Showing papers in "Journal of the American Chemical Society in 2003"

HADDOCK: a protein-protein docking approach based on biochemical or biophysical information.

Abstract: The structure determination of protein-protein complexes is a rather tedious and lengthy process, by both NMR and X-ray crystallography. Several methods based on docking to study protein complexes have also been well developed over the past few years. Most of these approaches are not driven by experimental data but are based on a combination of energetics and shape complementarity. Here, we present an approach called HADDOCK (High Ambiguity Driven protein-protein Docking) that makes use of biochemical and/or biophysical interaction data such as chemical shift perturbation data resulting from NMR titration experiments or mutagenesis data. This information is introduced as Ambiguous Interaction Restraints (AIRs) to drive the docking process. An AIR is defined as an ambiguous distance between all residues shown to be involved in the interaction. The accuracy of our approach is demonstrated with three molecular complexes. For two of these complexes, for which both the complex and the free protein structures have been solved, NMR titration data were available. Mutagenesis data were used in the last example. In all cases, the best structures generated by HADDOCK, that is, the structures with the lowest intermolecular energies, were the closest to the published structure of the respective complexes (within 2.0 A backbone RMSD).

Lanthanide Double-Decker Complexes Functioning as Magnets at the Single-Molecular Level

Abstract: Double-decker phthalocyanine complexes with Tb3+ or Dy3+ showed slow magnetization relaxation as a single-molecular property. The temperature ranges in which the behavior was observed were far higher than that of the transition-metal-cluster single-molecule magnets (SMMs). The significant temperature rise results from a mechanism in the relaxation process different from that in the transition-metal-cluster SMMs. The effective energy barrier for reversal of the magnetic moment is determined by the ligand field around a lanthanide ion, which gives the lowest degenerate substate a large |Jz| value and large energy separations from the rest of the substates in the ground-state multiplets.

Completely "green" synthesis and stabilization of metal nanoparticles.

Abstract: In the present Communication, a completely "green" synthetic method for producing silver nanoparticles is introduced. The process is simple, environmentally benign, and quite efficient. By gentle heating of an aqueous starch solution containing silver nitrate and glucose, we produce relatively monodisperse, starched silver nanoparticles. beta-d-Glucose serves as the green reducing agent, while starch serves as the stabilization agent.

Bioconjugation by Copper(I)-Catalyzed Azide-Alkyne [3 + 2] Cycloaddition

Abstract: The copper-catalyzed cycloaddition reaction between azides and alkynes functions efficiently in aqueous solution in the presence of a tris(triazolyl)amine ligand. The process has been employed to make rapid and reliable covalent connections to micromolar concentrations of protein decorated with either of the reactive moieties. The chelating ligand plays a crucial role in stabilizing the Cu(I) oxidation state and protecting the protein from Cu(triazole)-induced denaturation. Because the azide and alkyne groups themselves are unreactive with protein residues or other biomolecules, their ligation is of potential utility as a general bioconjugation method.

Polyaniline nanofibers: facile synthesis and chemical sensors.

Abstract: Polyaniline nanofibers with uniform diameters between 30 and 50 nm can be made in bulk quantities through a facile aqueous/organic interfacial polymerization method at ambient conditions. The nanofibers have lengths varying from 500 nm to several micrometers and form interconnected networks. Thin films made of the nanofibers have superior performance in both sensitivity and time response to vapors of acid (HCl) and base (NH3).

A mesoporous silica nanosphere-based carrier system with chemically removable CdS nanoparticle caps for stimuli-responsive controlled release of neurotransmitters and drug molecules.

Abstract: An MCM-41 type mesoporous silica nanosphere-based (MSN) controlled-release delivery system has been synthesized and characterized using surface-derivatized cadmium sulfide (CdS) nanocrystals as chemically removable caps to encapsulate several pharmaceutical drug molecules and neurotransmitters inside the organically functionalized MSN mesoporous framework. We studied the stimuli-responsive release profiles of vancomycin- and adenosine triphosphate (ATP)-loaded MSN delivery systems by using disulfide bond-reducing molecules, such as dithiothreitol (DTT) and mercaptoethanol (ME), as release triggers. The biocompatibility and delivery efficiency of the MSN system with neuroglial cells (astrocytes) in vitro were demonstrated. In contrast to many current delivery systems, the molecules of interest were encapsulated inside the porous framework of the MSN not by adsorption or sol−gel types of entrapment but by capping the openings of the mesoporous channels with size-defined CdS nanoparticles to physically block...

Highly Efficient Water Splitting into H2 and O2 over Lanthanum-Doped NaTaO3 Photocatalysts with High Crystallinity and Surface Nanostructure

Abstract: NiO-loaded NaTaO3 doped with lanthanum showed a high photocatalytic activity for water splitting into H2 and O2 in a stoichiometric amount under UV irradiation. The photocatalytic activity of NiO-loaded NaTaO3 doped with lanthanum was 9 times higher than that of nondoped NiO-loaded NaTaO3. The maximum apparent quantum yield of the NiO/NaTaO3:La photocatalyst was 56% at 270 nm. The factors affecting the highly efficient photocatalytic water splitting were examined by using various characterization techniques. Electron microscope observations revealed that the particle sizes of NaTaO3:La crystals (0.1−0.7 μm) were smaller than that of the nondoped NaTaO3 crystal (2−3 μm) and that the ordered surface nanostructure with many characteristic steps was created by the lanthanum doping. The small particle size with a high crystallinity was advantageous to an increase in the probability of the reaction of photogenerated electrons and holes with water molecules toward the recombination. Transmission electron microsc...

Large-scale synthesis of nearly monodisperse CdSe/CdS core/shell nanocrystals using air-stable reagents via successive ion layer adsorption and reaction.

Abstract: Successive ion layer adsorption and reaction (SILAR) originally developed for the deposition of thin films on solid substrates from solution baths is introduced as a technique for the growth of high-quality core/shell nanocrystals of compound semiconductors. The growth of the shell was designed to grow one monolayer at a time by alternating injections of air-stable and inexpensive cationic and anionic precursors into the reaction mixture with core nanocrystals. The principles of SILAR were demonstrated by the CdSe/CdS core/shell model system using its shell-thickness-dependent optical spectra as the probes with CdO and elemental S as the precursors. For this reaction system, a relatively high temperature, about 220−240 °C, was found to be essential for SILAR to fully occur. The synthesis can be readily performed on a multigram scale. The size distribution of the core/shell nanocrystals was maintained even after five monolayers of CdS shell (equivalent to about 10 times volume increase for a 3.5 nm CdSe na...

A General Model for Selectivity in Olefin Cross Metathesis

Abstract: In recent years, olefin cross metathesis (CM) has emerged as a powerful and convenient synthetic technique in organic chemistry; however, as a general synthetic method, CM has been limited by the lack of predictability in product selectivity and stereoselectivity. Investigations into olefin cross metathesis with several classes of olefins, including substituted and functionalized styrenes, secondary allylic alcohols, tertiary allylic alcohols, and olefins with α-quaternary centers, have led to a general model useful for the prediction of product selectivity and stereoselectivity in cross metathesis. As a general ranking of olefin reactivity in CM, olefins can be categorized by their relative abilities to undergo homodimerization via cross metathesis and the susceptibility of their homodimers toward secondary metathesis reactions. When an olefin of high reactivity is reacted with an olefin of lower reactivity (sterically bulky, electron-deficient, etc.), selective cross metathesis can be achieved using fee...

Hydrothermal synthesis of ZnO nanorods in the diameter regime of 50 nm.

Abstract: We report a novel wet-chemical approach at 180 °C for the synthesis of monodispersed ZnO nanorods with high single-crystallinity. The method has successfully brought the ZnO nanorod diameter from a reported 150 nm down to the 50 nm regime in this work. The aspect ratio of the synthesized nanorods achieved is exceptionally high (in the range of 30−40). This simple low-cost approach should promise us a future large-scale synthesis of ZnO nanostructures for many important applications in nanotechnology in a controlled manner.

Solubilization of carbon nanotubes by Nafion toward the preparation of amperometric biosensors.

Abstract: The ability to solubilize single-wall and multiwall carbon nanotubes (CNT) in the presence of the perfluorinated polymer Nafion is described. Such use of Nafion as a solubilizing agent for CNT overcomes a major obstacle for creating CNT-based biosensing devices. Their association with Nafion does not impair the electrocatalytic properties of CNT. The resulting CNT/Nafion modified glassy-carbon electrodes exhibit a strong and stable electrocatalytic response toward hydrogen peroxide. The marked acceleration of the hydrogen peroxide redox process is very attractive for the operation of oxidase-based amperometric biosensors, as illustrated for the highly selective low-potential (−0.05 V vs Ag/AgCl) biosensing of glucose. These findings open the door for using CNT in a wide range of chemical sensors and nanoscale electronic devices.

A Colorimetric Lead Biosensor Using DNAzyme-Directed Assembly of Gold Nanoparticles

Abstract: A highly sensitive and selective colorimetric lead biosensor based on DNAzyme-directed assembly of gold nanoparticles is reported. It consists of a DNAzyme and its substrate that can hybridize to a 5‘-thio-modified DNA attached to gold nanoparticles. The hybridization brings gold nanoparticles together, resulting in a blue-colored nanoparticle assembly. In the presence of lead, the DNAzyme catalyzes specific hydrolytic cleavage, which prevents the formation of the nanoparticle assembly, resulting in red-colored individual nanoparticles. The detection level can be tuned to several orders of magnitude, from 100 nM to over 200 μM, through addition of an inactive variant of the DNAzyme. The concept developed here can be applied to the design of nucleic acid enzyme/nanoparticle sensors for analytes that are subject to in vitro selection, and thus can significantly expand the scope of nanomaterial applications and provide a novel approach to designing simple colorimetric biosensors.

Type-II Quantum Dots: CdTe/CdSe(Core/Shell) and CdSe/ZnTe(Core/Shell) Heterostructures

Abstract: Type-II band engineered quantum dots (CdTe/CdSe(core/shell) and CdSe/ZnTe(core/shell) heterostructures) are described. The optical properties of these type-II quantum dots are studied in parallel with their type-I counterparts. We demonstrate that the spatial distribution of carriers can be controlled within the type-II quantum dots, which makes their properties strongly governed by the band offset of the comprising materials. This allows access to optical transition energies that are not restricted to band gap energies. The type-II quantum dots reported here can emit at lower energies than the band gaps of comprising materials. The type-II emission can be tailored by the shell thickness as well as the core size. The enhanced control over carrier distribution afforded by these type-II materials may prove useful for many applications, such as photovoltaics and photoconduction devices.

Enantioselective Michael Reaction of Malonates to Nitroolefins Catalyzed by Bifunctional Organocatalysts

Abstract: Michael reaction of malonates to nitroolefins with chiral bifunctional organocatalysts, bearing both a thiourea and tertiary amino group, afforded Michael adducts with high yields and enantioselectivities (up to 95%, up to 93% ee).

Homoleptic cyclometalated iridium complexes with highly efficient red phosphorescence and application to organic light-emitting diode.

Abstract: Phosphorescence studies of a series of facial homoleptic cyclometalated iridium(III) complexes have been carried out. The complexes studied have the general structure Ir(III)(C−N)3, where (C−N) is a monoanionic cyclometalating ligand: 2-(5-methylthiophen-2-yl)pyridinato, 2-(thiophen-2-yl)-5-trifluoromethylpyridinato, 2,5-di(thiophen-2-yl)pyridinato, 2,5-di(5-methylthiophen-2-yl)pyridinato, 2-(benzo[b]thiophen-2-yl)pyridinato, 2-(9,9-dimethyl-9H-fluoren-2-yl)pyridinato, 1-phenylisoquinolinato, 1-(thiophen-2-yl)isoquinolinato, or 1-(9,9-dimethyl-9H-fluoren-2-yl)isoquinolinato. Luminescence properties of all the complexes at 298 K in toluene are as follows: quantum yields of phosphorescence Φp = 0.08−0.29, emission peaks λmax = 558−652 nm, and emission lifetimes τ = 0.74−4.7 μs. Bathochromic shifts of the Ir(thpy)3 family [the complexes with 2-(thiophen-2-yl)pyridine derivatives] are observed by introducing appropriate substituents, e.g., methyl, trifluoromethyl, or thiophen-2-yl. However, Φp of the red em...

Synthesis and characterization of facial and meridional tris-cyclometalated iridium(III) complexes.

Abstract: The synthesis, structures, electrochemistry, and photophysics of a series of facial (fac) and meridional (mer) tris-cyclometalated Ir(III) complexes are reported. The complexes have the general formula Ir(C'N)(3) [where C'N is a monoanionic cyclometalating ligand; 2-phenylpyridyl (ppy), 2-(p-tolyl)pyridyl (tpy), 2-(4,6-difluorophenyl)pyridyl (46dfppy), 1-phenylpyrazolyl (ppz), 1-(4,6-difluorophenyl)pyrazolyl (46dfppz), or 1-(4-trifluoromethylphenyl)pyrazolyl (tfmppz)]. Reaction of the dichloro-bridged dimers [(C'N(2)Ir(mu-Cl)(2)Ir(C'N)(2)] with 2 equiv of HC( wedge )N at 140-150 degrees C forms the corresponding meridional isomer, while higher reaction temperatures give predominantly the facial isomer. Both facial and meridional isomers can be obtained in good yield (>70%). The meridional isomer of Ir(tpy)(3) and facial and meridional isomers of Ir(ppz)(3) and Ir(tfmppz)(3) have been structurally characterized using X-ray crystallography. The facial isomers have near identical bond lengths (av Ir-C = 2.018 A, av Ir-N = 2.123 A) and angles. The three meridional isomers have the expected bond length alternations for the differing trans influences of phenyl and pyridyl/pyrazolyl ligands. Bonds that are trans to phenyl groups are longer (Ir-C av = 2.071 A, Ir-N av = 2.031 A) than when they are trans to heterocyclic groups. The Ir-C and Ir-N bonds with trans N and C, respectively, have bond lengths very similar to those observed for the corresponding facial isomers. DFT calculations of both the singlet (ground) and the triplet states of the compounds suggest that the HOMO levels are a mixture of Ir and ligand orbitals, while the LUMO is predominantly ligand-based. All of the complexes show reversible oxidation between 0.3 and 0.8 V, versus Fc/Fc(+). The meridional isomers are easier to oxidize by ca. 50-100 mV. The phenylpyridyl-based complexes have reduction potentials between -2.5 and -2.8 V, whereas the phenylpyrazolyl-based complexes exhibit no reduction up to the solvent limit of -3.0 V. All of the compounds have intense absorption bands in the UV region assigned into (1)(pi --> pi) transitions and weaker MLCT (metal-to-ligand charge transfer) transitions that extend to the visible region. The MLCT transitions of the pyrazolyl-based complexes are hypsochromically shifted relative to those of the pyridyl-based compounds. The phenylpyridyl-based Ir(III) tris-cyclometalates exhibit intense emission both at room temperature and at 77 K, whereas the phenylpyrazolyl-based derivatives emit strongly only at 77 K. The emission energies and lifetimes of the phenylpyridyl-based complexes (450-550 nm, 2-6 micros) and phenylpyrazolyl-based compounds (390-440 nm, 14-33 micros) are characteristic for a mixed ligand-centered/MLCT excited state. The meridional isomers for both pyridyl and pyrazolyl-based cyclometalates show markedly different spectroscopic properties than do the facial forms. Isolated samples of mer-Ir(C( wedge )N)(3) complexes can be thermally and photochemically converted to facial forms, indicating that the meridional isomers are kinetically favored products. The lower thermodynamic stabilities of the meridional isomers are likely related to structural features of these complexes; that is, the meridional configuration places strongly trans influencing phenyl groups opposite each other, whereas all three phenyl groups are opposite pyridyl or pyrazolyl groups in the facial complexes. The strong trans influence of the phenyl groups in the meridional isomers leads to the observation that they are easier to oxidize, exhibit broad, red-shifted emission, and have lower quantum efficiencies than their facial counterparts.

Control of Charge Recombination Dynamics in Dye Sensitized Solar Cells by the Use of Conformally Deposited Metal Oxide Blocking Layers

Abstract: We report herein a methodology for conformally coating nanocrystalline TiO2 films with a thin overlayer of a second metal oxide. SiO2, Al2O3, and ZrO2 overlayers were fabricated by dipping mesoporous, nanocrystalline TiO2 films in organic solutions of their respective alkoxides, followed by sintering at 435 °C. These three metal oxide overlayers are shown in all cases to act as barrier layers for interfacial electron transfer processes. However, experimental measurements of film electron density and interfacial charge recombination dynamics under applied negative bias were vary significantly for the overlayers. A good correlation was observed between these observations and the point of zero charge of the different metal oxides. On this basis, it is found that the most basic overlayer coating, Al2O3 (pzc = 9.2), is optimal for retarding interfacial recombination losses under negative applied bias. These observations show good correlation with current/voltage analyses of dye sensitized solar cell fabricated...

Controlling the aqueous miscibility of ionic liquids: aqueous biphasic systems of water-miscible ionic liquids and water-structuring salts for recycle, metathesis, and separations.

Abstract: Hydrophilic ionic liquids can be salted-out and concentrated from aqueous solution upon addition of kosmotropic salts forming aqueous biphasic systems as illustrated by the phase behavior of mixtures of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and K3PO4.

Low-Temperature Synthesis of Soluble and Processable Organic-Capped Anatase TiO2 Nanorods

Abstract: We demonstrate the controlled growth of high aspect ratio anatase TiO2 nanorods by hydrolysis of titanium tetraisopropoxide (TTIP) in oleic acid (OLEA) as surfactant at a temperature as low as 80 °C. Chemical modification of TTIP by OLEA is proven to be a rational strategy to tune the reactivity of the precursor toward water. The most influential factors in shape control of the nanoparticles are investigated by simply manipulating their growth kinetics. The presence of tertiary amines or quaternary ammonium hydroxides as catalysts is essential to promote fast crystallization under mild conditions. The novelty of the present approach relies on the large-scale production of organic-capped TiO2 nanocrystals to which standard processing of colloidal nanocrystals, such as surface ligand exchange, can be applied for the first time. Concentrated colloidal titania dispersions can be prepared for a number of fundamental studies in homogeneous solutions and represent a new source of easily processable oxide materia...

Gelation of Ionic Liquid-Based Electrolytes with Silica Nanoparticles for Quasi-Solid-State Dye-Sensitized Solar Cells

Abstract: For the first time silica nanoparticles were used to solidify ionic liquids. These ionic liquid-based quasi-solid-state electrolytes were successfully employed for regenerative photoelectrochemical cells that yielded 7% efficiency at AM 1.5 sunlight in combination with an amphiphilic ruthenium polypyridyl photosensitizer.

A solution-phase, precursor route to polycrystalline SnO2 nanowires that can be used for gas sensing under ambient conditions.

Abstract: This paper describes a solution-based, precursor method for the facile synthesis of uniform nanowires containing rutile SnO2 nanocrystallites. In a typical procedure, nanowires of ∼50 nm in diamete...

Activity-Based Protein Profiling in Vivo Using a Copper(I)-Catalyzed Azide-Alkyne [3 + 2] Cycloaddition

Abstract: Toward the goal of assigning function to the tens of thousands of protein products encoded by eukaryotic and prokaryotic genomes, the field of proteomics requires new technologies that can functionally characterize proteins within the dynamic environment of the cell, where these biomolecules are subject to myriad posttranslational modifications and the actions of endogenous activators and inhibitors. Here, we report an advanced strategy for activity-based protein profiling (ABPP) that addresses this important need. We show that several enzymes can be labeled in an activity-based manner both in vitro and in vivo by an azido-sulfonate ester probe and that these labeling events can be detected in whole proteomes by copper-catalyzed ligation with a rhodamine-alkyne reagent. This click chemistry-based strategy for ABPP represents a unique and versatile method for functional proteome analysis.

Structure-Switching Signaling Aptamers

Abstract: Aptamers are single-stranded nucleic acids with defined tertiary structures for selective binding to target molecules. Aptamers are also able to bind a complementary DNA sequence to form a duplex structure. In this report, we describe a strategy for designing aptamer-based fluorescent reporters that function by switching structures from DNA/DNA duplex to DNA/target complex. The duplex is formed between a fluorophore-labeled DNA aptamer and a small oligonucleotide modified with a quenching moiety (denoted QDNA). When the target is absent, the aptamer binds to QDNA, bringing the fluorophore and the quencher into close proximity for maximum fluorescence quenching. When the target is introduced, the aptamer prefers to form the aptamer-target complex. The switch of the binding partners for the aptamer occurs in conjunction with the generation of a strong fluorescence signal owing to the dissociation of QDNA. Herein, we report on the preparation of several structure-switching reporters from two existing DNA aptamers. Our design strategy is easy to generalize for any aptamer without prior knowledge of its secondary or tertiary structure, and should be suited for the development of aptamer-based reporters for real-time sensing applications.

Ceramic-Based Nanoparticles Entrapping Water-Insoluble Photosensitizing Anticancer Drugs: A Novel Drug−Carrier System for Photodynamic Therapy

Abstract: A novel nanoparticle-based drug carrier for photodynamic therapy is reported which can provide stable aqueous dispersion of hydrophobic photosensitizers, yet preserve the key step of photogeneration of singlet oxygen, necessary for photodynamic action. A multidisciplinary approach is utilized which involves (i) nanochemistry in micellar cavity to produce these carriers, (ii) spectroscopy to confirm singlet oxygen production, and (iii) in vitro studies using tumor cells to investigate drug-carrier uptake and destruction of cancer cells by photodynamic action. Ultrafine organically modified silica-based nanoparticles (diameter approximately 30 nm), entrapping water-insoluble photosensitizing anticancer drug 2-devinyl-2-(1-hexyloxyethyl) pyropheophorbide, have been synthesized in the nonpolar core of micelles by hydrolysis of triethoxyvinylsilane. The resulting drug-doped nanoparticles are spherical, highly monodispersed, and stable in aqueous system. The entrapped drug is more fluorescent in aqueous medium than the free drug, permitting use of fluorescence bioimaging studies. Irradiation of the photosensitizing drug entrapped in nanoparticles with light of suitable wavelength results in efficient generation of singlet oxygen, which is made possible by the inherent porosity of the nanoparticles. In vitro studies have demonstrated the active uptake of drug-doped nanoparticles into the cytosol of tumor cells. Significant damage to such impregnated tumor cells was observed upon irradiation with light of wavelength 650 nm. Thus, the potential of using ceramic-based nanoparticles as drug carriers for photodynamic therapy has been demonstrated.

Melem (2,5,8-triamino-tri-s-triazine), an important intermediate during condensation of melamine rings to graphitic carbon nitride: synthesis, structure determination by X-ray powder diffractometry, solid-state NMR, and theoretical studies.

Abstract: Single-phase melem (2,5,8-triamino-tri-s-triazine) C6N7(NH2)3 was obtained as a crystalline powder by thermal treatment of different less condensed C−N−H compounds (e.g., melamine C3N3(NH2)3, dicyandiamide H4C2N4, ammonium dicyanamide NH4[N(CN)2], or cyanamide H2CN2, respectively) at temperatures up to 450 °C in sealed glass ampules. The crystal structure was determined ab initio by X-ray powder diffractometry (Cu Kα1: P21/c (No. 14), a = 739.92(1) pm, b = 865.28(3) pm, c = 1338.16(4) pm, β = 99.912(2)°, and Z = 4). In the solid, melem consists of nearly planar C6N7(NH2)3 molecules which are arranged into parallel layers with an interplanar distance of 327 pm. Detailed 13C and 15N MAS NMR investigations were performed. The presence of the triamino form instead of other possible tautomers was confirmed by a CPPI (cross-polarization combined with polarization inversion) experiment. Furthermore, the compound was characterized using mass spectrometry, vibrational (IR, Raman), and photoluminescence spectrosco...

Alloyed semiconductor quantum dots: tuning the optical properties without changing the particle size.

Abstract: Alloyed semiconductor quantum dots (cadmium selenium telluride) with both homogeneous and gradient internal structures have been prepared to achieve continuous tuning of the optical properties without changing the particle size. Our results demonstrate that composition and internal structure are two important parameters that can be used to tune the optical and electronic properties of multicomponent, alloyed quantum dots. A surprising finding is a nonlinear relationship between the composition and the absorption/emission energies, leading to new properties not obtainable from the parent binary systems. With red-shifted light emission up to 850 nm and quantum yields up to 60%, this new class of alloyed quantum dots opens new possibilities in band gap engineering and in developing near-infrared fluorescent probes for in vivo molecular imaging and biomarker detection.

Narrow (n,m)-distribution of single-walled carbon nanotubes grown using a solid supported catalyst.

Abstract: Unusually structure-selective growth of single-walled carbon nanotubes (SWNTs) has been attained using a CVD method with a solid supported catalyst. In this method, CO feedstock disproportionates on silica-supported catalytic nanoclusters of Co that are formed in situ from mixed salts of Co and Mo. The nanotube products are analyzed by spectrofluorimetry to reveal distributions resolved at the level of individual (n,m) structures. Two structures, (6,5) and (7,5), together dominate the semiconducting nanotube distribution and comprise more than one-half of that population. The average diameter of produced SWNTs is only 0.81 nm, and a strong propensity is found favoring chiral angles near the armchair limit.

Controlled formation of highly organized mesoporous titania thin films: from mesostructured hybrids to mesoporous nanoanatase TiO2.

Abstract: In this paper, we report the complete synthesis and characterization procedures to generate highly organized and oriented mesoporous titania thin films, using poly(ethylene oxide) (PEO)-based templates. Controlled conditions in the deposition, postsynthesis, and thermal treatment steps allow one to tailor the final mesostructure (2D hexagonal, p6m, or 3D cubic, Im3m). Various techniques were used to determine the time evolution of the mesostructure. Spectroscopic techniques (UV/vis, (17)O NMR) and EXAFS/XANES have been used to follow the chemical changes in the Ti(IV) environment. Crossing these techniques spanning all ranges permits a complete description of the chemistry all the way from solution to the mesostructured metal oxide. A critical discussion on all important chemical and processing parameters is provided; the understanding of these features is essential for a rational design and the reproducible construction of mesoporous materials.

Ionic Liquids by Proton Transfer: Vapor Pressure, Conductivity, and the Relevance of ΔpKa from Aqueous Solutions

Abstract: We describe the behavior of the conductivity, viscosity, and vapor pressure of various binary liquid systems in which proton transfer occurs between neat Bronsted acids and bases to form salts with melting points below ambient. Such liquids form an important subgroup of the ionic liquid (IL) class of reaction media and electrolytes on which so much attention is currently being focused. Such “protic ionic liquids” exhibit a wide range of thermal stabilities. We find a simple relation between the limit set by boiling, when the total vapor pressure reaches one atm, and the difference in pKa value for the acid and base determined in dilute aqueous solutions. For ΔpKa values above 10, the boiling point elevation becomes so high (>300 °C) that preemptive decomposition prevents its measurement. The completeness of proton transfer in such cases is suggested by the molten salt-like values of the Walden product, which is used to distinguish good from poor ionic liquids. For the good ionic liquids, the hydrogen bond...

Protein electrochemistry using aligned carbon nanotube arrays.

Abstract: The remarkable electrocatalytic properties and small size of carbon nanotubes make them ideal for achieving direct electron transfer to proteins, important in understanding their redox properties and in the development of biosensors. Here, we report shortened SWNTs can be aligned normal to an electrode by self-assembly and act as molecular wires to allow electrical communication between the underlying electrode and redox proteins covalently attached to the ends of the SWNTs, in this case, microperoxidase MP-11. The efficiency of the electron transfer through the SWNTs is demonstrated by electrodes modified with tubes cut to different lengths having the same electron-transfer rate constant.