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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

The synthesis and characterization of colloidal mesoporous silica (CMS) functionalized with vinyl-, benzyl-, phenyl-, cyano-, mercapto-, aminopropyl- or dihydroimidazole moieties is reported. Uniform mesoporous particles ranging in size from 40 to 150 nm are generated in a co-condensation process of tetraethylorthosilicate (TEOS) and organotriethoxysilanes (RTES) in alkaline aqueous media containing triethanolamine (TEA) in combination with cetyltrimethylammonium chloride (CTACl) serving as a structure-directing agent. The materials are obtained as colloidal suspensions featuring long-term stability after template removal by ion exchange with an ethanolic solution of ammonium nitrate or HCl. The spherical particles exhibit a wormlike pore system with defined pore sizes and high surface areas. Samples are analyzed by a number of techniques including TEM, SEM, DLS, TGA, Raman, and cross-polarized (29)Si-MAS NMR spectroscopy, as well as nitrogen sorption measurements. We demonstrate that co-condensation and grafting methods result in similar changes in the nitrogen adsorption behavior, indicating a successful internal lining of the pores with functional groups through both procedures.
ACS Nano 2008 Apr
PMID:Colloidal suspensions of functionalized mesoporous silica nanoparticles. 1920 12

Double-walled carbon nanotubes (DWNTs) doped with nitrogen and boron have been prepared by the decomposition of a CH(4) + Ar mixture along with pyridine (or NH(3)) and diborane, respectively, over a Mo(0.1)Fe(0.9)Mg(13)O catalyst, prepared by the combustion route. The doped DWNTs bave been characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and Raman spectroscopy. The dopant concentration is around 1 atom % for both boron and nitrogen. The radial breathing modes in the Raman spectra have been employed along with TEM to obtain the inner and outer diameters of the DWNTs. The diameter ranges for the undoped, N-doped (pyridine), N-doped (NH(3)), and B-doped DWNTs are 0.73-2.20, 0.74-2.30, 0.73-2.32, and 0.74-2.36 nm, respectively, the boron-doped DWNTs giving rise to a high proportion of the large diameter DWNTs. Besides affecting the G-band in the Raman spectra, N- and B-doping affect the proportion of semiconducting nanotubes.
ACS Nano 2007 Dec
PMID:Nitrogen- and boron-doped double-walled carbon nanotubes. 1920 71

Carbon nanotube growth in the presence of nitrogen has been the subject of much experimental scrutiny, sparking intense debate about the role of nitrogen in the formation of diverse structural features, including shortened length, reduced diameters, and bamboo-like multilayered nanotubules. In this paper, the origin of these features is elucidated using a combination of experimental and theoretical techniques, showing that N acts as a surfactant during growth. N doping enhances the formation of smaller diameter tubes. It can also promote tube closure which includes a relatively large amount of N atoms into the tube lattice, leading to bamboo-like structures. Our findings demonstrate that the mechanism is independent of the tube chirality and suggest a simple procedure for controlling the growth of bamboo-like nanotube morphologies.
ACS Nano 2007 Nov
PMID:Nitrogen-mediated carbon nanotube growth: diameter reduction, metallicity, bundle dispersability, and bamboo-like structure formation. 1920 89

We report the development of useful chemical sensors from chemically converted graphene dispersions using spin coating to create single-layer films on interdigitated electrode arrays. Dispersions of graphene in anhydrous hydrazine are formed from graphite oxide. Preliminary results are presented on the detection of NO(2), NH(3), and 2,4-dinitrotoluene using this simple and scalable fabrication method for practical devices. Current versus voltage curves are linear and ohmic in all cases, studied independent of metal electrode or presence of analytes. The sensor response is consistent with a charge transfer mechanism between the analyte and graphene with a limited role of the electrical contacts. A micro hot plate sensor substrate is also used to monitor the temperature dependence of the response to nitrogen dioxide. The results are discussed in light of recent literature on carbon nanotube and graphene sensors.
ACS Nano 2009 Feb 24
PMID:Practical chemical sensors from chemically derived graphene. 1923 64

The discovery of the metallopeptide Ni(Cysteine-Glycine-Cysteine)(2-), Ni(CGC)(2-), in the A-cluster active site of Acetyl CoA Synthase has prompted the synthesis of many small molecule models which employ M(N(2)S(2)) complexes as metalloligands. In vitro studies have shown that nickel incorporates into the N(2)S(2) binding pocket even when copper is in the enzyme growth medium, while copper is preferentially taken up in the proximal site, displacing the catalytically active nickel. (Darnault, C.; Volbeda, A.; Kim, E.J.; Legrand, P.; Vernede, X.; Lindahl, P.A.; Fontecilla-Camps, J.C. Nat. Struct. Biol. 2003, 10, 271-279.) The work herein has been designed to address the chemical viability of copper(II) within the tripeptide N(2)S(2) ligand set. To this end, a series of CuN(2)S(2)(2-) complexes, the resin-bound, O-Cu(CGC)(2-) (A) and free Cu(CGC)(2-) (B) complexes, as well as Cu(ema)(2-) (C) and Cu(emi)(2-) (D) dianions, have been characterized by UV-vis, electron paramagnetic resonance (EPR), and electrospray ionization mass spectrometry (ESI-MS) spectroscopies, cyclic voltammetry (CV), and, where appropriate, X-ray diffraction studies, and compared to the Ni(II) congeners. EPR spectroscopic results have indicated that, in frozen N,N-dimethylformamide (DMF) solution, the copper complexes are distorted square planar structures with nitrogen and sulfur donors. This is consistent with X-ray diffraction measurements which also show copper(II) in a distorted square planar environment that is bereft of CuN(2)S(2)(2-) intermolecular interactions. Density-functional theory (DFT) calculations resulted in optimized structures that are consistent with crystallographic data and indicated highest occupied molecular orbital (HOMO)-singly occupied molecular orbital (SOMO) gaps of 5.01 and 4.68 eV for C and D, respectively. Optimized structures of Ni(ema)(2-) and Ni(emi)(2-) share the same basic characteristics as the copper(II) congeners. Electrochemical characterization of C and D resulted in a reversible Cu(III/II) couple at -1.20 V and - 1.40 V, respectively. Reactivity studies with Rh(CO)(2)(+) show similar donor capabilities for complexes A-D. Analysis of A shows that transmetalation does not occur. From competitive metal uptake studies on immobilized tripeptide it is concluded that the N(2)S(2)(4-) ligating unit has a slight preference for Cu(2+) over Ni(2+) and that the biosynthetic pathway responsible for constructing the distal site of ACS must be selective for nickel insertion or copper exclusion, or both.
 ...
PMID:Chemical issues addressing the construction of the distal Ni[cysteine-glycine-cysteine]2- site of acetyl CoA synthase: why not copper? 1925 85

There has recently been an increasing interest in controlling macromolecular conformations and interactions through halogen bonding. Halogen bonds are favorable electrostatic interactions between polarized, electropositive chlorine, bromine, or iodine atoms and electronegative atoms such as oxygen or nitrogen. These interactions have been likened to hydrogen bonds in terms of their favored acceptor molecules, their geometries, and their energetics. We asked whether a halogen bond could replace a hydrogen bond in the oxyanion hole of ketosteroid isomerase, using semisynthetic enzymes containing para-halogenated phenylalanine derivatives to replace the tyrosine hydrogen bond donor. Formation of a halogen bond to the oxyanion in the transition state would be expected to rescue the effects of mutation to phenylalanine, but all of the halogenated enzymes were comparable in activity to the phenylalanine mutant. We conclude that, at least in this active site, a halogen bond cannot functionally replace a hydrogen bond.
ACS Chem Biol 2009 Apr 17
PMID:Evaluating the potential for halogen bonding in the oxyanion hole of ketosteroid isomerase using unnatural amino acid mutagenesis. 1926 Jun 91

Peroxynitrite is formed by the very fast reaction of nitric oxide and superoxide radicals, a reaction that kinetically competes with other routes that chemically consume or physically sequester the reagents. It can behave either as an endogenous cytotoxin toward host tissues or a cytotoxic effector molecule against invading pathogens, depending on the cellular source and pathophysiological setting. Peroxynitrite is in itself very reactive against a few specific targets that range from efficient detoxification systems, such as peroxiredoxins, to reactions eventually leading to enhanced radical formation (e.g., nitrogen dioxide and carbonate radicals), such as the reaction with carbon dioxide. Thus, the chemical biology of peroxynitrite is dictated by the chemical kinetics of its formation and decay and by the diffusion across membranes of the species involved, including peroxynitrite itself. On the other hand, most durable traces of peroxynitrite passing (such as 3-nitrotyrosine) are derived from radicals formed from peroxynitrite by routes that represent extremely low-yield processes but that have potentially critical biological consequences. Here we have reviewed the chemical kinetics of peroxynitrite as a biochemical transient species in order to estimate its rates of formation and decay and then its steady-state concentration in different intra- or extracellular compartments, trying to provide a quantitative basis for its reactivity; additionally, we have considered diffusion across membranes to locate its possible effects. Finally, we have assessed the most successful attempts to intercept peroxynitrite by pharmacological intervention in their potential to increment the existing biological defenses that routinely deal with this cytotoxin.
ACS Chem Biol 2009 Mar 20
PMID:Chemical biology of peroxynitrite: kinetics, diffusion, and radicals. 1926 56

We report the growth of ultrathin diamond nanorods (DNRs) by a microwave plasma assisted chemical vapor deposition method using a mixture gas of nitrogen and methane. DNRs have a diameter as thin as 2.1 nm, which is not only smaller than reported one-dimensional diamond nanostructures (4-300 nm) but also smaller than the theoretical value for energetically stable DNRs. The ultrathin DNR is encapsulated in tapered carbon nanotubes (CNTs) with an orientation relation of (111)diamond//(0002)graphite. Together with diamond nanoclusters and multilayer graphene nanowires/nano-onions, DNRs are self-assembled into isolated electron-emitting spherules and exhibit a low-threshold, high current-density (flat panel display threshold: 10 mA/cm2 at 2.9 V/microm) field emission performance, better than that of all other conventional (Mo and Si tips, etc.) and popular nanostructural (ZnO nanostructure and nanodiamond, etc.) field emitters except for oriented CNTs. The forming mechanism of DNRs is suggested based on a heterogeneous self-catalytic vapor-solid process. This novel DNRs-based integrated nanostructure has not only a theoretical significance but also has a potential for use as low-power cold cathodes.
ACS Nano 2009 Apr 28
PMID:Self-assembled growth, microstructure, and field-emission high-performance of ultrathin diamond nanorods. 1934 50


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