The RS-.HSR Hydrogen Bond: acidities of alpha,omega-dithiols and electron affinities of their monoradicals

Gas-phase acidities (deltaGo(acid)) have been measured for 1,2-ethanedithiol, 1,3-propanedithiol, and 1,4-butanedithiol, using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Adiabatic electron affinities (EAs) of the thiolate monoradicals of these compounds were assigned from electron photodetachment spectra of their corresponding thiolate monoanions, acquired using a cw-ICR. The dithiols exhibit enhanced acidities (up to 8.7 kcal/mol in deltaGo(acid)) and greater EAs (up to 6.7 kcal/mol) than analogous monothiol species. These differences are attributed to an intramolecular RS-.HSR hydrogen bond in the thiolate anion. Considerations of the RO-.HOR hydrogen bond in monoanions of alpha,omega-diols and in the [CH(3)O-.HOCH(3)] complex anion suggest that the RS-.HSR hydrogen bond provides up to 9 kcal/mol extra stabilization.     

Theoretical study of the effect of frit quality on chromatography using computational fluid dynamics

Summary Frits at both ends of a chromatographic column, especially for a preparative column, have significant influence on the flow distribution within the column and thus the column efficiency. However, frits have received little attention from chromatographers in the past. Here a theoretical study was conducted with the aid of CFD software FLUENT to investigate the effect of frits on the performance of homogeneous and heterogeneous chromatographic columns. A dimensionless number,FQ, was applied to characterize frit quality. This study visualized how frit quality affects the flow distribution and the concentration band, the shape of eluted pulse at the colum exit and column efficiency. Simulation results show that the development length of the flow distribution is related toFQ but has nothing to do with the packing heterogeneity. The curvature of the concentration band in a column depends onFQ and packing quality. This study shows column efficiency can be improved significantly by increasingFQ and/or frit permeability.     

Isoochotensine,a New Spirobenzyusoquinoline Alkaloid from: Corydalis Ochotensis Turcz

Separation of the phenolic fraction of Corydalis ochotensis afforded a new spirobenzylisoquinoline alkaloid, isoochotensine ( 1 ) and three known alkaloids, ochotensine ( 3 ), cheilanthifoline ( 7 ), and lienkonine ( 9 ) as their acetyl derivatives together with a known nonphenolic alkaloid, ochotensimine ( 5 ). Their structures were elucidated by the spectral data.     

Comparative Study on the Structure of Water in Reverse Micelles Stabilized with Sodium Bis(2-ethylhexyl) Sulfosuccinate or Sodium Bis(2-ethylhexyl) Phosphate in n-Heptane

The microstructure of water solubilized in H(2)O/surfactant/n-heptane ternary systems has been investigated by employing (1)H-NMR and FT-IR spectroscopic techniques. Two reverse micellar systems were prepared and studied, i.e., sodium bis(2-ethylhexyl) sulfosuccinate in n-heptane (H(2)O/AOT/n-heptane) and sodium bis(2-ethylhexyl) phosphate in n-heptane (H(2)O/NaDEHP/n-heptane). (1)H-NMR data showed that the chemical shift of water protons for the AOT and NaDEHP reverse micelles varied downfield and upfield, respectively, with an increase of the water content. The opposite shift directions with increasing water content are interpreted as due to a composition change of the solubilized water associated with head-groups and sodium counterions in reverse micellar systems. On the basis of deconvolution results of FT-IR spectra, a four-component model is proposed to interpret the FT-IR and (1)H-NMR results. Copyright 2000 Academic Press.     

When does gradient Ricci soliton have one end?

Annals of Global Analysis and Geometry - In this paper, we study a problem of finding compact hypersurfaces of prescribed mean curvature with free boundary in a ball. We transform the problem to an...     

Systematic studies of fission fragment kinetic energy distributions by Langevin simulations

Fission fluctuation-dissipation dynamics of heavy nuclei has been studied using Langevin Monte Carlo simulations. The covariant form of the fission transport equation and the coefficients related to it are investigated. To learn about the influence of the dynamics from the ground state to the saddle point on the kinetic energy distributions we have studied various systems and compared the calculations both starting from the ground state and from the saddle point. Both the mean total kinetic energy of the fission fragments and its variances can fit with the experimental values in terms of a finite neck radius as scission condition.This work was supported by the National Natural Science Foundation of China.