Study of alkyl phosphates in industrial petroleum mixtures by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

Dialkyl phosphate esters used as gellants in some oil well fracturing processes for conventional oil production can result in contamination of the collected crude. Though the exact mechanism is unclear, such compounds form volatile phosphorus that compromises refinery processes. Our initial research involved producing a comprehensive two-dimensional gas chromatographic method (GC × GC) for the detection and quantification of alkyl phosphate esters in petroleum samples, which surpassed the current method employed in sensitivity and speciation capabilities. However, selective detection is required for such analytes in petroleum matrices. This article describes the application of GC × GC with time-of-flight mass spectrometry for selective detection to the analysis of di- and tri-alkyl phosphates in petroleum samples. Features in the electron impact mass spectra of alkyl phosphates are discussed along with the GC × GC retention characteristics of the compounds. Based on these discussions, a preliminary classification and quantification of alkyl phosphate contamination in a suite of industrial samples is then presented.     

Magnetic circular dichroism and absorption spectra of methylidyne in a krypton matrix

Electronic absorption and magnetic circular dichroism spectra are reported for the A(2)Δ, B(2)Σ(-), and C(2)Σ(+) ← X(2)Π transitions of methylidyne radicals isolated in a Kr matrix at cryogenic temperatures. The results are interpreted in the framework of a model in which the X(2)Π term is split by combination of spin-orbit and crystal-field interactions with the atoms of the host matrix. Analysis of the zeroth moments of the spectra yields an empirical spin-orbit coupling constant A(Π) = 11 ± 2 cm(-1) and orbital reduction factor κ = 0.26 ± 0.05, corresponding to a crystal-field splitting of V(Π) = 43 ± 10 cm(-1) for the X(2)Π term. For the A(2)Δ excited-state term, analysis of the first MCD moments gives a spin-orbit coupling constant of A(Δ) = 4.4 ± 0.9 cm(-1).     

Accounting for non-optimal interactions in molecular recognition: a study of ion-π complexes using a QM/MM model with a dipole-polarisable MM region

For a quantitative understanding of molecular structure, interaction and dynamics, accurate modelling of the energetics of both near-equilibrium and less optimal contacts is important. In this work, we explore the potential energy surfaces of representative ion-π complexes. We examine the performance of a semi-empirical QM/MM approach and the corresponding QM/MMpol model, where inducible point dipoles are additionally employed in the MM region. The predicted potential energy surfaces of cation-benzene complexes are improved by inclusion of explicit MM polarisation of the π-molecule. For cation-formamide complexes, inducible dipoles appreciably improve energetic estimates at geometries forming non-optimal interactions. Energetic component analysis suggests that the implicit MM polarisation of the fixed charge QM/MM model mirrors the behaviour of the QM/MMpol dipole model for the energetics of near-equilibrium conformations. However, for complexes at less optimal orientations, the QM/MM model exhibits higher errors than the QM/MMpol approach, being unable to capture orientation-dependent variations in polarisation energy.     

Quantum field theory in curved spacetime

Quantum field theory predicts a number of unusual physical effects in non-Minkowskian manifolds (flat or curved) that have no immediate analogs in Minkowski spacetime. The following examples are reviewed: (1) The Casimir effect; (2) Radiation from accelerating conductors; (3) Particle production in manifolds with horizons, including both stationary black holes and black holes formed by collapse. In the latter examples curvature couples directly to matter through the stress tensor and induces the creation of real particles. However, it also induces serious divergences in the vacuum stress. These divergences are analyzed, and methods for handling them are reviewed.     

Magnetic circular dichroism and absorption spectra of phosphinidene in noble-gas matrices

Electronic magnetic circular dichroism and absorption spectra are reported for the A 3pi(i) <-- X 3sigma- transitions of phosphinidene (PH) isolated in Ar, Kr, and Xe matrices at cryogenic temperatures (approximately 1.4-20 K) and over a range of magnetic field strengths (0-5 T). The results are analyzed by the method of moments, and parameters are extracted by fitting the experimental data to a model in which the A 3pi(i) term is split by spin-orbit (SO) coupling interactions, while the X 3sigma- term is split by spin-spin and higher-order SO coupling. The analysis indicates that, unlike the equivalent imidogen (NH) systems, ground-state PH radicals isolated in noble-gas matrices do not behave as free rotors. Trends in excited-state SO coupling constants are attributed to the external heavy-atom effect and guest-host orbital mixing. It is tentatively concluded that librational amplitudes of the guest radical decrease in the order Ar > Xe > Kr, probably as a consequence of competition between stronger guest-host interactions and larger matrix sites in heavier hosts.     

Dibenzothiophene-S,S-dioxide-fluorene co-oligomers. Stable, highly-efficient blue emitters with improved electron affinity

Incorporation of dibenzothiophene-S,S-dioxide units into conjugated fluorene oligomers changes the frontier orbital energy levels and presents an effective way to increase the electron affinity of these materials, which are highly fluorescent with bright blue emission in both solution and the solid state.     

Quantitative analysis of 6,11-dihydro-11-oxo-dibenz[b,e] oxepin-2-acetic acid (isoxepac) in plasma and urine by gas--liquid chromatography

A method is described for the quantitative analysis of 6,11-dihydro-11-oxo-dibenz[b,e]-oxepin-2-acetic acid (isoxepac) in plasma and urine. Isoxepac and internal standard was analysed by gas-liquid chromatography using a flame ionization detector. The method is accurate and precise over the range 0.1--30 microgram/ml. The method has been applied to the analysis of plasma and urine from both healthy volunteers and patients receiving therapeutic oral doses of isoxepac.