Satellite Transition of the Resonance Doublet of the Na Atom in a Mixture with CF4

JETP Letters - The excitation spectrum of the resonance luminescence of Na atoms in a mixture with CF4 exhibits a satellite transition corresponding to the simultaneous optical excitation of the...     

Three‐Dimensional Branched and Faceted Gold–Ruthenium Nanoparticles: Using Nanostructure to Improve Stability in Oxygen Evolution Electrocatalysis

Achieving stability with highly active Ru nanoparticles for electrocatalysis is a major challenge for the oxygen evolution reaction. As improved stability of Ru catalysts has been shown for bulk surfaces with low‐index facets, there is an opportunity to incorporate these stable facets into Ru nanoparticles. Now, a new solution synthesis is presented in which hexagonal close‐packed structured Ru is grown on Au to form nanoparticles with 3D branches. Exposing low‐index facets on these 3D branches creates stable reaction kinetics to achieve high activity and the highest stability observed for Ru nanoparticle oxygen evolution reaction catalysts. These design principles provide a synthetic strategy to achieve stable and active electrocatalysts.     

Rapid and scalable synthesis of chiral bromolactones as precursors to α-exo-methylene-γ-butyrolactone-containing sesquiterpene lactones

The sesquiterpene lactones cover a diverse and pharmacologically important diversity space. In particular, the electrophilic α-exo-methylene-γ-butyrolactone moiety that is preponderant in this natural product family has been shown to readily engage in covalent inhibition via conjugate addition of cysteine residues in target proteins. However, the synthetic accessibility of sesquiterpenes or related probes to investigate their mode of action remains laborious. Herein, we present a rapid and scalable route to chiral bromolactones as enabling precursors in the synthesis of sesquiterpene lactones.     

Intra- vs intermolecular hydrogen bonding. The crystal structure of 5-methyl-2-hydroxyacetophenone thiosemicarbazone monohydrate and salicylaldehyde-2-methylthiosemicarbazone monohydrate

The crystal structure of 5-methyl-acetophenonethiosemicarbazone monohydrate,A, and salicylaldehyde-2-methylthiosemicarbazone monohydrate,B, were determined using single crystal X-ray diffraction.A crystallizes in the monoclinic space groupC2/c, with lattice parametersa=14.161(2),b=15.753(1) ?,c=11.084(1) ?, β=112.59(1)° andZ=4, yielding a calculated density ofD _calc=1.352 mg/m³.B crystallizes in the triclinic space groupP1, witha=7.233(2) ?,b=7.371(2) ?,c=11.841(2) ?, α=82.77(2)°, β=78.33(2)°, γ=63.06(2)° andD _calc=1.371 mg/m³ forZ=2,. In bothA andB the immine nitrogen and the sulfur atom areanti with respect to N2-C8. WhileA presents the usual intramolecular six membered hydrogen bond ring,B has instead an intermolecular hydrogen bond between the hydroxy moiety of the salicyladehyde and a water molecule. AM1 calculations agree with the experimental conformations observed in both compounds. Contribution No. 1619 of the Instituto de Química, UNAM.     

Cycloreversion of azetidines via oxidative electron transfer. steady-state and time-resolved studies

Cycloreversion of cis- and trans-1,2,3-triphenylazetidine (c-2 and t-2) is achieved by electron transfer to (tris(4-bromophenyl)aminium radical cation (5 (*+)). Stepwise C-N and C-C bond cleavage of azetidine radical cations leads to cis- and trans-stilbene, together with N-benzylideneaniline, as final products. Mechanistic evidence is provided by quenching studies, using laser flash photolysis to generate 5 (*+) from its neutral precursor.     

Langevin network model of myosin

Langevin mode theory and the coarse-grained elastic network model (ENM) for proteins are combined to yield the Langevin network model (LNM). Hydrodynamic radii of 6 A were assigned to each alpha-carbon on the basis of matching experimental translational and rotational diffusion constants of lysozyme, myoglobin, and hemoglobin with those calculated using a rigid body bead model with hydrodynamic interactions described by the Rotne-Prager tensor. LNM analysis of myosin II indicates that all ENM-like modes are overdamped at water viscosities. The low-frequency LNM modes in the pre-power stroke structure (PDB code: 1VOM) are substantially less mixed than the corresponding modes of the post-power stroke structure (1Q5G). Results from a four-bead model of the myosin "lever arm" indicate that coupling between modes increases as the array departs from linearity and are consistent with the results for 1VOM and 1Q5G. The decay times for all overdamped Langevin modes are shorter than the calculated rotational tumbling times found for lysozyme and myosin.     

Highly diastereoselective self-assembly of chiral tris(m-ureidobenzyl)amino capsules

The self-assembly of chiral tris(m-ureidobenzyl)amines to give dimeric capsules is a highly diastereoselective process in solution, while in the solid state, the formation of the corresponding capsules is not only diastereoselective but also regioselective.     

Determination of 3-MCPD by GC-MS/MS with PTV-LV injector used for a survey of Spanish foodstuffs

3-Monochloropropane-1,2-diol (3-MCPD) is the most common chemical contaminant of the group of chloropropanols. It can occur in foods and food ingredients at low levels as a result of processing, migration from packaging materials during storage and domestic cooking. A sensitive method for determination of 3-MCPD in foodstuffs using programmable temperature vaporization (PTV) with large-volume injection (LVI) gas chromatography (GC) with tandem mass spectrometry detection (MS/MS) has been developed and optimized. The optimization of the injection and detection parameters was carried out using statistical experimental design. A Plackett-Burman design was used to estimate the influence of resonance excitation voltage (REV), isolation time (IT), excitation time (ET), ion source temperature (IST), and electron energy (EE) on the analytical response in the ion trap mass spectrometer (ITMS). Only REV was found to have a statically significant effect. On the other hand, a central composite design was used to optimize the settings of injection temperature (T(inlet)), vaporization temperature (T(vap)), vaporization time (t(vap)) and flow (Flow). The optimized method has an instrumental limit of detection (signal-to-noise ratio 3:1) of 0.044 ng mL(-1). From Valencian, Spain, supermarkets 94 samples of foods were surveyed for 3-MCPD. Using the optimized method levels higher than the limit established for soy sauce by the European Union were found in some samples. The estimated daily intake of 3-MCPD throughout the investigated foodstuffs for adults and children was found about 0.005 and 0.01%, respectively, of the established provisional tolerable daily intake.     

Determination of PASHs by various analytical techniques based on gas chromatography-mass spectrometry: application to a biodesulfurization process

Polycyclic aromatic sulphur heterocyclic (PASH) compounds, such as dibenzothiophene (DBT) and alkylated derivatives are used as model compounds in biodesulfurization processes. The development of these processes is focused on the reduction of the concentration of sulphur in gasoline and gas–oil [D.J. Monticello, Curr. Opin. Biotechnol. 11 (2000) 540], in order to meet European Union and United States directives.

The evaluation of biodesulfurization processes requires the development of adequate analytical techniques, allowing the identification of any transformation products generated. The identification of intermediates and final products permits the evaluation of the degradation process.

In this work, seven sulfurated compounds and one non-sulfurated compound have been selected to develop an extraction method and to compare the sensitivity and identification capabilities of three different gas chromatography ionization modes. The selected compounds are: dibenzothiophene (DBT), 4-methyl-dibenzothiophene (4-m-DBT), 4,6-dimethyl-dibenzothiophene (4,6-dm-DBT) and 4,6 diethyl-dibenzothiophene (4,6 de-DBT), all of which can be used as model compounds in biodesulfurization processes; as well as dibenzothiophene sulfoxide (DBTO₂), dibenzothiophene sulfone (DBTO) and 2-(2-hydroxybiphenyl)-benzenesulfinate (HBPS), which are intermediate products in biodesulfurization processes of DBT [ A. Alcon, V.E. Santos, A.B. Martín, P. Yustos, F. García-Ochoa, Biochem. Eng. J. 26 (2005) 168]. Furthermore, a non-sulfurated compound, 2-hydroxybiphenyl (2-HBP), has also been selected as it is the final product in the biodesulfurization process of DBT [A. Alcon, V.E. Santos, A.B. Martín, P. Yustos, F. García-Ochoa. Biochem. Eng. J. 26 (2005) 168].

Since, typically, biodesulfurization reactions take place in a biphasic medium, two extraction methods have been developed: a liquid–liquid extraction method for the watery phase and a solid phase extraction method for the organic phase. Recoveries of the selected compound in both media were studied. They were in the range of 80–100% for the watery and in the range of 40–60% for the organic phase, respectively.

Gas chromatography coupled to mass spectrometry (GC–MS) has been employed for the identification of these selected compounds. Three different ionization modes were applied: conventional electron impact (EI); positive chemical ionization (PCI), using methane as the reagent gas; and a recently developed ionization mode known as hybrid chemical ionization (HCI), using perfluorotri-n-butylamine as the reagent gas. Limits of detection and identification capabilities have been compared between the three analytical techniques.

The sensitivity of the three analytical techniques was studied and LOD between 0.05 and 1, between 0.09 and 2 and between 0.001 and 0.043 were achieved for PCI, EI and HCI, respectively.

The developed method was applied in samples from a biodesulfurization process. The biodesulfurization reactions were conducted in resting cell operation mode, using Erlenmeyer flasks or an agitated tank bioreactor. The microorganism employed was Pseudomonas putida CECT 5279. The reaction was performed under controlled air flow, stirring and temperature conditions.