Alternating RF/DC Isolations for Quantitation with Coeluting Internal Standards in Gas Chromatography/Ion Trap Mass Spectrometry

A new ion trap scan function for gas chromatography/mass spectrometry (GC/MS) quantitation is described that employs alternating mass-selective storage (rf/dc isolation) of ions from an analyte and its coeluting isotopically labeled internal standard. This scan includes two separate ionization/isolation/mass analysis sequences within the same scan function, each optimized for either the analyte or the internal standard. This results in alternating between analyzing the analyte and the internal standard during their coelution. The method is conceptually similar to using two different scan functions to analyze either the analyte or the internal standard in alternating scans; however, it is much faster because it eliminates the slow procedure of continuously downloading alternating scan functions from disk. This allows more data points to be obtained over a GC peak, resulting in more reproducible GC peak profiles as well as better sensitivity and precision. Results of calibration curves spanning four orders of magnitude (0.5 pg to 5 pg injected on column) obtained by using this method give excellent linear correlations (r ² > 0.9990) and precision (relative standard deviations of triplicate injections < 10%).     

Solid-State 13C-NMR spectral evidence for charge transfer complex formation in aromatic diimides and dianhydrides

Solution and solid-state proton decoupled ¹³C-NMR spectra were determined on two diimides derived from 4, 4′-oxydiphthalic anhydride. Comparison of the individual diimide spectra to that of a mixture of the two diimides indicates that ordering of these materials occurs in the solid state via charge transfer complex formation. A similar study was conducted using two isomeric dianhydrides, 4, 4′-isophthaloyldiphthalic anhydride (IDPA) and 4, 4′-terephthaloyldiphthalic anhydride (TDPA). The solution spectra of these compounds are similar and are those which would be expected for these compounds. However, their solid state spectra differ from each other. The solid-state spectrum of TDPA resembles its solution spectrum, whereas, that of IDPA differs greatly from its solution spectrum and indicates charge transfer complex formation occurs with this molecule. This difference is explained in terms of the stereochemistry of the two isomeric dianhydrides.     

Neue 1,6-Methano[10]annulen-Derivate durch Umlagerungsreaktionen der Trimethylsilyl-Gruppe

New Derivatives of 1,6-Methano[10]annulene by Rearrangement of Trimethylsilyl Groups Oxidation of derivatives of trimethylsilyl-substituted bicyclo[4.4.1]undeca-1,3,5,7-tetraenes 1–3 leads to 1,6-methano[10]annulenes. In the case of 2 and 3a , rearrangement of the trimethylsilyl group takes place. This rearrangement can be used to prepare 2,9-disubstituted 1,6-methano[10]annulenes.     

Mesoionic 1,2,4-triazolo[4,3-c]quinazolines

Because of the close structural similarity between triazoloquinazolines and certain 5-membered ring mesoionic heterocycles, all of which possess antiinflammatory activity, we prepared several examples of the novel mesoionic 1,2,4-triazolo[4,3-c]quinazoline ring system for their therapeutic potential. These compounds can be prepared by the cyclization of the appropriately substituted 4-hydrazinoquinazolines with phosgene. When the mesoionic product was unsubstituted at the 5-position (i.e., quinazoline 2-position), it could only be isolated as its hydrochloride salt and not as its unstable free base. None of the mesoionic products were sufficiently stable in solution to allow for evaluation of their antiinflammatory activity.     

Force field for platinum binding to adenine

The antitumor drug cis-diamminedichloroplatinum(II) (cisplatin) binds preferentially to GpG and ApG sequences of DNA, forming N7,N7 intrastrand chelates. Molecular modeling of the intrastrand adducts have been handicapped, so far, by the lack of force-field data describing the Pt–guanine and Pt–adenine binding. We used ab initio calculations with relativistic pseudopotentials to evaluate three important parameters for the platinum–adenine model complex [Pt(NH₃)₃(Ade)]²⁺: (1) the force constant for the Pt? N7 bond bending out of the adenine plane; (2) the energy profile for the torsion about Pt? N7; (3) a set of fractional atomic charges that reproduce the ab initio potential for a number of space points placed around the adduct. A population analysis and comparative study on the tetrammine complex [Pt(NH₃)₄]²⁺ have shown that for platinum adenine is a better σ-donor than NH₃, but its capacity as a π-acceptor is weak. © 1993 John Wiley & Sons, Inc.     

Cluster synthesis. 42. The synthesis and crystal and molecular structures of the sulfur-bridged platinum-ruthenium carbonyl cluster compounds PtRu3(CO)9 L(PPh3)(μ3-S)2 (L=CO,PPh3) and PtRu4(CO)12(PPh3)(μ4-S)2

Two new mixed metal cluster complexes PtRu₃(CO)₁₀(PPh₃)(₃-S)₂,3 14% yield and PtRu₃(CO)₉(PPh₃)₂(₃-S)₂,4 23% yield were obtained from the reaction of Ru₃(CO)₉(₃-S)₂,1 with Pt(PPh₃)₂(C₂H₄) at 0°C. The cluster of4 consists of a spiked triangle of four metal atoms with two triply bridging sulfido ligands. The reaction of Ru₄(CO)₁₁(₄-S)₂,2 with Pt(PPh₃)₂(C₂H₄) yielded the expanded mixed-metal cluster complex PtRu₄(CO)₁₂(PPh₃)(₄-S)₂,5 in 12% yield. The structure of the cluster5 can be described as a pentagonal bipyramid of five metal atoms and two sulfido ligands with one metal-metal bond missing. Compounds4 and5 were characterized by a single-crystal X-ray diffraction analyses.     

The kinetics of silica reduction in hydrogen

The kinetics of the reduction of SiO₂ in hydrogen have been examined using a thermalgravimetric method. The mechanism of the reaction SiO₂ + H₂ = SiO + H₂O can be described on the basis of a reaction interface moving at a constant velocity toward the center of the reacting sample. The velocity of the moving interface depends on the reaction temperature and water vapor content of the ambient gas. The reaction was studied in the temperature range 1115–1630°C and was found to be isokinetic in this range. The activation energy for the reaction is 85 kcal/mole in pure, dry hydrogen and 135 kcal/mole in hydrogen with a dew point of 24°C.     

Zur photochemie der triafulvene—III: Photochemische umwandlungen des 2-(diphenylcyclopropenyliden)-indan-1.3-dions

The photochemical transformations of triafulvene 6 in solvents of different type are investigated. Irradiation of 6 in methanol/ethanol leads to products which are derived from quinodimethane 7 by addition of alcohol in 1.2 or 1.6 fashion. When 6 is irradiated in acetonitrile/benzonitrile, products of complex structural type $\text{17}\text{19}$ are obtained. For structure elucidation a X-ray crystallographic analysis is performed for 17a.     

The photolysis of platinacycloalkanes in solution

The photolysis of [I₂$\text{PtCH}{}_2\text{CH}{}_2\text{CH}{}_2\text{C}$H₂ (PMe₂ Ph)₂] gives ethylene and but-1-ene as volatile products, the latter probably being formed via a five-coordinate platinum intermediate. However, the formation of propene from the photolysis of [Cl₂$\text{PtCH}{}_2\text{CH}{}_2\text{C}$H₂ (1,10-phenanthroline) appears to involve a direct transfer of a hydrogen atom between neighbouring CH₂ groups in the ring. Other gaseous products, e.g. cyclopropane, ethylene, may be formed via a platinum ion radical.     

Fluorination of dimethylmercury,tetramethylsilane and tetramethylgermanium. Synthesis and characterization of polyfluorotetramethylsilanes,polyfluorotetramethylgermanes,bis(trifluoromethyl)mercury and tetrakis(trifluoromethyl)germanium

It has been found possible to preserve metal—carbon and metalloid—carbon bonds during direct fluorination. The reaction of dimethylmercury with fluorine gives bis(trifluoromethyl)mercury in 6.5% yield. Fluorination of tetramethylsilane has led to the isolation of the new polyfluorotetramethylsilanes of the following type, Si(CH₃)_x(CH₂F)_y(CHF₂)_z, x + y + z = 4. Also characterized were compounds containing SiCF₃. It has been possible to synthesize tetrakis(trifluoromethyl)germanium in 63.5% yield from the reaction of fluorine with tetramethylgermanium. Also characterized were many polyfluorotetramethylgermanes of the following type, Ge(CF₃)_x(CF₂H)_y(CFH₂)_z (x + y + z = 4).