Ultraviolet radiation stimulates the release of arachidonic acid from mammalian cells in culture

Abstract— C3H 10T½ cells in culture were prelabelled with [³H]arachidonic acid and exposed to UVB radiation. Almost immediately after irradiation cells released labelled arachidonate metabolites into media in a dose dependent manner. This release was inhibited by removing calcium ions from the system and by the addition of dexamethasone and parabromophenacyl bromide to the system. This suggests that the UVB stimulated release of arachidonic acid from membrane phospholipids is, in part, mediated by a phospholipase A₂ enzyme system. Thin layer chromatographic examination of media extracts revealed a dose dependent UVB stimulation of prostaglandin production by cultured cells.     

Applications of 2,5-bis(trimethylstannyl)thiophene. Synthesis of 3-methoxy-17α,-(5-iodothien-2-yl)-estra-1,3,5(10)trien-17β-ol

Monotransmetallation of 2,5-bis(trimethylstannyl)thiophene followed by the addition of estrone 3-methyl ether and iodine yields 3-methoxy-17α,-(5-iodothien-2-yl)estra-1,3,5(10)trien-17β-ol.     

A ring-closing metathesis strategy to phosphonosugars

[reaction: see text]. Syntheses of cyclic phosphonate (phostone) analogues of carbohydrates containing a phosphorus atom at the anomeric position are described. The ring-closing metathesis reaction of mixed allylic phenyl esters of allylphosphonic acid 2 and 22 generates the six-membered allylic phosphonates 3 and 23 in excellent yields. Introduction of the polyhydroxy functionality in these cyclic phosphonates provides facile entry into an array of phostone sugar analogues.     

Reduction of CuO and Cu2O with H2: H embedding and kinetic effects in the formation of suboxides

Time-resolved X-ray diffraction, X-ray absorption fine structure, and first-principles density functional calculations were used to investigate the reaction of CuO and Cu(2)O with H(2) in detail. The mechanism for the reduction of CuO is complex, involving an induction period and the embedding of H into the bulk of the oxide. The in-situ experiments show that, under a normal supply of hydrogen, CuO reduces directly to metallic Cu without formation of an intermediate or suboxide (i.e., no Cu(4)O(3) or Cu(2)O). The reduction of CuO is easier than the reduction of Cu(2)O. The apparent activation energy for the reduction of CuO is about 14.5 kcal/mol, while the value is 27.4 kcal/mol for Cu(2)O. During the reduction of CuO, the system can reach metastable states (MS) and react with hydrogen instead of forming Cu(2)O. To see the formation of Cu(2)O, one has to limit the flow of hydrogen, slowing the rate of reduction to allow a MS --> Cu(2)O transformation. These results show the importance of kinetic effects for the formation of well-defined suboxides during a reduction process and the activation of oxide catalysts.     

The magnetic susceptibility of AgPd alloys with Mn and Fe impurities

Measurements of the magnetic susceptibility of AgPd alloys with Fe and Mn impurities have been performed at temperatures from 1.4 K to 300 K. Alloys with 5 and 10 at.% Pd, 2 and 6 at. ppm Fe and with Mn concentrations in the range 10 to 7,000 at. ppm were investigated. The temperature variation of the impurity susceptibility was analysed according to a Curie-Weiss law. The effective moment for Fe varies with the Pd concentration, which is interpreted as due to interactions between near neighbour Fe and Pd atoms. These interactions tend to lower the characteristic temperature of single Fe impurities and induce a spin on the Pd atom ferromagnetically coupled to the Fe spin. InAgPdMn one finds no such induced moment on the Pd atoms. The effective momentµ _eff =(5.36±0.10)µ _B per Mn atom and the Curie-Weiss temperature=(0.08±0.09) K are independent of Pd as well as Mn concentrations.µ _eff is slightly higher than for Mn in very diluteAgMn, which may be due to a different polarisation of the conduction electron gas around the impurities.     

ROMP-generated oligomeric sulfonyl chlorides as versatile soluble scavenging agents

[reaction: see text] A new method for homogeneous nucleophilic scavenging employing oligomeric sulfonyl chloride (OSC) reagents is described. The method utilizes OSC to rapidly scavenge a variety of amines that are present in excess. The OSC reagents are generated from ROM polymerization of 2-chlorosulfonyl-5-norbornene utilizing the second generation Grubbs catalyst to produce oligomers of varying size as stable, free-flowing powders. Following the scavenging event, these oligomers are precipitated with ethyl acetate leaving products in excellent yield and purity.     

Experimental and theoretical studies on the reaction of H(2) with NiO: role of O vacancies and mechanism for oxide reduction.

Reduction of an oxide in hydrogen is a method frequently employed in the preparation of active catalysts and electronic devices. Synchrotron-based time-resolved X-ray diffraction (XRD), X-ray absorption fine structure (NEXAFS/EXAFS), photoemission, and first-principles density-functional (DF) slab calculations were used to study the reaction of H(2) with nickel oxide. In experiments with a NiO(100) crystal and NiO powders, oxide reduction is observed at atmospheric pressures and elevated temperatures (250-350 degrees C), but only after an induction period. The results of in situ time-resolved XRD and NEXAFS/EXAFS show a direct NiO-->Ni transformation without accumulation of any intermediate phase. During the induction period, surface defect sites are created that provide a high efficiency for the dissociation of H(2). A perfect NiO(100) surface, the most common face of nickel oxide, exhibits a negligible reactivity toward H(2). The presence of O vacancies leads to an increase in the adsorption energy of H(2) and substantially lowers the energy barrier associated with the cleavage of the H-H bond. At the same time, adsorbed hydrogen can induce the migration of O vacancies from the bulk to the surface of the oxide. A correlation is observed between the concentration of vacancies in the NiO lattice and the rate of oxide reduction. These results illustrate the complex role played by O vacancies in the mechanism for reduction of an oxide. The kinetic models frequently used to explain the existence of an induction time during the reduction process can be important, but a more relevant aspect is the initial production of active sites for the rapid dissociation of H(2).     

Structure and reactivity of Ru nanoparticles supported on modified graphite surfaces: a study of the model catalysts for ammonia synthesis

Supported ruthenium metal catalysts have higher activity than traditional iron-based catalysts used industrially for ammonia synthesis. A study of a model Ru/C catalyst was carried out to advance the understanding of structure and reactivity correlations in this structure-sensitive reaction where dinitrogen dissociation is the rate-limiting step. Ru particles were grown by chemical vapor deposition (CVD) via a Ru(3)(CO)(12) precursor on a highly oriented pyrolytic graphite (HOPG) surface modified with one-atomic-layer-deep holes mimicking activated carbon support. Scanning tunneling microscopy (STM) has been used to investigate the growth, structure, and morphology of the Ru particles. Thermal desorption of dissociatively adsorbed nitrogen has been used to evaluate the reactivity of the Ru/HOPG model catalysts. Two different Ru particle structures with different reactivities to N(2) dissociation have been identified. The initial sticking coefficient for N(2) dissociative adsorption on the Ru/HOPG model catalysts is approximately 10(-6), 4 orders larger compared to that of Ru single-crystal surfaces.