The separation of the enantiomers of diquats by capillary electrophoresis using randomly sulfated cyclodextrins as chiral selectors

Diquats, derivatives of the widely used herbicide diquat, represent a new class of functional organic molecules. A combination of their special electrochemical properties and axial chirality could potentially result in their important applications in supramolecular chemistry, chiral catalysis, and chiral analysis. However, prior to their practical applications, the diquats have to be prepared in enantiomerically pure forms and the enantiomeric purity of their P- and M-isomers has to be checked. Hence, a chiral capillary electrophoresis (CE) method has been developed and applied for separation of P- and M-enantiomers of 11 new diquats. Fast and better than baseline CE separations of enantiomers of all 11 diquats within a short time 5–7 min were achieved using acidic buffer, 22 mM NaOH, 35 mM H₃PO₄, pH 2.5, as a background electrolyte, and 6 mM randomly sulfated α-, β-, and γ-cyclodextrins as chiral selectors. The most successful selector was sulfated γ-cyclodextrin, which baseline separated the enantiomers of all 11 diquats, followed by sulfated β-cyclodextrin and sulfated α-cyclodextrin, which baseline separated enantiomers of 10 and nine diquats, respectively. Using this method, a high enantiopurity degree of the isolated P- and M-enantiomers of three diquats with a defined absolute configuration was confirmed and their migration order was identified.     

Carrier mobility in nonstoichiometric n-Bi2Te3−x Sex solid solutions

A study has been made of the thermoelectric and galvanomagnetic properties of n-Bi₂Te_3−x Se_x solid solutions (x=0.3 and 0.36) in the temperature range 80–300 K. The lowest carrier concentrations, (0.8–1)×10¹⁸ cm⁻³, were obtained by displacing the solid solution from the stoichiometric to a Te-rich composition. At such carrier concentrations, the second subband in the conduction band of n-Bi₂Te_3−x Se_x is not filled, which results in a growth of mobility because of the absence of interband scattering, and brings about an increase of thermoelectric efficiency in the 80–120-K range. Fiz. Tverd. Tela (St. Petersburg) 39, 483–487 (March 1997)     

Multiphoton-induced X-ray emission and amplification from clusters

The development of a unified picture of short-pulse high-intensity multiphoton processes, embracing atoms, molecules, and solids, appears possible through the study of clusters. Of particular significance are possible intra-cluster processes that can influence the mechanism of ionization and lead to the production of inner-shell vacancies. Inner-shell excitation leading to prompt X-ray emission is specifically considered and the treatment leads to the definition of a critical cluster size n _c representing the achievement of maximal X-ray emission from the ensemble. These results suggest the possibility of designing a new class of molecular materials optimized for the efficient production and amplification of X-rays.