Resonance-enhanced multiphoton ionization of molecular hydrogen via the E,F1Σg+ state: Photoelectron energy and angular distributions

Photoelectron energy and angular distributions are measured for the 2+1 multiphoton ionization process H₂ X¹Σ_g⁺ (ν = 0,J) + 2hv → E,F¹Σ_g⁺(ν_E,J_E = J) + hν → H₂⁺X²Σ_g⁺ (ν⁺) + e^?, for ν_E = 0, 1, or 2 and for J_E = 0 or 1 of the inner well of the double-minimum E,F state. Although a strong preference is found for ν⁺ = ν_E, the detailed H₂⁺ vibrational distribution does not exhibit Franck-Condon behavior, and the photoelectron angular distributions vary markedly with both the J_E value of the intermediate state and the ν⁺ value of the ion.     

A note on residually small varieties of semigroups

It is proved for any varietyG of groups that if the subdirectly irreducible groups inG form a set, and if the subdirectly irreducible representation algebras of groups inG form a set, then every finite group inG is Abelian. The result is essential for the characterization of residually finite varieties of semigroups.     

Stereoselective syntheses of highly functionalized bicyclo[3.1.0]hexanes: a general methodology for the synthesis of potent and selective mGluR2/3 agonists

[Chemical reaction: See text] A Et3Al mediated intramolecular epoxide opening, cyclopropanation reaction is described. The transformation provided highly functionalized bicyclo[3.1.0]hexane systems in high efficiency and with perfect H or F endo selectivity. Application of this reaction to the synthesis of mGluR2/3 agonist 1 (43% overall yield) and a few intermediates suitable for the synthesis of other bicyclo[3.1.0]hexane mGluR2/3 agonists is discussed.     

A PRELIMINARY INVESTIGATION OF THE USE OF LIMONENE FOR DETECTING SINGLET OXYGEN AS A COMPONENT OF POLLUTED AIR

Abstract— Exploratory experiments using simulated conditions indicate that the terpene, (+)-limonene can serve to detect O₂(¹Δ_g) in polluted atmospheres. ¹O₂ attack on limonene results in the formation of specific oxidation products in a specific distribution; quantitative identification of these products is a highly specific test for ¹O₂.     

Validation and application of a high-performance liquid chromatography/tandem mass spectrometry assay for sumatriptan in human plasma

A sensitive and convenient high-performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS) assay is described for the (5-HT(lB/lD)) receptor agonist sumatriptan in human plasma. Sumatriptan was recovered from plasma (81.8 +/- 6.8%) by liquid-liquid extraction. The mobile phase flow rate was 0.3 mL/min and consisted of methanol:water:formic acid (90:10:0.1, v/v/v). The analytical column (4.6 x 100 mm) was packed with Partisil C(8) (5 micro m). The standard curve was linear from 0.7 to 70.4 ng/mL (r(2) > 0.99). The lower limit of quantitation was 0.7 ng/mL. The assay was specific, accurate (percentage deviation from nominal concentrations were <15%), precise and reproducible (within- and between-day coefficients of variation <10.3%). Sumatriptan in plasma was stable over three freeze/thaw cycles and at room temperature for one day. The utility of the assay was demonstrated by following sumatriptan plasma concentrations in two healthy subjects for 8-12 h following a single 20 mg intranasal dose.     

Blends of starch with ethylene vinyl alcohol copolymers: effect of water,glycerol, and amino acids as plasticizers

Blends of thermoplastic starch with poly(ethylene‐co‐vinyl alcohol) copolymer (EVOH) were melt extruded with water/glycerol as plasticizer and a series of amino acid additives. The biggest factor in end‐use mechanical properties proved to be the relative humidity (RH) during storage. Plasticized starch‐EVOH blends stored at 0 and 50% RH changed significantly over time, with, for example, the tensile strength (TS) of the glycerol‐plasticized blend increasing from 4.7 to 26.3 MPa over 8 weeks when maintained at 0% RH. In contrast, the TS of this same sample stored at 75% RH remained unchanged for 8 weeks. Amino acids provided relatively minor, but significant changes in mechanical properties with time. Based on TS, elongation‐to‐break, and modulus, it may be concluded that β‐alanine, sarcosine, and L ‐proline were more effective than glycerol at maintaining strong flexible blends. Increases in crystallinity and changes in morphology with time, as described by modulated DSC were correlated to these changes in mechanical properties. Published in 2007 by John Wiley & Sons, Ltd.     

Electrochemistry of 6-methyl-5,6,7,8-tetrahydropterin

The electrochemical oxidation of 6-methyl-5,6,7,8-tetrahydropterin (6-MTHP), the most effective of the synthetic aromatic amino acid hydroxylase pseudo cofactors, has been studied in aqueous solution over a wide pH range at a pyrolytic graphite electrode. The first electrooxidation of 6-WTHP occurs by a quasi-reversible 2e-2H⁺ reaction giving an unstable quinonoid-dihydropterin. The latter undergoes a first order chemical follow-up reaction yielding 6-methyl-7,8-dihydropterin (6-MDHP). At pH values ?5.6 6-MDHP forms an equilibrium mixture of a covalently hydrated species and non-hydrated species. The covalently hydrated form of 6-MDHP is electrooxidized in a 2e-2H⁺ quasi-reversible reaction to another unstable quinonoid that appears to undergo a two-step rearrangement to 6-methylpterin. Non-hydrated 6-MDHP is electrooxidized at the most positive potential in an irreversible 2e-2H⁺ reaction giving 6-methylpterin.     

Li2H4I2O10, das erste Tetrahydrogendimesoperiodat

Li₂H₄I₂O₁₀, the First Tetrahydrogendimesoperiodate Li₂H₄I₂O₁₀ has been obtained as an intermediate during the dehydration of LiH₄IO₆ · H₂O to LiIO₄, for the first time. According to the results of an X-ray structure determination (monoclinic, P2₁/n, a = 533.98(4), b = 471.85(4), c = 1431.48(10) pm, β = 91.614(7)°, Z = 2, 726 diffractometer data, R = 0.056), Li₂H₄I₂O₁₀ contains the previously unknown tetrahydrogendimesoperiodate ion H₄I₂O₁₀^2?, consisting of two edge-shared IO₆ octahedra. They are connected with LiO₆ octahedra via common edges and vertices. The crystals are non-merohedrally twinned along (100).     

THE VISUAL PROCESS: PHOTOPHYSICS and PHOTOISOMERIZATION OF MODEL VISUAL PIGMENTS and THE PRIMARY REACTION

Abstract— A systematic comprehensive consideration of the emission spectroscopy, emission lifetimes, transient spectroscopy, as well as quantum yields of fluorescence, triplet occupation and photoisomeriz-ation is given for a wide variety of polyene derivatives including retinyl and longer, as well as shorter chainlength homologs. Absorption spectral properties and the results and significance of theoretical calculations are also included. Chainlength, solvent and temperature effects on state order and photophysical as well as photoisomerization properties are evaluated. The mechanism for the primary light step in vision is considered in light of photophysical and photoisomerization data on model visual pigments and rhodopsin.