Synthesis and structure determination of bimetallic Au/Cu nanoparticles

The synthesis of bimetallic nanoparticles has become so important in recent times due to its multi-faceted applications. The structure of the synthesised particles influences directly their properties. In this paper, we report the synthesis of Au/Cu nanoparticles by a simultaneous reduction method, considering three different molar concentrations (AuCu, AuCu₃ and Au₃Cu) of the components. In order to determine the size and structure of the obtained clusters, the particles were examined by optical spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. One of the major factors, the minimum bimetal formation energy, was calculated by an embedded-atom method. The relation between the Au/Cu proportions has been demonstrated to affect the size of the particles and the corresponding structures. From the basic structural analysis it is found that the particles were fcc-like, multiple twin or multiple defect particles for the different Au/Cu concentrations. The smallest particles were identified for the Au/Cu sample with 50% of each, and the most crystalline structures were also obtained in the same sample. PACS 61.46.+w; 61.16.-d; 31.15.Qg     

Preparation of Ultrafine Colloidal Gold Particles using a Bioactive Molecule

Synthesis of nanometer-sized particles with new physical properties is an area of tremendous interest. In metal particles, the changes in size modify the electron density in the particles, which shifts the plasmon band. The most significant size effects occur when the particles are ultrafine (size is <10 nm). Thus the synthesis of ultrafine metal particles is enormously important to exploit their unique and selective application. Here we report a novel method for the synthesis of ultrafine gold particles in the size range of 0.5–3 nm using dopamine hydrochloride (dhc), an important neurotransmitter. This is the first time where such an important bioactive molecule like dhc has been used as a reagent for the transformation of Au(III) to Au(0). The synthesis is carried out, for the first time, either in simple aqueous or in a nonionic micellar (for example Triton X-100 (TX-100)) medium. The gold sol has a beautiful yellow–brown color showing _max at 470 nm. The appearance of the absorption peak at substantially shorter wavelength (usually gold sol absorbs at 520 nm) indicates that the particles are very small. The method discussed here is very simple, reproducible and does not involve any reagent, which contains 'P' or 'S' atoms. Also in this case no polymer or dendrimer or thiol-related stabilizer is used. The effects of different parameters (such as the presence or absence of O₂, temperature, TX-100 concentration and dhc concentration) on the formation of ultrafine gold particles are discussed. The effects of 3-mercapto propionic acid and pyridine on the ultrafine gold sol are also studied and compared with those on photochemically prepared gold sol. It is observed that 3-mercapto propionic acid dampens the plasmon absorption at 470 nm of ultrafine gold particles. Pyridine, on the other hand, has no effect on the particles.     

Dramatic enhancement of third-harmonic generation in three-dimensional photonic crystals

We have observed a dramatic enhancement of third-harmonic generation in 3D polystyrene-air photonic crystals pumped by a near infrared laser beam. As the pump wavelength is tuned, the peak of the enhancement occurs when the third-harmonic wavelength approaches the short-wavelength edge of the band gap. We show that the origin of the enhancement is phase matching provided by the periodic structure of the photonic crystals.     

Solution phase evolution of AuSe nanoalloys in Triton X-100 under UV-photoactivation

A solution phase UV-irradiation technique has been exploited to produce an AuSe nanoalloy through fusion of preformed Au (photoproduced) and Se (chemically prepared) in a micellar (TX-100) medium.     

Contents of Volume 2 (2003)

Volume Contents

Contents of Volume 2 (2003)     

A dimeric pervanadyl (VO2+) complex with a tridentate Schiff base ligand

A di(-oxo)-bridged dinuclear complex, [VO₂(pamh)]₂ was isolated by reacting bis(acetylacetonato)vanadium(IV) and the Schiff base, N-(anisoyl)-N-(picolinylidene)-hydrazine (Hpamh) in acetonitrile. The complex crystallizes in the space group ;1; (#2) on crystallographic inversion center. Crystal data: a = 8.2202(12) Å, b = 9.8389(19) Å, c = 10.1907(17) Å, = 68.245(15)°, = 74.47(2)°, = 66.710(19)°, V = 696.0(2) ų, and Z = 1. The physical properties of the complex and the structural parameters are consistent with the +5 oxidation state of the metal ions. The monomeric VO₂(pamh) unit is square-pyramidal. The planar mononegative ligand (pamh^–) coordinates the metal ion via the pyridine-N, the imine-N, and the amide-O atoms. One of the oxo groups completes the NNOO basal plane and also participates in the Vndash;Ondash ;V bridge formation. The other oxo group satisfies the fifth apical coordination site. The molecular structure of the dimeric complex, [VO₂(pamh)]₂ can be described as two edge-shared distorted VO₄N₂ octahedra.     

Study of gain flatness for multi-channel amplification in single stage EDFA for WDM applications

In this paper, gain flatness is studied for simultaneous 16-ITU-T channel amplifications at C-band (1,532–1,558 nm) in a single stage EDFA for WDM application at different average inversion levels. The inversion levels are varied due to the change of the input signal levels from the targeted operating point and also for dropping few numbers of channels. Specially designed gain flattening filter (GFF) is used in order to get the flat gain with gain variation ±0.5 dB for −20 dBm/ch input signal power (total input signal power is −8.0 dBm) at a fixed average inversion level which is maintained by proper selection of optimum fibre length and pump power. A specific loss spectrum of GFF is obtained by writing a chirped fibre Bragg grating of length 20 mm. Gain variations are studied by changing the total input signal levels from −8.0 dBm to −20.0 dBm and maintained within 20.0 ± 0.5 dB by using automatic gain control (AGC) circuit. About 15 out of 16 channels are dropped and observed ± 0.5 dB gain-variation which is an important parameter in optical network system.     

Synthesis of new fluorescently labeled glycosylphosphatidylinositol (GPI) anchors

The borondipyrromethene (BODIPY) labeled new glycosylphosphatidylinositol (GPI) molecules were synthesized as cellular probes to study the chemical basis of microdomain organization of GPI-anchored proteins and cholesterol in plasma membrane. The synthesis enabled by a new stereo-selective glycosylation of myo-d-inositol acceptor led to the preparation of optically pure glucosaminyl-(1-6)-α-phosphatidyl-myo-d-inositol and its unnatural stereoisomer.     

Visibility with One Reflection

We extend the concept of the polygon visible from a source point S in a simple polygon by considering visibility with two types of reflection, specular and diffuse. In specular reflection a light ray reflects from an edge of the polygon according to the rule: the angle of incidence equals the angle of reflection. In diffuse reflection a light ray reflects from an edge of the polygon in all inward directions. Several geometric and combinatorial properties of visibility polygons under these two types of reflection are described, when at most one reflection is permitted. We show that the visibility polygon Vs(S) under specular reflection may be nonsimple, while the visibility polygon Vd(S) under diffuse reflection is always simple. We present a Θ(n ² ) worst-case bound on the combinatorial complexity of both Vs(S) and Vd(S) and describe simple O(n ² log ² n) time algorithms for constructing the sets. Received September 27, 1995, and in revised form October 24, 1997.     

An efficient and facile synthesis of Zn(II) complexes with 2-substituted benzothiazoles and glycine- and alanine-based ligands having antifungal and antibacterial activities

We carried out an efficient and facile synthesis of Zn(II) complexes with heterocyclic ligands based on 2-substituted benzothiazole moieties, 2-(2′-hydroxynaphthyl)benzothiazole, 2-(2′-hydroxyphenyl)benzothiazole, and 2-(2′-merceptophenyl)benzothiazole, and amino acids, glycine and alanine, are reported and also examined for antifungal and antibacterial activities. Ligands and complexes were characterized by FTIR, ¹H NMR, and elemental analysis.