Validated HPLC–MS–MS method for simultaneous determination of atorvastatin and 2-hydroxyatorvastatin in human plasma—pharmacokinetic study

Cholesterol-reducing statin drugs are the most frequently prescribed agents for reducing morbidity and mortality related to coronary heart disease. In this publication a validated, highly sensitive, and selective isocratic HPLC method is reported for quantitative determination of the major statin drug atorvastatin (ATV) and its metabolite 2-hydroxyatorvastatin (HATV). Detection was performed with an electrospray ionization triple-quadrupole mass spectrometer equipped with an ESI interface operating in positive-ionization mode. Multiple reaction monitoring (MRM) was used for MS–MS detection. The calibration plot was linear in the concentration range 0.10–40.00 ng mL⁻¹ for both ATV and HATV. Inter-day and intra-day precision and accuracy of the proposed method were characterized by measurement of relative standard deviation (RSD) and percentage deviation, respectively; both were less than 8% for both analytes. The limit of quantitation was 0.02 ng mL⁻¹ for ATV and 0.07 ng mL⁻¹ for HATV. The method was used for pharmacokinetic study of ATV and HATV. Pharmacokinetic data for all analytes are also reported.     

Doped biocompatible layers prepared by laser

The contribution deals with KrF laser synthesis and study of doped biocompatible materials with focus on diamond-like carbon (DLC) and hydroxyapatite (HA). Overview of materials used for dopation is given. Experimental results of study of HA layers doped with silver are presented. Films properties were characterized using profilometer, SEM, WDX, XRD and optical transmission. Content of silver in layers moved from 0.06 to 13.7 at %. The antibacterial properties of HA, silver and doped HA layers were studied in vivo using Escherichia coli cells.     

Application of mid-infrared laser radiation for lithotripsy

The perforation effects of Er:YAG (2940 nm) and Ho:YAG (2100 nm) lasers radiation on human urinary stones model made from compressed plaster and real human samples were compared in vitro. For mid-infrared laser radiation delivery the special COP/Ag hollow glass waveguides were used. From the interaction experiments the perforation rates were derived and compared for both lasers. From the results it can be evaluated that Er:YAG laser radiation is favourable in comparison with Ho:YAG laser in case of artificial samples perforation efficiency.     

Study of the plasmas produced during the deposition of TiC/SiC thin films in a hybrid magnetron-laser system

Time- and spatially-resolved optical emission spectroscopy was performed to characterize the plasma produced in a hybrid magnetron-sputtering-laser deposition system, which is used for TiC or SiC thin films preparation. A graphite target was ablated by a KrF excimer laser (λ=248 nm,τ=20 ns) and either Ti or Si targets were used for DC magnetron sputtering in argon ambient. Spectra were measured in the range 250–850 nm. The evolution of the spectra with varying magnetron powers (0–100 W) and argon pressures (0.3–10 Pa) was studied. Spectra of the plasmas produced by a) the magnetron alone, b) the ablation laser alone, and c) the magnetron and the ablation laser together, were recorded. Spectra (a) were dominated by Ar atoms and Ar⁺ ions. Emission lines of Ti and Si were detected, when Ti target and Si target was used, respectively. Spectra (b) revealed emission of C, C⁺, C₂, Ar, Ar⁺. Spectra (c) showed presence of all previously mentioned species and further of Ti⁺ ions emission was detected. The research was supported by Grant Agency of the Czech Republic No. 202/06/02161, GA ASCR project number A1010110/01 and Institutional Research Plan AV CR No. AV0Z 10100522.     

Some properties of a-C:N films prepared by KrF laser ablation

Thin a-C:N films were prepared by pulsed laser ablation using a KrF excimer laser and a graphite target. The influence of the substrate temperatureT _s (27°C and 330°C), and the nitrogen gas ambient pressurep n (1.5 Pa, 13.3 Pa and 40 Pa) on the film properties was studied. The films were characterized by scanning electron microscopy, Rutherford backscattering, spectroscopic ellipsometry and by Raman scattering. The nitrogen content in the films was in the range from 20 to 31 at.%, and those of oxygen from 5.6 to 10.7 at.%. For lowerp n andT _s the film delamination was observed.The authors wish to thank J. Sobota from the Institute of Scientific Instruments of ASCR, Brno, for valuable discussions.This work was supported by Grant Agency of the Academy of Sciences of the Czech Republic under Grant No. 202/93/0464.     

Forces and currents in carbon nanostructures: are we imaging atoms?

First-principles calculations show that the rich variety of image patterns found in carbon nanostructures with the atomic force and scanning tunneling microscopes can be rationalized in terms of the chemical reactivity of the tip and the distance range explored in the experiments. For weakly reactive tips, the Pauli repulsion dominates the atomic contrast and force maxima are expected on low electronic density positions as the hollow site. With reactive tips, the interaction is strong enough to change locally the hybridization of the carbon atoms, making it possible to observe atomic resolution in both the attractive and the repulsive regime although with inverted contrast. Regarding STM images, we show that in the near-contact regime, due to current saturation, bright spots correspond to hollow positions instead of atomic sites, providing an explanation for the most common hexagonal pattern found in the experiments.     

Low-threshold parametric Raman generation of high-order Raman components in crystals

The theoretical and experimental study of the axial transient multiwave parametric Raman generation via four-wave mixing of arbitrary neighboring Stokes components in simple tungstate crystals is carried out. In agreement of the theoretical modeling with the experimental results, we have found that because of the four-wave mixing of arbitrary Stokes components in the short crystals, the stimulated Raman scattering (SRS) generation thresholds of the high-order Stokes components are significantly reduced relative to the values defined by the cascade-like mechanism of SRS.     

Hydrogen dissociation over Au nanowires and the fractional conductance quantum

The dissociation of H2 molecules over stretched Au nanowires and its effect on the conductance are analyzed using a combination of density functional theory (DFT) total energy calculations and nonequilibrium Keldysh-Green function methods. Our DFT simulations reproduce the characteristic formation of Au monatomic chains with a conductance close to G0=2e2/h. These stretched Au nanowires are shown to be better catalysts for dissociation than Au surfaces. This is confirmed by the nanowire conductance evidence: while insensitive to molecular hydrogen, atomic hydrogen induces the appearance of fractional conductances (G approximately 0.5G0) as observed experimentally.     

Corrections to the density-functional theory electronic spectrum: copper phthalocyanine

A method for improving the electronic spectrum of standard Density-Functional Theory (DFT) calculations (i.e., LDA or GGA approximations) is presented, and its application is discussed for the case of the copper phthalocyanine (CuPc) molecule. The method is based on a treatment of exchange and correlation in a many-body Hamiltonian, and it leads to easy-to-evaluate corrections to the DFT eigenvalues. Self-interaction is largely corrected, so that the modified energy levels do not suffer from spurious crossings, as often encountered for CuPc in DFT, and they remedy the standard underestimation of the gap. As a specific example we study the sequence and position of the CuPc molecular orbitals, which are wrongly calculated by standard DFT, and show that they are correctly reproduced after our corrections are included. The suggested method is fast and simple and, while not as accurate as hybrid or semiempirical functionals for molecular levels, it can be easily applied to any local-orbital DFT approach, improving on several important limitations of standard DFT methods.     

Power factor of very thin thermoelectric layers of different thickness prepared by laser ablation

Room temperature conductivity and the Seebeck coefficient of thin layers prepared by laser ablation from Bi₂Te₃ target were explored. The power factor was calculated for samples prepared at substrate temperature of 360°C with the density of the laser beam 5 J cm⁻² and at substrate temperature of 410°C with the density of the laser beam 2 J cm⁻² during the deposition. Oscillations of the conductivity and the power factor with the layer thickness were observed at room temperature. The oscillations of conductivity were also verified at the temperature of 77 K. The period of oscillations depends on the preparation conditions. This behavior has been theoretically explained by the quantum size effect in the layers containing different phases and in addition, it was demonstrated by the X-ray Diffraction measurement. The behavior of the power factor of the layers is compared to the behavior of the figure of merit of the layers published earlier.