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21.
Pihlainen K Grigoras K Franssila S Ketola R Kotiaho T Kostiainen R 《Journal of mass spectrometry : JMS》2005,40(4):539-545
The suitability of atmospheric pressure desorption/ionization on silicon mass spectrometry (AP-DIOS-MS) and matrix-assisted laser desorption ionization mass spectrometry (AP-MALDI-MS) for the identification of amphetamines and fentanyls in forensic samples was studied. With both ionization techniques, the mass spectra recorded showed abundant protonated molecules, and the background did not disturb the analysis. The use of tandem mass spectrometry (MS/MS) allowed unambiguous identification of the amphetamines and fentanyls. AP-DIOS-MS/MS and AP-MALDI-MS/MS were also successfully applied to the identification of authentic compounds from drug seizures. Common diluents and tablet materials did not disturb the analysis and compounds were unequivocally identified. The limits of detection (LODs) for amphetamines and fentanyls with AP-DIOS-MS/MS were 1-3 pmol, indicating excellent sensitivity of the method. The LODs with AP-MALDI-MS/MS were about 5-10 times higher. 相似文献
22.
Dr. N. Arul Murugan Dr. Kestutis Aidas Dr. Jacob Kongsted Dr. Zilvinas Rinkevicius Prof. Dr. Hans Ågren 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(37):11677-11684
Herein, we explore the use of spin–spin coupling constants (SSCCs) in merocyanine (MCYNE) dyes as indicators of polarity. For this purpose, we use Car–Parrinello hybrid quantum mechanics/molecular mechanics (QM/MM) to determine the structures of MCYNE in solvents of different polarity, followed by computations of the SSCCs by using QM/MM linear‐response theory. The molecular geometry of MCYNE switches between neutral, cyanine‐like, and zwitterionic depending on the polarity of the solvent. This structural variation is clearly reflected in the proton SSCCs in the polymethine backbone, which are highly sensitive to the dielectric nature of the environment; this mechanism can be used as a “polarity indicator” for different microenvironments. This result is highlighted by computing the SSCCs of the MCYNE probe in the cavity of the beta‐lactoglobulin protein. The computed SSCCs clearly indicate a non‐polar hydrophobic dielectric nature of this cavity. 相似文献
23.
Agne Bankauskaite Kestutis Baltakys Gundars Mezinskis 《Journal of Thermal Analysis and Calorimetry》2014,118(2):711-718
In this work, a synthesis route of (Na,K)Mg/Al spinel-type compounds, which combines hydrothermal synthesis at low temperatures (<200 °C) and solid-state sintering (>800 °C) methods, is presented. It was examined that NaOH and KOH additives induce the reaction between initial Mg and Al components and the formation of hydrotalcite during hydrothermal treatment. It should be noted that after 1 h of calcination of synthetic precursors at 850 °C spinel-type compounds are formed only in the samples with alkali addition. Meanwhile in the pure system only traces of the mentioned compounds are observed at 900 °C. Moreover, the increase in solid-state sintering temperature and duration lead to the higher-crystallinity (Na,K)MgAl2O4 spinel-type compounds. It should be noted that textural properties of formed (Na,K)Mg/Al spinel-type compounds depend on the chemical composition of precursors. The synthetic and calcined products are characterised by XRD, STA, FT-IR analyses and BET method. 相似文献
24.
Malinauskas T Tomkute-Luksiene D Daskeviciene M Jankauskas V Juska G Gaidelis V Arlauskas K Getautis V 《Chemical communications (Cambridge, England)》2011,47(27):7770-7772
Star-shaped charge transporting materials with a triphenylamine core and a varying number of diphenylethenyl sidearms, obtained using a one step synthesis procedure from commercially available and relatively inexpensive starting materials and possessing comparatively high hole drift mobility (up to 0.017 cm(2) V(-1) s(-1)), are reported. 相似文献
25.
Ramon Herrero I.V. BarashenkovN.V. Alexeeva Kestutis Staliunas 《Chaos, solitons, and fractals》2011,44(12):1070-1074
We study solitons in the two-dimensional defocusing nonlinear Schrödinger equation with the spatio-temporal modulation of the external potential. The spatial modulation is due to a square lattice; the resulting macroscopic diffraction is rotationally symmetric in the long-wavelength limit but becomes anisotropic for shorter wavelengths. Anisotropic solitons-solitons with the square (x, y)-geometry - are obtained both in the original nonlinear Schrödinger model and in its averaged amplitude equation. 相似文献
26.
We consider the FitzHugh–Nagumo model axon under action of a homogeneous high-frequency stimulation (HFS) current. Using a
multiple scale method and a geometrical singular perturbation theory, we derive analytically the main characteristics of the
traveling pulse. We show that the effect of HFS on the axon is determined by a parameter proportional to the ratio of the
amplitude to the frequency of the stimulation current. When this parameter is increased, the pulse slows down and shrinks.
At some threshold value, the pulse stops and its width becomes zero. The HFS prevents the pulse propagation when the parameter
exceeds the threshold value. The analytical results are confirmed by numerical experiments performed with the original system
of partial differential equations. 相似文献
27.
The transport properties of microcrystalline silicon, namely, mobility and conductivity, are investigated by a new method, for which the simple theory as well as numerical modeling is presented. The basic idea of the new method is verified on amorphous hydrogenated silicon by comparison with the widely used time-of-flight method. Contrary to time of flight, the new method can be used even for relatively conductive materials. Preliminary results on microcrystalline silicon clearly indicate the critical role of amorphouslike tissue in transport in microcrystalline silicon. 相似文献
28.
Balevicius V Balevicius VJ Aidas K Fuess H 《The journal of physical chemistry. B》2007,111(10):2523-2532
The temperature dependencies of NMR shifts in the critical region of two coexisting phases have been simulated using statistical thermodynamics and graph-theory consideration of equilibrium processes of molecular association. Microparameters of magnetic screening of various water and water/pyridine structures used in the statistical averaging have been evaluated by density functional theory calculations (PBE1PBE and B3PW91 functionals in the 6-311++G** basis set). The gauge-including atomic orbital (GIAO) approach has been applied to ensure gauge invariance of the results. Solvent effects were taken into account by a polarized continuum model (PCM). NMR shifts "order parameters" (Deltadelta = |delta+ - delta-|) and "diameters" (phidelta = |(delta+ + delta-)/2 - deltaC|, where delta+, delta-, and deltaC are the chemical shifts of coexisting phases and at the critical point respectively) have been calculated in each case close to the lower critical solution point (TL) and processed using linear regression analysis of Deltadelta approximately |T - TL| and phidelta approximately |T - TL| in the log-log plot. It has been shown that the critical index beta can be evaluated with high precision from the slope of Deltadelta = f(T - TL) at any realistic set of model input parameters. The slope of diameter has been found to depend on both input beta and alpha values. The obtained phidelta slopes (0.58-0.63) are very close to 2beta values. The results are discussed within the concept of complete scaling. Results of simulation are compared and supported by experimental NMR data for water/2,6-lutidine, acetic anhydride/n-heptane, and acetic anhydride/cyclohexane systems. 相似文献
29.
Aidas K Møgelhøj A Kjaer H Nielsen CB Mikkelsen KV Ruud K Christiansen O Kongsted J 《The journal of physical chemistry. A》2007,111(20):4199-4210
The gas-to-aqueous solution shifts of the 17O and 13C NMR isotropic shielding constants for the carbonyl chromophore in formaldehyde and acetone are investigated. For the condensed-phase problem, we use the hybrid density functional theory/molecular mechanics approach in combination with a statistical averaging over an appropriate number of solute-solvent configurations extracted from classical molecular dynamics simulations. The PBE0 exchange-correlation functional and the 6-311++G(2d,2p) basis set are used for the calculation of the shielding constants. London atomic orbitals are employed to ensure gauge-origin independent results. The effects of the bulk solvent molecules are found to be crucial in order to calculate accurate solvation shifts of the shielding constants. Very good agreement between the computed and experimental solvation shifts is obtained for the shielding constants of acetone when a polarizable water potential is used. Supermolecular results based on geometry-optimized molecular structures are presented. We also compare the results obtained with the polarizable continuum model to the results obtained using explicit MM molecules to model the bulk solvent effect. 相似文献
30.
Anatoly M. Zyakun Artem I. Muravyev Boris P. Baskunov Kestutis S. Laurinavichius Vladimir N. Zakharchenko Valentina P. Peshenko 《Isotopes in environmental and health studies》2013,49(1):78-90
Using a theoretical model and mass isotopic balance, biogas (methane and CO2) released from buried products at their microbial degradation was analysed in the landfill of municipal and non-toxic industrial solid organic waste near Kaluga city, Russia. The landfill contains about 1.34×106 tons of waste buried using a ‘sandwich technique’ (successive application of sand–clay and waste layers). The δ13C values of biogenic methane with respect to CO2 were?56.8 (±2.5) ‰, whereas the δ13C of CO2 peaked at+9.12‰ (+1.4±2.3‰ on average), reflecting a virtual fractionation of carbon isotopes in the course of bacterial CO2 reduction at the landfill body. After passing through the aerated soil layers, methane was partially oxidised and characterised by δ13C in the range of?50.6 to?38.2‰, evidencing enrichment in 13C, while the released carbon dioxide had δ13C of?23.3 to?4.04‰, respectively. On the mass isotopic balance for the δ13C values, the methane production in the landfill anaerobic zone and the methane emitted through the aerated landfill surface to the atmosphere, the portion of methane oxidised by methanotrophic bacteria was calculated to be from 10 to 40% (averaged about 25%). According to the theoretical estimation and field measurements, the annual rate of methane production in the landfill reached about 2.9(±1.4)×109 g C CH4 yr?1 or 5.3(±2.6)×106 m3 CH4 yr?1. The average rates of methane production in the landfill and methane emission from landfill to the atmosphere are estimated as about 53 (±26) g C CH4 m?2 d?1 (or 4 (±2) mol CH4 m?2 d?1) and 33 (±12) g C CH4 m?2 d?1 (or 2.7 (±1) mol CH4 m?2 d?1), respectively. The calculated part of methane consumed by methanotrophic bacteria in the aerated part of the landfill was 13(±7) g C CH4 m?2 d?1 (or 1.1(±0.6) mol CH4 m?2 d?1) on average. 相似文献