We report ab initio spectroscopic constants for the recently identified 1(5)Π(g) state of C(2) [P. Bornhauser, Y. Sych, G. Knopp, T. Gerber, and P. P. Radi, J. Chem. Phys. 134, 044302 (2011)]. The calculations are performed at the multi-reference configuration interaction level of theory with Davidson's correction using aug-cc-pV6Z basis sets and include core-valence correlation and relativistic corrections obtained with quadruple-zeta bases. Such treatment accurately reproduces the experimentally observed constants of the a(3)Π(u) and other states. Thus, we expect our calculated ω(e) value for the 1(5)Π(g) state to be within a few cm(-1), and rotational constants to be within 0.1% of experiment. Agreement with available spectroscopic data is excellent, with the calculations strongly suggesting that the 1(5)Π(g) vibrational level observed by Bornhauser et al. is v = 0. 相似文献
Stereoselective CE method for investigations of pharmacokinetics of ketoprofen enantiomers (KTP) in patients taking also other drugs is proposed, to establish relation between levels of KTP enantiomers in blood and synovial fluid of patients with rheumatoid arthritis. Resolution of the analytes was obtained in silica capillary filled with chiral selector-heptakis 2,3,6-tri-O-methyl–β-cyclodextrin in triethanolamine-phosphate buffer. Calibration curves for enantiomers in plasma and synovial fluid were linear in the range of 0.25–50.0 mg L−1, but 1.0–250.0 mg L−1 in urine. Concentrations of KTP enantiomers in synovial fluid measured at 4 h after the administration of a tablet with racemic KTP were insignificantly greater [(−)-R = 1.07 ± 0.66; (+)-S-KTP = 1.13 ± 0.65 mg L−1] than in plasma [(−)-R = 0.86 ± 0.37; (+)-S-KTP = 0.96 ± 0.42 mg L−1]. The validated method has been successfully applied for the determination of KTP enantiomers in biological fluids of patients with rheumatoid arthritis.
The present study aimed at determining selected alkaloid components in the nectar of Datura species, to elucidate whether the alkaloid content of the floral nectar can lead to intoxication. A simple and rapid liquid chromatography coupled with electrospray mass spectrometry analysis was developed for the quantitative determination of atropine and scopolamine, the main toxic alkaloids of the Datura species. This method allowed the direct coupling of an electrospray mass selective detector to the LC system. Under these conditions, atropine and scopolamine were well separated from other components and detected with mass spectrometry (mass selective detector). Simultaneous determination of atropine and scopolamine was performed with gradient elution on an Ascentis Express C18 (Supelco) reversed-phase column based on a new fused core particle design. Liquid chromatography coupled with electrospray mass spectrometry was used in positive ion mode. Atropine and scopolamine produced protonated species at m/z 290 and 304 (which are also the base peaks). Our data confirmed that the alkaloid characteristics for the vegetative and reproductive parts of the Datura plants may also occur in the nectar secreted by the flowers. In Datura species with large flowers and high nectar amounts, the alkaloid content increases proportionately and thus the nectar may be a potential source of intoxication. 相似文献
Finite field perturbation theory coupled with configuration interaction techniques have been used to evaluate the components of the polarisability tensor of H2 at and near its equilibrium internuclear separation. The values are fitted to a polynomial which then yields the derivatives of the polarisability with respect to internuclear distance. Our results compare favourably with theoretical values obtained by the use of highly accurate correlated wavefunctions. 相似文献
Quantum chemistry computations have been used to investigate hydrogen-atom abstraction by chlorine atom from protonated and N-acetylated amino acids. The results are consistent with the decreased reactivity at the backbone α-carbon and adjacent side-chain positions that is observed experimentally. The individual effects of NH(3)(+), COOH, and NHAc substituents have been examined and reveal important insights. The NH(3)(+) group in isolation is found to be deactivating at the α-position, while the acetamido group is activating. For the COOH group, polar effects lead to a contrathermodynamic deactivation of the thermodynamically most favorable α-abstraction. In the N-acetylamino acid, the α-position is deactivated by the combined inductive effect of the substituents and the presence of an early transition structure, again overriding the greater thermodynamic stability of the α-centered radical product. Deactivation of the α-, β-, and γ-positions results in a peculiar stability for amino acids and peptides and their derivatives with respect to radical degradation. 相似文献
An investigation of the factors responsible for the sense and magnitude of regioselectivity in the Sharpless asymmetric aminohydroxylation (AA) has been conducted. Theoretical investigations of ligand-osmium binding geometry and experimental investigations of the Sharpless AA reaction on a series of functionalized pent-2-enoic acid ester substrates demonstrate that the opposite regioselectivity afforded using PHAL and AQN ligands results from a change in substrate orientation with respect to the catalyst. Two distinct ligand binding domains within the catalyst have been proposed that undergo attractive interactions with the substrates. Selective access to each of the four potential regio- and stereo-isomeric AA products could be achieved through the appropriate choice of ligand and substrate. These results have been applied toward the efficient stereoselective synthesis of naturally occurring and regioisomeric 3- and 4-aminosugar derivatives. 相似文献
The 1,4-pentadienyl (vinylallyl) radical has been observed for the first time by optical spectroscopy. An excitation spectrum is recorded on m/z 67 by resonant two-color two-photon ionization spectroscopy. Several bands are observed with the origin transition identified at 19 449 cm(-1). The spectrum is assigned by a comparison with ab initio frequencies calculated at the CASPT2/cc-pVTZ level of theory, with an accompanying Franck-Condon calculation of the excitation spectrum, including Dushinsky mixing. The b(1) and a(2) outer C-C bond torsional modes are calculated to halve in frequency upon electronic excitation, bringing about their appearance in the excitation spectrum. This can be readily understood by considering the torsional sensitivity of the frontier molecular orbital energies. High-level quantum chemical calculations of the radical stabilization energy, resulting in a value of nearly 120 kJ mol(-1), provide quantitative confirmation that this radical is highly stabilized. 相似文献
A method is reported for measuring Se and Sn in human brain tissue. The patients from whom the samples were taken had no
diseases in their central nervous system. Microwave energy was applied to digest the brain samples. The digested samples were
analyzed without dilution by transversely heated graphite atomizer for atomic absorption spectrometry with longitudinal Zeeman
background correction. The dependence of integrated absorbance on various chemical modifiers has been examined. The most appropriate
technique proved to be 5 μl sample injection using 20 μg prereduced palladium-nitrate for Se determination, and 20 μl sample
injection applying 10 μg palladium-nitrate + 3 μg magnesium-nitrate for the measurements of Sn. The optimal temperature program
was found to be 1200 °C pyrolysis and 2100 °C atomisation temperature for Se and 1500 °C pyrolysis and 2300 °C atomisation
temperature for Sn. Accuracy of the applied techniques was tested by the analysis of standard reference materials. The precision
was ±5% for Se and ±10% for Sn. The range of recovery values was 85–95% for Se and 95–105% for Sn. The mean Se concentrations
in the investigated brain parts ranged from 200 to 700 ng/g, while the Sn concentrations were between 20 and 300 ng/g dry
weight.
Received October 3, 2000. Revision February 1, 2001. 相似文献