Chiral separations of piperidine-2,6-dione analogues on Chiralpak IA and Chiralpak IB columns by using HPLC

Recently, two new immobilized polysaccharides based CSPs, namely tris-(3,5-dimethylphenylcarbamate) derivatives of amylose and cellulose known as Chiralpak IA and Chiralpak IB were introduced, which may be used with a wide range of solvents including standard and prohibited ones. Several racemic piperidine-2,6-dione analogues [aminoglutethimide, p-nitro-glutethimide, p-nitro-5-aminoglutethimide, cyclohexylaminoglutethimide, phenglutarimide and thalidomide] have been resolved on Chiralpak IA and Chiralpak IB columns (25 cm × 0.46 cm). The non-conventional mobile phases used were methyl-tert-butyl ether-THF (90:10, v/v) [I], 100% dichloromethane [II] and 100% acetonitrile [III] separately at a flow rate of 1.0 mL/min using a UV detector at 254 nm. The resolution factors for Chiralpak IA and Chiralpak IB columns were 1.00-5.33 and 0.33-0.67, respectively. Chiralpak IA column gave better results than Chiralpak IB column for the reported molecules using the developed HPLC conditions. Experimental conditions and the possible chiral recognition mechanisms have been discussed.     

Cycloisomerization of activated (2E,4Z)-heptatrienoate and its relevance to crispatene (bio)synthesis. A case of concerted and stepwise uncertainty

A single transition structure was located on the potential energy surface of the cycloisomerization of protic and Lewis acid activated (2E,4Z)-heptatrienal and the corresponding methyl ester to provide the bicyclo[3.1.0]hexene derivatives, the central skeleton of the crispatene natural products. A two-dimensional scan of the C-C bond-forming reactions revealed a barrierless cyclopropane closure following the pentadienyl cycloisomerization, with preservation of the stereochemical information.     

Regio‐, Peri‐, and Torquoselectivity in Hydroxy Heptatrienyl Cation Electrocyclizations: The Iso/Homo‐Nazarov Reaction

Competition : The electrocyclizations of 1‐ and 3‐hydroxyheptatrienyl cations (see scheme) have been computationally studied at the B3LYP/6‐311G(d) level. The 1‐hydroxy system clearly favors a 4e^? over a 6e^? process, while for the 3‐hydroxy isomer these mechanisms compete.

     

Kinetic Instability of Anisotropic Drift Wave Accompanied by Field Aligned Currents in Solar Coronal Loop

Solar coronal loops are frequently accompanied by the field-aligned currents, which drive instabilities if the drift velocity u0 v A the Alfv′en velocity. For our choice of parameters, the critical threshold value of u0/v A is ～ 3.0 for growth and the corresponding current filling factor ～ 10-3-10-4. Below this value we are no longer in the kinetic regime.The coronal loops also have short-scale density gradients within each loop. The electron resonance in the presence of density gradient causes the drift mode to grow. We study the effect of these two free energy sources, the electron drift and the density gradient, in the presence of temperature anisotropy T⊥_α T∥_α. These effects simultaneously exist in the coronae. Using gyrokinetic theory, we investigate the influence of these effects, examine how they interplay with each other and study the consequent growth of the magnetosonic wave. We observe that kinetic instability driven by density gradient can be suppressed by field-aligned currents. The temperature anisotropy with chosen signatures causes further stabilizing effect. The results may prove useful to study the heating mechanism of solar coronal loops, acceleration of particles and confinement of particles in the thermonuclear reactors.     

Damping in the Interaction of a Field and Two Three-Level Atoms Through Quantized Caldirola–Kanai Hamiltonian

We investigate the damped interaction between two Λ-type three-level atoms and a quantized single-mode cavity field, for which the Hamiltonian of the field is rewritten in Caldirola–Kanai form. We obtain the wave functions for the case where the two atoms are initially prepared in arbitrary pure states and the field is initially prepared in the coherent state. We investigate numerically the influence of the damping parameter on the temporal behavior of the Mandel Q-parameter, linear entropy, and normal squeezing. We find the damping parameter and initial atomic states to play central roles in the nonclassical features and the degree of entanglement.     

2-Alkylidenesulfol-3-enes by (regio- and) stereoselective cheletropic addition of SO2 to (di)vinylallenes

[reaction: see text] The cheletropic addition of SO(2) to divinylallenes is regioselective, taking place at the most substituted vinylallene and at the E unit if vinyl groups of opposite geometry are competing. Diastereofacial differentiation results from the approach of the reagent from the less-substituted direction of the allene and from the concomitant disrotatory movement of the termini of the vinylallene to afford the sterically more congested 2-alkylidenesulfol-3-ene isomer. DFT computations confirm the regio- and the stereoselectivity of these cheletropic additions.     

Electric quadrupole interaction of 212Rn isomers in Bi

The electric quadrupole interaction of the ²¹² Rn 8⁺ and 6⁺ isomers in a Bi single crystal was measured. The experimental results together with a shell-model calculation of the quadrupole moments provide a calibration of the electric field gradient for Rn impurities in Bi, to be used in future quadrupole-moment measurements of Rn isomers. A two-level analysis procedure was employed for the combined data of the 8⁺ and 6⁺ isomers.     

Solubilization of paraffin gases in aqueous solutions of sodium octanoate

The solubilities of methane, ethane, propane and n-butane were measured in aqueous solutions of sodium octanoate of molar concentrations between 0–0.8M. From these measurements we have computed the standard free energies, entropies and enthalpies for the process of transferring the solute molecules from the gaseous phase into the solutions. We found that propane and n-butane behave as expected at, and beyond, the cmc, namely the solubility takes a steep turn upwards. On the other hand, methane and ethane seem to cross the cmc with almost no change in their solubility. A tentative interpretation of this behavior is suggested, based on the competing effects of salting out and solubilization.     

Analytical applications of ultraviolet resonance Raman spectroscopy

UV resonance Raman spectroscopy (UVRR) is a new analytical technique with a unique selectivity which is capable of speciating individual analytes in complex samples. The new instrumentation is discussed as are applications of this technique to studies of polycyclic aromatic hydrocarbons (PAHs) in coal liquids and in tissue. UVRR can also be used to speciate PAHs eluting from high-performance liquid chromatography columns. Other applications to studies of protein structure are also described.     

High Temperature Liquid Chromatography of Tocol-Derivatives on Polybutadiene-Coated Zirconia Stationary Phases

High temperature reversed-phase high performance liquid chromatography is evaluated as a new approach for the separation of vitamin E isomers (α-, γ-, δ-tocopherol, and α-, γ-, δ-tocotrienol) and α-tocopherol acetate. The separations of each analyte were examined by varying the eluent composition and column temperature. Using a polybutadiene-coated zirconia column at temperatures of 80 °C–140 °C, complete separations were achieved within 10–20 min using organic modifier (acetonitrile) in the range of 40–50%. Irregularity of the Van’t Hoff analysis was noted over the temperature studied. The plot tends to deviate from linearity at higher operating temperatures (140 °C and 150 °C) with linear deviation errors of 12.7% and 41.6%, respectively, for the mobile phase examined.