An overview of the state-of-the-art in LC enantiomer separation is presented. This tutorial review is mainly focused on mechanisms of chiral recognition and enantiomer distinction of popular chiral selectors and corresponding chiral stationary phases including discussions of thermodynamics, additivity principle of binding increments, site-selective thermodynamics, extrathermodynamic approaches, methods employed for the investigation of dominating intermolecular interactions and complex structures such as spectroscopic methods (IR, NMR), X-ray diffraction and computational methods. Modern chiral stationary phases are discussed with particular focus on those that are commercially available and broadly used. It is attempted to provide the reader with vivid images of molecular recognition mechanisms of selected chiral selector–selectand pairs on basis of solid-state X-ray crystal structures and simulated computer models, respectively. Such snapshot images illustrated in this communication unfortunately cannot account for the molecular dynamics of the real world, but are supposed to be helpful for the understanding. The exploding number of papers about applications of various chiral stationary phases in numerous fields of enantiomer separations is not covered systematically. 相似文献
The design characteristics of the optical cuvette suggested here provide the possibility of accomplishing the uniaxial orientation
of gels with retention of the constancy of their volume, which makes it possible to carry out highly accurate polarization
measurements with commercial spectropolarimeters in directions parallel and perpendicular to the axis of orientation. Using
as examples polyacrylamide gels containing biologically important molecules and membranes, the possibility of measuring absorption
spectra, the linear dichroism, and the dispersion of optical rotation is demonstrated.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 286–289, March–April, 1999. 相似文献
We report a quantitative measure of the nonexponential 1H spin–lattice relaxation resulting from methyl group (CH3) rotation in six polycrystalline van der Waals solids. We briefly review the subject in general to put the report in context. We then summarize several significant issues to consider when reporting 1H or 19F spin–lattice relaxation measurements when the relaxation is resulting from the rotation of a CH3 or CF3 group in a molecular solid. 相似文献
The rotational spectra of four isotopologues of the 1:1 complex between chloromethane and water revealed the presence of only one rotamer in a pulsed jet expansion. The two subunits are linked through two weak hydrogen bonds, O? H???Cl (RH???Cl=2.638(2) Å) and C? H???O (RH???O=2.501(2) Å), forming a five‐membered ring. All transitions display the hyperfine structure due to the 35Cl (or 37Cl) nuclear quadrupole effects. Dynamical features in the spectrum are caused by two large‐amplitude motions. Each component line appears as an asymmetric doublet with a relative intensity ratio of 1:3. The splittings led to the determination of barrier to internal rotation of water around its symmetry axis, V2=320(10) cm?1. Finally, an unexpected small value of the inertial defect (?0.96 uÅ2 rather than ?3.22 uÅ2) allowed the estimation of the barrier to the internal rotation of the CH3 group, V3≈8 cm?1. 相似文献
This paper discusses experimental results from a multiple cavity test rig representative of a high pressure compressor internal air system. Measurements of the axial, tangential and radial velocity components are presented. These were made using a two component, laser doppler anemometry (LDA) system for a range of non-dimensional parameters representative of engine conditions (Re up to 4 × 106 and Rez up to 1.8 × 105). Tests were carried out for two different sizes of annular gap between the (non-rotating) drive shaft and the disc bores.
The axial and radial velocities inside the cavities are virtually zero. The size of the annular gap between disc bore and shaft has a significant effect on the radial distribution of tangential velocity. For the narrow annular gap (dh/b = 0.092), there is an increase of non-dimensional tangential velocity V/Ωr with radial location from V/Ωr < 1 at the lower radii to solid body rotation V/Ωr = 1 further into the cavity. For the wider annular gap (dh/b = 0.164), there is a decrease from V/Ωr > 1 at the lower radii to solid body rotation further into the cavity. An analysis of the frequency spectrum obtained from the tangential velocity measurements is consistent with a flow structure in the r– plane consisting of pairs of contra rotating vortices. 相似文献