Indole alkaloids of Rauwolfia reflexa. Carbon-13 nuclear magnetic resonance analysis of the diindole alkaloid flexicorine

This article does not have an abstract

New developments in fluorofullerenes chemistry

Flurofullerenes were among the first chemical derivatives prepared from new spherical forms of carbon, yet it took 3 years of research to isolate the first single compound, C{sub 60}F{sub 48}. Subsequent studies provided a better understanding of physical and chemical properties of this compound. Here we present new data concerning synthesis, reactions, and properties of C{sub 60}F{sub 48}

Distribution of 1‑Butyl-3-methylimidazolium Bistrifluoromethylsulfonimide in Mesoporous Silica As a Function of Pore Filling

Rotational dynamics of the ionic liquid (IL) 1-butyl-3-methylimidazolium bistrifluoromethylsulfonimide, [C₄mim]­[Tf₂N], <b>1</b>, as a neat liquid, and confined in mesoporous silica were investigated by ¹H spin–spin (<i>T</i>₂) and spin–lattice (<i>T</i>₁) relaxation measurements and ¹³C NMR spectroscopy. Translational dynamics (self-diffusion) were monitored via the diffusion coefficient, <i>D</i>, obtained with ¹H pulsed field gradient NMR measurements. These data were used to determine the distribution of <b>1</b> in the pores of KIT-6, a mesoporous silica with a bicontinuous gyroid pore structure, as a function of filling fraction. Relaxation studies performed as a function of filling factor and temperature reveal a dynamic heterogeneity in both translational and rotational motions for <b>1</b> at filling factors, <i>f</i> = 0.2–1.0 (<i>f</i> = 1 corresponds to fully filled pores). Spin–lattice and spin–spin relaxation times reveal that the motion of <b>1</b> in silica mesopores conforms to that expected for a two-dimensional relaxation model. The relaxation dynamics are interpreted using a two-state, fast exchange model for all motions; a slow rotation (and translation) of molecules in contact with the surface and a faster motion approximated by the values for bulk relaxation and diffusion. Compound <b>1</b> retains liquid-like behavior at all filling factors and temperatures that extend to ca. 50 degrees below the bulk melting point. Translational motion in these systems, interpreted with MD-simulated diffusivity limits, confirms the high propensity of <b>1</b> to form a monolayer film on the silica surface at low filling factors. The attractive interaction of <b>1</b> with the surface is greater than that for self-association of <b>1</b>. The trends in diffusion data at short and long diffusion time suggest that the population of surface-bound <b>1</b> is in intimate contact with <b>1</b> in the pores. This condition is most easily met at higher filling fractions with successive additions of <b>1</b> increasing the layer thickness built up on the surface layer