Correlation of spectroscopically determined ligand donor strength and nucleophilicity of substituted pyrazoles

The relative ligand donor strengths of 10 pyrazole-derived ligands has been determined with great accuracy, making use of the interdependence between the donor strength of the co-ligand and the (13)C NMR chemical shift of the (i)Pr(2)-bimy carbene signal in trans-[PdBr(2)((i)Pr(2)-bimy)L] complexes ((i)Pr(2)-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene; L = pyrazole-derived ligand). Even subtle variations in the substitution pattern of the pyrazole backbone up to three bonds away from the coordinating nitrogen could be detected reliably using this methodology. Alkylation experiments conducted on the pyrazoles using electrophiles of varied reactivity (ethyl bromide, ethyl iodide, and trimethyloxonium tetrafluoroborate) served as a benchmark to rank the pyrazoles in three groups of gradually increasing nucleophilicity, which correlated well with their determined donor strength.     

Determination of the total bremsstrahlung photon flux from electron accelerators by simultaneous activation of two monitors

We have determined the total bremsstrahlung photon fluxes with end-point energies in the giant dipole resonance (GDR) region produced by electron accelerator Microtron MT??25 (the Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, Dubna, Russia) and that of 65 MeV bremsstrahlung produced by the linear electron accelerator (the Pohang Neutron Facility, Pohang, South Korea). The method that we used was the photon activation technique. To ensure the accuracy of the results, we carried out simultaneous photon activation of two monitors made of Cu and Au foils in the same irradiation conditions. The results are discussed in the paper.     

Hemilabile behavior of a thioether-functionalized N-heterocyclic carbene ligand

The truly hemilabile nature of a novel thioether-functionalized N-heterocyclic carbene ligand is demonstrated in a range of Pd(II) complexes.     

PDMS-based microfluidics for proteomic analysis

A microfluidic poly(dimethylsiloxane) (PDMS) microdevice was realized, combining on-line protein electrophoretic separation, selection, and digestion of a protein of interest for identification by mass spectrometry. The system includes eight integrated valves and one micropump dedicated to control the flow operations. Myoglobin was successfully isolated from bovine serum albumin (BSA), then selected using integrated valves and digested in a rotary micromixer. Proteolytic peptides were recovered from the micromixer for protein identification. Total analysis from sample injection to protein identification is performed under 30 minutes, with samples of tens of nanolitres. The paper shows that PDMS technology can be successfully used for integrating complex preparation protocols of proteic samples prior to MS analysis.     

Magneto-optical study of Er-related center in selectively doped Si:Er

Photoluminescence at λ=1.54 μm from an Er³⁺-related center dominant in a sublimation MBE-grown multi-layer Si/Si:Er structure is investigated in magnetic fields up to 6 T. The magnetic-field-induced splitting is observed for all the main lines of the Er-related photoluminescence spectrum. For the most intense emission line, angular dependence of the splitting is measured in the (011) crystallographic plane of the sample. The effective g-tensor, corresponding to the difference between individual g-tensors of the lowest multiplets of the ground and the first excited states, is experimentally determined. In this way the symmetry of the Er-related optically active center dominant in the structure is found to be orthorhombic I (C_2v). From temperature dependence of the intensity of the magnetic field split components, individual g-tensors of the ground and the excited states are separated. No influence of the growth direction on the symmetry of Er-related center was found.     

Study of the isomeric ratios in 107Ag(γ, n)106m,gAg reaction of natural silver induced by bremsstrahlungs with endpoint energies in the giant dipole resonance region

We measured for the first time the isomeric ratios in ¹⁰⁷Ag(γ, n)^106m,gAg reaction by using the activation method and γ-ray spectroscopic method for the whole giant dipole resonance region. The high-purity natural Ag foils in disc shape were irradiated with bremsstrahlungs generated from an electron accelerator Microtron. The induced gamma spectra in the irradiated foils were measured by the high resolution γ-ray spectroscopic system which consists of a high-purity germanium detector and a multichannel analyzer. In order to improve the accuracy of the experimental results, necessary corrections were made in the γ-ray activity measurements and data analysis. The results were analyzed, discussed and compared with those of other authors. For the above mentioned reaction, the isomeric ratios in the energy range from 14 to 24 MeV bremsstrahlungs in this work (except the values at 14, 18 and 20) are new measurements.     

Internal Rotation of the Acetyl Methyl Group in Methyl Alkyl Ketones: The Microwave Spectrum of Octan-2-one

Methyl n-alkyl ketones form a class of molecules with interesting internal dynamics in the gas-phase. They contain two methyl groups undergoing internal rotations, the acetyl methyl group and the methyl group at the end of the alkyl chain. The torsional barrier of the acetyl methyl group is of special importance, since it allows for the discrimination of the conformational structures. As part of the series, the microwave spectrum of octan-2-one was recorded in the frequency range from 2 to 40 GHz, revealing two conformers, one with C₁ and one with C_s symmetry. The barriers to internal rotation of the acetyl methyl group were determined to be 233.340(28) cm⁻¹ and 185.3490(81) cm⁻¹, respectively, confirming the link between conformations and barrier heights already established for other methyl alkyl ketones. Extensive comparisons to molecules in the literature were carried out, and a small overview of general trends and rules concerning the acetyl methyl torsion is given. For the hexyl methyl group, the barrier height is 973.17(60) cm⁻¹ for the C₁ conformer and 979.62(69) cm⁻¹ for the C_s conformer.     

Two Equivalent Internal Rotations in the Microwave Spectrum of 2,6-Dimethylfluorobenzene

Large amplitude motion of methyl groups in isolated molecules is a fundamental phenomenon in molecular physics. The methyl torsional barrier is sensitive to the steric and electronic environment in the surrounding of the methyl group, making the methyl group a detector of the molecular structure. To probe this effect, the microwave spectrum of 2,6-dimethylfluorobenzene, one of the six isomers of dimethylfluorobenzene, was measured using two pulsed molecular jet Fourier transform microwave spectrometers operating in the frequency range from 2 to 40 GHz. Due to internal rotations of two equivalent methyl groups with relatively low torsional barriers, all rotational transitions split into quartets with separations of up to several hundreds of MHz. The splittings were analyzed and modeled to deduce a torsional barrier of 236.7922 (21) cm⁻¹. The results are compared to those obtained from quantum chemical calculations and with other fluorine substituted toluene derivatives of the current literature where the methyl group is adjacent to a fluorine atom.