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- Crystal structure (2)
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- 8 Zerstörungsfreie Prüfung (3)
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- 4 Material und Umwelt (2)
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Complex formation and the coordination of zirconium with acetic acid were investigated with Zr K-edge extended X-ray absorption fine structure spectroscopy (EXAFS) and single-crystal diffraction. Zr K-edge EXAFS spectra show that a stepwise increase of acetic acid in aqueous solution with 0.1 M Zr(IV) leads to a structural rearrangement from initial tetranuclear hydrolysis species [Zr4(OH)8(OH2)16]8+ to a hexanuclear acetate species Zr6(O)4(OH)4(CH3COO)12. The solution species Zr6(O)4(OH)4(CH3COO)12 was preserved in crystals by slow evaporation of the aqueous solution. Single-crystal diffraction reveals an uncharged hexanuclear cluster in solid Zr6(μ3-O)4(μ3-OH)4(CH3COO)12·8.5H2O. EXAFS measurements show that the structures of the hexanuclear zirconium acetate cluster in solution and the solid state are identical.
In this study, we investigated galacturonic (GalAc)- and mannuronic (ManAc) acids as novel targeting ligands for receptor-mediated gene delivery. GalAc and ManAc were coupled to either polyethyleneimine (PEI) or PEIpolyethyleneglycol (PEG). Furthermore, lactobionic acid (LacAc), which comprises a GalAc-related carbohydrate ring, was coupled to each of the polymers through its open-chain gluconic acid moiety. The molar mass distributions of the polymers were characterized by analytical ultracentrifugation and size exclusion chromatography. PEI-conjugatepDNA complexes were transfected into HepG2-, HeLa-, and 16HBE14o--cells. Gene expression mediated by GalAc- and LacAc-functionalized PEI-conjugates was lower than for PEI. In contrast, gene expression mediated by ManAc-functionalized PEI-conjugates was up to three orders of magnitude higher than for the other tested PEI-conjugates, in particular for negatively charged gene vectors at low N/P ratios, independent of the cell line. Pre-incubation of cells with an excess of ManAc before transfection significantly inhibited transfection rates only for ManAc-functionalized PEI-conjugates. Coupling of methyl-α-D-mannuronic acid to PEI resulted in significantly lower transfection rates than for ManAc-PEI based complexes. Together with fluorescence microscopy images of fluorescein-labelled ManAc-functionalized dextrans and FACS analyses of cells, these results demonstrate that receptor-mediated endocytosis of ManAcPEI-conjugatepDNA complexes via ManAc-specific receptors was involved in gene transfer. In conclusion, ManAc-modification of PEI-polymers represents a novel strategy for receptor-mediated gene delivery which could be promising for in vivo application.