Dioxygen-promoted regioselective oxidative heck arylations of electron-rich olefins with arylboronic acids

Arylations of electron-rich heteroatom-substituted olefins were performed with arylboronic acids. This appears to constitute the first example of palladium(II)-catalyzed internal Heck arylations. The novel protocol exploits oxygen gas for environmentally benign reoxidation and a stable 1,10-phenanthroline bidentate ligand to promote the palladium(II) regeneration and to control the regioselectivity. Internal arylation is strongly favored with electron-rich arylboronic acids. DFT calculations support a charge-driven selectivity rationale, where phenyls substituted with electron-donating groups prefer the electron-poor alpha-carbon of the olefin. Experiments, verified by calculations, confirm the cationic nature of the catalytic route. This Heck methodology provides a facile and mild access to functionalized enamides. Controlled microwave heating and increased oxygen pressure were used to further reduce the reaction time to 1 h.     

Microwave-promoted and chelation-controlled double arylations of terminal olefinic carbon of vinyl ethers

Herein we report a rapid, palladium-catalyzed terminal diarylation of the chelating olefin N,N-dimethyl(2-ethenyloxy)ethanamine under noninert conditions utilizing controlled microwave heating as a convenient energy source. Among the aryl bromides examined, both electron-rich and electron-poor substrates were demonstrated to furnish useful yields after only 10-120 min of directed microwave heating at 160-200 degrees C. The good terminal regioselectivity suggests that the precatalyst (Herrmann's palladacycle) serves as a source of weakly coordinated palladium(0) in the investigated high-temperature Heck process.     

An efficient method to perform milliliter-scale PCR utilizing highly controlled microwave thermocycling

This communication describes the development of a controlled microwave methodology for rapid milliliter-scale PCR.     

Ultrafast molecular dissociation of water in ice

Using x-ray emission and photoemission spectroscopies to measure the occupied valence levels in a thin crystalline ice film, we resolve the ionization-induced dissociation of water in ice on a femtosecond time scale. Isotope substitution confirms proton transfer during the core-hole lifetime in spite of the nonresonant excitation. Through ab initio molecular dynamics on the core-ionized state, the dissociation and spectrum evolution are followed at femtosecond intervals. The theoretical simulations confirm the experimental analysis and allow for a detailed study of the dissociative reaction path.     

A chemometric study of active parameters and their interaction effects in a nebulized sheath-liquid electrospray interface for capillary electrophoresis-mass spectrometry

A chemometrics approach has been used for evaluating the effect of four experimental parameters when coupling capillary electrophoresis (CE) to electrospray ionization-mass spectrometry (ESI-MS). Electrospray voltage, sheath-liquid flow rate, nebulizing gas flow rate, and spray needle position in respect to the MS orifice were varied according to a full factorial design. In addition to main effects, two interaction effects could be identified as significant when measuring the peak intensity of the analytes, from a sample mixture containing peptides and pharmaceuticals. The first interaction effects, between the nebulizing gas flow rate and the sheath-liquid flow rate, and the second interaction effect, between the nebulizing gas flow rate and the spray position, could further explain the impact that these variables have on the spray performance. The number of theoretical plates and the baseline noise were also measured. The sheath-liquid flow was found to significantly affect the separation efficiency, while the noise level mainly was controlled by the nebulizing gas flow. The same factorial design was also used for a CE capillary with lower internal diameter (ID) and the effects of the same variables were compared on those capillaries using equal injection volume for both capillaries. Similar trends were obtained in both capillaries but capillary ID was shown to be a significant variable when evaluating both capillaries in a single model. It was found that a capillary with 25 microm ID provided improved CE-MS performance over than corresponding 50 microm ID capillary. Enhanced sensitivity was obtained using the narrow-bore capillary, and at lower sheath-liquid flow rate the 25 microm ID capillary also gave rise to more efficient peaks.     

Effect of hindered diffusion on the adsorption of proteins in agarose gel using a pore model

The hindered diffusion and binding of proteins of different sizes (lysozyme, BSA and IgG) in an agarose gel is described using adsorption kinetic and diffusional data together with an experimentally determined pore size distribution in the gel. The validity of the pore model, including variable diffusion coefficients and porosities is tested against experimental confocal microscopy data. No fitting parameters were used in the present model. The importance of knowing the gel structure is demonstrated especially for large proteins such as IgG. Experimental confocal microscopy data can be explained by the present model.     

Long-time-storage mechanism for Tm:YAG in a magnetic field

We obtained a long-time-storage mechanism for spectral features in thulium ions doped into YAG by applying a magnetic field that splits the electronic ground state. We show experimentally that the storage time can be more than 30 s, which is 3 orders of magnitude longer than that of the metastable state that normally is used for information storage in this material. Level splitting and storage lifetimes for various magnetic field strengths of as much as 5 T were investigated. This storage mechanism will be relevant in the many coherent transient-based signal-processing schemes in which Tm:YAG is being used, and we demonstrate long-time storage in a basic data storage application.     

The t+n+n system and 5H

The one-proton knockout channel from 6He (240 MeV/u) impinging on a carbon target has been investigated. The triton fragments originating from this channel were detected in coincidence with the two neutrons. A broad structure, peaked at 3 MeV above the t+2n threshold, is observed in the t+n+n-relative energy spectrum. It is shown that this structure is mainly due to a I(pi)=1/2(+) resonance as expected for the 5H ground state, and from the observed angular and energy correlations, being used for the first time in 5H studies, that the neutrons to a large extent occupy the p shell.     

Halo structure of (14)Be

The two-neutron halo nucleus (14)Be has been investigated in a kinematically complete measurement of the fragments ((12)Be and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross sections, neutron angular distributions, and invariant mass spectra were measured, and the contributions from electromagnetic dissociation (EMD) were deduced. Comparison with three-body model calculations suggests that the halo wave function contains a large nu(2s(1/2))(2) admixture. The EMD invariant mass spectrum exhibited enhanced strength near threshold consistent with a nonresonant soft-dipole excitation.     

High-energy, high-power ytterbium-doped Q-switched fiber laser

We report on a Q -switched, cladding-pumped, ytterbium-doped large-mode-area fiber laser operating at 1090 nm that is capable of generating 2.3 mJ of output pulse energy at a 500-Hz repetition rate and more than 5 W of average output power at higher repetition rates in a high-brightness beam (M(2) = 3) . Using a similar fiber with a smaller core, we generated >0.5-mJ pulses in a diffraction-limited beam. Our results represent a threefold increase in pulse energy over previously published values for Q-switched fiber lasers and firmly establish fiber lasers as compact, multiwatt, multimillijoule pulse sources with large scope for both industrial and scientific applications.