Synthesis of heteroaryl substituted α‐mercapto acids from thiomalic acid using hexafluoroacetone as protecting and activating reagent

The synthesis of heterocyclic α‐mercapto acids starting from (RS)‐thiomalic acid using hexafluoroacetone as protecting and activating agent is described. The new compounds are useful building blocks for peptide and depsipeptide modification as well as for drug design.     

A stereoselective synthesis of asymmetrically substituted calix[4]arenecarbamates

Calix[4]arenes bearing a methoxy and an R or S α-phenylethylacetamido group at the narrow rim of macrocycles are stereoselectively acylated with 1 equiv of trichloroacetyl isocyanate to give chiral asymmetrically substituted calix[4]arenecarbamates in preparative yields and high diastereomeric excess.     

Role of resonances in building cross sections: Comparison between the Mittag–Leffler and the T‐matrix Green function expansion approaches

Peaks in collision cross sections are often interpreted as resonances. The complex dilation method, as well as other methods relying on analytic continuation of the scattering formalism, can be used to clarify whether these structures are true resonances in the sense that they are poles of the S‐matrix and the associated Green function. The performance of the Mittag–Leffler expansion and T‐matrix Green function expansion methods are formally and computationally compared. The two methods are applied to two model potentials. Eigenenergies, s‐wave residues, and cross sections are computed with both methods. The resonance contributions to the cross sections are further analyzed by removing the residue contributions from the Mittag–Leffler and Green function expansion sums, respectively. It is suggested that the contribution of a resonance to a cross section should be defined through its S‐matrix residue. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

A comparison of electron ionization mass spectra obtained at 70 eV,low electron energies,and with cold EI and their NIST library identification probabilities

Electron ionization (EI) mass spectra of 46 compounds from several different compound classes were measured. Their molecular ion abundances were compared as obtained with 70‐eV EI, with low eV EI (such as 14 eV), and with EI mass spectra of vibrationally cold molecules in supersonic molecular beams (Cold EI). We further compared these mass spectra in their National Institute of Standards and Technology (NIST) library identification probabilities. We found that

1. Low eV EI is not a soft ionization method, and it has little or no influence on the molecular ion relative abundances for large molecules and those with weak or no molecular ions.
2. Low eV EI for compounds with abundant or dominant molecular ions in their 70 eV mass spectra results in the reduction of low mass fragment ions abundances thereby reducing their NIST library identification probabilities thus rarely justifies its use in real‐world applications.
3. Cold EI significantly enhances the relative abundance of the molecular ions particularly for large compounds; yet, it retains the low mass fragment ions; hence, Cold EI mass spectra can be effectively identified by the NIST library.
4. Different standard EI ion sources provide different 70 eV EI mass spectra. Among the Agilent technologies ion sources, the “Extractor” exhibits relatively abundant molecular ions compared with the “Inert” ion source, while the “High efficiency source” (HES) provides mass spectra with depleted molecular ions compared with the “Inert” ion source or NIST library mass spectra.

These conclusions are demonstrated and supported by experimental data in nine figures and two tables.     

K10Ga3Bi6.65 – The First Compound in the Ternary A-Ga-Bi System Comprising Cyclic Tris-meta Borate-Analogous [Ga3Bi6]9– Units and Bi2 Dumbbells

K₁₀Ga₃Bi_6.65 is the first representative in the ternary system A-Ga-Bi (A = alkali metal). It contains [Ga₃Bi₆]^9– anions with planar triangular-coordinated Ga atoms as the main structural feature, accompanied by isolated Bi–Bi dumbbells. Alkali metal cations are counterbalancing the charges and fill the space between the anionic units. According to the Zintl-Klemm concept charge balance is reached if an almost equal ratio of single and double-bonded Bi₂ dumbbells are present according to (K⁺)₁₀[Ga₃Bi₆]^9–([Bi-Bi]^4–)_1/6([Bi=Bi]^2–)_1/6.     

Nickel(II) and cobalt(II) complexes with 4,5-dichloro-isothiazole-3-carboxylic acid and 1,10-phenanthroline: synthesis,crystal structures and cytotoxicity

Transition Metal Chemistry - In this study, Ni(II) and Co(II) complexes [Co(H2O)2L2] (1), [Ni(H2O)2L2] (2), [Co(phen)L2] (3), [Ni(phen)L2]·2H2O·EtOH (4·2H2O), and...     

Experimental demonstration of a narrowband, angular tolerant, polarization independent, doubly periodic resonant grating filter

Resonant grating filters are promising components for free-space narrowband filtering. Unfortunately, due to their weak angular tolerance, their performances are strongly deteriorated when they are illuminated with a standard collimated beam. Yet this problem can be overcome by resorting to a complex periodic pattern known as the doubly periodic grating [Lemarchand et al., Opt. Lett.23, 1149 (1998)]. We report what we believe to be the first experimental fabrication and characterization of a bidimensional doubly periodic grating filter. We obtained a 0.5 nm bandpass polarization independent reflection filter for telecom wavelengths (1520-1570 nm) that presents a transmittivity minimum of 18% with a standard incident collimated beam.     

Three-Dimensional Structure of Thermostable D-Amino Acid Transaminase from the Archaeon Methanocaldococcus jannaschii DSM 2661

Crystallography Reports - Pyridoxal 5′-phosphate (PLP)-dependent transaminases catalyze the stereospecific amino-group transfer from an amino acid or amine to ketone or keto acid....