Wai Yip Fan

Preparation of rhenium nanoparticles via pulsed-laser decomposition and catalytic studies.

Rhenium (Re) nanoparticles have been synthesized by pulsed-laser decomposition of ammonium perrhenate (NH(4)ReO(4)) or dirhenium decacarbonyl (Re(2)(CO)(10)) in the presence of 3-mercaptopropionic acid (MPA) as capping agent, in both aqueous and organic media. Preliminary studies showed that the MPA-capped Re nanoparticles are capable of catalyzing the isomerization of 10-undecen-1-ol to internal alkenols via long chain migration of the C=C double bond at ca. 200°C. A one-pot synthesis of graphite-coated Re nanoparticles has also been achieved by pulsed-laser decomposition of Re(2)(CO)(10), due to photo-induced catalytic graphitization of the phenyl groups of PPh(3) on the surface of rhenium nanoparticles.

Intramolecular C–C Bond Coupling of Nitriles to a Diimine Ligand in Group 7 Metal Tricarbonyl Complexes

Dissolution of M(CO)3(Br)(L(Ar)) [L(Ar) = (2,6-Cl2-C6H3-NCMe)2CH2] in either acetonitrile [M = Mn, Re] or benzonitrile (M = Re) results in C-C coupling of the nitrile to the diimine ligand. When reacted with acetonitrile, the intermediate adduct [M(CO)3(NCCH3)(L(Ar))]Br forms and undergoes an intramolecular C-C coupling reaction between the nitrile carbon and the methylene carbon of the β-diimine ligand.

Colloidal beading: sonication-induced stringing of selenium particles.

We report the preparation of monodispersed Se colloidal aggregates (dimers and trimers) via sonication-induced aggregation of spherical monomers. Control over the size and morphology of the products was achieved by changing the aging and sonication times, respectively. The possible mechanisms for the formation of colloidal aggregates were discussed. This method can provide a simple and versatile approach to the production of colloidal molecules of particles composed of different materials, which will be useful for fundamental studies related to colloidal systems.

Facile Synthesis of Single Crystalline Rhenium (VI) Trioxide Nanocubes with High Catalytic Efficiency for Photodegradation of Methyl Orange

Single-crystalline rhenium trioxide (ReO3) nanocubes have been prepared for the first time without the need of surfactants via controlled reduction of rhenium (VII) oxide (Re2O7), sandwiched between silicon wafers at 250°C. The metallic ReO3 nanocubes are magnetic and possess surface plasmon resonance (SPR) bands down to the NIR region. The nanocubes also show very high catalytic activity toward the photodegradation of methyl orange (MO) under ambient conditions. A mechanism has been proposed to account for the photodegradation process.

Cyclopentadienyl iron dicarbonyl (CpFe(CO)2) derivatives as apoptosis-inducing agents

Iron has been found to serve multiple purposes besides being an oxygen carrier. Of particular note is the generation of deleterious free radicals which can lead to the formation of tumours. However, in this work, we have found that cyclopentadienyl iron carbonyl complexes CpFe(CO)2X (X = halide, NCS, BF4− and CpFe(CO)2) can induce apoptosis in breast cancer and HeLa cell lines. Normal cells are however unaffected. A detailed study on CpFe(CO)2I shows that the complex is metabolic-stable and easily permeable across a lipid barrier. Preliminary investigations into the mode of action suggest that a Fenton-type reaction caused by CpFe(CO)2 complexes may be related to cell death.

Catalytic hydrogen evolution from hydrolytic oxidation of organosilanes with silver nitrate catalyst

In the light of uncertainty over the amount of recoverable fossil fuel reserves, hydrogen is touted to be a promising energy carrier in the future. Nevertheless, hydrogen storage remains a daunting challenge but a potential reaction for the generation of hydrogen on demand is the hydrolytic oxidation of organosilanes. Here, we demonstrate that silver nitrate, a readily available ionic salt, can catalyze the hydrolysis of organosilanes to produce hydrogen and organosilanols. In particular, turnover numbers and turnover frequencies in excess of 5 × 103 and 102 min−1 respectively are obtainable for the hydrolysis of triethylsilane at room temperature. This proposed silver nitrate mediated system is, by far, the simplest and cheapest catalytic hydrolysis of organosilanes. Results from the kinetic studies suggested a mechanistic scenario in which the hydrolysis of organosilanes is third order overall and first order in organosilane, water, and catalyst. The high hydrogen yield observed makes the silver nitrate catalyst an attractive material for hydrogen evolution.

Ligand Substitution from the (η5-DMP)Mn(CO)2(Solv) [DMP = 2,5-dimethylpyrrole, Solv = solvent] Complexes: To Ring Slip or Not to Ring Slip?

The mechanism and energetics of the displacement of solvent from photolytically generated (eta(5)-DMP)Mn(CO)(2)(Solv) complexes has been studied [DMP = 2,5-dimethylpyrrole, Solv = solvent]. Rate enhancement relative to the eta(5)-cyclopentadienyl (Cp) system is not observed in the displacement of weakly bound solvents. The bond dissociation enthalpies obtained from the kinetic analysis are in good agreement with the values obtained by detailed density functional theory (DFT) calculations. The results indicate that for both the Cp and the DMP based systems the displacement of weakly bound solvents proceeds by a dissociative or I(d) mechanism. This is in sharp contrast to CO displacement from (eta(5)-DMP)Mn(CO)(3), which is known to proceed by an associative mechanism by way of an eta(3) ring slip intermediate. The associative substitution pathway only becomes competitive with the dissociative channel when the Mn-Solv bond dissociation enthalpy is more than 33 kcal/mol.

Characterization of SiN and other transient species in a silicon tetrachloride-nitrogen discharge

Abstract Infrared diode laser absorption spectroscopy has been used to detect the A–X electronic spectrum of diatomic SiN in a SiCl 4 /N 2 plasma. The intensity of the SiN transitions with respect to the ratio of SiCl 4 :N 2 flow rate was investigated. A correlation between intense signals of SiN and the optimal growth conditions for a-SiN films reported in literature was found. This observation lends support to the importance of diatomic SiN as a film precursor. The electronic emission spectra of silicon-containing transient species were also recorded in the plasma. A brief discussion of the plasma reaction pathways of SiN is presented.

Ancillary Ligand Effects upon the Photochemistry of Mn(bpy)(CO)3X Complexes (X = Br–, PhCC–)

The photochemistry of two Mn(bpy)(CO)3X complexes (X = PhCC-, Br-) has been studied in the coordinating solvents THF (terahydrofuran) and MeCN (acetonitrile) employing time-resolved infrared spectroscopy. The two complexes are found to exhibit strikingly different photoreactivities and solvent dependencies. In MeCN, photolysis of 1-(CO)(Br) [1 = Mn(bpy)(CO)2] affords the ionic complex [1-(MeCN)2]Br as a final product. In contrast, photolysis of 1-(CO)(CCPh) in MeCN results in facial to meridional isomerization of the parent complex. When THF is used as solvent, photolysis results in facial to meridional isomerization in both complexes, though the isomerization rate is larger for X = Br-. Pronounced differences are also observed in the photosubstitution chemistry of the two complexes where both the rate of MeCN exchange from 1-(MeCN)(X) by THFA (tetrahydrofurfurylamine) and the nature of the intermediates generated in the reaction are dependent upon X. DFT calculations are used to support analysis of some of the experiments.

Modelling fluorescence lifetimes with TD-DFT: a case study with syn-bimanes

Syn-bimanes are a class of fluorophores that are widely used for labelling thiol containing biological systems. We used time-dependent density functional theory (TD-DFT) with various hybrid exchange–correlation functionals (B3LYP, PBE0, M06, BMK, CAM-B3LYP, and M06-2X) within the adiabatic approximation to study various photophysical properties of syn-bimanes, such as the absorption and emission to and from the lowest optically bright state, solvatochromism, and fluorescence lifetimes. The mean unsigned errors (MUEs) for absorption with the hybrid functionals B3LYP, PBE0, and M06, were found to be around 0.1 eV, while errors for BMK and CAM-B3LYP were higher than 0.2 eV. With the exception of B3LYP, the MUEs for emission calculated using other functionals were less than 0.2 eV. PBE0 and M06 were found to yield the most accurate fluorescence lifetime results among the tested functionals, with MUEs under 2.0 ns.