Nanostructured Composites of Bi1-xSbx Nanoparticles and Carbon Nanotubes and the Characterization of Their Thermoelectric Properties.

The impact of inclusions of carbon nanotubes (CNT) on the thermoelectric properties of nanostructured Bi1-xSbx alloys with an Sb content between 10 and 20% was investigated for varying amounts of CNT. Three series of Bi1-xSbx pellets with 0, 0.3, and 0.5 wt % CNT were synthesized by mechanical alloying followed by uniaxial pressing. The resistivity was investigated in the temperature range from 30 to 500 K, revealing an enlargement of the band gap due to nanostructuring of the Bi1-xSbx alloy, which is even more pronounced for alloys including CNT. This enlargement is attributed to a modification of the interface between the Bi1-xSbx nanoparticles by a graphene-like coating, which is formed during the fabrication process due to the addition of CNT. Measurements of the Seebeck coefficient and the thermal conductivity were also performed to determine the thermoelectric properties. In total, the CNT-containing samples show a significant improvement of the figure of merit up to 250% for the Bi0.88Sb0.12 composition with 0.3 wt % CNT due to the interface modification between the nanoparticles, demonstrating the beneficial effect of CNT on the thermoelectric properties.

Effects of multivalent histamine supported on gold nanoparticles: activation of histamine receptors by derivatized histamine at subnanomolar concentrations.

Colloidal gold nanoparticles with a functionalized ligand shell were synthesized and used as new histamine receptor agonists. Mercaptoundecanoic acid moieties were attached to the surface of the nanoparticles and derivatized with native histamine. The multivalent presentation of the immobilized ligands carried by the gold nanoparticles resulted in extremely low activation concentrations for histamine receptors on rat colonic epithelium. As a functional read-out system, chloride secretion resulting from stimulation of neuronal and epithelial histamine H1 and H2 receptors was measured in Ussing chamber experiments. These responses were strictly attributed to the histamine entities as histamine-free particles Au-MUDOLS or the monovalent ligand AcS-MUDA-HA proved to be ineffective. The vitality of the tissues used was not impaired by the nanoparticles.

Metal-enhanced luminescence in colloidal solutions of CdSe and metal nanoparticles: investigation of density dependence and optical band overlap.

The photoluminescence (PL) of semiconductor nanoparticles (SNP) is strongly modified when the semiconductor is in the proximity of a metal surface or a metal nanoparticle (MNP). The effect may be due to two different phenomena which are (a) (Förster) resonant energy transfer ((F)RET) between the semiconductor and the metal and (b) the enhanced electric field around metallic structures that arises from surface plasmon oscillations. Here we present experimental evidence for enhancement and quenching of the PL of dilute SNP colloidal solutions depending on the amount of admixed MNP and the position of the MNP plasmon band with respect to the excitation wavelength and the optical bands in the SNP. The average distance between an MNP and its next neighbor MNP is varied between ∼0.1 and 2 µm by varying the MNP concentration, whereas that between MNP and SNP as well as between SNP and SNP is kept at about 0.1 µm. A model function based on the rate equations of the system is developed that yields a satisfactory description of the measured data by considering solely FRET between the particle species. The derived function is an extension of the Stern-Volmer equation, as it not only accounts for the energy transfer from the fluorescent SNPs to the MNPs, but also for the transfer of excitation from MNPs to SNPs and between MNPs. This theory provides a deeper insight into the mechanisms of metal-enhanced fluorescence and fluorescence quenching phenomena.

Synthesis of tumor-associated MUC1-glycopeptides and their multivalent presentation by functionalized gold colloids.

The mucin MUC1 is a glycoprotein involved in fundamental biological processes, which can be found over-expressed and with a distinctly altered glycan pattern on epithelial tumor cells; thus it is a promising target structure in the quest for effective carbohydrate-based cancer vaccines and immunotherapeutics. Natural glycopeptide antigens indicate only a low immunogenicity and a T-cell independent immune response; however, this major drawback can be overcome by coupling of glycopeptide antigens multivalently to immunostimulating carrier platforms. In particular, gold nanoparticles are well suited as templates for the multivalent presentation of glycopeptide antigens, due to their remarkably high surface-to-volume ratio in combination with their high biostability. In this work the synthesis of novel MUC1-glycopeptide antigens and their coupling to gold nanoparticles of different sizes are presented. In addition, the development of a new dot-blot immunoassay to test the potential antigen-antibody binding is introduced.

Evaluation of nucleocapsid and phosphoprotein p functionality as critical factors during the early phase of paramyxoviral infection.

In the beginning of a paramyxovirus infection after cell entry viral survival depends on efficient primary (1°) transcription and on the stability of only one input nucleocapsid. Here we examined the influence of the viral polymerase co-factor phosphoprotein P on the very early phase of an infection, i.e. before progeny nucleocapsids are synthesized. We used a novel set-up with Sendai virus (SeV) mutants incapable of genome replication: SeV-ΔP with the entire P ORF deleted, SeV-PΔ2-77 with the deletion of aa 2-77. These mutants allow maintaining the state of the very beginning of an infection when statistically one viral genome is present in the cell. This single genome serves as template for transcription. During SeV-ΔP infections only early 1° transcription takes place at low levels. However, when the truncated P protein is expressed in SeV-PΔ2-77 infections, 1° transcription levels rise significantly up to an 8-fold increased amount of viral mRNA. This shows that the P protein is able to support transcription and thereby mediates the transition from early to late 1° transcription. Importantly, nucleocapsids of both mutants could be shown to remain stable and functional for at least 5 days - even without de novo P protein synthesis. These results describe a novel function of the P protein: enhancing viral gene expression even before genome replication has started. Thus, the since long postulated supportive function of the P protein is not related to stabilization of the nucleocapsid but rather enhances the processivity of the viral polymerase during late 1° and secondary (2°) transcription and genome replication.

Overcoming lability of extremely long alkane carbon-carbon bonds through dispersion forces.

Steric effects in chemistry are a consequence of the space required to accommodate the atoms and groups within a molecule, and are often thought to be dominated by repulsive forces arising from overlapping electron densities (Pauli repulsion). An appreciation of attractive interactions such as van der Waals forces (which include London dispersion forces) is necessary to understand chemical bonding and reactivity fully. This is evident from, for example, the strongly debated origin of the higher stability of branched alkanes relative to linear alkanes and the possibility of constructing hydrocarbons with extraordinarily long C-C single bonds through steric crowding. Although empirical bond distance/bond strength relationships have been established for C-C bonds (longer C-C bonds have smaller bond dissociation energies), these have no present theoretical basis. Nevertheless, these empirical considerations are fundamental to structural and energetic evaluations in chemistry, as summarized by Pauling as early as 1960 and confirmed more recently. Here we report the preparation of hydrocarbons with extremely long C-C bonds (up to 1.704 Å), the longest such bonds observed so far in alkanes. The prepared compounds are unexpectedly stable--noticeable decomposition occurs only above 200 °C. We prepared the alkanes by coupling nanometre-sized, diamond-like, highly rigid structures known as diamondoids. The extraordinary stability of the coupling products is due to overall attractive dispersion interactions between the intramolecular H•••H contact surfaces, as is evident from density functional theory computations with and without inclusion of dispersion corrections.

Multivalent interaction and selectivities in selectin binding of functionalized gold colloids decorated with carbohydrate mimetics.

Colloidal gold particles with functionalized organic shells were applied as novel selectin binders. The ligand shell was terminated with different monocyclic carbohydrate mimetics as simplified analogs of the sLe(x) unit found in biological selectin ligands. The multivalent presentation of the sulfated selectin binding epitopes on the gold particles led to extremely high binding affinities towards L- and P-selectin and IC(50) values in the subnanomolar range. Depending on the ring size of the sulfated carbohydrate mimetic, its substitution pattern and its configuration, different selectivities for either L-selectin or P-selectin were obtained. These selectivities were not found for gold particles with simple acyclic sulfated alcohols, diols and triols in the ligand shell. In addition, the influence of the particle size and the thickness of the hydrophobic organic shell were systematically investigated.

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.

Low-temperature formation of cubic ß-PbF2: precursor-based synthesis and first-principles phase stability study.

A precursor-based approach to the cubic ß-phase of PbF(2) was developed and allowed the preparation of this high-temperature phase well below the temperature for transition from the orthorhombic α- to the cubic ß-phase. The formation of ß-PbF(2) from the molecular precursors Pb[Se(C(6)H(2)(CF(3))(3))](2) and Pb(C(6)H(2)(CF(3))(3))(2) is facilitated by the presence of several short PbF contacts in these molecules. The cubic form of PbF(2) was obtained as macroscopic crystals as well as nanoparticulate powder. Its formation at relatively low temperature suggested a theoretical re-investigation of the phase stabilities of the two polymorphs. The theoretical results from the Kohn-Sham density functional theory indicate that the energy content for the ß-phase is slightly lower than the one for the α-phase, by 0.5-1.7 kJ mol(-1) depending on the density functional used (zero-point vibrational energy correction included).

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.

Polymer-assisted preparation of nanoscale films of thermoelectric PbSe and PbTe and of lead chalcogenide-polymer composite films.

Polymer films of polyethyleneoxide (PEO) or poly(L-lactide) (PLLA) containing a single-source precursor for either PbSe or PbTe were used to produce films of nanoparticles of these thermoelectric materials. The monomeric homoleptic chalcogenolates lead(II) bis-(2,4,6-trifluoromethylphenylselenolate) Pb[SeC(6)H(2)(CF(3))(3)](2) and lead(II) bis-[tris(trimethylsilyl)silyl-tellurolate] Pb[TeSi(SiMe(3))(3)](2) were used as single-source precursors for the thermolytic formation of the lead chalcogenides. The thickness and the quality of as-obtained thin films depended decisively on the spin-coating conditions, on the polymer, on the precursor concentration in the composite film before thermolysis and on the annealing time. Thin layers of particles of 30-50 nm size and high crystallinity were obtained. They were characterized by X-ray diffraction, thermal analysis and electron microscopy.

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.

Thin-walled Er3+:Y2O3 nanotubes showing up-converted fluorescence.

Up-converted red and green fluorescence has been measured in low-crystallinity Er3+:Y2O3 nanotubes upon IR excitation. A new preparation procedure for thin-walled erbium doped yttria nanotubes using alumina templates as shape defining tools and rare earth nitrates as precursors for a purely thermolytic production of erbium doped yttria was developed. The products with a diameter of approximately 40-50 nm and a wall thickness of only 6-8 nm showed up-converted fluorescence with green and red emission bands when excited at 815 nm. The fluorescence properties are compared to the ones of bulk erbium-doped yttria obtained from the same precursor system.

Inhibition of selectin binding by colloidal gold with functionalized shells.

Gold colloids with terminally functionalized sulfated thiol shells were found to bind to P- and L-selectins with IC(50) values in the picomolar range; branched acyclic epitopes show the highest affinity, whereas a sulfated carbohydrate mimetic provides the best selectivity.

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.

De novo synthesis of N and P proteins as a key step in Sendai virus gene expression.

Among the members of the paramyxovirus family, the transcription process and the components involved have been studied under in vitro conditions thus far. Here, we reexamined the function of the viral RNA-dependent RNA polymerase through infection studies with Sendai virus (SeV) N and P deletion (Delta) mutants. To elucidate solely transcription-specific processes, all virus mutants also were rendered deficient in genome replication. Using mutant SeV DeltaP, the earlier suspected supplemental role of P protein was clearly demonstrated to be essential during viral gene expression. Moreover, when SeV DeltaN or DeltaN PDelta2-77 (with the 5' end of the P gene deleted) mutant was used for infections, a completely unexpected new and essential role for N protein was discovered for viral gene expression. In the early phases of an infection and in the absence of de novo viral protein synthesis, primary transcription occurs at hardly detectable levels. In contrast, if newly synthesized N protein is present, primary viral transcription reaches normal levels. From our data, we conclude that de novo synthesis of SeV N and P proteins is a key step for viral gene expression that facilitates the transition from preliminary to normal primary transcriptional activity.

Nanoscale zinc antimonides: synthesis and phase stability.

Highly crystalline single-phase nanoparticles of the important thermoelectric materials Zn4Sb3 and ZnSb were prepared from solvochemically activated powders of elemental zinc and elemental antimony. Low-temperature reactions with reaction temperatures of 275-300 degrees C were applied using an excess of elemental zinc. The nanoscale thermoelectrics obtained were characterized by X-ray powder diffraction, transmission electron microscopy, and thermal analysis. nc-Zn4Sb3 showed particle sizes of 50-70 nm, whereas particle sizes of 15-20 nm were observed for nc-ZnSb. Calorimetric investigations showed an increased heat capacity, Cp, for nc-Zn4Sb3 with respect to the bulk material which could be reduced to the bulk value by annealing nc-Zn4Sb3 at 190 degrees C. Interestingly, nc-Zn4Sb3 showed exothermic decomposition into zinc-poorer ZnSn at 196 degrees C in an open system, indicating that Zn4Sb3 is metastable in nanocrystalline form at room temperature.

Stabilization of the thermodynamically favored polymorph of cadmium chalcogenide nanoparticles CdX (X = S, Se, Te) in the polar mesopores of SBA-15 silica.

A versatile synthetic approach to cadmium chalcogenide nanoparticles in the mesopores of SBA-15 silica as a host matrix was developed. The use of cadmium organochalcogenolates of the type Cd(XPh)(2).TMEDA (X = S, Se, Te) allowed the preparation of nanoparticles of all three cadmium chalcogenides following the same experimental protocol. Particles of CdS, CdSe, and CdTe with a particle size of 7 nm were prepared from this class of single-source precursors. The incorporation of the precursor molecules into the pores was achieved by melt infiltration at a temperature of 140 degrees C. Subsequent pyrolysis of the precursors in the mesopores yielded the semiconductor particles. Owing to the high polarity of the silanol-covered pore walls, which lower the surface energy of the particles to a large extent, the dimorphic cadmium chalcogenides are obtained in their thermodynamically favored modifications; e.g., CdS particles crystallize in the wurtzite type, CdTe particles are obtained in the zinc blende structure, and CdSe (where no unambiguous preference exists) crystallizes as a "mixture" of both structures with a rather random stacking sequence.