Extended fenske-hall calculation of inner-shell binding energies using (Z + 1)-bazis sets: Sulfur-containing molecules

It is shown that the S1s and S2p binding energies and their chemical shifts in the molecules H₂S, SO₂, SF₆ and COS obtained with hole-state calculations using an extended Fenske-Hall method are in good agreement with experimental values if mixed (Z + 1)-basis sets are applied.     

Lokalisierung von Substituenten bei Porphyrinen: Das Massenspektroskopische Fragmentierungsverhalten von Porphyrinogenen

The possibilities and limitations for localization of substituents in porphyrins from the fragmentation patterns of porphyrinogens are discussed.     

Landfill Gas: From Rubbish to Resource

The prospects of using landfill gas (LFG) as a high-grade fuel in the immediate future, in view of environmental regulations, the Kyoto Protocols, and energy prices, are discussed. Adsorption cycles suggested in the late 1980s by Sircar and co-workers for treating LFG are reviewed: one produced CO₂-free methane and the other produced both CO₂-free methane and methane-free CO₂. Neither of those could be used to produce pipeline quality gas from LFG, due to contaminants such as nitrogen. Two new three-stage flowsheets are discussed as a means to separate pipeline-grade methane from LFG. One is a hybrid membrane—PSA system. The other is a TSA—PSA system. The third stage of both of these systems is crucial to obtaining pipeline quality gas, i.e., a PSA unit to extract the nitrogen and other light gases from methane. A novel PSA cycle is suggested and explained in terms of: a model by which the recovery, power requirements, and adsorbent bed size can be estimated.     

Syntheses and structures of dimesitylbismuth(III) bromide, Mes2BiBr, and bis(diphenyldithiophosphinato)mesitylbismuth(III), MesBi(S2PPh2)2

Addition of BiBr₃ to Mes₃Bi (Mes = 2, 4, 6-Me₃C₆H₂) in Et₂O gives 86% of Mes₂BiBr (1) as yellow crystals. Reaction of 1 with Ph₂PS₂NH₄ in a 1 : 1 molar ratio gives a quantitative yield of MesBi(S₂PPh₂)₂ (2) rather than the expected dimesitylbismuth compound. The crystal and molecular structures of 1 and 2 were determined at 153 K and 173 K, respectively. They contain Mes₂BiBr molecules with trigonal pyramidal coordination around Bi. The mean Bi---C bond distance is 2.27 Å and the Bi---Br bond distance is 2.690(2) Å. The angles around Bi vary between 89.4 and 106.4°. Intermolecular Bi…Br contacts of 3.795 Å, indicating weak secondary bonding, give rise to zig-zag shaped (Bi---Br)_x chains. In the polymeric chain the coordination geometry around bismuth atoms can be described as pseudo-trigonal bipyramidal. The crystals of 2 consist of discrete monomeric MesBi(S₂PPh₂)₂ molecules with a symmetry plane containing the metal atom and the aromatic ring of the attached mesityl group. The dithiophosphinato ligands exhibit an anisobidentate coordination pattern with long and short phosphorus—sulfur bonds, i.e. P(1)---S(1) 2.051(31) Å and P(1)---S(2) 1.980(3) Å, related to short and long bismuth—sulfur distances, respectively, i.e. Bi---S(1) 2.662(2) Å and Bi---S(2) 3.123(3) Å. This leads to a square-pyramidal geometry around the bismuth atom, with the metal lying 0.33 Å above the basal plane formed by the four sulfur atoms.     

Reactivity of the Donor‐Stabilized Silylenes [iPrNC(Ph)NiPr]2Si and [iPrNC(NiPr2)NiPr]2Si: Activation of CO2 and CS2

Activation of CO₂ by the bis(amidinato)silylene 1 and the analogous bis(guanidinato)silylene 2 leads to the structurally analogous six‐coordinate silicon(IV ) complexes 4 (previous work) and 8 , respectively, the first silicon compounds with a chelating carbonato ligand. Likewise, CS₂ activation by silylene 1 affords the analogous six‐coordinate silicon(IV ) complex 10 , the first silicon compound with a chelating trithiocarbonato ligand. CS₂ activation by silylene 2 , however, yields the five‐coordinate silicon(IV ) complex 13 with a carbon‐bound CS₂^2? ligand, which also represents an unprecedented coordination mode in silicon coordination chemistry. Treatment of the dinuclear silicon(IV ) complexes 5 and 6 with CO₂ also affords the six‐coordinate carbonatosilicon(IV ) complexes 4 and 8 , respectively.     

LC-MS/MS method for the simultaneous quantification of artesunate and its metabolites dihydroartemisinin and dihydroartemisinin glucuronide in human plasma

Artesunate (AS), a hemisuccinate derivative of artemisinin, is readily soluble in water and can easily be used in formulations for parenteral treatment of severe malaria. AS is rapidly hydrolyzed to the active metabolite dihydroartemisinin (DHA) and primarily eliminated by biliary excretion after glucuronidation. To investigate systematically the AS metabolism and pharmacokinetics, a novel liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the simultaneous quantification of AS and its metabolites DHA and DHA glucuronide (DHAG) in human plasma samples was developed. Compared to previous methods, our method includes for the first time the quantification of the glucuronide metabolite using a newly synthesized stable isotope-labeled analogue as internal standard. Sample preparation was performed with only 50 μL plasma by high-throughput solid-phase extraction in the 96-well plate format. Separation of the analytes was achieved on a Poroshell 120 EC-C₁₈ column (50*2.1 mm, 2.7 μm, Agilent Technologies, Waldbronn, Germany). The method was validated according to FDA guidelines. Calibration curves were linear over the entire range from 1 to 2,500 nM (0.4–961.1 ng/mL), 165 to 16,500 nM (46.9–4,691.8 ng/mL), and 4 to 10,000 nM (1.8–4,604.7 ng/mL) for AS, DHA, and DHAG, respectively. Intra- and interbatch accuracy, determined as a deviation between nominal and measured values, ranged from ?5.7 to 3.5 % and from 2.7 to 5.8 %, respectively. The assay variability ranged from 1.5 to 10.9 % for intra- and interbatch approaches. All analytes showed extraction recoveries above 85 %. The method was successfully applied to plasma samples from patients under AS treatment.

Neutral Pentacoordinate Silicon(IV) Complexes with a Tridentate Dianionic O,N,O or N,N,O Ligand,an Anionic PhX Ligand (X = O,S, Se), and a Phenyl Group: Synthesis and Structural Characterization in the Solid State and in Solution

A series of neutral pentacoordinate silicon(IV) complexes with a SiO₃NC, SiO₂SNC, SiO₂SeNC, SiO₂N₂C, SiOSN₂C, or SiOSeN₂C skeleton was synthesized and structurally characterized by multinuclear NMR spectroscopy in the solid state and in solution and by single‐crystal X‐ray diffraction. The compounds studied contain a tridentate dianionic O,N,O or N,N,O ligand, an anionic PhX ligand (X = O, S, Se), and a phenyl group. The structures, NMR spectroscopic parameters, and chemical properties of these silicon(IV) complexes were compared with those of related compounds that contain a tridentate dianionic S,N,O ligand instead of the O,N,O or N,N,O ligand.     

The hexacoordinate silicate dianions mer-tris[glycolato(2-)-O(1),O(2)]silicate and fac-tris[benzilato(2-)-O(1),O(2)]silicate: syntheses and structural characterization

Treatment of tetramethoxysilane with glycolic acid and morpholine (molar ratio 1:3:2) in methanol, followed by crystallization from methanol/tetrahydrofuran, yielded morpholinium mer-tris[glycolato(2-)-O(1),O(2)]silicate (mer-7). Treatment of benzilic acid with sodium hydride, followed by addition of tetrachlorosilane and triethylamine (molar ratio 3:4:1:2), afforded, after crystallization from 1,4-dioxane/acetonitrile/diethyl ether/n-pentane, triethylammonium fac-tris[benzilato(2-)-O(1),O(2)]silicate-hemi-1,4-dioxane (fac-8.(1)/(2)C(4)H(8)O(2)). Single-crystal X-ray diffraction studies showed that the Si-coordination polyhedra of the hexacoordinate silicon(IV) complexes mer-7 and fac-8.(1)/(2)C(4)H(8)O(2) are distorted octahedra. Both compounds were additionally characterized by solid-state VACP/MAS NMR studies ((13)C, (29)Si), and fac-8.(1)/(2)C(4)H(8)O(2) was studied in solution by (1)H, (13)C, and (29)Si NMR experiments. The structural investigations were complemented by computational studies (MP2 studies, TZP level) of the dianions of fac-7 and mer-7.