Electronic basis of the comparable hydrogen bond properties of small H2CO/(H2O)n and H2NO/(H2O)n systems (n = 1, 2)

The electronic and structural properties of dihydronitroxide/water clusters are investigated and compared to the properties of formaldehyde/water clusters. Exploring the stationary points of their potential energy surfaces (structurally, vibrationally, and energetically) and characterizing their hydrogen bonds (by both atoms in molecules and natural bond orbitals methods) clearly reveal the strong similarity between these two kind of molecular systems. The main difference involves the nature of the hydrogen bond taking place between the X-H bond and the oxygen atom of a water molecule. All the properties of the hydrogen bonds occurring in both kind of clusters can be easily interpreted in terms of competition between intermolecular and intramolecular hyperconjugative interactions.     

Development of a mass-directed preparative supercritical fluid chromatography purification system

In this paper, we report the development of a mass-directed supercritical fluid chromatography (SFC) purification system. We have addressed issues on software compatibility, the interface between the preparative SFC and the mass spectrometer, and fraction collection. Good peak shape and signal were achieved in the mass spectrometry (MS) trace, allowing accurate peak detection and reliable fraction collection. Simple modifications on a commercially available fraction collector enabled fractionation at atmospheric pressure with high recovery. The SFC/MS purification system has been used in support of high-throughput library purification and has been proven to be a valuable tool in complementing our reversed-phase high-performance liquid chromatograph (RP-HPLC/MS)-based technology platform.     

Profiling the Active Site of a Copper Enzyme through Its Far-Infrared Fingerprint

Vibrations of the metal active site of the Cu,Zn-superoxide dismutase enzyme were analyzed by far-infrared difference spectroscopy and theoretical normal mode calculation. Both electrochemically triggered Cu(I) and Cu(II) redox states show well-defined infrared vibrational modes, notably modes of the histidine ligands, the Cu(II) -His(61) -Zn(II) bridge and of the water pseudo-ligand.     

Positron and deuteron depth profiling in helium-3-implanted electrum-like alloy

In spite of previous extensive studies, the helium behavior in metals still remains an issue in microelectronics as well as in nuclear technology. A gold-silver solid solution (Au₆₀Ag₄₀: synthetic gold-rich electrum) was chosen as a relevant model to study helium irradiation of heavy metals. After helium-3 ion implantation at an energy ranging from 4.2 to 5.6 MeV, nuclear reaction analysis (NRA) based on the ³He(d,p)⁴He reaction, was performed in order to study the thermal diffusion of helium atoms. At room temperature, NRA data reveal that a single Gaussian can fit the He-distribution, which remains unchanged after annealing at temperatures below 0.45 of the melting point. Slow positron implantation spectroscopy, used to monitor the fluence dependence of induced defects unveils a positron saturation trapping, which occurs for He contents of the order of 50-100 appm, whereas concentrations larger than 500 appm seem to favor an increase in the S-parameter of Doppler broadening. Moreover, at high temperature, NRA results clearly show that helium long range diffusion occurs, though, without following a simple Fick law.     

Equations-of-motion method: Calculation of the k lowest or highest solutions

The method of optimal relaxation to determine the eigenvalues of symmetric matrices, as proposed by Shavitt, has been adapted to solve the equation-of-motion problem. Matrices Z and Y are obtained by one diagonalization, while matrices A and B remain unchanged. This procedure is particularly useful for high-dimensional or nonorthogonal bases, if one needs only the lowest transition energies.     

Synthesis of propylure, sex pherome of Pectinophora gossypiela Saunders

10-Propyl-trans-trideca-5, 9-dien-1-yl acetate (propylure), the sex pheromone of the female pink bollworm moth, has been synthesized by an original procedure. The spectroscopic and physiological properties of the material are identical to that of the natural attractant.     

Sur l'arǒme de viande de bœuf grillée III. Pyrrolo [1,2-a]pyrazines,identification et synthèse

Synthesis of alkylpyrrolo[1,2-a]pyrazines, roasted meat flavor constituents Seven alkylpyrrolo[1,2-a]pyrazines have been identified for the first time in a roasted meat aroma obtained by thermolysis of the hydrosoluble flavor precursors of raw meat. Identification of individual components was done by capillary gas chromatography/mass spectroscopy coupling. The structure of these nitrogen heterocyclic compounds was for some time in doubt because of the similarity of the MS. with those of other diazaindene and diazanaphthalene derivatives such as benzimidazoles, indazoles, cyclopenta [b]pyrazines and dihydroquinoxalines. The structure of these new flavor components was completely elucidated in some cases by interpretation of NMR. spectra, the others being deduced by analogy. Hypotheses are formulated concerning the formation of this skeleton by a non-enzymatic browning reaction between carbohydrates and amino acids. Four different schemes have been adopted to synthesize substituted isomers selectively.     

Synthesis of alkyl-5H-cyclopenta[b]pyrazines (author's transl)]

Synthesis of alkyl-5H-cyclopenta[b]pyrazines. Alkyl-5H-cyclopenta[b]-pyrazines (sometimes together with 5-alkylidene-5H-6,7-dihydrocyclopenta[b]pyrazines) are prepared by thermal degradation of 5-acetoxy-5H-6,7-dihydrocyclopenta[b]pyrazines; these are obtained by treatment of alkyl-5H-6,7-dihydrocyclopenta[b]pyrazine N-oxides with acetic anhydride. Cyclopenta[b]pyrazines which are potentially present in roasted food flavors possess interesting organoleptic properties.     

Surface waves in ferrofluids under vertical magnetic field

We present here new experimental results about the waves at the horizontal free surface of a magnetic fluid submitted to a normal magnetic field. The waves are generated by a small modulation at frequency of the vertical field . Using a shadowgraph method, we are able to measure the wavevector k of the 2D waves for a given value of and . The dispersion relation of the surface waves is established experimentally. On the other hand, we propose a theoretical derivation of the dispersion equation which includes a more complete treatment of the magnetic term than the previous works. Finally, we conclude that a linear and inviscid analysis is sufficient to fit well the experimental data, except in the vicinity of the critical field where a surface instability occurs. Received 11 May 1998     

Spin-orbit configuration interaction study of the electronic structure of the 5f (2) manifold of U(4+) and the 5f manifold of U(5+)

The energy levels of the 5f configuration of U(5+) and 5f(2) configuration of U(4+) have been calculated in a dressed effective Hamiltonian relativistic spin-orbit configuration interaction framework. Electron correlation is treated in the scalar relativistic scheme with either the multistate multireference second-order multiconfigurational perturbation theory (MS-CASPT2) or with the multireference single and double configuration interaction (MRCI) and its size-extensive Davidson corrected variant. The CASPT2 method yields relative energies which are lower than those obtained with the MRCI method, the differences being the largest for the highest state (1)S(0) of the 5f(2) manifold. Both valence correlation effects and spin-orbit polarization of the outer-core orbitals are shown to be important. The satisfactory agreement of the results with experiments and four-component correlated calculations illustrates the relevance of dressed spin-orbit configuration interaction methods for spectroscopy studies of heavy elements.