Hydrothermal synthesis and properties of controlled α-Fe2O3 nanostructures in HEPES solution.

A facile, template-free, and environmentally friendly hydrothermal strategy was explored for the controllable synthesis of α-Fe(2)O(3) nanostructures in HEPES solution (HEPES=2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid). The effects of experimental parameters including HEPES/FeCl(3) molar ratio, pH value, reaction temperature, and reaction time on the formation of α-Fe(2)O(3) nanostructures have been investigated systematically. Based on the observations of the products, the function of HEPES in the reaction is discussed. The different α-Fe(2)O(3) nanostructures possess different optical, magnetic properties, and photocatalytic activities, depending on the shape and size of the sample. In addition, a novel and facile approach was developed for the synthesis of Au/α-Fe(2)O(3) and Ag/α-Fe(2)O(3) nanocomposites in HEPES buffer solution; this verified the dual function of HEPES both as reductant and stabilizer. This work provides a new strategy for the controllable synthesis of transition metal oxide nanostructures and metal-supported nanocomposites, and gives a strong evidence of the relationship between the property and morphology/size of nanomaterials.

Synthesis, photophysical properties, and molecular aggregation of gold(I) complexes containing carbon-donor ligands.

A series of gold(I) complexes with N-heterocyclic carbene (NHC) and acetylide ligands, namely [Au(NHC(1))(C≡CAr)] (NHC(1)=1-(9-anthracenylmethyl)-3-(n)-butylimidazol-2-ylidene; 1b-1g), [Au(NHC(2))(C≡CAr)] (NHC(2)=1,3-diethylimidazol-2-ylidene; 2b-2f) and [Au(C≡NAr)(2)](+) (C≡NAr=arylisocyanide; 3a-3f) have been synthesized. At room temperature, most of these gold(I) complexes are emissive in the solid state and in solutions with lifetimes in the nanosecond to submicrosecond regime. The emissions of complexes 1b-1g in solutions are assigned to (1)π-π* excited states of the NHC ligand, while that of 2b-2f and 3a-3f are phosphorescent in nature. The intriguing solvatochromism of complex 3a was also investigated. Complexes 1b, 1d, 3a, and 3e aggregate into crystalline nanowires in freshly prepared THF/water dispersions. The X-ray crystallographic data reveal that 1b and 1d possess intermolecular π-π and C-H···π interactions; while 3a was found to display intermolecular gold(I)···π interactions.

Hydrothermal synthesis of platinum-group-metal nanoparticles by using HEPES as a reductant and stabilizer.

Platinum-group-metal (Ru, Os, Rh, Ir, Pd and Pt) nanoparticles are synthesized in an aqueous buffer solution of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) (200 mM, pH 7.4) under hydrothermal conditions (180 degrees C). Monodispersed (monodispersity: 11-15%) metal nanoparticles were obtained with an average particle size of less than 5 nm (Ru: 1.8+/-0.2, Os: 1.6+/-0.2, Rh: 4.5+/-0.5, Ir: 2.0+/-0.3, Pd: 3.8+/-0.4, Pt: 1.9+/-0.2 nm). The size, monodispersity, and stability of the as-obtained metal nanoparticles were affected by the HEPES concentration, pH of the HEPES buffer solution, and reaction temperature. HEPES with two tertiary amines (piperazine groups) and terminal hydroxyl groups can act as a reductant and stabilizer. The HEPES molecules can bind to the surface of metal nanoparticles to prevent metal nanoparticles from aggregation. These platinum-group-metal nanoparticles could be deposited onto the surface of graphite, which catalyzed the aerobic oxidation of alcohols to aldehydes.

Oxidative dissolution of silver nanoparticles by biologically relevant oxidants: a kinetic and mechanistic study.

The oxidative dissolution of silver nanoparticles (AgNPs) plays an important role in the synthesis of well-defined nanostructured materials, and may be responsible for their activities in biological systems. In this study, we use stopped-flow spectrophotometry to investigate the kinetics and mechanism of the oxidative dissolution of AgNPs by H(2)O(2) in quasi-physiological conditions. Our results show that the reaction is first order with respect to both [Ag(0)] and [H(2)O(2)], and parallel pathways that involve the oxidation of H(2)O(2) and HO(2)(-) are proposed. The order of the reaction is independent of the size of the AgNPs (approximately 5-20 nm). The rate of dissolution increases with increasing pH from 6.0 to 8.5. At 298 K and I=0.1 M, the value of k(b) is five orders of magnitude higher than that of k(a) (where k(a) and k(b) are the rate constants for the oxidative dissolution of AgNPs by H(2)O(2) and HO(2)(-), respectively). In addition, the effects of surface coating and the presence of halide ions on the dissolution rates are investigated. A possible mechanism for the oxidative dissolution of AgNPs by H(2)O(2) is proposed. We further demonstrate that the toxicities of AgNPs in both bacteria and mammalian cells are enhanced in the presence of H(2)O(2), thereby highlighting the biological relevance of investigating the oxidative dissolution of AgNPs.

Graphite-supported gold nanoparticles as efficient catalyst for aerobic oxidation of benzylic amines to imines and N-substituted 1,2,3,4-tetrahydroisoquinolines to amides: synthetic applications and mechanistic study.

Selective oxidation of amines using oxygen as terminal oxidant is an important area in green chemistry. In this work, we describe the use of graphite-supported gold nanoparticles (AuNPs/C) to catalyze aerobic oxidation of cyclic and acyclic benzylic amines to the corresponding imines with moderate-to-excellent substrate conversions (43-100%) and product yields (66-99%) (19 examples). Oxidation of N-substituted 1,2,3,4-tetrahydroisoquinolines in the presence of aqueous NaHCO3 solution gave the corresponding amides in good yields (83-93%) with high selectivity (up to amide/enamide=93:4) (6 examples). The same protocol can be applied to the synthesis of benzimidazoles from the reaction of o-phenylenediamines with benzaldehydes under aerobic conditions (8 examples). By simple centrifugation, AuNPs/C can be recovered and reused for ten consecutive runs for the oxidation of dibenzylamine to N-benzylidene(phenyl)methanamine without significant loss of catalytic activity and selectivity. This protocol "AuNPs/C+O2" can be scaled to the gram scale, and 8.9 g (84 % isolated yield) of 3,4-dihydroisoquinoline can be obtained from the oxidation of 10 g 1,2,3,4-tetrahydroisoquinoline in a one-pot reaction. Based on the results of kinetic studies, radical traps experiment, and Hammett plot, a mechanism involving the hydrogen-transfer reaction from amine to metal and oxidation of M-H is proposed.

Controlled self-assembly of functional metal octaethylporphyrin 1 D nanowires by solution-phase precipitative method.

Metal octaethylporphyrin M(OEP) (M = Ni, Cu, Zn, Pd, Ag, and Pt) nanowires are fabricated by a simple solution-phase precipitative method. By controlling the composition of solvent mixtures, the diameters and lengths of the nanowires can be varied from 20 to 70 nm and 0.4 to 10 microm, respectively. The Ag(OEP) nanowires have lengths up to 10 microm and diameters of 20-70 nm. For the M(OEP) nanowires, the growth orientation and packing of M(OEP) molecules are examined by powder XRD and SAED measurements, revealing that these M(OEP) nanowires are formed by the self-assembly of M(OEP) molecules through intermolecular pi...pi interactions along the pi...pi stacking axis, and the M(2+) ion plays a key role in the nanowire formation. Using the bottom contact field effect transistor structure and a simple drop-cast method, a single-crystal M(OEP) nanowires-based field effect transistor can be readily prepared with prominent hole transporting behaviour and charge-carrier mobility up to 10(-3)-10(-2) cm(2) V(-1) s(-1) for holes, which are 10 times higher than that of vacuum-deposited M(OEP) organic thin-film transistors (OTFTs).

A non-cross-linked soluble polystyrene-supported ruthenium catalyst for carbenoid transfer reactions.

Ruthenium nanoparticles supported on non-cross-linked soluble polystyrene were prepared by reacting [RuCl(2)(C(6)H(5)CO(2)Et)](2) with polystyrene in open air. They effectively catalyze intra- and intermolecular carbenoid insertion into C-H and N-H bonds, alkene cyclopropanation, and ammonium ylide/[2,3]-sigmatropic rearrangement reactions. This supported ruthenium catalyst is much more reactive than [RuCl(2)(p-cymene)](2) and [Ru(Por)CO] for catalytic intermolecular carbenoid C-H bond insertion into saturated alkanes. By using alpha-diazoacetamide as a substrate for intramolecular carbenoid C-H insertion, the supported ruthenium catalyst can be recovered and reused for ten successive iterations without significant loss of activity.

Fabrication of bismuth subcarbonate nanotube arrays from bismuth citrate.

Bismuth subcarbonate ((BiO)2CO3) nanotubes with uniform diameters of about 3-5 nm were fabricated from bismuth citrate; these nanotubes exhibit antibacterial properties against Helicobacter pylori (50% inhibition at 10 microg mL(-1)), a bacterium causing peptic ulcers and gastritis.