124 research outputs found
A flexible one-pot route to metal/metal oxide nanocomposites
We report a one-pot route to Au/CeO2 nanocomposites. A readily-available biopolymer, sodium alginate, is exploited for controlled formation and stabilisation of gold nanoparticles followed by in situ growth of a sponge-like network of CeO2 nanoparticles. The flexible nature of this method as a general route to mixed metal/metal oxide nanocomposites is also demonstrated
The evolution of 'sol-gel' chemistry as a technique for materials synthesis
From its initial use to describe hydrolysis and condensation processes, the term ‘sol–gel’ is now used for a diverse range of chemistries.</p
Doped-carbon electrocatalysts with trimodal porosity from a homogeneous polypeptide gel
One of the biggest challenges for materials science is to design facile routes to structurally complex materials, which is particularly important for global applications such as fuel cells. Doped nanostructured carbons are targeted as noble metal-free electrocatalysts for this purpose. Their intended widespread use, however, necessitates simple and robust preparation methods that do not compromise on material performance. Here, we demonstrate a versatile one-pot synthesis of nitrogen-doped carbons that exploits the templating ability of biological polymers. Starting with just metal nitrates and gelatin, multiphase C/Fe3C/MgO nanomaterials are formed, which are then etched to produce active carbon electrocatalysts with accessible trimodal porosity. These show remarkable performance in the oxygen reduction reaction – a key process in proton exchange membrane fuel cells. The activity is comparable to commercial platinum catalysts and shows improved stability with reduced crossover effects. This simple method offers a new route to widely applicable porous multicomponent nanocomposites
Triple templating of graphitic carbon nitride to enhance photocatalytic properties
Graphitic carbon nitride materials show some promising properties for applications such as photocatalytic water splitting. However, the conversion efficiency is still low due to factors such as a low surface area and limited light absorption. In this paper, we describe a “triple templating” approach to generating porous graphitic carbon nitride. The introduction of pores on several length-scales results in enhanced photocatalytic properties
Flourescent liquid pyrene derivative-in-water mircoemulsions
A fluorescent liquid pyrene derivative with a high fluorescence quantum yield (65%) in the bulk state is reported. With this as the sole oil phase, stable luminescent oil-in-water microemulsions have been prepared. Increasing the loading of liquid pyrene swells the droplets, as detected by small-angle neutron scattering. These larger droplets have a greater proportion of pyrene excimer emission contribution in their photoluminescence spectra, which leads to a red shift in the chromaticity of the emission
The aggregation of an alkyl-C60 derivative as a function of concentration, temperature and solvent type.
Contrast-variation small-angle neutron scattering (CV-SANS), small-angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR) measurements of diffusion and isothermal titration calorimetry (ITC) are used to gain insight into the aggregation of an alkyl-C60 derivative, molecule 1, in n-hexane, n-decane and toluene as a function of concentration and temperature. Results point to an associative mechanism of aggregation similar to other commonly associating molecules, including non-ionic surfactants or asphaltenes in non-aqueous solvents. Little aggregation is detected in toluene, but small micelle-like structures form in n-alkane solvents, which have a C60-rich core and alkyl-rich shell. The greatest aggregation extent is found in n-hexane, and at 0.1 M the micelles of 1 comprise around 6 molecules at 25 °C. These micelles become smaller when the concentration is lowered, or if the solvent is changed to n-decane. The solution structure is also affected by temperature, with a slightly larger aggregation extent at 10 °C than at 25 °C. At higher concentrations, for example in solutions of 1 above 0.3 M in n-decane, a bicontinuous network becomes apparent. Overall, these findings aid our understanding of the factors driving the assembly of alkyl-p-conjugated hydrophobic amphiphiles such as 1 in solution and thereby represent a step towards the ultimate goal of exploiting this phenomenon to form materials with well-defined order
Wannier-function description of the electronic polarization and infrared absorption of high-pressure hydrogen
We have constructed maximally-localized Wannier functions for prototype
structures of solid molecular hydrogen under pressure, starting from LDA and
tight-binding Bloch wave functions. Each occupied Wannier function can be
associated with two paired protons, defining a ``Wannier molecule''. The sum of
the dipole moments of these ``molecules'' always gives the correct macroscopic
polarization, even under strong compression, when the overlap between nearby
Wannier functions becomes significant. We find that at megabar pressures the
contributions to the dipoles arising from the overlapping tails of the Wannier
functions is very large. The strong vibron infrared absorption experimentally
observed in phase III, above ~ 150 GPa, is analyzed in terms of the
vibron-induced fluctuations of the Wannier dipoles. We decompose these
fluctuations into ``static'' and ``dynamical'' contributions, and find that at
such high densities the latter term, which increases much more steeply with
pressure, is dominant.Comment: 17 pages, two-column style with 14 postscript figures embedded. Uses
REVTEX and epsf macro
Silencing and Un-silencing of Tetracycline-Controlled Genes in Neurons
To identify the underlying reason for the controversial performance of tetracycline (Tet)-controlled regulated gene expression in mammalian neurons, we investigated each of the three components that comprise the Tet inducible systems, namely tetracyclines as inducers, tetracycline-transactivator (tTA) and reverse tTA (rtTA), and tTA-responsive promoters (Ptets). We have discovered that stably integrated Ptet becomes functionally silenced in the majority of neurons when it is inactive during development. Ptet silencing can be avoided when it is either not integrated in the genome or stably-integrated with basal activity. Moreover, long-term, high transactivator levels in neurons can often overcome integration-induced Ptet gene silencing, possibly by inducing promoter accessibility
Adeno-Associated Viral Vector-Mediated Transgene Expression Is Independent of DNA Methylation in Primate Liver and Skeletal Muscle
Recombinant adeno-associated viral (rAAV) vectors can support long-term transgene expression in quiescent tissues. Intramuscular (IM) administration of a single-stranded AAV vector (ssAAV) in the nonhuman primate (NHP) results in a peak protein level at 2–3 months, followed by a decrease over several months before reaching a steady-state. To investigate transgene expression and vector genome persistence, we previously demonstrated that rAAV vector genomes associate with histones and form a chromatin structure in NHP skeletal muscle more than one year after injection. In the mammalian nucleus, chromatin remodeling via epigenetic modifications plays key role in transcriptional regulation. Among those, CpG hyper-methylation of promoters is a known hallmark of gene silencing. To assess the involvement of DNA methylation on the transgene expression, we injected NHP via the IM or the intravenous (IV) route with a recombinant ssAAV2/1 vector. The expression cassette contains the transgene under the transcriptional control of the constitutive Rous Sarcoma Virus promoter (RSVp). Total DNA isolated from NHP muscle and liver biopsies from 1 to 37 months post-injection was treated with sodium bisulfite and subsequently analyzed by pyrosequencing. No significant CpG methylation of the RSVp was found in rAAV virions or in vector DNA isolated from NHP transduced tissues. Direct de novo DNA methylation appears not to be involved in repressing transgene expression in NHP after gene transfer mediated by ssAAV vectors. The study presented here examines host/vector interactions and the impact on transgene expression in a clinically relevant model
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