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 78,058 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Traditional small-molecule fluorophores are always fluorescent. This attribute can obscure valuable information in biological experiments. Here, we report on a versatile "latent" fluorophore that overcomes this limitation. At the core of the latent fluorophore is a derivative of rhodamine in which one nitrogen is modified as a urea. That modification enables rhodamine to retain half of its fluorescence while facilitating conjugation to a target molecule. The other nitrogen of rhodamine is modified with a "trimethyl lock", which enables fluorescence to be unmasked fully by a single user-designated chemical reaction. An esterase-reactive latent fluorophore was synthesized in high yield and attached covalently to a cationic protein. The resulting conjugate was not fluorescent in the absence of esterases. The enzymatic activity of esterases in endocytic vesicles and the cytosol educed fluorescence, enabling the time-lapse imaging of endocytosis into live human cells and thus providing unprecedented spatiotemporal resolution of this process. The modular design of this "fluorogenic label" enables the facile synthesis of an ensemble of small-molecule probes for the illumination of numerous biochemical and cell biological processes.
ACS Chem Biol 2006 May 23
PMID:Fluorogenic label for biomolecular imaging. 1716 79

S-Nitrosylation, the covalent addition of a nitrogen monoxide group to a cysteine thiol, has been shown to modify the function of a broad spectrum of mammalian, plant, and microbial proteins and thereby to convey the ubiquitous influence of nitric oxide on cellular signal transduction and host defense. Accumulating evidence indicates that dysregulated, diminished, or excessive S-nitrosylation may be implicated in a wide range of pathophysiological conditions. A recent study establishes a functional relationship between inhibitory S-nitrosylation of the redox enzyme protein disulfide isomerase (PDI), defects in regulation of protein folding within the endoplasmic reticulum (ER), and neurodegeneration. Further, an examination of human brains afflicted with Parkinson's or Alzheimer's disease supports a causal role for the S-nitrosylation of PDI and consequent ER stress in these prevalent neurodegenerative disorders.
ACS Chem Biol 2006 Jul 21
PMID:Nitrosative stress in the ER: a new role for S-nitrosylation in neurodegenerative diseases. 1716 72

Mesoporous graphitic carbon nitride was used as both a nanoreactor and a reactant for the synthesis of ternary metal nitride nanoparticles. By infiltration of a mixture of two metal precursors into mesoporous carbon nitride, the pores act first as a nanoconfinement, generating amorphous mixed oxide nanoparticles. During heating and decomposition, the carbon nitride second acts as reactant or, more precisely, as a nitrogen source, which converts the preformed mixed oxide nanoparticles into the corresponding nitride (reactive templating). Using this approach, ternary metal nitride particles with diameters smaller 10 nm composed of aluminum gallium nitride (Al-Ga-N) and titanium vanadium nitride (Ti-V-N) were synthesized. Due to the confinement effect of the carbon nitride matrix, the composition of the resulting metal nitride can be easily adjusted by changing the concentration of the preceding precursor solution. Thus, ternary metal nitride nanoparticles with continuously adjustable metal composition can be produced.
ACS Nano 2008 Dec 23
PMID:Synthesis of ternary metal nitride nanoparticles using mesoporous carbon nitride as reactive template. 1920 83

Compared with noble metals and quantum dots, dielectric complex oxide nanoparticles are significantly less popular due to their high crystallization temperature, making difficult their synthesis in the 10-100 nm range for which surface effects are reduced. We report here an original process permitting thermal annealing of complex oxide nanoparticles at high temperature without aggregation and growth. Thus, after thermal treatment, these annealed particles can be dispersed in water, leading to concentrated aqueous colloidal dispersions containing isolated highly crystalline particles. This contrasts with usual colloidal techniques for which the production of particles in the 10-100 nm range generally leads to poorly crystallized particles, especially for multicomponent oxides. From two examples, we show some possibilities offered by this type of process. This concerns the synthesis of lanthanide-doped oxide nanoparticles exhibiting a bulk behavior for their luminescence properties and the control of the composition in nitrogen-doped titanium oxide particles without sintering and size change.
ACS Nano 2008 Dec 23
PMID:High temperature strategy for oxide nanoparticle synthesis. 1920 85

We demonstrate the effect of differently shaped CdSe nanoscale building blocks (dots, rods, branched nanoparticles, and hyperbranched nanoparticles) on the morphologies, surface characteristics, and optical properties of resultant porous CdSe nanostructured aerogels. Monolithic CdSe aerogels were produced by controlled oxidative removal of surface thiolate ligands from differently shaped CdSe nanoparticles to yield a wet gel, followed by CO(2) supercritical drying. The X-ray diffraction data show that the resultant CdSe aerogels maintain the crystalline phase of the building blocks without significant grain growth. However, the transmission electron microscopy images indicate that the morphology of CdSe aerogels changes from a colloid-type morphology to a polymer-type morphology when the building block changes from dot to rod or the branched nanoparticle. The morphology of the CdSe aerogel assembled from hyperbranched nanoparticles appears to be intermediate between the colloid-type and the polymer-type. Nitrogen physisorption measurements suggest that the surface areas and porosity are a direct function of the shape of the primary building blocks, with aerogels formed from rods or branched particles exhibiting the greatest surface areas (>200 m(2)/g) and those prepared from hyperbranched nanoparticles exhibiting the least (<100 m(2)/g). Band gap measurements and photoluminescence studies show that the as-prepared CdSe aerogels retain to a large extent the intrinsic quantum confinement of the differently shaped building blocks, despite being connected into a 3D network.
ACS Nano 2008 Aug
PMID:Effects of nanoparticle shape on the morphology and properties of porous CdSe assemblies (aerogels). 1920 58

The synthesis of extremely small mesoporous silica nanoparticles via a specific co-condensation process with phenyl groups is demonstrated. The suspensions are ideally suited for the production of nanoscale thin films by spin-coating. Thanks to the small particle size and the resulting low surface roughness, the films show excellent optical qualities and exhibit good diffusion properties and a highly accessible pore system. The availability of such homogeneous porous thin films made it possible to use ellipsometric porosimetry (EP) as a convenient method to determine the effective porosity of the films on their original support without destroying it. It was possible to record sorption isotherms of the thin films with ellipsometry and to correlate the data with nitrogen sorption data of dried powders of the same material. The thin films showed very low refractive indices of around 1.2.
ACS Nano 2008 Nov 25
PMID:Porous thin films of functionalized mesoporous silica nanoparticles. 1920 99

Isolated, carbon nanotube cups with diameters of 12-40 nm have been synthesized by chemical vapor deposition through incorporation of nitrogen atoms into graphitic carbon structure and subsequent mechanical separation. Incorporation of nitrogen affords carbon nanotube cups with a unique composition comprising multiwalled, graphitic lattice with nitrogen groups on the exterior rim and hollow interior cavities. These nanostructures demonstrate the ability to participate in hydrogen bonding because of nitrogen functionalities on their open edges. Furthermore, reaction with these nitrogen functionalities results in the coupling of gold nanoparticles (GNPs) to the open rim of carbon nanotube cups. Through atomic force microscopy manipulation and adhesion force measurements, we compare the mobility of these structures on a hydrophilic surface before and after GNP coupling. Understanding of these forces will aid in useful nanostructure assembly for energy and biomedical applications.
ACS Nano 2008 Sep 23
PMID:Synthesis, characterization, and manipulation of nitrogen-doped carbon nanotube cups. 1920 32

A unique nanostructured polyaniline (PANI)/mesoporous TiO(2) composite was synthesized and explored as an anode in Escherichia coli microbial fuel cells (MFCs). The results of X-ray diffraction, morphology, and nitrogen adsorption-desorption studies demonstrate a networked nanostructure with uniform nanopore distribution and high specific surface area of the composite. The composite MFC anode was fabricated and its catalytic behavior investigated. Optimization of the anode shows that the composite with 30 wt % PANI gives the best bio- and electrocatalytic performance. A possible mechanism to explain the excellent performance is proposed. In comparison to previously reported work with E. coli MFCs, the composite anode delivers 2-fold higher power density (1495 mW/m(2)). Thus, it has great potential to be used as the anode for a high-power MFC and may also provide a new universal approach for improving different types of MFCs.
ACS Nano 2008 Jan
PMID:Nanostructured polyaniline/titanium dioxide composite anode for microbial fuel cells. 1920 54

Arrays of multiwalled carbon nanotubes doped with phosphorus (P) and nitrogen (N) are synthesized using a solution of ferrocene, triphenyl-phosphine, and benzylamine in conjunction with spray pyrolysis. We demonstrate that iron phosphide (Fe(3)P) nanoparticles act as catalysts during nanotube growth, leading to the formation of novel PN-doped multiwalled carbon nanotubes. The samples were examined by high resolution electron microscopy and microanalysis techniques, and their chemical stability was explored by means of thermogravimetric analysis in the presence of oxygen. The PN-doped structures reveal important morphology and chemical changes when compared to N-doped nanotubes. These types of heterodoped nanotubes are predicted to offer many new opportunities in the fabrication of fast-response chemical sensors.
ACS Nano 2008 Mar
PMID:Heterodoped nanotubes: theory, synthesis, and characterization of phosphorus-nitrogen doped multiwalled carbon nanotubes. 1920 68

The photoluminescence (PL) of 2D monolayers of CdSe/CdS/ZnS semiconductor nanocrystals (NCs) deposited on gold substrates and incorporated into electrochemical cells has been studied. By combining simultaneous cyclic voltammetry and confocal microscopy it is demonstrated that when a positive potential is applied to the film in an acetonitrile electrolyte, the PL is irreversibly quenched. This is irrespective of whether the samples are under an inert atmosphere or exposed to air or water vapor. When a negative potential is applied under nitrogen, quenching is also observed; however, it is reversible. Conversely when a negative potential is applied to the NC films in aerated acetonitrile, the PL intensity increases. The enhancement of the PL is stable for at least 180 s while the potential is held at -1.0 V (vs Ag quasi-reference electrode). When the potential is removed the PL intensity returns to the starting value. These results clearly indicate that photobrightening and charge carrier injection are coupled processes. On the basis of these data, we propose a simple kinetic model that explains the origins of photobrightening.
ACS Nano 2008 Apr
PMID:The effects of electron and hole injection on the photoluminescence of CdSe/CdS/ZnS nanocrystal monolayers. 1920 97


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