Oxidation of formic acid and carbon monoxide on gold electrodes studied by surface-enhanced Raman spectroscopy and DFT.

The oxidation of formic acid and carbon monoxide was studied at a gold electrode by a combination of electrochemistry, in situ surface-enhanced Raman spectroscopy (SERS), differential electrochemical mass spectrometry, and first-principles DFT calculations. Comparison of the SERS results and the (field-dependent) DFT calculations strongly suggests that the relevant surface-bonded intermediate during oxidation of formic acid on gold is formate HCOO- ad*. Formate reacts to form carbon dioxide via two pathways: at low potentials, with a nearby water to produce carbon dioxide and a hydronium ion; at higher potentials, with surface-bonded hydroxyl (or oxide) to give carbon dioxide and water. In the former pathway, the rate-determining step is probably related to the reaction of surface-bonded formate with water, as measurements of the reaction order imply a surface almost completely saturated with adsorbate. The potential dependence of the rate of the low-potential pathway is presumably governed by the potential dependence of formate coverage. There is no evidence for CO formation on gold during oxidation of formic acid. The oxidation of carbon monoxide must involve the carboxyhydroxyl intermediate, but SERS measurements do not reveal this intermediate during CO oxidation, most likely because of its low surface coverage, as it is formed after the rate-determining step. Based on inconclusive spectroscopic evidence for the formation of surface-bonded OH at potentials substantially below the surface oxidation region, the question whether surface-bonded carbon monoxide reacts with surface hydroxyl or with water to form carboxyhydroxyl and carbon dioxide remains open. The SERS measurements show the existence of both atop and bridge-bonded CO on gold from two distinguishable low-frequency modes that agree very well with DFT calculations.     

Characterization of the inhibition of enveloped virus infectivity by the cationic acrylate polymer eudragit E100

The antiviral effects of the cationic acrylate polymer E100 on a panel of lipid-enveloped viruses and the interactions involved are studied. The treatment of several common viruses with E100 induced a dose-dependent inhibition of the infectivity of viruses below the detection limit of the assays employed. Similarly, the treatment of human sera infected with HIV or HCV reduced virus RNA plasma levels to undetectable values. This implies that Eudragit E100 can interact with enveloped viruses, even in the presence of proteins, through a mechanism that is not reversed by titration of the positively charged groups of the polymer, opening the possibility to remove viral particles with the polymer as it is eliminated.     

Interface capacitance of nano-patterned electrodes

By employing numerical solutions of the Poisson–Boltzmann equation we have studied the interface capacitance of flat electrodes with stripes of different potentials of zero charge ?_pzc. The results depend on the ratio of the width of the stripes l to the dielectric screening length in the electrolyte, the Debye length d_Debye, as well as on the difference Δ?_pzc in relation k_BT/e. As expected, the capacitance of a striped surface has its minimum at the mean potential of the surface if l/d_Debye << 1 and displays two minima if l/d_Debye >> 1. An unexpected result is that for Δ?_pzc ? 0.2V, the transition between the two extreme cases does not occur when l ? d_Debye, but rather when l > 10d_Debye. As a consequence, a single minimum in the capacitance is observed for dilute electrolytes even for 100 nm wide stripes. The capacitance at the minimum is however higher than for homogeneous surfaces. Furthermore, the potential at the minimum deviates significantly from the potential of zero mean charge on the surface if l > 3d_Debye and Δ?_pzc is larger than about 4k_BT/e. The capacitance of stepped, partially reconstructed Au(11n) surfaces is discussed as an example. Consequences for Parsons–Zobel-plots of the capacitances of inhomogeneous surfaces are likewise discussed.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

Dielectric spectroscopy of bidisperse colloidal suspensions

Tuning the luminescence intensity of fluorophores using nanoparticles has shown great potential for the detection of inorganic metal ions, viruses, and proteins. The enhancement or quenching of a dye's fluorescence intensity is strongly dependent on the spatial separation of the dye from the nanoparticle surface. To extend luminescence probing from the solution platform to the solid-state platform, we explored and performed dye quenching assessment using an array format in this study. We report the distance-dependent fluorescence behavior of Au-DNA conjugates prepared by equilibrating phosphine-stabilized gold nanoparticles (AuNPs) of 10-nm size with the designed spacer ds-DNA consisting of thiol-modified target and Cy3-labeled complementary probe of different lengths (5-20 nm). The Cy3-labeled products were immobilized onto MPTMS (3-mercaptopropyltrimethoxysilane)-modified glass substrates and then excited with a 532-nm laser source. Quenching efficiency of AuNPs with increasing Au-to-dye distance was assessed using ligand exchange of the thiolated oligonucleotide by 2-mercaptoethanol (ME) to obtain free Cy3-DNA probe, thus eliminating nanoparticle effect on the dye's luminescence intensity. Effective exchange, revealed by UV-vis absorption and fluorescence profiles, was achieved in a few minutes. It was observed that fluorescence quenching of Au-DNA-Cy3 assessed using the array format was consistent with the result in solution phase for the conjugates with up to 10-nm Au-to-Cy3 separation distance.     

Reduction of NO adlayers on Pt(110) and Pt(111) in acidic media: evidence for adsorption site-specific reduction

We present a combined in situ Fourier transform infrared reflection-absorption spectroscopy and voltammetric study of the reduction of saturated and subsaturated NO adlayers on Pt(111) and Pt(110) single-crystal surfaces in acidic media. The stripping voltammetry experiments and the associated evolution of infrared spectra indicate that different features (peaks) observed in the voltammetric profile for the electrochemical reduction of NO adlayers on the surfaces considered are related to the reduction of NO(ads) at different adsorption sites and not to different (consecutive) processes. More specifically, reduction of high- and intermediate-coverage (ca. 0.5-1 monolayers (ML)) NO adlayers on Pt(110) is accompanied by site switching from atop to bridge position, in agreement with the ultra-high-vacuum data. On Pt(111) linearly bonded (atop) NO and face-centered cubic 3-fold-hollow NO species coexist at high coverages (0.25-0.5 ML) and can be reduced consecutively and independently. On Pt(111) and Pt(110) electrodes, linearly bonded NO species are more reactive than multifold-bonded NO species. Both spectroscopic and voltammetric data indicate that ammonia is the main product of NO(ads) reduction on the two surfaces examined.     

Amphipathic and membrane-destabilizing properties of the cationic acrylate polymer Eudragit E100

The cationic acrylate polymer Eudragit E100 (E100) produces a biphasic effect on the stability of casein micelles disrupting their internal structure. These results suggested that this polymer could have some amphipathic character. Therefore, in this study the polymer was characterized with respect to its interaction with different amphipathic systems (bile-acid micelles, lipoproteins and liposomes), cell membranes (red blood cells) and virus membranes (Herpes simplex type 2 virus). As with caseins, a biphasic effect was observed with bile acids with a precipitation phase at low polymer/bile acid ratio and a solubilization phase when the polymer concentration was increased. Upon interaction with human plasma, an important reduction in cholesterol and triglycerides was observed upon remotion of E100 by a rise in pH to 8.5 and centrifugation. In agreement with this finding, an important reduction in plasma lipoproteins was observed upon its treatment with E100 and further remotion by pH rise and centrifugation. However, the amount of the major protein components of human plasma and the activity of several enzymes and antibodies were not affected by their treatment with E100. The membrane-destabilizing properties of E100 were confirmed by its lytic activity on liposomes and red blood cells and by an important antiviral effect of E100 on Herpes simplex virus type 2. Altogether, these results show that, despite its water solubility and cationic character, E100 displays a significative amphipathic and membrane-destabilizing character with potential biotechnological applications. [diagram in text].