nuclear energy is converted to electrical energy via heat engines. We study an alternative approach where the kinetic energy of nuclear reaction products is directly converted into electric energy in a stack of charged capacitors with a gap size of 500 nm and graphene electrodes. Graphene is expected to be chemically and mechanically stable in high‐radiation environments, because its tensile strength of 130 GPa is very large, about 100 times larger than most metals. The dielectric strength of such nanocapacitors exceeds 1 GV/m, because avalanching is suppressed at small gap sizes. In a 1 GV/m electric field charged nuclear reaction products, such as 5.6 MeV alpha particles, come to rest in of a stack with 5000 nanocapacitors. We show that during the deceleration process more than 90% of kinetic energy of charged nuclear reaction products is converted to electric energy and stored as electric energy in the stack. Each stack is 2.5‐mm thick and produces a high‐voltage DC current. A device with a 1‐Ci²⁴¹Am source is expected to generate 22 mW of electric power.     

An analysis of energy deposition in a tissue equivalent proportional counter onboard the space shuttle.

An improved prediction for space radiations in the lower earth orbits measured by the shuttle TEPC is obtained when energy loss straggling and chord length distribution of the detector are considered. A generalized analytic model is used to describe the energy deposition of direct ion interaction events in a micron-size detector. The transport calculation accounting for the shuttle configuration is accomplished by using a new version of HZETRN that has been extensively verified with laboratory and flight data. The agreement of predicted and measured lineal energy spectra is within 70% for the region above 2 keV/micrometer but within a factor of 2.3 underpredicted for the region below this value. The inclusion of indirect delta ray events in the model is needed before possible causes for the underprediction below 2 keV/micrometer can be assessed.     

New experimental limit on photon hidden-sector paraphoton mixing

We report on the first results of a search for optical-wavelength photons mixing with hypothetical hidden-sector paraphotons in the mass range between 10⁻⁵ and 10⁻² electron volts for a mixing parameter greater than 10⁻⁷. This was a generation-regeneration experiment using the “light shining through a wall” technique in which regenerated photons are searched for downstream of an optical barrier that separates it from an upstream generation region. The new limits presented here are the most stringent limits to date on the mixing parameter. The present results indicate no evidence for photon-paraphoton mixing for the range of parameters investigated.