Transformed steroids. 123. Synthesis of 5α(H)- and 5α(OH)-6-ketosteroids with an additional 17α,20ξ-dihydroxytetrahydropyran ring E

The paper is devoted to the synthesis of 3,17α,20-trihydroxy-16β,23-epoxy-21,24-dinor-5αH-cholan-6-one and 3,5α,17α,20-tetrahydroxy-16β,23-epoxy-21,24-dinorcholan-6-one and derivatives of them. It has been shown that the reduction of 3,17α-dihydroxy-16β,23-epoxy-21,24-dinorchol-5-en-20-one with sodium tetrahydroborate and with diborane takes place stereospecifically with different spatial directivities: in the products of diborane reduction, ring E exists in the boat form, as has been shown by¹H and¹³C NMR methods. The trans linkage of rings A/B in the modified steroids has been confirmed by their circular dichroism spectra.     

Development and validation of a liquid chromatographic/tandem mass spectrometric assay for the quantitation of nucleoside HIV reverse transcriptase inhibitors in biological matrices

Besides liquid chromatographic (LC)/UV methods adapted to therapeutic drug monitoring, there is still a need for more powerful techniques that can be used for pharmacological research and clinical purposes. We developed an LC method coupled with tandem mass spectrometry (MS/MS) to separate, detect and quantify with high sensitivity the nucleoside analogues used in multitherapies (zidovudine, stavudine, zalcitabine, didanosine, lamivudine and abacavir) in plasma and in the intracellular medium. We worked on two essential issues: (i) the need to use two ionization modes in order to achieve the best sensitivity, which leads to the optimization of the chromatographic separation of drugs detected in the positive ionization mode and drugs detected in the negative ionization mode, and (ii) the need to optimize the extraction step in order to enhance sample recovery. The peripheral blood mononuclear cells were lysed in Tris buffer-MeOH. A clean-up procedure was performed by solid-phase extraction only for plasma samples. The LC separation was carried out on a Zorbax Stable Bond C(18) column followed by MS/MS analysis after electrospray ionization in either the negative or positive mode. The positive ionization mode was applied at the beginning of the run to detect zalcitabine and lamivudine, then the ionization mode was changed to negative for the detection of didanosine, stavudine, internal standard and zidovudine. The calibration range for all the analytes was 0.5-200 ng ml(-1). The recoveries were between 64 and 90%, with coefficients of variation (CVs) lower than 15%. The inaccuracy (bias) was +/-15% with CVs always lower than 12%. The analytes were stable at room temperature and in the extraction solvent for at least 24 h, after storage at -80 degrees C for 3 months, after three freeze-thaw cycles and in the injection solvent after 48 h at 4 degrees C. Together with the measurement of intracellular triphosphorylated metabolites thanks to the powerful plasma and intracellular assay method for intact drugs, it is possible to describe the behaviour of nucleoside analogues against HIV through plasma pharmacokinetics, cell membrane diffusion including drug transport involvement, and also the intracellular metabolism.     

Raman scattering: Orientational motions and collision frequency in liquid tetrafluoromethane from the triple to the critical point

The molecular reorientational motion of pure liquid CF₄, from the triple to the critical point, is quite well simulated by the Gordon's “j” diffusion model. The mean time between collisions identified with the parameter τ_J^(j) is compared with the predictions of the cell model.     

Air processed P3HT:PCBM photovoltaic cells: Morphology correlation to annealing,degradation, and recovery

Systematically varied annealing, encapsulation, and solvent vapor treatments are conducted to produce stable OPV devices with controlled film morphology and high performance when produced in air. Active layer films are analyzed by AFM, nanomechanical mapping, UV–vis spectroscopy, and XRD. Devices prepared with isopropanol solvent vapor annealing (SVA) combined with thermal annealing (TA) show the highest environmental resistance and performance. Such devices yield average PCE of 3.3%, with stability to atmospheric exposure of up to 60 min prior to encapsulation. Encapsulated devices exposed to the laboratory environment for 30 days exhibit a decrease in PCE of ～15%. On application of a second TA step PCE is recovered to over 90% of the original value. The unprecedented air stability of the cells is attributed to the formation of an active layer with a stable, favorable morphology during the SVA process, which is associated with lower oxygen content films. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1511–1520