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101.
D. Andrae U. Häußermann M. Dolg H. Stoll H. Preuß 《Theoretical chemistry accounts》1990,77(2):123-141
Summary Nonrelativistic and quasirelativisticab initio pseudopotentials substituting the M(Z–28)+-core orbitals of the second row transition elements and the M(Z–60)+-core orbitals of the third row transition elements, respectively, and optimized (8s7p6d)/[6s5p3d]-GTO valence basis sets for use in molecular calculations have been generated. Additionally, corresponding spin-orbit operators have also been derived. Atomic excitation and ionization energies from numerical HF as well as from SCF pseudopotential calculations using the derived basis sets differ in most cases by less than 0.1 eV from corresponding numerical all-electron results. Spin-orbit splittings for lowlying states are in reasonable agreement with corresponding all-electron Dirac-Fock (DF) results. 相似文献
102.
The thermal expansion properties of crystalline organic compounds are investigated by data mining of the Cambridge Structural Database (CSD). The mean volumetric thermal expansion coefficient is 168.8 × 10−6 K−1 and the mean uniaxial thermal expansion coefficient is 71.4 × 10−6 K−1, based on 745 and 1129 different observations, respectively. Normal and anomalous coefficients can be identified using these values and the associated standard deviations. The anisotropy of the thermal expansion is also evaluated and found to have a very broad distribution. 4719 different structures, comprising 4093 different molecular compounds and 626 additional polymorphs have been analyzed on their thermal expansion properties. Approximately 34% of these structures may have at least one orthogonal axis with negative thermal expansion, much more than generally believed. Moreover 127 structures have been identified which could have negative volumetric thermal expansion. Experimental validation using a robust protocol with data collected at more than 2 different temperatures is required to validate these cases.The thermal expansion properties of crystalline organic compounds are investigated by data mining of the Cambridge Structural Database (CSD). Negative uniaxial thermal expansion is much more common than generally believed. 相似文献
103.
Dhont GS van Lenthe JH Groenenboom GC van der Avoird A 《The Journal of chemical physics》2005,123(18):184302
We present the ab initio potential-energy surfaces of the NH-NH complex that correlate with two NH molecules in their 3sigma- electronic ground state. Three distinct potential-energy surfaces, split by exchange interactions, correspond to the coupling of the S(A) = 1 and S(B) = 1 electronic spins of the monomers to dimer states with S = 0, 1, and 2. Exploratory calculations on the quintet (S = 2), triplet (S = 1), and singlet (S = 0) states and their exchange splittings were performed with the valence bond self-consistent-field method that explicitly accounts for the nonorthogonality of the orbitals on different monomers. The potential surface of the quintet state, which can be described by a single Slater determinant reference function, was calculated at the coupled cluster level with single and double excitations and noniterative treatment of the triples. The triplet and singlet states require multiconfiguration reference wave functions and the exchange splittings between the three potential surfaces were calculated with the complete active space self-consistent-field method supplemented with perturbative configuration interaction calculations of second and third orders. Full potential-energy surfaces were computed as a function of the four intermolecular Jacobi coordinates, with an aug-cc-pVTZ basis on the N and H atoms and bond functions at the midpoint of the intermolecular vector R. An analytical representation of these potentials was given by expanding their dependence on the molecular orientations in coupled spherical harmonics, and representing the dependence of the expansion coefficients on the intermolecular distance R by the reproducing kernel Hilbert space method. The quintet surface has a van der Waals minimum of depth D(e) = 675 cm(-1) at R(e) = 6.6a0 for a linear geometry with the two NH electric dipoles aligned. The singlet and triplet surfaces show similar, slightly deeper, van der Waals wells, but when R is decreased the weakly bound NH dimer with S = 0 and S = 1 converts into the chemically bound N2H2 diimide (also called diazene) molecule with only a small energy barrier to overcome. 相似文献
104.
Aalders MC van der Vange N Star WM Sterenborg HJ 《Photochemistry and photobiology》2001,74(2):311-317
The in vivo pharmacokinetics of protoporphyrin IX (PpIX) after administration of 5-aminolevulinic acid (ALA) cannot be described accurately by mathematical models using first-order rate processes. We have replaced first-order reaction rates by dose-dependent (Michaelis-Menten [MM]) reaction rates in a mathematical compartment model. Different combinations of first-order and dose-dependent reaction rates were evaluated to see which one would improve the goodness-of-fit to experimentally determined in vivo PpIX fluorescence kinetics as a function of concentration. The mathematical models that were evaluated are all based on a three-compartment model for drug distribution, conversion to PpIX and subsequent conversion to heme. Implementation of dose-dependent reaction rates improved the goodness-of-fit and enabled interpolation to other drug doses. For most data sets the time constant for delivery to the target cells turned out to be dose dependent. For all data sets the use of MM rates for the conversion of ALA to PpIX yielded better fits. The clearance of PpIX turned out to be a first-order process for all doses and types of administration. Fluorescence curves measured on a specific tissue type but obtained in different studies with different measurement techniques could be described with a single set of parameters. 相似文献
105.
E. Röder I. Pigulla und J. Troschütz 《Fresenius' Journal of Analytical Chemistry》1977,288(1-2):56-58
Zusammenfassung Die Trennung und quantitative Bestimmung von fünf biogenen aliphatischen Aminen aus wäßriger Lösung gelingt mit Hilfe der Hochdruckflüssig-Chromatographie. Dabei werden die Amine als Derivate der Chinolin-8-sulfonsäure mit einem Vierkomponenten-Verteilungssystem chromatographiert. Die Eichkurven sind im vermessenen Gewichtsbereich linear, die Erfassungsgrenze liegt bei ca. 20 ng. Norephedrin dient als interner Standard.
High-pressure liquid chromatographic determination of aliphatic biogenic amines after derivatization with quinoline-8-sulphonic acid chloride
Summary High-speed liquid chromatography is shown to be useful for the separation and quantitation of five aliphatic biogenic amines in aqueous solution. The amines are converted into derivates of quinoline-8-sulphonic acid and chromatographed with a four-component two-phase system. Calibration curves are linear within the tested range of weight. The sensivity is about 20 ng. Norephedrine is used as internal standard.
Unser Dank gilt der Deutschen Forschungsgemeinschaft für großzügige finanzielle Unterstützung dieser Arbeit sowie dem Fonds der Chemischen Industrie für die Bereitstellung von Sachbeihilfen. 相似文献
106.
The molecular electric dipole moments are reported for the series of tin-substituted tetracarbonyl cobalt compounds RnYm?nSn{Co(CO)4}4?m (m = 1–3; n ? m; R = alkyl, phenyl; Y = halogen). The effect of the substituents at the tin atom on the nature of the CoSn bond is established on calculating the (CO)4CoSn group dipole moments. It is shown that the charge transfer in the CoSn bond is mainly determined by the inductive properties of the ligands attached to tin. 相似文献
107.
Winfried Haumesser Werner Gerlach und Claus -Henning Röder 《Fresenius' Journal of Analytical Chemistry》1977,287(4-5):291-295
Zusammenfassung Eine direkte maßanalytische Methode zur Bestimmung diverser Carbamate wird beschrieben. Die potentiometrische Titration mit käuflicher Tetra-n-butylammoniumhydroxid-Lösung, verdünnt mit Propanol-(2), ist bequem durchzuführen, und die erhaltenen Titrationskurven gestatten eine korrekte Auswertung.
Direct volumetric determination of carbamates as very weak acids
Summary A volumetric procedure for the determination of some carbamates is described. The potentiometric titration with commercial tetra-n-butylammonium hydroxide solution diluted with propanol-(2) is convenient and the obtained titration curves permit a correct calculation.相似文献
108.
A microwave-assisted click chemistry synthesis of 1,4-disubstituted 1,2,3-triazoles via a copper(I)-catalyzed three-component reaction 总被引:4,自引:0,他引:4
A microwave-assisted three-component reaction was used to prepare a series of 1,4-disubstituted-1,2,3-triazoles from corresponding alkyl halides, sodium azide, and alkynes. This procedure eliminates the need to handle organic azides, as they are generated in situ, making this already powerful click process even more user-friendly and safe. 相似文献
109.
Macásek F Brúder P Patakyová A Búriová E 《European journal of mass spectrometry (Chichester, England)》2003,9(2):129-137
2-Fluoro-2-deoxy-D-glucose (FDG) labeled by fluorine-18 is the most widely used radiopharmaceutical for positron emission tomography (PET). For high-performance liquid chromatography (HPLC)/MS assay and quality control, the mass spectra of FDG and glucose (Glc) in organic + water solutions were studied by flow injection analysis (FIA) and in a chromatographic eluate. In acetonitrile (MeCN) + 0.025% ammonium formate (NH(4)HCO(2)) solvent (80 : 20), electrospray ionisation (ESI) of glucose-FDG provides M.NH(4)(+) and 2M.Na(+) (M = Glc or FDG) as the most intense positive ions. Formation of the latter ions and also of M.MeCN.Na(+) and 2MeCN. Na(+) is typical of the presence of NaCl in the ESI inlet. The positive ions include heavier ions corresponding to the impurities separated by HPLC and also to the cross-ring fragmentation of complexes (2FDG. aMeCNX)L, where a = 0 or 1, L is either Na(+) or NH(4)(+) and X is a fragmented pyranose or anhydropyranose residue. The second most abundant Glc negative ion is m/z = 359 which was interpreted as (2GlcH(+))(). The negative-ion spectrum of FDG has dominating lines due to FDG.HCO(2)() ions at m/z 227 and also (2FDGH(+))() at m/z 363. The m/z 363 signal is suppressed in the presence of NaCl at a molar ratio of 4 : 1 to NH(4)HCO(2), while the ions at m/z 217 and 219, i.e. FDG.Cl(), become three times more intense than FDG.HCO(2)(). The latter ion appears to be most suitable as an analytical signal for chemical analysis of FDG at m/z 226 and 227. Limits of FDG quantitation (LOQ) of 19 ng and 21 ng were found for the 200(+) and 227() ion signals, respectively, and are wholly adequate for verification of total FDG content in radiopharmaceuticals. 相似文献
110.
TRANSMISSION OF HUMAN EPIDERMIS AND STRATUM CORNEUM AS A FUNCTION OF THICKNESS IN THE ULTRAVIOLET AND VISIBLE WAVELENGTHS 总被引:8,自引:1,他引:8
Wiel A. G. Bruls H. Slaper Jan C. van der Leun L. Berrens 《Photochemistry and photobiology》1984,40(4):485-494
Abstract The dependence of radiation transmission on sample thickness was studied in isolated samples of human stratum corneum and full-thickness epidermis. The investigation also included samples of skin repeatedly exposed to UV-B. Transmission was measured in the ultraviolet and in the visible from 248–546 nm. Two methods, one microscopic and the other mechanical, were used to measure thickness. There was a good correlation between the results.
The dependence of transmission on thickness in these samples could be described satisfactorily by an exponential function, implying that the Lambert-Beer law is approximately valid. Thus, a single parameter, such as the half-value layer ( d½ ), is sufficient to characterize absorption in the skin samples.
Water content of the isolated stratum corneum was influenced by maintenance conditions: samples floating on water containing a small amount of NaCl were more hydrated than samples floating on a more concentrated salt solution, or stored in air. Changes in water content of the samples resulted in changes of thickness and, to a lesser extent, of transmission. Approximate in vivo values of d½ were computed after estimating the in vivo water content of stratum corneum.
Differences found in the shape of the transmission spectra of stratum corneum and full-thickness epidermis may reflect differences in chemical composition. The influence of wetting of the skin on its sensitivity to sunlight is explained in a new way. 相似文献
The dependence of transmission on thickness in these samples could be described satisfactorily by an exponential function, implying that the Lambert-Beer law is approximately valid. Thus, a single parameter, such as the half-value layer ( d
Water content of the isolated stratum corneum was influenced by maintenance conditions: samples floating on water containing a small amount of NaCl were more hydrated than samples floating on a more concentrated salt solution, or stored in air. Changes in water content of the samples resulted in changes of thickness and, to a lesser extent, of transmission. Approximate in vivo values of d
Differences found in the shape of the transmission spectra of stratum corneum and full-thickness epidermis may reflect differences in chemical composition. The influence of wetting of the skin on its sensitivity to sunlight is explained in a new way. 相似文献