The second virial coefficient of 3-centerLennard-Jones molecules and its relation to 1- and 2- center molecules

The second virial coefficients of homonuclear three-centerLennard-Jones molecules are calculated with various parameters of the isosceles triangle connecting the three sites. A special effort is made to establish the reducedBoyle temperaturesT _B and the values of the second virial coefficients atT/T _B=0.3 for the sake of comparison with one- and two-centerLennard-Jones molecules. It is shown that it is possible to find parameter values of the interaction potential of one- and two-centerLennard-Jones molecules which give very similar values of second virial coefficients forT/T _B0.3, and the equivalence conditions are established. These conditions might not only give a basis for a microscopic scaling of state variables, but also some restrictions for the validity of the group contribution concept.Presented in part at the DFG-Colloquium at Paderborn, 19th April 1982, and at the 5th Conference on Mixtures of Nonelectrolytes and Intermolecular Interactions, April 18–22, 1983, at Halle (GDR).     

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Zur Kenntnis der Dioxyditolylsulfone

Zusammenfassung Es wird der Verlauf der Sulfurierung des m-Kresols auf Grund der zwei dabei gebildeten Sulfone, dem - und -m-Oxytolylsulfon vonZehenter, geklärt. Die Konstitution des -m-Oxytolylsulfons wird als die des 2,2-Dioxy-4,4-dimethyldiphenylsulfons erkannt; für das -m-Oxytolylsulfon wird die Konstitution des 4,2-Dioxy-2,4-dimethyldiphenylsulfons wahrscheinlich gemacht.     

Chiral relaxation reagents (CRR) in 13C NMR spectroscopy

Enantiomers and chiral relaxation reagents (CRR) afford diastereomeric complexes, which differ clearly in their ¹³C spin-lattice relaxation times.     

Charge ordering in lithium vanadium phosphates: electrode materials for lithium-ion batteries

The delithiation process in monoclinic Li3V2(PO4)3 has been determined by powder neutron diffraction coupled with 7Li solid-state NMR techniques. Charge ordering of vanadium (V3+/V4+) was observed in Li2V2(PO4)3 as shown by the gray and blue V-O octahedra, respectively, indicating that the electrons are pinned in this phase and hence transport is limited.     

The direct synthesis of methylchlorosilanes: New aspects concerning its mechanism

New results are given regarding the mechanism of the chemical process of copper alloyed silicon with methyl chloride (the `direct process'). As indicated by Photo-EMF measurements, carried out with doped silicon samples the reactivity of silicon significantly depends on the type of the doping with elements like phosphorus (n-type) tin, boron, indium (p-type). In-situ trapping experiments with 2,3-dimethylbutadiene are consistent with the creation of silylene intermediates SiMeCl and SiCl₂ . Theselectivity of their competitive insertion steps can be controlled by the doping type and concentrations of the doping elements, especially the phosphorus/tin ratio criterion. n-Type doping favors the silylene insertion into the C-Cl bond due to the electronic silylene stabilization on the silicon surface. In case of p-type doping silylene insertion into Si-Cl bond is favored more intensively leading to the formation of disilanes.     

Characterizing correlation changes of complex pattern transitions: The case of epileptic activity

We analyze the time-dependent spectrum of eigenvalues of the correlation matrix for multivariate EEG data at the transition to epileptic seizures. By a mechanism of level repulsion between states at both edges of the spectrum of the correlation matrix, relevant information about quantitative correlation changes is reflected in the largest and smallest eigenvalues and corresponding eigenvectors. By the application of measures from random matrix theory we provide evidence that statistically relevant information can be obtained both at the upper and the lower end of the spectrum. In addition, information about spatial characteristics of correlation changes can be extracted.     

Simultaneous quantitative analysis of letrozole, its carbinol metabolite, and carbinol glucuronide in human plasma by LC-MS/MS

Letrozole is an efficient endocrine treatment of postmenopausal breast cancer, however, not all patients benefit from this treatment, and moreover, severe side-effects like arthralgia frequently lead to discontinuation. To better understand inter-individual variability in drug response and side-effects, plasma analysis of steady-state concentrations of letrozole and its major metabolites is crucial. We developed a rapid, sensitive, and specific method for the simultaneous quantification of letrozole and its metabolites 4,4′-(hydroxymethylene)dibenzonitrile (carbinol) and bis(4-cyanophenyl)methyl hexopyranosiduronic acid (carbinol-gluc) by UHPLC-ESI-MS/MS using in-house synthesized, stable isotope-labeled internal standards. Following solid-phase extraction in BondElut C18 96-well plates, the analytes were separated on a ZORBAX Eclipse XDB-C18 column (1.8 μm, 4.6 × 50 mm) with a gradient of acetonitrile in 0.1% acetic acid in water and detected on a triple quadrupole mass spectrometer with electrospray ionization in the multiple reaction monitoring mode. Lower limits of quantification were 20, 0.2, and 2 nM for letrozole, carbinol, and carbinol-gluc, respectively. The assay has been validated according to FDA guidance and applied to the analysis of 20 plasma samples of postmenopausal breast cancer patients treated with 2.5 mg of letrozole per day. Mean plasma levels (±SD) were 366 ± 173, 0.38 ± 0.09, and 34 ± 12 nM for letrozole, carbinol, and carbinol-gluc, respectively. Our rapid and sensitive mass spectrometry based method enables future pharmacokinetic investigations of letrozole outcome.