The behavior of formic acid on Au(111) in perchloric acid solution at room temperature has been investigated by electrochemical methods and in situ scanning tunneling microscopy (STM) in the ...potential region negative to surface oxidation. Specific adsorption of formate lifts the reconstruction of the Au(111) surface. Currents for formate adsorption have been separated from those of formic acid oxidation by varying the sweep rate between 0.01 and 50 V s–1. A 2D phase transition within the formate layer adsorbed on long-range Au(111) terraces gives rise to a characteristic voltammetric needle-peak. Parallel chains of strongly bound formate have been imaged by in situ STM. Steady-state voltammetry at different formic acid concentrations shows a characteristic bell-shaped current maximum and a pronounced current jump related with the adlayer phase transition at more positive potentials. Oxidation kinetics of formic acid strongly depends on formate adsorption, which is determined by the electrode potential, the pH, and the formic acid concentration. Various adsorbates (bidentate and monodentate formate and/or carboxylate) with entirely different reactivity are supposed to play a role in the formic acid oxidation mechanism.
The effect of roasting of coffee beans and the extraction of ground coffee with different volumes of hot pressurised water on the caffeine and the total caffeoylquinic acids (CQAs) content of the ...resultant beverages was investigated. While caffeine was stable higher roasting temperatures resulted in a loss of CQAs so that the caffeine/CQA ratio was a good marker of the degree of roasting. The caffeine and CQA content and volume was determined for 104 espresso coffees obtained from coffee shops in Scotland, Italy and Spain, limited numbers of cappuccino coffees from commercial outlets and several instant coffees. The caffeine content ranged from 48-317 mg per serving and CQAs from 6-188 mg. It is evident that the ingestion of 200 mg of caffeine per day can be readily and unwittingly exceeded by regular coffee drinkers. This is the upper limit of caffeine intake from all sources recommended by US and UK health agencies for pregnant women. In view of the variable volume of serving sizes, it is also clear that the term "one cup of coffee" is not a reproducible measurement for consumption, yet it is the prevailing unit used in epidemiology to assess coffee consumption and to link the potential effects of the beverage and its components on the outcome of diseases. More accurate measurement of the intake of coffee and its potentially bioactive components are required if epidemiological studies are to produce more reliable information.
We develop a coherent beam splitter for single electrons driven through two tunnel-coupled quantum wires by surface acoustic waves (SAWs). The output current through each wire oscillates with gate ...voltages to tune the tunnel coupling and potential difference between the wires. This oscillation is assigned to coherent electron tunneling motion that can be used to encode a flying qubit and is well reproduced by numerical calculations of time evolution of the SAW-driven single electrons. The oscillation visibility is currently limited to about 3%, but robust against decoherence, indicating that the SAW electron can serve as a novel platform for a solid-state flying qubit.
•We measure antioxidant capacity and phenolics of vegetables after frying or griddling.•Heat treatments increased the concentration of phenolic compounds in vegetables.•The thermal destruction of ...cell walls and compartments release phenolic compounds.•Increment in phenolics after cooking correlates with higher antioxidant capacity.•Griddled vegetables showed the highest amounts of phenolic compounds.
The impact of cooking heat treatments (frying in olive oil, frying in sunflower oil and griddled) on the antioxidant capacity and (poly)phenolic compounds of onion, green pepper and cardoon, was evaluated. The main compounds were quercetin and isorhamnetin derivates in onion, quercetin and luteolin derivates in green pepper samples, and chlorogenic acids in cardoon. All heat treatments tended to increase the concentration of phenolic compounds in vegetables suggesting a thermal destruction of cell walls and sub cellular compartments during the cooking process that favor the release of these compounds. This increase, specially that observed for chlorogenic acids, was significantly correlated with an increase in the antioxidant capacity measured by DPPH (r=0.70). Griddled vegetables, because of the higher temperature applied during treatment in comparison with frying processes, showed the highest amounts of phenolic compounds with increments of 57.35%, 25.55% and 203.06% compared to raw onion, pepper and cardoon, respectively.
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Faceting and nanostructuring of polycrystalline gold electrodes by cathodic corrosion in concentrated potassium hydroxide electrolytes has been systematically studied at different ...electrode potentials. Current-potential curves for the restructured Au electrodes in 0.1 M H2SO4 show characteristics of Au(111) in the double-layer and oxidation region. Thus, the modified Au electrodes adopt properties typically known for well-defined single crystal surfaces. Besides the preferential surface faceting, the electrochemically active surface area (EASA) is enhanced as a function of potential, concentration and time. Scanning electron micrographs show the formation of triangular pits and nanostructures with a specific orientation confirming the formation of (111)-facets. In this way, the behavior of single crystals is accompanied with the properties of nanoparticles which are of utmost interest in electrocatalysis and surface-enhanced Raman spectroscopy (SERS). The electrocatalytic activity of the newly formed “Au(111)” surface from an Au wire has been tested towards the hydrogen evolution reaction (HER) and for the formic acid oxidation reaction (FAOR). The study of electrocatalytic reactions at these nanostructured electrodes allows to identify active centers, which are absent for extended single crystal surfaces. Adsorbed pyridine on the nanostructured Au electrodes directly shows SERS activity, while untreated polycrystalline Au is SERS-inactive. The use of cathodic corrosion of simple wires is a paradigm of SERS-applications in electrochemistry with clean Au electrodes that provide properties of Au(111) single crystals.
The electrocatalytic hydrogen evolution reaction (HER) is employed to monitor the kinetics of potential-induced surface reconstruction of Au(111) in contact with either 0.1 M H2SO4 or 0.1 M HClO4 in ...the temperature range between 17 and 25 °C. An apparent activation energy varying between 0.6 and 0.7 eV is found for the reconstruction process at 20 °C in the potential range between −0.1 and −0.7 V vs. saturated mercury-mercurous sulfate electrode (MSE). The rate constant of the first-order formation kinetics shows an exponential dependence on electrode potential and decreases with more negative potentials. The potential-dependence is associated with an increase in bond strength for Au surface atoms with increasing negative excess charge. Specific adsorption of anions hinders surface reconstruction at potentials close to the potential of zero charge, while the presence of carbon monoxide causes a significant enhancement of the rate for potential-induced Au(111) reconstruction.
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•The hydrogen evolution reaction (HER) is used as structure-sensitive probe.•Au(111) surface reconstruction rate decreases for more negative potentials.•First-order kinetics is observed for potential-induced surface reconstruction.•The activation energy ranges from 0.6 to 0.73 eV.•Adsorption of carbon monoxide enhances surface reconstruction rate.
We extract the phase coherence of a qubit defined by singlet and triplet electronic states in a gated GaAs triple quantum dot, measuring on time scales much shorter than the decorrelation time of the ...environmental noise. In this nonergodic regime, we observe that the coherence is boosted and several dephasing times emerge, depending on how the phase stability is extracted. We elucidate their mutual relations, and demonstrate that they reflect the noise short-time dynamics.
Electrical stimulation of the brain has become a mainstay of fundamental neuroscience research and an increasingly prevalent clinical therapy. Despite decades of use in basic neuroscience research ...and the growing prevalence of neuromodulation therapies, gaps in knowledge regarding activation or inactivation of neural elements over time have limited its ability to adequately interpret evoked downstream responses or fine‐tune stimulation parameters to focus on desired responses. In this work, in vivo two‐photon microscopy was used to image neuronal calcium activity in layer 2/3 neurons of somatosensory cortex (S1) in male C57BL/6J‐Tg(Thy1‐GCaMP6s)GP4.3Dkim/J mice during 30 s of continuous electrical stimulation at varying frequencies. We show frequency–dependent differences in spatial and temporal somatic responses during continuous stimulation. Our results elucidate conflicting results from prior studies reporting either dense spherical activation of somas biased toward those near the electrode, or sparse activation of somas at a distance via axons near the electrode. These findings indicate that the neural element specific temporal response local to the stimulating electrode changes as a function of applied charge density and frequency. These temporal responses need to be considered to properly interpret downstream circuit responses or determining mechanisms of action in basic science experiments or clinical therapeutic applications.
Neuronal microstimulation can treat neurological disorders, but the therapeutic mechanism is not well understood. Microstimulation in mouse cortex produced a spatiotemporal response, activating a sparse population of neurons only at the onset of stimulation (red), and a dense population of neurons throughout the stimulation duration (yellow). Vessels shown in blue.
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