The syntheses of three new diamide-linked γ-cyclodextrin dimers joined by substitution at either a glucopyranose C6A or C3A carbon are reported. The syntheses involve the reaction of either C6A or C3A amino-substituted γ-cyclodextrin with bis(4-nitrophenyl)succinate to form succinamide linked γ-cyclodextrin dimers or reaction of C6A azide-substituted γ-cyclodextrin with carbon dioxide to form a urea linked γ-cyclodextrin dimer. 相似文献
This tutorial review covers recent developments in using single-molecule fluorescence microscopy to study nanoscale catalysis. The single-molecule approach enables following catalytic and electrocatalytic reactions on nanocatalysts, including metal nanoparticles and carbon nanotubes, at single-reaction temporal resolution and nanometer spatial precision. Real-time, in situ, multiplexed measurements are readily achievable under ambient solution conditions. These studies provide unprecedented insights into catalytic mechanism, reactivity, selectivity, and dynamics in spite of the inhomogeneity and temporal variations of catalyst structures. Prospects, generality, and limitations of the single-molecule fluorescence approach for studying nanocatalysis are also discussed. 相似文献
Easy to prepare solid materials based on fumed silica impregnated with polyethylenimine (PEI) were found to be superior adsorbents for the capture of carbon dioxide directly from air. During the initial hours of the experiments, these adsorbents effectively scrubbed all the CO(2) from the air despite its very low concentration. The effect of moisture on the adsorption characteristics and capacity was studied at room temperature. Regenerative ability was also determined in a short series of adsorption/desorption cycles. 相似文献
The emission properties, including luminescence lifetimes, of the lanthanide complexes Ln(Tf(2)N)(3) (Tf(2)N = bis(trifluoromethanesulfonyl)amide); Ln(3+) = Eu(3+), Tm(3+), Dy(3+), Sm(3+), Pr(3+), Nd(3+), Er(3+)) in the ionic liquid bmpyr Tf(2)N (bmpyr = 1-n-butyl-1-methylpyrrolidinium) are presented. The luminescence quantum efficiencies, η, and radiative lifetimes, τ(R), are determined for Eu(3+)((5)D(0)), Tm(3+)((1)D(2)), Dy(3+)((4)F(9/2)), Sm(3+)((4)G(5/2)), and Pr(3+)((3)P(0)) emission. The luminescence lifetimes in these systems are remarkably long compared to values typically reported for Ln(3+) complexes in solution, reflecting weak vibrational quenching. The 1.5 μm emission corresponding to the Er(3+) ((4)I(13/2)→(4)I(15/2)) transition, for example, exhibits a lifetime of 77 μs. The multiphonon relaxation rate constants are determined for 10 different Ln(3+) emitting states, and the trend in multiphonon relaxation is analyzed in terms of the energy gap law. The energy gap law does describe the general trend in multiphonon relaxation, but deviations from the trend are much larger than those normally observed for crystal systems. The parameters determined from the energy gap law analysis are consistent with those reported for crystalline hosts. Because Ln(3+) emission is known to be particularly sensitive to quenching by water in bmpyr Tf(2)N, the binding properties of water to Eu(3+) in solutions of Eu(Tf(2)N)(3) in bmpyr Tf(2)N have been quantified. It is observed that water introduced into these systems binds quantitatively to Ln(3+). It is demonstrated that Eu(Tf(2)N)(3) can be used as a reasonable internal standard, both for monitoring the dryness of the solutions and for estimating the quantum efficiencies and radiative lifetimes for visible-emitting [Ln(Tf(2)N)(x)](3-x) complexes in bmpyr Tf(2)N. 相似文献
In vivo endocannabinoid (EC) microdialysis has only seldom been performed, mostly in rodent brain tissue. Low solubility in aqueous media, adsorption to surfaces, and instability with co-present human serum albumin (HSA) are the major obstacles in EC microdialysis. The addition of hydroxypropyl-ß-cyclodextrine (HPCD) to the perfusion fluid has been previously described to facilitate lipid microdialysis, but the general biophysical properties of HPCD, especially with respect to peripheral EC microdialysis, have not been described before. We report on the characterization of EC microdialysis using an in vitro system using Ringer’s solution with 10% HPCD as the perfusion fluid and with fatty acid-free HSA as the matrix fluid. The endocannabinoids anandamide (AEA) and 2-arachidonoyl glycerol (2AG) were measured using LC-MS/MS. AEA was stable in the perfusion and matrix fluids, whereas 2AG was only stable in the perfusion fluid. In the matrix fluid, 2AG underwent rapid isomerization to 1-arachidonoyl glycerol. A relative recovery of 3.5% for AEA was found with 10% HPCD in the perfusion fluid and a flow rate of 1 μL/min. For 2AG, a similar relative recovery of 3.5% was estimated. Since 2AG was found unstable in the matrix fluid, a reliable calculation of the relative recovery rates was not possible. Delivery and recovery experiments revealed unequal inward and outward EC transport across the microdialysis membrane. Contrary to usual microdialysis findings, we observed increasing recovery rates for AEA with increasing flow rates. Long equilibration times of several hours were necessary to obtain constant relative recovery rates. In a proof-of-concept study in humans, we collected AEA from subcutaneous abdominal adipose tissue employing the described methodology. Our study suggests that the microdialysis technique is not suitable for the exact quantification of tissue EC concentrations, but it allows for their rough estimation.
The hydroxypyrroloindolenine (Hpi) motif forms the fundamental core of the pentacyclic natural product, brevianamide E, the concise stereoselective synthesis of which, via oxidative cyclization, is described. 相似文献
Certain lipid monolayers at the air-water interface undergo a second-order transition from a tilted to an untilted liquid-crystalline state of their lipid hydrocarbon chains at sufficiently large lateral pressure. Recent experimental observations demonstrate that in the presence of divalent cations DNA adsorbs onto a zwitterionic lipid monolayer and decreases the tilt transition pressure. Lowering of the tilt transition pressure indicates that the DNA condenses the lipid monolayer laterally. To rationalize this finding we analyze a theoretical model that combines a phenomenological Landau approach with an extension of the Poisson-Boltzmann model to zwitterionic lipids. Based on numerical calculations of the mean-field electrostatic free energy of a zwitterionic lipid monolayer-DNA complex in the presence of divalent cations, we analyze the thermodynamic equilibrium of DNA adsorption. We find that adsorbed DNA induces a 10% reduction of the electrostatic contribution to the lateral pressure exerted by the monolayer. This result implies a small but notable decrease in the tilt transition pressure. Additional mechanisms due to ion-ion correlations and headgroup reorientations are likely to further enhance this decrease. 相似文献