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We assessed the mechanisms by which specialized hypothalamic ventromedial nucleus (VMN) neurons utilize both glucose and long-chain fatty acids as signaling molecules to alter their activity as a potential means of regulating energy homeostasis. Fura-2 calcium (Ca(2+)) and membrane potential dye imaging, together with pharmacological agents, were used to assess the mechanisms by which oleic acid (OA) alters the activity of dissociated VMN neurons from 3- to 4-wk-old rats. OA excited up to 43% and inhibited up to 29% of all VMN neurons independently of glucose concentrations. In those neurons excited by both 2.5 mM glucose and OA, OA had a concentration-dependent effective excitatory concentration (EC(50)) of 13.1 nM. Neurons inhibited by both 2.5 mM glucose and OA had an effective inhibitory concentration (IC(50)) of 93 nM. At 0.5 mM glucose, OA had markedly different effects on these same neurons. Inhibition of carnitine palmitoyltransferase, reactive oxygen species formation, long-chain acetyl-CoA synthetase and ATP-sensitive K(+) channel activity or activation of uncoupling protein 2 (UCP2) accounted for only approximately 20% of OA's excitatory effects and approximately 40% of its inhibitory effects. Inhibition of CD36, a fatty acid transporter that can alter cell function independently of intracellular fatty acid metabolism, reduced the effects of OA by up to 45%. Thus OA affects VMN neuronal activity through multiple pathways. In glucosensing neurons, its effects are glucose dependent. This glucose-OA interaction provides a potential mechanism whereby such "metabolic sensing" neurons can respond to differences in the metabolic states associated with fasting and feeding.
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PMID:Characteristics and mechanisms of hypothalamic neuronal fatty acid sensing. 1953 76

Cobalt core/platinum shell nanoparticles were prepared by the electroless deposition (ED) of Pt on carbon-supported cobalt catalyst (Co/C) and verified by HRTEM images. For a 2.0 wt % Co/C core, the ED technique permitted the Pt loading to be adjusted to obtain a series of bimetallic compositions with varying numbers of monolayers (ML). The tendency for corrosion of Co and the electrochemical (i.e., oxygen reduction reaction (ORR)) activity of the structures were measured. The results from temperature-programmed reduction (TPR) analysis suggest that a single Pt ML coverage is formed at a Pt weight loading between 0.5 and 0.7% on the 2.0% Co/C. HRTEM analysis indicates that the continuity of the Pt shell on the Co core depends on the precursor Co particle size, where "large" Co particles (>10 nm) favor noncontinuous, three-dimensional Pt structures and "small" Co particles (<6 nm) favor layer-by-layer growth. For these larger core-shell particles, Co was observed to quickly corrode in 0.3 M H(2)SO(4). Surface area specific ORR activity, measured by chemisorption techniques, revealed that the Pt-Co/C catalysts performed better than a commercial Pt/C catalyst; however, on a Pt mass basis, only the lower Pt:Co atomic ratio Pt-Co/C catalysts outperformed the Pt/C catalyst.
ACS Nano 2009 Sep 22
PMID:Preparation and structural analysis of carbon-supported Co core/Pt shell electrocatalysts using electroless deposition methods. 1965 23

Graphene can be viewed as an individual atomic plane extracted from graphite, as unrolled single-walled carbon nanotube or as an extended flat fullerene molecule. In this paper, a facile approach to the synthesis of high quality graphene nanosheets in large scale through electrochemical reduction of exfoliated graphite oxide precursor at cathodic potentials (completely reduced potential: -1.5 V) is reported. This method is green and fast, and will not result in contamination of the reduced material. The electrochemically reduced graphene nanosheets have been carefully characterized by spectroscopic and electrochemical techniques in comparison to the chemically reduced graphene-based product. Particularly, FTIR spectra indicate that a variety of the oxygen-containing functional groups have been thoroughly removed from the graphite oxide plane via electrochemical reduction. The chemically converted materials are not expected to exhibit graphene's electronic properties because of residual defects. Indeed, the high quality graphene accelerates the electron transfer rate in dopamine electrochemistry (DeltaE(p) is as small as 44 mV which is much smaller than that on a glassy carbon electrode). This approach opens up the possibility for assembling graphene biocomposites for electrocatalysis and the construction of biosensors.
ACS Nano 2009 Sep 22
PMID:A green approach to the synthesis of graphene nanosheets. 1969 Dec 85

Reactive oxygen species are heavily involved in the pathogenesis of diabetes mellitus (DM) because the insulin-producing beta cells are particularly vulnerable to free-radical-mediated cytotoxicity. Catalytic anti-oxidants have been successfully applied for attenuation of DM and its consequences, but most recent research revealed that preventing the nitration of vital proteins/enzymes might be an even more powerful strategy. We now report an unprecedented efficiency of manganese(III) corroles regarding the protection of rat pancreatic beta cells against intracellular nitration by peroxynitrite and subsequent cell death. A comparison between analogous corroles and porphyrin metal complexes reveals significant superiority of the former in all examined aspects. This is particularly true for the positively-charged manganese(III) corrole, which decomposes peroxynitrite fast enough and through a unique catalytic mechanism that is devoid of potentially nitrating reaction intermediates.
ACS Chem Biol 2009 Nov 20
PMID:Manganese corroles prevent intracellular nitration and subsequent death of insulin-producing cells. 1971 43

We observe pore formation with diameters in the 10 nm range in silicon when it is covered with gold particles. This pore etching occurs when the sample is put in 5 wt % hydrofluoric acid (HF) solution for a few minutes. The pores form along the 100 direction, which is also the preferred direction of macro- and mesopores electrochemically etched into silicon. No etching occurs if the dissolved oxygen is removed from the aqueous HF solution or the gold is removed from the silicon surface. This leads to the assumption that the dissolved oxygen acts as an oxidant as in the case of stain etching with gold as cathodic material. A tentative model is suggested to explain why all of the observed nanopores have roughly the same diameter of about 10 nm. These pores can occur for inhomogeneously gold-covered planar silicon surfaces but also in MBE (molecular beam epitaxy) grown silicon nanowires since these nanowires are covered unintentionally with gold nanoclusters at their cylindrical surface.
ACS Nano 2009 Oct 27
PMID:Formation of straight 10 nm diameter silicon nanopores in gold decorated silicon. 1976 Nov 94

We fabricated diamond-like microstructures from epoxy-functionalized cyclohexyl polyhedral oligomeric silsesquioxanes (POSS) through four-beam interference lithography. The 3D structure was maintained when calcined at a temperature up to 1100 degrees C, and crack-free samples over a large area ( approximately 5 mm in diameter) were obtained when the POSS films were heated at 500 degrees C under an Ar environment or treated with a low intensity oxygen plasma. In the latter, the volume fraction of the 3D porous structures could be fine-tuned by plasma etching time and power. Both Fourier transform infrared (FT-IR) spectroscopy and energy-dispersive X-ray (EDX) spectroscopy analysis suggested that the presence of carbon materials in the films enhanced the crack resistance of 3D POSS structures treated under Ar or oxygen plasma. Since POSS and its derivatives could be easily removed by HF solution at room temperature, we demonstrated high fidelity replication of the 3D porous structures to biocompatible poly(glycidyl methacrylate) (PGMA) and elastomeric poly(dimethylsiloxane) (PDMS). Importantly, the whole fabrication process (template fabrication, infiltration, and removal) was carried out at room temperature. Finally, we illustrated the application of 3D PDMS film as a reversible and repeatable color-changing, flexible photonic crystal.
ACS Nano 2009 Oct 27
PMID:Crack-free 3D hybrid microstructures from photosensitive organosilicates as versatile photonic templates. 1977 6

Organometallic nanomaterials hold the promise for molecular hydrogen (H(2)) storage by providing nearly ideal binding strength to H(2) for room-temperature applications. Synthesizing such materials, however, faces severe setbacks due to the problem of metal clustering. Inspired by a recent experimental breakthrough ( J. Am. Chem. Soc. 2008 , 130 , 6992 ), which demonstrates enhanced H(2) binding in Ti-grafted mesoporous silica, we propose combining the graphene oxide (GO) technique with Ti anchoring to overcome the current synthesis bottleneck for practical storage materials. Similar to silica, GO contains ample hydroxyl groups, which are the active sites for anchoring Ti atoms. GO can be routinely synthesized and is much lighter than silica. Hence, higher gravimetric storage capacity can be readily achieved. Our first-principles computations suggest that GO is primarily made of low-energy oxygen-containing structural motifs on the graphene sheet. The Ti atoms bind strongly to the oxygen sites with binding energies as high as 450 kJ/mol. This is comparable to that of silica and is indeed enough to prevent the Ti atoms from clustering. Each Ti can bind multiple H(2) with the desired binding energies (14-41 kJ/mol-H(2)). The estimated theoretical gravimetric and volumetric densities are 4.9 wt % and 64 g/L, respectively.
ACS Nano 2009 Oct 27
PMID:Graphene oxide as an ideal substrate for hydrogen storage. 1985 79

It is well-known that the electrical properties and performance of carbon nanotube field-effect transistors (CNTFETs) are largely dominated by their nanotube/metal contacts. Such nanometer-scaled contacts are typically different from traditional bulk semiconductor/metal contacts, as a thin layer of molecules could be unintentionally introduced between the CNTs and metal electrodes through either adsorption of environmental molecules or device fabrication processes. Here, we present a nanocontact model, in which the energy band bending in the CNTs near the contacts is quantitatively characterized through establishment of electrostatic charge balance between the CNTs and metallic pads under the influences of environmental oxygen. The concept of dipole polarization along the CNT channel in the FET geometry is, for the first time, introduced in order to interpret puzzling findings from several CNT Schottky transistors with asymmetric source and drain contacts.
ACS Nano 2009 Dec 22
PMID:Nanoscale contacts between carbon nanotubes and metallic pads. 1989 95

We show that strong photoluminescence (PL) can be induced in single-layer graphene using an oxygen plasma treatment. The PL is spatially uniform across the flakes and connected to elastic scattering spectra distinctly different from those of gapless pristine graphene. Oxygen plasma can be used to selectively convert the topmost layer when multilayer samples are treated.
ACS Nano 2009 Dec 22
PMID:Making graphene luminescent by oxygen plasma treatment. 1992 14

Hydrogen peroxide (H(2)O(2)) acts as a second messenger that can mediate intracellular signal transduction via chemoselective oxidation of cysteine residues in signaling proteins. This Review presents current mechanistic insights into signal-mediated H(2)O(2) production and highlights recent advances in methods to detect reactive oxygen species (ROS) and cysteine oxidation both in vitro and in cells. Selected examples from the recent literature are used to illustrate the diverse mechanisms by which H(2)O(2) can regulate protein function. The continued development of methods to detect and quantify discrete cysteine oxoforms should further our mechanistic understanding of redox regulation of protein function and may lead to the development of new therapeutic strategies.
ACS Chem Biol 2010 Jan 15
PMID:Orchestrating redox signaling networks through regulatory cysteine switches. 1995 67


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