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1.
2.
Kammerer B Kahlich R Ufer M Laufer S Gleiter CH 《Rapid communications in mass spectrometry : RCM》2004,18(4):458-464
Phenprocoumon is a commonly used oral anticoagulant of the coumarin type, and has found extensive clinical use in the treatment of thrombophlebitis, pulmonary embolism and atrial fibrillation. In the course of a clinical study to investigate the influence of genetic polymorphisms of the CYP2C9 enzyme on phenprocoumon metabolism, we developed a new enantioselective liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/MS/MS) method to quantify (R)- and (S)-phenprocoumon in human plasma. HPLC separation of the enantiomers was achieved on a Chira-Grom-2 column under isocratic conditions using a water/acetonitrile/formic acid eluent. For detection and quantification a triple-quadrupole MS system was used in the selected reaction monitoring (SRM) mode. As an internal standard the structurally homologous compound warfarin was chosen. The detector response was linear with a correlation coefficient of 0.988-0.999 for (R)-phenprocoumon and 0.989-0.999 for (S)-phenprocoumon in the investigated concentration range between 62.5 and 1000 ng/mL (per enantiomer). The limit of detection (LOD) was 12.5 ng/mL. 相似文献
3.
Ab initio molecular orbital calculations with a double-ζ basis have been carrried out on five models of beryllocene, Cp2Be, with fixed geometries. The lowest energies are obtained for the π-Cp, σ-Cp and D5d models.
The He(I) photoelectron spectrum of Cp2Be was recorded and the ionization potentials of the first bands were compared with the orbital energies obtained from the molecular orbital calculations. A satisfactory fit between experiment and calculations was obtained for a slip sandwich model of Cs symmetry. A model of C5v symmetry is only compatible with the PE spectrum if the Jahn—Teller splitting of the lowest 2E1 state of the molecular ion is exceptionally large, 1.0 eV. 相似文献
4.
The vertical ionization potentials of bis(-allyl)nickel (see (1) in Fig. 1) are calculated by means of the Green's function approach within a semiempirical INDO extension to the first transition metal series. The computed ionization potentials are in good agreement with an experimentally deduced assignment. In contrast to earlier theoretical and experimental studies, the 7a
u
() level is predicted on top of the levels corresponding to the Ni 3d orbitals. Our approach leads to a complete assignment of the PE spectrum of (1) in the outer valence region. 相似文献
5.
The photoelectron spectra of the six propellanes 1 to 6 have been recorded. Those bands which correspond to ejection of an electron from a π-orbital have been assigned, using the concept of through bond and through space interaction. Homoconjugative interaction between the π-systems of the two butadiene moieties of 6 is of the same order as that of the π-orbitals in norbornadiene. 相似文献
6.
The photoelectron(PE)spectrum of tricyclo[3.1.0.02,6] hex-2-ene(benzvalene 1) has been recorded. The first four bands in the PE spectrum of 1 can be assigned to transitions to 2B2, 2A1, 2A2 and 2B1 states of 11. This assignment is discussed in terms of the results of semiempirical and ab initio calculations on 1. Furthermore the highest occupied MO's of 1 are derived qualitatively from an interaction diagram between a distorted bicyclobutane and an ethylene moiety. 相似文献
7.
As a model for the squalene cyclization the interaction between a methyl cation or a methyl radical and two double bonds has been studied using the CNDO/2 and INDO method. In both cases bond formation between the CH3-group and one double bond is facilitated by a second one, but not in a concerted way. 相似文献
8.
From a molecular orbital study of model systems we derive the electronic requirements for the Grob fragmentation. The necessary condition for an allowed fragmentation in an X-C1-C2-C3-N system, or the amino cation +C1-C2-C3-N is the level ordering A below S . This in turn is set by maximal through-bond coupling of the empty cation orbital and the nitrogen lone pair. The conformational dependence of through-bond coupling is exactly that derived by Grob, namely parallel orientation of the cation orbital (or the C-X bond), the C2-C3-σ-bond, and the N-lone-pair. When the C1-C2-C3 and C2-C3-N angles are small, the through-space interaction dominates, reversing the level ordering to S below A , and consequently makes the fragmentation forbidden even though the conformational requirements for it are met. Ring closure becomes allowed. Some examples exploiting this result are presented, as well as procedures for enhancing through-bond coupling and thus fragmentation. The through-bond-effect has also kinetic consequences, allowing the definition of a new type of remote neighbouring group participation operative through bonds and not by direct overlap. The position of equilibria in nitrogen inversion processes should also be influenced by remote substituents which are π-acceptors or donors. 相似文献
9.
The experimental and theoretical basis of a recently proposed reassignment of the bands in the PE. spectra of pyridine, pyridazine, pyrimidine and pyrazine is discussed in detail. A characteristic feature of the derived orbital sequence is that it takes the ‘through-space’ and ‘through-bond’ interaction between the ‘lone pair’ basis orbitals explicitly into account. A simple parametrization of the orbital energies, based on HMO-type models for the π-orbitals and for the ‘lone pair’ linear combinations, yields excellent agreement with the observed band positions in the PE. spectra of s-triazine and s-tetrazine. Our new assignment is compared to those proposed previously. 相似文献
10.
Edgar Heilbronner Rolf Gleiter Toshihiko Hoshi Armin de Meijere 《Helvetica chimica acta》1973,56(5):1594-1604
To obtain further information concerning the interaction between Walsh-orbitols of ‘conjugated’ cyclopropane rings, the photoelectron spectra of the following compounds have been recorded: bicyclo[4.1.0]heptane 1 , cis- and trans-tricyclo[5.1.03, 5]octane 2, 3 , diademane 4 , trans-pentacyclo[3.3.2.02, 9.04, 10, 06, 8]decan 5 and bicyclo[4.1.0]heptene-2 6 . The first bands in the PE.-spectra of these compounds have been assigned on the basis of a ZDO HMO-approximation. For 2 and 4 the value for resonance integral between linked 2p atomic orbitals of two adjacent eclipsed cyclopropane rings is found to be ?1.73 eV. 相似文献