Chlorotrimethylsilane: a suitable reagent for the synthesis of chlorohydrin esters

A new methodology for obtaining chlorohydrin esters using a one-pot esterification-chlorination reaction, in which one of the reagents, chlorotrimethylsilane, acts as solvent, is described. The reaction is stereospecific and its regioselectivity depends on the number of carbons between the hydroxyl groups present in the starting material. A mechanism is proposed.     

Ab initio melting curve of copper by the phase coexistence approach

Ab initio calculations of the melting properties of copper in the pressure range 0-100 GPa are reported. The ab initio total energies and ionic forces of systems representing solid and liquid copper are calculated using the projector augmented wave implementation of density functional theory with the generalized gradient approximation for exchange-correlation energy. An initial approximation to the melting curve is obtained using an empirical reference system based on the embedded-atom model, points on the curve being determined by simulations in which solid and liquid coexist. The approximate melting curve so obtained is corrected using calculated free energy differences between the reference and ab initio system. It is shown that for system-size errors to be rendered negligible in this scheme, careful tuning of the reference system to reproduce ab initio energies is essential. The final melting curve is in satisfactory agreement with extrapolated experimental data available up to 20 GPa, and supports the validity of previous calculations of the melting curve up to 100 GPa.     

Coordination features of ditopic oxa-azamacrocycles toward Ni(II) and Co(II). Dioxygen uptake by their dinuclear Co(II) complexes

The coordination properties of the ditopic oxa-aza macrocycles L1-L3 toward Ni(II) and Co(II) have been investigated by means of potentiometric and UV-vis spectrophotometric measurements. L1-L3 contain two triamine and/or tetraamine chains separated by two dioxa chains and form both mono- and dinuclear complexes in aqueous solution. In the [ML]2+ complexes, the metal ion is coordinated by one of the two polyamine moieties, while the other does not participate in the coordination. In the dinuclear complexes each metal ion is coordinated, almost independently, to a single polyamine moiety. Under aerobic conditions the binuclear Co(II) complexes of the ligands L1-L3 are able to bind molecular oxygen, with a bridging coordination of O2 between the two metals.     

Alternative syntheses of the new D2d symmetric tetramethyl tricyclo- [3.3.0.0(3,7)]octane-1,3,5,7-tetracarboxylate

Two alternative syntheses of the new D2d symmetric tetramethyl tricyclo[3.3.0.0(3,7)]octane-1,3,5,7-tetracarboxylate from the known dimethyl 3,7-dioxo-cis-bicyclo[3.3.0]octane-1,5-dicarboxylate and 1,5-(2,2'-biphenylene)-cis-bicyclo[3.3.0]octane-3,7-dione are described.     

Determination of atorvastatin and its metabolite ortho-hydroxyatorvastatin in human plasma by on-line anion-exchange solid-phase extraction and liquid chromatography tandem mass spectrometry

A rapid, sensitive, and specific method was developed and validated using liquid chromatography-tandem mass spectrometry for the simultaneous quantitation of atorvastatin (ATV) and its major metabolite ortho-hydroxyatorvastatin (o-HATV) in human plasma. The sample preparation involved a liquid–liquid extraction without chlorinated solvents and an on-line solid-phase extraction exploring the possibilities that anion exchange offers. The analytical method presented intraday and day-to-day variation below 10%; intraday and day-to-day accuracy stood between 94% and 105%; the limit of quantification was 0.1 ng/mL for ATV and 0.5 ng/mL for o-HATV; and the recovery was above 75% for both molecules. This method was applied successfully to quantitate ATV and o-HATV concentrations in an unstudied renal transplant recipient cohort treated with an immunosuppressive regime of tacrolimus and mycophenolic acid and a cohort of hypercholesterolemic patients included in the study as a control group. It can be used to evaluate patient adherence, drug–drug interactions, and pharmacokinetic/pharmacodynamic relationships. The results in our study showed that ATV and o-HATV levels in the renal transplant group were significantly increased (p < 0.001), compared to the hypercholesterolemic group.     

Poly(N,N‐dimethylacrylamide) hydrogels obtained by frontal polymerization

Frontal polymerization (FP) has been used as an alternative technique for the preparation of poly(N,N‐dimethylacrylamide) hydrogels. Samples were synthesized in bulk, water, or dimethyl sulfoxide (DMSO), and the obtained materials were characterized and compared in terms of their yield, swelling behavior, thermal properties, and morphology. It was found that their features are dependent on the presence and type of the solvent used. Samples prepared in bulk are characterized by the lowest yields and the highest front temperatures (T_max) and velocities (V_f), whereas those synthesized in water have the highest yields and the lowest values of T_max and V_f. No significant differences have been found in terms of T_g among the three series of samples. By contrast, the reaction conditions influenced the porous morphology of the samples and, consequently, their swelling capability in water. The swelling ratio ranges from about 670–700% for some samples prepared in water up to 3500% for a sample obtained in DMSO, thus indicating that this parameter can be properly tuned by using the most suitable FP conditions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1422–1428, 2009     

Recent developments in X-UV optics and X-UV diagnostics

Metrology of XUV beams (X-ray lasers, high-harmonic generation and VUV free-electron lasers) is of crucial importance for the development of applications. We have thus developed several new optical systems enabling us to measure the optical properties of XUV beams. By use of a Michelson interferometer working as a Fourier-transform spectrometer, the line shapes of different X-ray lasers have been measured with a very high accuracy (/10^-6). Achievement of the first XUV wavefront sensor has enabled us to measure the beam quality of laser-pumped as well as discharge-pumped X-ray lasers. A capillary discharge X-ray laser has demonstrated a very good wavefront allowing us to achieve an intensity as high as 3×10¹⁴ Wcm^-2 by focusing with a f=5 cm mirror. The sensor accuracy has been measured using a calibrated spherical wave generated by diffraction. The accuracy has been estimated to be as good as /120 at 13 nm. Commercial developments are underway. At Laboratoire dOptique Appliquée, we are setting up a new beamline based on high-harmonic generation in order to start the femtosecond, coherent XUV optic . PACS 07.85.Nc;32.70.Jz;41.50.+h;42.15.Dp;42.55.Vc;52.70.La     

Optimization of the focused flux of high harmonics

Following the theoretical predictions [1], the observation of two-photon processes by interaction of vacuum ultraviolet (VUV) radiation with inner-shell levels of atoms requires focused intensities in the 10¹³-10¹⁴ W/cm² range. Our aim is to reach this regime in order to study non-linear optics at these wavelengths. We first optimized the high harmonic conversion efficiency in argon by studying the best experimental conditions for phase-matching, concentrating on focus geometry related to laser energy, cell length and position relative to the focus. We then studied the resulting harmonic beam focusability by a toroidal mirror (f=10 cm) and made an image of the harmonic focus. We conclude with an evaluation of the focused intensity that we are able to reach experimentally.Received: 28 January 2003, Published online: 24 April 2003PACS: 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation     

Magnetotunneling spectroscopy of dilute Ga(AsN) quantum wells

We use magnetotunneling spectroscopy to explore the admixing of the extended GaAs conduction band states with the localized N-impurity states in dilute GaAs(1-y)N(y) quantum wells. In our resonant tunneling diodes, electrons can tunnel into the N-induced E- and E+ subbands in a GaAs(1-y)N(y) quantum well layer, leading to resonant peaks in the current-voltage characteristics. By varying the magnetic field applied perpendicular to the current direction, we can tune an electron to tunnel into a given k state of the well; since the applied voltage tunes the energy, we can map out the form of the energy-momentum dispersion curves of E- and E+. The data reveal that for a small N content (approximately 0.1%) the E- and E+ subbands are highly nonparabolic and that the heavy effective mass E+ states have a significant Gamma-conduction band character even at k=0.     

Hartmann wave-front measurement at 13.4 nm with lambdaEUV/120 accuracy

We report, for the first time to our knowledge, experimental demonstration of wave-front analysis via the Hartmann technique in the extreme ultraviolet range. The reference wave front needed to calibrate the sensor was generated by spatially filtering a focused undulator beam with 1.7- and 0.6-microm-diameter pinholes. To fully characterize the sensor, accuracy and sensitivity measurements were performed. The incident beam's wavelength was varied from 7 to 25 nm. Measurements of accuracy better than lambdaEUV/120 (0.11 nm) were obtained at lambdaEUV = 13.4 nm. The aberrations introduced by an additional thin mirror, as well as wave front of the spatially unfiltered incident beam, were also measured.