When Langmuir is too simple: H2 dissociation on Pd(111) at high coverage

Recent experiments of H2 adsorption on Pd(111) [Nature (London) 422, 705 (2003)]] have questioned the classical Langmuir picture of second order adsorption kinetics at high surface coverage requiring pairs of empty sites for the dissociative chemisorption. Experiments find that at least three empty sites are needed. Through density functional theory, we find that H2 dissociation is favored on ensembles of sites that involve a Pd atom with no direct interaction with adsorbed hydrogen. Such active sites are formed by aggregation of at least 3 H-free sites revealing the complex structure of the "active sites."     

Networks of innovation or networks of opportunity? The making of the Spanish antibiotics industry

The pharmaceutical industry is a typically research-intensive, first world-industry. This article seeks to explain why it has been so difficult for late industrialised nations to reproduce the networks of innovation on which the design and manufacturing of new drugs has historically based, and why alternative concepts are needed in order to understand the dynamics of science-based industries in emerging countries. The article analyses the development of the Spanish antibiotics industry, build after the World War II under the strong influence of the new international order and Spain's political framework, academic traditions and business groups. Focusing on the long-term relationships established between two Spanish companies (Antibióticos SA and Compa?ía Espa?ola de Penicilina y Antibióticos, CEPA), their American technological partners (Schenley and Merck), and their social and scientific environment, the article identifies networks of opportunity as the key institutional arrangement of this new industry in Spain. Opportunity (as opposed to innovation) networks are thus proposed to conceptualise the development of technologically complex industries in the European periphery.     

Dispersion relations and low-energy elastic scattering of charged particles from nuclei: (I). Theory

Dispersion relations for the elastic scattering of charged particles from nuclei are deduced for the case of potential scattering. The inclusion of the Coulomb interaction leads to a simple modification of the formalism developed so far for uncharged projectiles only.     

Catalytic CO oxidation by a gold nanoparticle: a density functional study

Gold is usually considered very noble. It does not oxidize, and the surface of gold cannot adsorb most molecules from the gas phase. Yet it has been found that nanometer size gold particles on different oxide supports can act as catalysts even at or below room temperature. We present self-consistent density functional calculations showing that even an isolated Au10 cluster should be able to catalyze the CO oxidation reaction even below room temperature. We use the calculations to analyze the origin of this effect and suggest that the extraordinary reactivity can be traced back to special reaction geometries available at small particles in combination with an enhanced ability of low coordinated gold atoms to interact with molecules from the surroundings.     

New method of automatic photometric determination of proteins in whole milk. II. Linearity, selectivity, and specificity

A new procedure for the preconcentration of p.p.b. concentrations of chromate from aqueous solutions has been developed. Water samples containing chromate are acidified to pH 5 and passed through an anion-exchange resin bed (AG1-X4, 100–200 mesh. Cl^? form) in ascending flow, so that the chromate is adsorbed in a narrow zone at the lower end of the resin bed. The chromate is eluted rapidly with small volumes of an acidic reductant solution which reacts with chromate on the column to form chromium(III) during the actual elution step, thus producing very high concentration factors.     

Elasticp+12C scattering between 0.3 and 2 MeV

Absolute differential cross-sections ofp+¹²C elastic scattering have been measured at _cm=89.1°, 118.7°, 146.9° for bombarding energies between 0.3 and 2.0 MeV. Revised level parameters of the first three excited states in¹³N have been extracted with aR-matrix analysis. It is shown that the influence of the bound ground-state of¹³N has an appreciable effect on low-energy scattering. Recent predictions concerning Mott-Schwinger polarization are also discussed.     

On the Reactivity of 1H‐Pyrazino[2,3‐c][1,2,6]thiadiazine 2,2‐Dioxide and Derivatives: Nucleophilic Substitution,Amination, Aldol‐Type Condensation,Oxidation, and Hydrolysis

The reactivity of the 1H‐pyrazino[2,3‐c][1,2,6]thiadiazine 2,2‐dioxide system, structurally related to pteridine, was studied, and a number of novel derivatives were synthesized. The chemical behaviors of these two related fused polyaza systems were compared.     

Quantitative gas chromatography and gas chromatography-mass spectrometry of cephalotaxus alkaloids

Plants of the genus Cephalotaxus contain many alkaloids, some of which have demonstrated antitumor activity. Analysis of crude alkaloid mixtures by gas chromatography provides quantitation of the active principles and other, non-active, alkaloids. Mass spectrometry is used to identify known alkaloids in extracts and to confirm the presence of previously unknown ones. Such data provide a means for predicting the biological activity of new plant accessions.     

Understanding the role of nanosilica particle surfaces in the thermal degradation of nanosilica-poly(methyl methacrylate) solution-blended nanocomposites: From low to high silica concentration

Nanocomposites of poly(methyl methacrylate) and 12 nm silica particles have been prepared by a casting procedure which allows the homogeneous dispersion of up to 35 wt% of silica. Twelve nanocomposites with compositions ranging from 1 to 35 wt% have been prepared and studied by Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry, Thermogravimetric Analysis and Isothermal Chemiluminescence. Thermal stability increases outstandingly as soon as 1 wt% of silica is added to PMMA. This effect is well-known but had not been explained up to now. Of the two main processes which initiate degradation in PMMA, radical formation at labile chain ends and random chain scission, it is the former which disappears in composites with 3 wt% of silica. The origin of the thermal stabilization in these polymer composites is thus the blocking of the PMMA chain end by the silica particle. At the same time, viscous flow decreases progressively, and composites with 20 wt% of silica or over are dimensionally stable even if heated at 300 °C for several hours. The concomitant decrease of viscous flow and increase of low temperature thermal stability shift the temperature range of application of these composites strongly, and the understanding of the silica surface role allows envisaging the control of the behaviour.     

Development of a group-specific immunoassay for sulfonamides: Application to bee honey analysis

A set of haptens has been synthesized in order to raise generic polyclonal antibodies against sulfonamides using different strategies. After the screening of all the immunorreagents, a highly sensitive enzyme-linked immunosorbent assay was set-up for simultaneous determination of six of these antibiotics.The developed procedure allows the screening of: sulfathiazole, sulfamethoxypyridazine, sulfapyridine, sulfamethizole, sulfasalazine and N⁴-phtalylsulfathiazole with good accuracy and precision at level 0.13 ng mL⁻¹ in buffer.The suitability of developed ELISA for its application to honey analysis has been investigated. The antimicrobials were extracted from samples with acetate buffer, and cleaned up by solid phase extraction. The mean recovery found for honey samples, spiked from 1.5 to 4.5 ng mL⁻¹ equivalents of sulfathiazole (24-72 μg sulfathiazole kg⁻¹ honey), was 106%.