Electroreflectance spectra of Ag(111) electrodes

Electroreflectance (ER) spectra of Ag(111) evaporated electrodes on mica in aqueous electrolytes were measured within the wavelength range of 500 to 200 nm for p- and s-polarized light as a function of the angle of incidence, bias potential and surface roughness. These spectra show structures which were not seen in previously obtained ER spectra on slightly rough, polycrystalline Ag electrodes. The effect of volume and surface plasma excitation on the spectra is clearly indicated. The experimental results cannot be reproduced satisfactorily by any currently employed theoretical model which takes only free electron effects into account. The influence of the electric field on the bound electrons in the surface layer obviously cannot be neglected. It is demonstrated that the surface plasma resonance is shifted in energy by the applied electric field.     

Concerted Determination of the Hydrogen Atom and Electron Transfer Capacity of Lipid Soluble Reducing Agents

This paper describes a method based on square wave voltammetry to evaluate either the electron transfer or the hydrogen atom transfer of lipid soluble antioxidants such as dl ‐mix‐tocopherol, BHT, ethoxyquin and retynil acetate. The electron transfer (ET) capacity was evaluated by the peak current, peak potential and the area under the anodic wave, whereas the hydrogen atom transfer (HAT) capacity by the kinetic rate of the reaction between antioxidants and 2,2‐Azobis(2‐methylpropionamidine) dihydrochloride (AAPH). The results indicate that ethoxyquin and tocopherol have the highest ET and HAT capacity. However, HAT capacity of tocopherol, BHT and retinyl acetate depend on the concentration. The approach has the advantage to assess HAT and ET capacity of lipid soluble antioxidant in a single concerted protocol.     

The ammonia dimer equilibrium dissociation energy: convergence to the basis set limit at the correlated level

The low-energy region of the intermolecular potential energy hypersurface (PES) of the ammonia dimer was studied at the level of second-order Moller-Plesset perturbation theory (MP2) using a very large basis set. Individual minima were located on the PES employing the counterpoise (CP) correction to account for the basis set superposition error (BSSE). Apart from these canonical MP2 calculations local MP2 (LMP2) calculations were performed. For the latter the BSSE at the correlated level is inherently absent by virtue of the local truncation of the virtual space. Results from canonical and local MP2 calculations are compared and the reliability of the LMP2 method for intermolecular complexes and clusters is discussed. The canonical MP2 calculations predicted five minimum structures, the four most stable ones lying energetically very close. For these four structures single point MP2 energy calculations with a further extended basis set (1024 functions for the ammonia dimer) were performed. The equilibrium dissociation energies so obtained are close to the one-particle basis set limit, as illustrated by a remaining BSSE of less than 0.2 kJ mol^?1. The geometry optimizations at the LMP2 level, using the three most stable canonical MP2 structures as initial geometries, all collapsed to a single minimum corresponding to an asymmetric structural arrangement. A canonical MP2 single point calculation, at that geometry, revealed that the LMP2 minimum structure is virtually as stable as the lowest minima on the canonical MP2 PES. Based on these calculations the global minimum of the ammonia dimer was assigned to a part of the PES represented by an asymmetric structure with an equilibrium dissociation energy of 13.5±0.3 kJ mol^?1     

Functionalized porous silicon surfaces as MALDI-MS substrates for protein identification studies

Alkyl monolayer modified porous silicon functional surfaces are employed for selective binding of proteins from complex mixtures (through washing of the deposited mixture spot using appropriate buffer) and MALDI-MS is used to detect the components retained on the surface.     

Dosimetric depth distribution of Fukushima-derived 137Cs in coniferous forest soil

Journal of Radioanalytical and Nuclear Chemistry - The ambient dose rate (ADR) in a coniferous forest floor contaminated by Fukushima-derived 137Cs was calculated for small temporal scale as a...     

Chemical force titrations of functionalized Si(111) surfaces

Chemical force titrations-plots of the adhesive force between an atomic force microscope tip and sample as a function of pH-were acquired on alkyl monolayer-derivatized Si(111) surfaces. Gold-coated AFM tips modified with thioalkanoic acid self-assembled monolayers (SAM) were employed. Alkyl monolayer-derivatized Si(111) surfaces terminated with methyl, carboxyl, and amine groups were produced via hydrosilylation reactions between 1-alkene reagents and H-terminated silicon. The functionalized surfaces were characterized using standard surface science techniques (AFM, FTIR, and XPS). Titration of the methyl-terminated surface using the modified (carboxyl-terminated) atomic force microscope tip resulted in a small pH-independent hydrophobic interaction. Titration of the amine-terminated surface using the same tip resulted in the determination of a surface pKa of 5.8 for the amine from the pH value from the maximum in the force titration curve. A pK(1/2) of 4.3 was determined for the carboxyl-terminated Si(111) in a similar way. These results will be discussed in relation to the modified Si(111) surface chemistry and organic layer structure, as well as with respect to existing results on Au surfaces modified with SAMs bearing the same functional groups.