H 2MoO 4 and H 2WO 4 upon direct laser desorption produce small clusters in the gas phase, extending up to 4500 and 7200 Da, respectively. The clustering patterns are quite similar for the two systems. The mass difference between successive peaks differ with increasing mass number as different kinds of structures become possible. A distinct planar to three-dimensional structural cross over is observed around the M 8 cluster. Possible structures of these clusters are presented. MoO 3 and WO 3 were also used as starting materials, which yielded the same clusters. © 2004 Elsevier B.V. All rights reserved.

Pradeep Thalappil

Department Of Chemistry

D. M. David Jeba Singh

alcohol derivative

alkane derivative

Molybdenum

oxide

TUNGSTEN DERIVATIVE

article

chemical analysis

chemical reaction

chemical structure

Desorption

laser

matrix assisted laser desorption ionization time of flight mass spectrometry

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Chemical Physics Letters

During the course of a study on the clustering of WSe and WS mixtures in the gas phase using laser desorption ionization (LDI) mass spectrometry, we observed several anionic WO clusters. Three distinct species, W 6O19, W13O29, and W 14O32, stand out as intense peaks in the regular mass spectral pattern of tungsten oxide clusters suggesting unusual stabilities for them. Moreover, these clusters do not fragment in the postsource decay analysis. While trying to understand the precursor material, which produced these clusters, we found the presence of nanoscale forms of tungsten oxide. The structure and thermodynamic parameters of tungsten clusters have been explored using relativistic quantum chemical methods. Our computed results of atomization energy are consistent with the observed LDI mass spectra. The computational results suggest that the clusters observed have closed-cage structure. These distinct W13 and W14 clusters were observed for the first time in the gas phase. © 2010 American Chemical Society.

Fulltext

Journal of Physical Chemistry A

Closed-cage tungsten oxide clusters in the gas phase

Positively charged ions, TenS4+ (n = 1-4), are detected in the laser desorption mass spectra of bulk TeS. Enhanced intensities for these species are seen only for the positive ions. The clusters are formed as a result of the ion chemistry in the gas phase as elemental mixtures of Te and S also give the same clusters, albeit with different intensity distribution. Computational studies confirm the structural and electronic stability of these species. Te3S4+ and Te4S4+ clusters are observed for the first time in the gas phase. © 2005 Elsevier B.V. All rights reserved.

TenS4+ (n = 1-4) clusters in the gas phase

The antibacterial drug ciprofloxacin (cfH) has been used to protect gold nanoparticles of two different mean diameters, 4 and 20 nm. The protection is complete with about 65 and 585 cfH molecules covering 4 and 15 nm particles, respectively. The nature of binding has been investigated by several analytical techniques. The nitrogen atom of the NH moiety of piperazine group binds on the gold surface, as revealed by voltammetric and spectroscopic studies. The cfH-adsorbed particles are stable in the dry state as well as at room temperature, and as a result, redispersion is possible. The rate of release of the drug molecule from the nanoparticles is more in the basic medium than in pure water, and the kinetics depend on the size of the particle; faster desorption is seen in smaller particles. The bound cfH is fluorescent, and this property could be used in biological investigations. This study shows that metal nanoparticles could be useful carriers for cfH and fluoroquinolone molecules. Most of the bound molecules could be released over an extended period of time.

Langmuir

Ciprofloxacin-protected gold nanoparticles

Temperature-dependent dynamics of monolayer-protected Au and Ag nanoclusters and silver thiolates have been investigated with quasielastic neutron scattering. The simplest motion in these systems is the uniaxial rotation of the chain, which evolves slowly with temperature. While longer chain monolayers (above C 8) on Au clusters are rotationally frozen at room temperature, dynamic freedom exists in lower chain lengths. In the superlattice solids of Ag clusters, the dynamics evolve slowly, and at superlattice melting, all the chains are dynamic. The data are consistent with a structure in which the monolayers form bundles on the planes of metal clusters and such bundles interdigitate, forming the cluster assemblies. In thiolates, the dynamics is distinctly different in long- and short-chain systems. It arises abruptly at the melting temperature in C 12 but a bit sluggishly in C 18, whereas in C 6 and C 8, it evolves with temperature. The data are correlated with temperature-dependent infrared spectroscopy, which preserves some of the progression bands even after the bulk melting temperature, but loses them completely above 498 K, suggesting a possible partially ordered phase in this temperature window. Our studies have established the fact that (a) no rotational freedom exists in several of the alkyl chain monolayers on metal cluster solids at room temperature, (b) simple uniaxial rotation explains the dynamics of these systems, (c) the dynamics evolves slowly, and (d) such motions arise abruptly in long-chain layered thiolates which are similar to planar thiolates. We find that longer chains can possess conformational defects at higher temperatures, which slow the rotational dynamics.

Journal of Physical Chemistry B

Dynamics of alkyl chains in monolayer-protected au and ag clusters and silver thiolates: A comprehensive quasielastic neutron scattering investigation

29 kDa gold cluster molecules with thiol protection were synthesized and size separated by chromatography. Their direct laser desorption leads to large scale clustering and the mass spectral features extend up to 500 kDa. Effect of alkanethiol chain length on clustering suggests that monolayer interaction is the key to this phenomenon. Role of different matrices on clustering in the matrix assisted laser desorption ionization (MALDI) process has been investigated. © 2004 Elsevier B.V. All rights reserved.

Gas phase aggregates of protected clusters

Nanometer sized gold and silver clusters protected with 2- mercaptobenzothiazole monolayers have been prepared and characterized by various spectroscopic methods. Optical absorption spectra show features assigned to charge-transfer excitation between the monolayer and the cluster, in addition to a red shifting and reduction of plasmon absorption. The monolayers on clusters are compared with the corresponding 2D-monolayers investigated previously. The dominant adsorbate geometries on these clusters are different. Whereas the temperature dependent dynamics are minimal for 2D- SAMs, they are significant for monolayers on 3D surfaces, which is attributed to the decreased packing density on the cluster surfaces. The thermal stability of these monolayers is high and comparable to that of alkanethiolate monolayers. The monolayers undergo irreversible structural changes upon heating, which have been studied by differential scanning calorimetry and IR spectroscopy.

Journal of Materials Chemistry

2-Mercaptobenzothiazole protected Au and Ag clusters

Child Abuse Review

Female Genital Mutilation Awareness, CFAB, London, 2014. Available free: http://www.safeandsecureinfo.com/fgm_awareness/fgm_read_section1.html Female Genital Mutilation: Recognising and Preventing FGM, Home Office, London, 2014. Available free: http://www

Journal	Chemical Physics Letters
ISSN	00092614
Open Access	No