Sabine Schlecht

Inhibition of Influenza Virus Infection by Multivalent Sialic‐Acid‐Functionalized Gold Nanoparticles

An efficient synthesis of sialic-acid-terminated glycerol dendron to chemically functionalize 2 nm and 14 nm gold nanoparticles (AuNPs) is described. These nanoparticles are highly stable and show high activity towards the inhibition of influenza virus infection. As the binding of the viral fusion protein hemagglutinin to the host cell surface is mediated by sialic acid receptors, a multivalent interaction with sialic-acid-functionalized AuNPs is expected to competitively inhibit viral infection. Electron microscopy techniques and biochemical analysis show a high binding affinity of the 14 nm AuNPs to hemagglutinin on the virus surface and, less efficiently, to isolated hemagglutinin. The functionalized AuNPs are nontoxic to the cells under the conditions studied. This approach allows a new type of molecular-imaging activity-correlation and is of particular relevance for further application in alternative antiviral therapy.

Nanoparticle‐Induced Folding and Fibril Formation of Coiled‐Coil‐Based Model Peptides

Nanomedicine is a rapidly growing field that has the potential to deliver treatments for many illnesses. However, relatively little is known about the biological risks of nanoparticles. Some studies have shown that nanoparticles can have an impact on the aggregation properties of proteins, including fibril formation. Moreover, these studies also show that the capacity of nanoscale objects to induce or prevent misfolding of the proteins strongly depends on the primary structure of the protein. Herein, light is shed on the role of the peptide primary structure in directing nanoparticle-induced misfolding by means of two model peptides. The design of these peptides is based on the alpha-helical coiled-coil folding motif, but also includes features that enable them to respond to pH changes, thus allowing pH-dependent beta-sheet formation. Previous studies showed that the two peptides differ in the pH range required for beta-sheet folding. Time-dependent circular dichroism spectroscopy and transmission electron microscopy are used to characterize peptide folding and aggregate morphology in the presence of negatively charged gold nanoparticles (AuNPs). Both peptides are found to undergo nanoparticle-induced fibril formation. The determination of binding parameters by isothermal titration calorimetry further reveals that the different propensities of both peptides to form amyloid-like structures in the presence of AuNPs is primarily due to the binding stoichiometry to the AuNPs. Modification of one of the peptide sequences shows that AuNP-induced beta-sheet formation is related to the structural propensity of the primary structure and is not a generic feature of peptide sequences with a sufficiently high binding stoichiometry to the nanoparticles.

Switchable electrostatic interactions between gold nanoparticles and coiled coil peptides direct colloid assembly

The nanoparticle-peptide interaction described here is based on electrostatic forces and the pH value can act as a trigger to direct the organization of functionalized nanoparticles in a reversible and repeatable manner. The ability of the peptide to interact with the charged gold nanoparticles is directly related to its helical structure and was not found for a random coil peptide with the same net charge. Interestingly, the interaction with nanoparticles seems to induce a fibrillation of the coiled coil peptide.

Adsorption Behavior of 4-Methoxypyridine on Gold Nanoparticles

We demonstrate a phase transfer method to create stable colloidal solutions of Au nanoparticles with 4-methoxypyridine ligands. We then investigate the adsorption behavior of 4-methoxypyridine onto gold surfaces by Raman spectroscopy, DFT calculations, and (1)H NMR. In contrast to unsubstituted pyridine and the frequently used (N,N-dimethylamino)pyridine (DMAP), a flat adsorption of 4-methoxypyridine on gold was found.

Die Kristallstrukturen der Azido‐Platinate (AsPh4)2[Pt(N3)4] und (AsPh4)2[Pt(N3)6]

Die Kristallstrukturen der beiden homoleptischen Azido-Platinate (AsPh4)2[Pt(N3)4] (1) und (AsPh4)2[Pt(N3)6] (2) wurden rontgenographisch an Einkristallen ermittelt. In 1 sind die [Pt(N3)4]2–-Ionen ohne kristallographische Lagesymmetrie und die Platin-Atome weisen planare Umgebung auf. Die [Pt(N3)6]2–-Ionen in 2 sind zentrosymmetrisch (Ci) mit oktaedrischer Umgebung an den Platin-Atomen. Wahrend 1 brisant ist, hat 2 eine deutlich grosere Stabilitat. Dieses Verhalten wird durch die Packungsverhaltnisse erklart. 1: Raumgruppe P21/n, Z = 6, Gitterkonstanten bei –80 °C: a = 1045,3(1); b = 1620,2(1); c = 4041,0(3) pm; β = 96,70(1)°; R1 = 0,0654. 2: Raumgruppe P1, Z = 1, Gitterkonstanten bei –80 °C: a = 1027,6(1); b = 1049,1(2); c = 1249,9(3) pm; α = 88,27(1)°; β = 74,13(1)°; γ = 67,90(1)°; R1 = 0,0417. Crystal Structures of the Azido Platinates (AsPh4)2[Pt(N3)4] and (AsPh4)2[Pt(N3)6] The crystal structures of the two homoleptic azido platinates (AsPh4)2[Pt(N3)4] (1) and (AsPh4)2[Pt(N3)6] (2) were determined by X-ray diffraction at single crystals. In 1 the [Pt(N3)4]2– ions are without crystallographic site-symmetry, and the platinum atoms show a planar surrounding. The [Pt(N3)6]2– ions in 2 are centrosymmetric (Ci) with an octahedral surrounding at the platinum atoms. While 1 is highly explosive, 2 is of significantly greater stability. This behaviour is explained by the packing conditions. 1: Space group P21/n, Z = 6, lattice dimensions at –80 °C: a = 1045.3(1), b = 1620.2(1), c = 4041.0(3) pm; β = 96.70(1)°; R1 = 0.0654. 2: Space group P1, Z = 1, lattice dimenstions at –80 °C: a = 1027.6(1), b = 1049.1(2), c = 1249.9(3) pm; α = 88.27(1)°, β = 74.13(1)°, γ = 67.90(1)°; R1 = 0.0417.

Nanoscale FeS2 (Pyrite) as a Sustainable Thermoelectric Material

We have synthesized undoped, Co-doped (up to 5%), and Se-doped (up to 4%) FeS2 materials by mechanical alloying in a planetary ball mill and investigated their thermoelectric properties from room temperature (RT) to 600 K. With decreasing particle size, the undoped FeS2 samples showed higher electrical conductivity, from 0.02 S cm−1 for particles with 70 nm grain size up to 3.1 S cm−1 for the sample with grain size of 16 nm. The Seebeck coefficient of the undoped samples showed a decrease with further grinding, from 128 μV K−1 at RT for the sample with 70-nm grains down to 101 μV K−1 for the sample with grain size of 16 nm. The thermal conductivity of the 16-nm undoped sample lay within the range from 1.3 W m−1 K−1 at RT to a minimal value of 1.2 W m−1 K−1 at 600 K. All doped samples showed improved thermoelectric behavior at 600 K compared with the undoped sample with 16 nm particle size. Cobalt doping modified the p-type semiconducting behavior to n-type and increased the thermal conductivity (2.1 W m−1 K−1) but improved the electrical conductivity (41 S cm−1) and Seebeck coefficient (-129 μV K−1). Isovalent selenium doping led to a slightly higher thermal conductivity (1.7 W m−1 K−1) as well as to an improved electrical conductivity (26 S cm−1) and Seebeck coefficient (110 μV K−1). The ZT value of FeS2 was increased by a factor of five by Co doping and by a factor of three by Se doping.

Structural and Thermoelectric Properties of Bi1−xSbx Nanoalloys Prepared by Mechanical Alloying

Bi1−xSbx nanoparticles were prepared by mechanical alloying and compacted using different techniques. The influence of the composition as well as the pressing conditions on the thermoelectric performance was investigated. A strong dependence of the thermoelectric properties on the composition was found, which deviates from the behavior of single crystals. The results indicate a significant change in the band structure of the material induced by the reduced size. The influence of the pressing conditions on the thermoelectric properties also showed composition dependence. The results show that the compacting method has to be chosen carefully.

Effect of nanostructuring on the band structure and the galvanomagnetic properties in Bi1−xSbx alloys

Magnetotransport measurements were performed on a series of nanostructured Bi1−xSbx alloy samples with an Sb content in the range between 0% and 60%. The samples were prepared by cold pressing and annealing of crystalline Bi1−xSbx nanoparticles, which were synthesized by mechanical alloying. The incorporation of Sb changes the band structure of these nanotextured alloys as well as their transport behavior. With increasing Sb content the band gap increases and reaches a maximum band gap of 42 meV at an Sb concentration of about 14% determined from temperature dependent resistivity measurements. For even higher Sb content, the band gap decreases again. The bands and thus the band gaps are shifted with respect to bulk material due to quantum confinement effects in the nanostructures. The change of the band structure with varying Sb content strongly affects the magnetoresistance behavior as well as the magnetic field dependence of the Hall-coefficient. Using a three band model in order to describe both proper...

Substituent effects in solution speciation of the mononuclear and dinuclear trimethylplatinum(iv) iodide complexes of pyridines

A series of mononuclear trimethylplatinum(IV) complexes, [PtMe3L2I] [L = 4-cyanopyridine (4-NCpy), 4-methoxypyridine (4-MeOpy), 4-methylpyridine (4-Mepy), 4-ethylpyridine (4-Etpy), 4-tbutylpyridine (4-tBupy) and 4-dimethylaminopyridine (4-Me2Npy)] have been synthesized in good yield via a series of reactions of trimethylplatinum(IV) iodide with excess pyridine ligands (L) in chloroform. The synthesized mononuclear [PtMe3L2I] complexes on treatment with [(PtMe3I)4] in equimolar ratio result in the formation of syn- and anti-forms of iodo bridged dinuclear complexes [PtMe3LI]2 in chloroform. The complexes were characterized using proton nuclear magnetic resonance spectroscopy. Population of the mononuclear and dinuclear forms in solution depends on the electronic effect as well as on the steric influences of the pyridine substituents. The formation of the dinuclear complexes in solution was confirmed using X-ray crystal structure determination of anti-[PtMe3(4-NCpy)I]2, syn-[PtMe3(4-NCpy)I]2, syn-[PtMe3(4-MeOpy)I]2 and syn-[PtMe3(4-Etpy)I]2. The X-ray structural analysis of the complexes confirms that the two bridging iodine atoms hold the two platinum metal centers together, giving an edge sharing bi-octahedral structure. Furthermore, the crystal structures of the three mononuclear complexes [PtMe3L2I] (L = 4-NCpy, 4-Mepy and 4-Etpy) were also investigated in this research.

Exchange of pyridine and bipyridine ligands in trimethylplatinum(IV) iodide complexes: substituent and solvent effects

A series of mononuclear trimethylplatinum(IV) complexes of bipyridine ligands, [PtMe3(L–L)I] (L–L = bipy, 4-Mebipy, 4-MeObipy and 4-Me2Nbipy) has been synthesized by the reaction of trimethylplatinum(IV) iodide with bipyridine ligands L–L in an equimolar ratio. Also, treatment of mononuclear trimethylplatinum(IV) iodide complexes of pyridine ligands, [PtMe3L2I] (L = py, 4-Mepy, 4-MeOpy and 4-Me2Npy) with the corresponding bipyridine ligands leads to the exchange of the pyridines by the bipyridine ligands, thereby resulting in the formation of the more stable chelate bipyridine complexes. The ligand-exchange reactions have been studied by 1H NMR spectroscopy. The 1H NMR spectra of a 1 : 1 mixture of mononuclear pyridine complexes [PtMe3L2I] and corresponding bipyridine ligands L–L reveal the formation of two chelate bipyridine complexes, [PtMe3(L–L)I] and [PtMe3(L–L)L]I, in solution. Speciation of the pyridine and bipyridine complexes in solution was found to be dependent on the substituent as well as on the nature of the solvent. Furthermore, crystal structures of three bipyridine complexes [PtMe3(L–L)I] (L–L = 4-Mebipy, 4-MeObipy and 4-Me2Nbipy) have also been investigated here.