The metallation of imino(triphenyl)phosphorane by ethylmagnesium chloride: The synthesis, isolation and X-ray structure of [Ph3P=NMgCl·O=P(NMe2)3]2

Imino(triphenyl)phosphorane, Ph₃P=NH 1a, is metallated by ethylmagnesium chloride to give the N-magnesioiminophosphorane complex [Ph₃P=NMgCl·O=P(NMe₂)₃]₂ 4, whose X-ray structure has been determined.     

Compensation for source nonstationarity in multireference,scan-based near-field acoustical holography

Multireference, scan-based near-field acoustical holography is a useful measurement tool that can be applied when an insufficient number of microphones is available to make measurements on a complete hologram surface simultaneously. The scan-based procedure can be used to construct a complete hologram by joining together subholograms captured using a relatively small, roving scan array and a fixed reference array. For the procedure to be successful, the source levels must remain stationary for the time taken to record the complete hologram; that is unlikely to be the case in practice, however. Usually, the reference signal levels measured during each scan differ from each other with the result that spatial noise is added to the hologram. A procedure to suppress the effects of source level, and hence reference level, variations is proposed here. The procedure is based on a formulation that explicitly features the acoustical transfer functions between the sources and both the reference and scanning, field microphones. When it is assumed that source level changes do not affect the sources' directivity, a nonstationarity compensation procedure can be derived that is based on measured transfer functions between the reference and field microphones. It has been verified both experimentally and in numerical simulations that the proposed procedure can help suppress spatially distributed noise caused by the type of source level nonstationarity that is characteristic of realistic sources.     

Thermal physics in carbon nanotube growth kinetics

The growth of single wall carbon nanotubes (SWNTs) mediated by metal nanoparticles is considered within (i) the surface diffusion growth kinetics model coupled with (ii) a thermal model taking into account heat release of carbon adsorption-desorption on nanotube surface and carbon incorporation into the nanotube wall and (iii) carbon nanotube-inert gas collisional heat exchange. Numerical simulations performed together with analytical estimates reveal various temperature regimes occurring during SWNT growth. During the initial stage, which is characterized by SWNT lengths that are shorter than the surface diffusion length of carbon atoms adsorbed on the SWNT wall, the SWNT temperature remains constant and is significantly higher than that of the ambient gas. After this stage the SWNT temperature decreases towards that of gas and becomes nonuniformly distributed over the length of the SWNT. The rate of SWNT cooling depends on the SWNT-gas collisional energy transfer that, from molecular dynamics simulations, is seen to be efficient only in the SWNT radial direction. The decreasing SWNT temperature may lead to solidification of the catalytic metal nanoparticle terminating SWNT growth or triggering nucleation of a new carbon layer and growth of multiwall carbon nanotubes.     

THE ASSOCIATION OF THE 5-METHYLPHENAZINIUM CATION AND THE 5-METHYL-10-HYDRO-PHENAZINIUM RADICAL CATION WITH MICELLES*

Abstract— 5-Methylphenazinium (MP⁺) cation salts are known to stimulate photophosphorylation in photosynthetic systems. The mechanism is thought to involve the translocation of protons across the thylakoid membrane although few details are known concerning the mechanism and the identity of the proton carrier. As there is some indication that the semireduced species, the 5-methyl-10-hydro-phenazinium (MPH⁺) cation radical, may be the proton carrier, we have studied the interaction of MPH⁺ with micelles as a model system for aqueouslipid interactions in a membrane. In this study we have used the techniques of NMR and EPR. In the presence of sodium dodecyl sulfate (NaLS) micelles the EPR spectrum of MPH ⁺ is broadened indicating specific binding of MPH⁺ to the micelle. A binding constant of -10⁵M^-1 was obtained. The 220 MHz NMR spectrum of a micellar solution with added MPH! shows specific broadening of the alkyl protons. The use of model paramagnetic adducts has allowed us to infer from the NMR results that the MPH⁺ ion penetrates the hydrocarbon part of the micelle to a considerable extent. This would indicate to us that MPH⁺ can indeed function as a proton carrier as it should be able to penetrate deeply into the lipid layer of the membrane. From these results, we conclude that:

• 1 Both MP⁺ and MPH⁺ interact strongly with NaLS micelles. MPH⁺ interacts more weakly with neutral Triton X-100 micelles while in this case, no evidence of interaction is seen for MP⁺. No binding of either MP⁺ or MPH⁺ is observed with cationic micelles from CTAB.
• 2 MP⁺ is adsorbed to NaLS micelles in a very hydrophilic region, probably In the Stern layer. MPH⁺, however, is much less hydrophilic than MP⁺ and appears to reside in the Palisade layer a few angstroms below the head groups.

On the basis of these results, we make the following proposals:

• 1 MPH⁺ is sufficiently hydrophobic to be a candidate for the reduced MP⁺ species which actually carries the proton across the thylakoid membrane.
• 2 The site at which MP⁺ is reduced by X must be anionic in nature in order for MP⁺ to be bound strongly.

     

Search for the standard model Higgs boson in the H→WW→lνq'q decay channel

We present a search for the standard model Higgs boson (H) in pp collisions at sqrt(s)=1.96 TeV in events containing a charged lepton (?), missing transverse energy, and at least two jets, using 5.4 fb(-1) of integrated luminosity recorded with the D0 detector at the Fermilab Tevatron Collider. This analysis is sensitive primarily to Higgs bosons produced through the fusion of two gluons or two electroweak bosons, with subsequent decay H→WW→?νq'q, where ? is an electron or muon. The search is also sensitive to contributions from other production channels, such as WH→?νbb. In the absence of a signal, we set limits at the 95% C.L. on the cross section for H production σ(pp→H+X) in these final states. For a mass of M(H)=160 GeV, the limit is a factor of 3.9 larger than the cross section in the standard model and consistent with an a priori expected sensitivity of 5.0.     

The Synthesis of 4-Amino-2-methyl-3-(1-oxo) Pent-4-ynyl-5,6,7,8-tetrahydrobenzo[b]thieno[2,3-b]pyridine

The synthesis of ketone 1 from the ethyl ester of 4-amino-2-methyl-5,6,7,8-tetrahydrobenzo[b]thieno[2,3-b]pyridine-3-carboxylic acid using β-ketosulfone methodology is described.     

Zum Filtriren bei h?heren Temperaturen

Ohne Zusammenfassung     

Untersuchunz von Fetten

Ohne Zusammenfassung     

Charge stripping reactions of ions formed from methane,ammonia, water and hydrogen sulphide by protonation and by electron impact

The minimum energy, Q_min, necessary to convert an ion m₁⁺ to a doubly charged ion m₁²⁺ is obtained for 19 different ions from methane, ammonia, water and hydrogen sulphide by charge stripping using nitrogen collision gas. The ions studied include the [MH]⁺ ions formed by chemical ionization in a high pressure source. Stable m₁²⁺ ions could not be formed in the case of [NH₄]⁺, [NH]^+˙, [H₂O]^+˙ and [OH]⁺. Even in these cases the value of Q_min could be estimated by studying the fragments formed from the unstable m₂₊ ions. In several cases, the energy required to form m₁²⁺ ions is less than the literature value for the ionization energy of m₁⁺. This is discussed in terms of the possibility of the presence of excited states of m₁⁺ in the present experiments.