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1.
《Journal of separation science》2018,41(10):2288-2295
New psychoactive substances represent serious social and health problem as tens of new compounds are detected in Europe annually. They often show structural proximity or even isomerism, which complicates their analysis. Two methods based on ultra high performance supercritical fluid chromatography and ultra high performance liquid chromatography with mass spectrometric detection were validated and compared. A simple dilute‐filter‐and‐shoot protocol utilizing propan‐2‐ol or methanol for supercritical fluid or liquid chromatography, respectively, was proposed to detect and quantify 15 cathinones and phenethylamines in human urine. Both methods offered fast separation (<3 min) and short total analysis time. Precision was well <15% with a few exceptions in liquid chromatography. Limits of detection in urine ranged from 0.01 to 2.3 ng/mL, except for cathinone (5 ng/mL) in supercritical fluid chromatography. Nevertheless, this technique distinguished all analytes including four pairs of isomers, while liquid chromatography was unable to resolve fluoromethcathinone regioisomers. Concerning matrix effects and recoveries, supercritical fluid chromatography produced more uniform results for different compounds and at different concentration levels. This work demonstrates the performance and reliability of supercritical fluid chromatography and corroborates its applicability as an alternative tool for analysis of new psychoactive substances in biological matrixes. 相似文献
2.
Ab initio calculations showed that the tetrachlorodibenzo-para-dioxin radical cations (TCDD RCs) with a planar structure have two steady states with asymmetric dioxin cycles. The activation barriers between these states are up to 2 kcal/mole, so that the RCs may be regarded as being structurally nonrigid within the dioxin cycle. The 2,3,7,8-TCDD RC is more stable than the 1,4,6,9-TCDD RC, the energy difference being 5.2 kcal/mole. The adiabatic ionization potential of 2,3,7,8-TCDD (7.54 eV) is 0.1 eV smaller than the corresponding potential of 1,4,6,9-TCDD. These factors account for the increased hemoproteide affinity and hence increased biological activity of 2,3,7,8-TCDD. 相似文献
3.
The rotational spectra of three low-energy conformers of thiodiglycol (TDG) (HOCH2CH2SCH2CH2OH) have been measured in a molecular beam using a pulsed-nozzle Fourier-transform microwave spectrometer. To determine the likely conformational structures with ab initio approach, conformational structures of 2-(ethylthio)ethanol (HOEES) (CH3CH2SCH2CH2OH) were used as starting points together with the consideration of possible intramolecular hydrogen bonding in TDG. Three lower-energy conformers have been found for TDG at the MP2=Full/6311G** level and ab initio results agree nicely with experimentally determined rotational constants. In addition, Stark measurements were performed for two of the three conformers for dipole moment determinations, adding to our confidence of the conformational structure matches between experimental observations and ab initio calculations. Of the three lower-energy conformers, one displays a compact folded-like structure with strong hydrogen bonding between the two hydroxyl groups and the central sulfide atom. Two other conformers have relatively open chain-like structures with hydrogen bonding between each of the hydroxyl groups to the central sulfur atom, of which one has pure b-type dipole moment according to the ab initio results. 相似文献
4.
Robert H. Crabtree 《Journal of organometallic chemistry》2004,689(24):4083-4091
The title topic is reviewed with emphasis on catalysis and on recent advances. Alkane σ complexes, Shilov chemistry and oxidative addition routes are covered. Attention is also given to σ bond metathesis, surface-bound organometallics and CH activation involving carbene complexes. Closely related reactions of non-alkane substrates such as the Murai reaction are also discussed. 相似文献
5.
聚醚醚酮链结构与反应的模型化合物的量子化学研究 总被引:1,自引:1,他引:0
利用AM1方法对聚醚醚酮模型化合物全优化,结果为:芳环平均相互扭转角为33.0度,桥键角117.0-118.0度,其分子结构拓扑图形表明:所有苯环(核)为平面构型,但其内角扭曲;其氢原子对苯环构型无实质性贡献,在更长链的计算中,冻结苯核与氢原子也得出满意结果,根据Mulliken键序与电荷讨论了醚交换与磺化反应。 相似文献
6.
Enrique J. Baran 《Monatshefte für Chemie / Chemical Monthly》1991,122(6-7):479-481
Summary Mean amplitudes of vibration for OTeF
5
–
have been calculated from known spectroscopic and structural data in a wide temperature range. The results are briefly discussed in comparison with those of related species. 相似文献
7.
Yu. Gangrsky 《Hyperfine Interactions》2006,171(1-3):203-208
This review summarizes the experimental data on charge radii differences among ground state and high spin isomeric states
determined by high-resolution laser spectroscopic methods. A comparison is presented between radii changes obtained from the
isomeric shifts in the atomic spectra and from the quadrupole moments of both ground and isomeric states under the assumption
that the radii changes are determined by the difference of the quadrupole deformations. Special attention is paid to isomers
arising from the break-up of nucleon pairs and isomers of odd–odd nuclei. The characteristic features of the radii changes
for isomeric states of different origin are discussed. 相似文献
8.
Push-pull dithiafulvenes with reduced bond length alternation (BLA) and high optical nonlinearities have been prepared. The interplay between the proaromaticity of the donor and the structural and optical properties of these merocyanines is discussed. The donor ability of dithiafulvenes can reach that of ferrocene or dialkylaminophenyl groups. 相似文献
9.
The behavior of three-dimensional bond fluctuation model chains tethered on an adsorbing flat surface was simulated by the Monte Carlo method. The dependence of the number of surface contacts M on the interaction strength e and the chain length N was investigated by a finite-size scaling law M = N[a0 + a1N1/vk + O((N 1/vk)2)] for e near the critical adsorption point ec, i.e., k ≡(e-ec)/ec closes to 0. The critical adsorption point was estimated to be ec = 0.93, and the exponents 61542; = 0.49 and 1/v= 0.57. 相似文献
10.
H. Serier M. Gaudon A. Demourgues A. Tressaud 《Journal of solid state chemistry》2007,180(12):3485-3492
Zinc hydroxyfluoride (ZnOHF), obtained by coprecipitation of a zinc salt in aqueous HF, exhibits a variable stoichiometry Zn(OH)2−xFx, where x is tuneable from 0.63 to 0.87 by controlling the pH of the solution. The structure was determined from Rietveld refinements using X-ray powder diffraction data. Crystallizing with the orthorhombic symmetry (SG : Pna21), the ZnOHF-type structure exhibits two different anionic sites. A bond valence analysis shows that fluorine exclusively occupies the anionic site that has shorter contacts to zinc. This site is split into two partially occupied sites, one corresponding to the position of a fluoride ion and the other to the position of a hydroxide ion. Bond valence calculations show that the split site model gives a more accurate picture of the local coordination of the anions on this site. 相似文献