Diffusion of dextran within poly(methacrylic acid) hydrogels

We describe an investigation of fluorescence correlation spectroscopy into the diffusion of fluorescein‐tagged dextran (FDEX) in a poly(methacrylic acid) (PMAA) hydrogel. The temperature dependence of FDEX diffusion is shown to follow Zimm behavior in pure water, and the decrease in the diffusion coefficient when in the PMAA hydrogel has been modeled. The addition of acid and alkali (HCl and NaOH, respectively) not only control the swelling and collapse of the hydrogel but also reveal a strong pH dependence of the dextran diffusion coefficient, which shows a (nonmonatonic) increase with pH. The addition of NaCl and CaCl₂ salts similarly showed evidence of network swelling, most notably at low salt concentration, but also that the diffusion coefficient within the gel at these low concentrations is larger than that in the equivalent solution without the hydrogel, indicating that the combination of hydrogel and salt works to increase the diffusion coefficient above that in pure water. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Study of the Discrepancies between Crystallographic Porosity and Guest Access into Cadmium–Imidazolate Frameworks and Tunable Luminescence Properties by Incorporation of Lanthanides

An extended member of the isoreticular family of metal–imidazolate framework structures, IFP‐6 (IFP=imidazolate framework Potsdam), based on cadmium metal and an in situ functionalized 2‐methylimidazolate‐4‐amide‐5‐imidate linker is reported. A porous 3D framework with 1D hexagonal channels with accessible pore windows of 0.52 nm has been synthesized by using an ionic liquid (IL) linker precursor. IFP‐6 shows significant gas uptake capacity only for CO₂ and CH₄ at elevated pressure, whereas it does not adsorb N₂, H₂, and CH₄ under atmospheric conditions. IFP‐6 is assumed to deteriorate at the outside of the material during the activation process. This closing of the metal–organic framework (MOF) pores is proven by positron annihilation lifetime spectroscopy (PALS), which revealed inherent crystal defects. PALS results support the conservation of the inner pores of IFP‐6. IFP‐6 has also been successfully loaded with luminescent trivalent lanthanide ions (Ln^III=Tb, Eu, and Sm) in a bottom‐up one‐pot reaction through the in situ generation of the linker ligand and in situ incorporation of photoluminescent Ln ions into the constituting network. The results of photoluminescence investigations and powder XRD provide evidence that the Ln ions are not doped as connectivity centers into the frameworks, but are instead located within the pores of the MOFs. Under UV light irradiation, Tb@IFP‐6 and Eu@IFP‐6 (λ_exc=365 nm) exhibit observable emission changes to a greenish and reddish color, respectively, as a result of strong Ln 4 f emissions.     

Bestimmung, Trennung und Eigenschaften der unverseifbaren Bestandteile der Fette

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Über das quadratische Spektralmittel von Fourierkoeffizienten reell-analytischer automorpher Formen halbzahligen Gewichts

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