Multiple adsorbate interactions between reduced CO₂ adsorbates and either allyl alcohol or propargyl alcohol residues on platinum in 0.5 M sulphuric acid

The interaction of propargyl alcohol and allyl alcohol with a platinum (Pt) electrode modified by the presence of reduced CO2 adsorbates (r-CO2) is studied through voltammetry and potentiostatic current transients by using a flow cell technique. The interaction between each alcohol and r-CO2 is promoted at three constant potentials corresponding to different degrees of Pt surface coverage by H-atoms. For both alcohols the anodic stripping peaks and the charge balance are interpreted in terms of the formation of composed adsorbates. Based upon the probable r-CO2 structure and H-bonding interactions between r-CO2 and the alcohol molecules or their adsorbed residues, average alcohol residues/r-CO2 molecular ratios are estimated.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

A contribution to the mechanism of “reduced” CO₂ adsorbates electro-oxidation from combined spectroelectrochemical and voltammetric data

The nature of reduced CO2 adsorbates, as well as the mechanisms for their electro-oxidation on platinum, have been reviewed through the light of new experimental data obtained by cyclic voltammetry and by Fourier transform infrared reflectance spectroscopy. Three different “reduced” CO2 adsorbates are described as “‘ensembles”. It is suggested that they involve different extents of adsorbed entities, among which weakly bound and strongly bound hydrogen atoms play the most important role.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

A Semiempirical Quantum Approach to the Formation of Carbon Dioxide Adsorbates on Pt(100) and Pt(111) Cluster Surfaces

The geometries and binding energies of CO2 adsorbates on Pt(100) and Pt(111) cluster surfaces were calculated by means of an improved version of the extended Hückel molecular orbital method. The polarization of the surface by an applied electric potential and coadsorption of H atoms were included in the model. For simulated applied potentials in the range -1.0 to 1.0 V, CO2 coordination geometries (side-on, formate) involving two adsorbate atoms bonded to the surface are favored, regardless the surface topology and the presence of coadsorbed H atoms. In agreement with experiment, larger binding energies are always calculated for the Pt(100) cluster surface.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Multiple adsorbate interactions between reduced CO₂ adsorbates and either allyl alcohol or propargyl alcohol residues on platinum in 0.5 M sulphuric acid

The interaction of propargyl alcohol and allyl alcohol with a platinum (Pt) electrode modified by the presence of reduced CO2 adsorbates (r-CO2) is studied through voltammetry and potentiostatic current transients by using a flow cell technique. The interaction between each alcohol and r-CO2 is promoted at three constant potentials corresponding to different degrees of Pt surface coverage by H-atoms. For both alcohols the anodic stripping peaks and the charge balance are interpreted in terms of the formation of composed adsorbates. Based upon the probable r-CO2 structure and H-bonding interactions between r-CO2 and the alcohol molecules or their adsorbed residues, average alcohol residues/r-CO2 molecular ratios are estimated.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

A contribution to the mechanism of “reduced” CO₂ adsorbates electro-oxidation from combined spectroelectrochemical and voltammetric data

The nature of reduced CO2 adsorbates, as well as the mechanisms for their electro-oxidation on platinum, have been reviewed through the light of new experimental data obtained by cyclic voltammetry and by Fourier transform infrared reflectance spectroscopy. Three different “reduced” CO2 adsorbates are described as “‘ensembles”. It is suggested that they involve different extents of adsorbed entities, among which weakly bound and strongly bound hydrogen atoms play the most important role.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Second harmonic generation response by gold nanoparticles at the polarized water/2-octanone interface: from dispersed to aggregated particles

Gold nanoparticles with a diameter of approximately 20 nm have been observed at the polarized water/2-octanone interface by the nonlinear optical technique of second harmonic generation. Electric field induced adsorption of the gold particles at this liquid/liquid interface is clearly observed and confirms that these are negatively charged. The process is quasi-reversible at high potential sweep rates, but aggregation at the interface is observed at slower sweep rates through the loss of the nonlinear optical signal. The time evolution of the second harmonic signal is also reported during potential step experiments. After a rapid increase due to adsorption, a continuous decrease in the nonlinear optical signal intensity is observed due to aggregation of the particles into large islands at the interface. Diffusion of these large islands at the interface was observed for a longer timescale through large signal fluctuations

A Semiempirical Quantum Approach to the Formation of Carbon Dioxide Adsorbates on Pt(100) and Pt(111) Cluster Surfaces

The geometries and binding energies of CO2 adsorbates on Pt(100) and Pt(111) cluster surfaces were calculated by means of an improved version of the extended Hückel molecular orbital method. The polarization of the surface by an applied electric potential and coadsorption of H atoms were included in the model. For simulated applied potentials in the range -1.0 to 1.0 V, CO2 coordination geometries (side-on, formate) involving two adsorbate atoms bonded to the surface are favored, regardless the surface topology and the presence of coadsorbed H atoms. In agreement with experiment, larger binding energies are always calculated for the Pt(100) cluster surface.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Rivaroxaban or aspirin for patent foramen ovale and embolic stroke of undetermined source: a prespecified subgroup analysis from the NAVIGATE ESUS trial

Background: Patent foramen ovale (PFO) is a contributor to embolic stroke of undetermined source (ESUS). Subgroup analyses from previous studies suggest that anticoagulation could reduce recurrent stroke compared with antiplatelet therapy. We hypothesised that anticoagulant treatment with rivaroxaban, an oral factor Xa inhibitor, would reduce the risk of recurrent ischaemic stroke compared with aspirin among patients with PFO enrolled in the NAVIGATE ESUS trial. Methods: NAVIGATE ESUS was a double-blinded, randomised, phase 3 trial done at 459 centres in 31 countries that assessed the efficacy and safety of rivaroxaban versus aspirin for secondary stroke prevention in patients with ESUS. For this prespecified subgroup analysis, cohorts with and without PFO were defined on the basis of transthoracic echocardiography (TTE) and transoesophageal echocardiography (TOE). The primary efficacy outcome was time to recurrent ischaemic stroke between treatment groups. The primary safety outcome was major bleeding, according to the criteria of the International Society of Thrombosis and Haemostasis. The primary analyses were based on the intention-to-treat population. Additionally, we did a systematic review and random-effects meta-analysis of studies in which patients with cryptogenic stroke and PFO were randomly assigned to receive anticoagulant or antiplatelet therapy. Findings: Between Dec 23, 2014, and Sept 20, 2017, 7213 participants were enrolled and assigned to receive rivaroxaban (n=3609) or aspirin (n=3604). Patients were followed up for a mean of 11 months because of early trial termination. PFO was reported as present in 534 (7·4%) patients on the basis of either TTE or TOE. Patients with PFO assigned to receive aspirin had a recurrent ischaemic stroke rate of 4·8 events per 100 person-years compared with 2·6 events per 100 person-years in those treated with rivaroxaban. Among patients with known PFO, there was insufficient evidence to support a difference in risk of recurrent ischaemic stroke between rivaroxaban and aspirin (hazard ratio [HR] 0·54; 95% CI 0·22–1·36), and the risk was similar for those without known PFO (1·06; 0·84–1·33; pinteraction=0·18). The risks of major bleeding with rivaroxaban versus aspirin were similar in patients with PFO detected (HR 2·05; 95% CI 0·51–8·18) and in those without PFO detected (HR 2·82; 95% CI 1·69–4·70; pinteraction=0·68). The random-effects meta-analysis combined data from NAVIGATE ESUS with data from two previous trials (PICSS and CLOSE) and yielded a summary odds ratio of 0·48 (95% CI 0·24–0·96; p=0·04) for ischaemic stroke in favour of anticoagulation, without evidence of heterogeneity. Interpretation: Among patients with ESUS who have PFO, anticoagulation might reduce the risk of recurrent stroke by about half, although substantial imprecision remains. Dedicated trials of anticoagulation versus antiplatelet therapy or PFO closure, or both, are warranted. Funding: Bayer and Janssen