49 research outputs found
Characterization of CdSe nanocrystals coated with amphiphiles. A capillary electrophoresis study
We have synthesized CdSe nanocrystals (NCs) possessing a trioctylphosphine surface passivation layer and modified with amphiphilic molecules to form a surface bilayer. The NCs covered with single amphiphiles are not stable in aqueous solution, but a mixed amphiphilic system is shown to provide stability in solution over several months. The solutions of the modified NCs were characterized by UV-Vis absorbance, photoluminescence, and transmission electron microscopy. An electrophoretic study revealed two operational modes. The first relies on the enrichment of NCs using a micellar plug as a tool. The accumulation of NCs at the plug-electrolyte buffer interface results in a sharp peak. By controlling the electrophoretic conditions, nanocrystals were forced to exit a micellar plug into an electrolyte buffer. We conclude that a system consisting of modified nanocrystals and a micellar plug can act as a mixed pseudomicellar system, where modified nanocrystals play the role of pseudomicelles
Capillary electrophoretic separation of nanoparticles
In the present work, CdSe nanocrystals (NCs) synthesized with a trioctylphosphine surface passivation layer were modified using amphiphilic molecules to form a surface bilayer capable of providing stable NCs aqueous solutions. Such modified nanocrystals were used as a test solute in order to analyze new electrophoretic phenomena, by applying a micellar plug as a separation tool for discriminating nanocrystals between micellar and micelle-free zones during electrophoresis. The distribution of NCs between both zones depended on the affinity of nanocrystals towards the micellar zone, and this relies on the kind of surface ligands attached to the NCs, as well as electrophoretic conditions applied. In this case, the NCs that migrated within a micellar zone can be focused using a preconcentration mechanism. By modifying electrophoretic conditions, NCs were forced to migrate outside the micellar zone in the form of a typical CZE peak. In this situation, a two-order difference in separation efficiencies, in terms of theoretical plates, was observed between focused NCs (N ~ 107) and a typical CZE peak for NCs (N ~ 105). By applying the amino-functionalized NCs the preconcentration of NCs, using a micellar plug, was examined, with the conclusion that preconcentration efficiency, in terms of the enhancement factor for peak height (SEFheight) can be, at least 20. The distribution effect was applied to separate CdSe/ZnS NCs encapsulated in silica, as well as surface-modified with DNA, which allows the estimation of the yield of conjugation of biologically active molecules to a particle surface
Determining the composition of gold nanoparticles: a compilation of shapes, sizes, and calculations using geometric considerations
Synthese und Charakterisierung chelatisierender Silicagele und ihre Erprobung als stationaere Phasen zur fluessigkeits-chromatographischen Trennung aromatischer Amine
Available from TIB Hannover: DW 5363 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Diffusion as a major source of band broadening in field-amplified sample stacking under negligible electroosmotic flow
Theory of field-amplified sample stacking (FASS) also called field-enhanced sample stacking is reevaluated considering the early work of Chien, Burgi and Helmer. The classical theory presented by Chien, Helmer and Burgi predicts the existence of maxima, which are ascribed to the counteracting principles of zone focusing and hydrodynamic dispersion. In contrast to their work, we here focus on cationic analytes separated in an acidic background electrolyte providing a very low electroosmotic flow velocity. Therefore, peak broadening due to differences in the local electroosmotic flow velocities in different compartments of the capillary can be regarded to be negligible. Consequently, peak broadening resulting from hydrodynamic dispersion will not be the dominant limitation of the accessible enrichment efficiency. In our experimental studies we, however, obtain an optimum value for the field enhancement factor (maximum of the enrichment efficiency, when varying the electric conductivity of the sample and the size of the sample injection plug) corresponding to a 10-fold dilution of the BGE in the sample solution. Comparing these experimental data with data modeled according to the revised theory, we show that this limitation of the loadability is caused by the unavoidable decrease of the analyte migration velocity in the BGE compartment of the capillary when injecting of a sample plug of lower electric conductivity (decrease in the local electric field strength). The additional diffusional band broadening limits the obtainable enrichment efficiency
Capillary electrochromatography with polymeric continuous beds synthesized via free radical polymerization in aqueous media using derivatized cyclodextrins as solubilizing agents
(S)-(+)-2-Octanol as a Chiral Oil Core for the Microemulsion Electrokinetic Chromatographic Separation of Chiral Basic Drugs
Elucidation of the enantiodiscrimination properties of a nonracemic chiral alignment medium through gel-based capillary electrochromatography: Separation of the mefloquine stereoisomers.
Enantiodiscrimination and enantioseparation are two highly important processes in chemistry, often performed by using NMR spectroscopy and chromatography. For a better understanding of the mechanistic details, the same system should be studied by both methods. In addition, isotropic and anisotropic NMR parameters should be obtained, the latter using alignment media so that residual dipolar couplings and chemical-shift anisotropies can be measured. Consequently, a chiral alignment medium was used for the first time in chiral gel-based capillary electrochromatography with the four stereoisomers of the antimalaria drug mefloquine as test compounds. Chromatographic data verify that enantiodiscrimination obtained with this alignment gel is caused by differences in the equilibrium constants related to associate formation. Hence, the chromatographic separation provides physicochemical data that form a basis for the understanding and optimization of alignment processes, and vice versa