Effect of the electrolyte composition on the electroreduction of palladium oxide films

The voltammetric electroreduction of Pd oxide layers grown at 2.00 V (RHE) was studied in H2SO4 and HClO4 solutions containing different concentrations of LiClO4, Na2SO4 and KHSO4. The voltammetric electroreduction profiles show two main regions; the first is in the range 1.2–1.6 V and is related to the electroreduction of a fast redox system; the second region extends through the range 1.1-0.40 V, where the electroreduction of the thick oxide matrix takes place. This latter process is strongly affected by the solution composition, including the pH, in a manner contrasting to the effect on Pd oxide growth. The thick oxide layer electroreduction charge increases as the solution pH is decreased. These results are discussed in terms of specific interaction between sulphate ions and the oxide layer, so that the electroreduction process is favoured owing to the likely formation of sulphate-containing complex species.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Anodisation of copper in thiourea-containing acid solution : Part II. In situ transversal imaging observations. Kinetics of anodic film growth

The formation of anodic films during the anodisation of copper, at different applied potentials E, in aqueous 0.5 M sulphuric acid containing different amounts of dissolved thiourea was investigated following the corroding electrode profile by on line in situ imaging. For E0.07 V, the main reactions are the electro-decomposition of formamidine disulphide and Cu(I)–thiourea complexes yielding a copper sulphide-containing film (film II) and the electrodissolution of copper as aqueous Cu(II) ions through film II. The relative contribution of these processes depends on thiourea concentration in the solution, the applied electric potential and anodisation time. The growth kinetics of films I and II were determined from the evolution of the average film height〈h〉obtained from in situ imaging. The kinetics of film I fit a parabolic rate law, whereas those of film II approach a linear〈h〉versus anodisation time relationship. The rupture of film II assists the localised corrosion of copper. Likely physical mechanisms for the formation of these anodic films are discussed.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Anodisation of copper in thiourea- and formamidine disulphide-containing acid solution : Part I. Identification of products and reaction pathway

The anodic behaviour of copper in aqueous 0.5 M sulphuric acid containing different amounts of dissolved thiourea or formamidine disulphide was investigated at 298 K, combining data from electrochemical polarisation, chemical analysis, UV–vis spectroscopy, XPS and EDAX analysis, and structural information on copper–thiourea complexes. The main reactions depend on the applied potential and initial thiourea concentration. In the potential range −0.30≤E≤0.075 V (versus SCE), the electro-oxidation of thiourea to formamidine disulphide, the formation of Cu(I)–thiourea soluble complexes, and Cu(I)–thiourea complex polymer-like films, are the most relevant processes. The formation of this film depends on certain critical thiourea/copper ion molar concentration ratios at the reaction interface. At low positive potentials, the former reaction is under intermediate kinetic control, with the diffusion of thiourea from the solution playing a key role. For E≥0.075 V, soluble Cu(II) ions in the solution are formed and the anodic film is gradually changed to another one consisting of copper sulphide and residual copper. The new film assists the localised electrodissolution of copper. A complex reaction pathway for copper anodisation in these media for the low and high potential range is advanced.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Left ventricular filling patterns in patients with previous myocardial infarction measured by conventional cine cardiac magnetic resonance

To explore left ventricular filling patterns in patients with a history of previous myocardial infarction (MI) using time-volume curves obtained from conventional cine-cardiac magnetic resonance (CMR) examinations. Consecutive patients with a history of previous MI who were referred for CMR evaluation constituted the study population, and a consecutive cohort of sex and age-matched patients with a normal CMR constituted the control group. The following CMR diastolic parameters were evaluated: peak filling rate (PFR), time to PFR (tPFR), normalised PFR adjusted for diastolic volume at PFR (nPFR), and percent RR interval between end systole and PFR. Fifty patients were included, 25 with a history of previous MI and 25 control. The mean age was 59.6 ± 13.9 years and 27 (54%) were male. Within the control group, age was significantly related to PFR (r = -0.53, p = 0.007), whereas among patients with previous MI age was not related to PFR (r = -0.16, p = 0.44). PFR (252.4 ± 96.7 ml/s vs. 316.0 ± 126.4 ml/s, p = 0.05) and nPFR (1.6 ± 1.2 vs. 3.3 ± 1.5, p<0.001) were significantly lower in patients with previous MI, whereas no significant differences were detected regarding tPFR (143.0 ± 67.5 ms vs. 176.2 ± 83.9 ms, p = 0.13) and % RR to PFR (18.1 ± 9.7% vs. 20.6 ± 12.2%, p = 0.44). MI size was related to LV ejection fraction (r = -0.76, p<0.001), PFR (r = -0.40, p = 0.004), nPFR (r = -0.52, p<0.001) and left atrium area (r = 0.40, p = 0.004). Patients at the lowest PFR quartile (<200 ml/s) showed a larger MI size (Q1 26.5 ± 25.5%, Q2 15.5 ± 20.9%, Q3 6.3 ± 12.4%, Q4 8.8 ± 14.1%, p = 0.04). At multivariate analysis, MI size was the only independent predictor of the lowestPFR (p = 0.017). Infarct size has an impact on LV filling profiles, as assessed by conventional cine CMR without additional specific pulse sequences.Fil: Rodriguez Granillo, Gaston Alfredo. Sanatorio "Otamendi y Miroli S.A.". Servicio de Diagnóstico por Imágenes. Departamento de Imágenes en Cardiología. Centro de Investigaciones Cardiovasculares; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mejía Campillo, Marlon. No especifíca;Fil: Rosales, Miguel A.. Sanatorio "Otamendi y Miroli S.A.". Servicio de Diagnóstico por Imágenes. Departamento de Imágenes en Cardiología. Centro de Investigaciones Cardiovasculares; ArgentinaFil: Bolzán, Gabriel. No especifíca;Fil: Ingino, Carlos. No especifíca;Fil: López, Federico. No especifíca;Fil: Degrossi, Elina. Sanatorio "Otamendi y Miroli S. A."; ArgentinaFil: Lylyk, Pedro. Sanatorio "Otamendi y Miroli S. A."; Argentin

Comparative voltammetric and FTIRRAS study on the electro-oxidation of thiourea and methyl-thioureas on platinum in aqueous acid solutions

A comparative voltammetric and spectroscopic study on thiourea, methylthiourea, 1,3 dimethylthiourea and tetramethylthiourea electro-oxidation is presented. The investigation was performed at platinum electrodes in aqueous acid solutions in the potential range between 0.05 and 1.6 V (versus SHE). The electro-oxidation of thioureas starts at ca. 0.55 V and it involves at least two reaction stages irrespective of their nature. The first electro-oxidation stage occurs in the range 0.55–0.9 V and involves the formation of a soluble disulphide derivative influenced by the blockage of the electrode surface. The second electro-oxidation stage occurs in the range 0.9–1.6 V and it involves a complex electrochemical process yielding products such as carbon dioxide, sulphate ions, CN- and CO-containing species. The second electro-oxidation stage is likely mediated by the oxygen-containing layer that is produced electrochemically on platinum in that range of potential. The gradual depletion of thioureas and the progressive formation of soluble products in the thin solution layer in contact with the electrode are followed through changes in the band intensities of IR spectra. From the correlation between voltammetric and spectroscopic data a description of global reactions involving the electro-oxidation of thioureas to soluble products in both potential ranges is presented. The proposed reaction pathways are consistent with the participation of different adsorbates as was reported earlier for thioureas on platinum.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Comparative voltammetric and FTIRRAS study on the electro-oxidation of thiourea and methyl-thioureas on platinum in aqueous acid solutions

A comparative voltammetric and spectroscopic study on thiourea, methylthiourea, 1,3 dimethylthiourea and tetramethylthiourea electro-oxidation is presented. The investigation was performed at platinum electrodes in aqueous acid solutions in the potential range between 0.05 and 1.6 V (versus SHE). The electro-oxidation of thioureas starts at ca. 0.55 V and it involves at least two reaction stages irrespective of their nature. The first electro-oxidation stage occurs in the range 0.55–0.9 V and involves the formation of a soluble disulphide derivative influenced by the blockage of the electrode surface. The second electro-oxidation stage occurs in the range 0.9–1.6 V and it involves a complex electrochemical process yielding products such as carbon dioxide, sulphate ions, CN- and CO-containing species. The second electro-oxidation stage is likely mediated by the oxygen-containing layer that is produced electrochemically on platinum in that range of potential. The gradual depletion of thioureas and the progressive formation of soluble products in the thin solution layer in contact with the electrode are followed through changes in the band intensities of IR spectra. From the correlation between voltammetric and spectroscopic data a description of global reactions involving the electro-oxidation of thioureas to soluble products in both potential ranges is presented. The proposed reaction pathways are consistent with the participation of different adsorbates as was reported earlier for thioureas on platinum.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Anodisation of copper in thiourea-containing acid solution : Part II. In situ transversal imaging observations. Kinetics of anodic film growth

The formation of anodic films during the anodisation of copper, at different applied potentials E, in aqueous 0.5 M sulphuric acid containing different amounts of dissolved thiourea was investigated following the corroding electrode profile by on line in situ imaging. For E0.07 V, the main reactions are the electro-decomposition of formamidine disulphide and Cu(I)–thiourea complexes yielding a copper sulphide-containing film (film II) and the electrodissolution of copper as aqueous Cu(II) ions through film II. The relative contribution of these processes depends on thiourea concentration in the solution, the applied electric potential and anodisation time. The growth kinetics of films I and II were determined from the evolution of the average film height〈h〉obtained from in situ imaging. The kinetics of film I fit a parabolic rate law, whereas those of film II approach a linear〈h〉versus anodisation time relationship. The rupture of film II assists the localised corrosion of copper. Likely physical mechanisms for the formation of these anodic films are discussed.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Anodisation of copper in thiourea- and formamidine disulphide-containing acid solution : Part I. Identification of products and reaction pathway

The anodic behaviour of copper in aqueous 0.5 M sulphuric acid containing different amounts of dissolved thiourea or formamidine disulphide was investigated at 298 K, combining data from electrochemical polarisation, chemical analysis, UV–vis spectroscopy, XPS and EDAX analysis, and structural information on copper–thiourea complexes. The main reactions depend on the applied potential and initial thiourea concentration. In the potential range −0.30≤E≤0.075 V (versus SCE), the electro-oxidation of thiourea to formamidine disulphide, the formation of Cu(I)–thiourea soluble complexes, and Cu(I)–thiourea complex polymer-like films, are the most relevant processes. The formation of this film depends on certain critical thiourea/copper ion molar concentration ratios at the reaction interface. At low positive potentials, the former reaction is under intermediate kinetic control, with the diffusion of thiourea from the solution playing a key role. For E≥0.075 V, soluble Cu(II) ions in the solution are formed and the anodic film is gradually changed to another one consisting of copper sulphide and residual copper. The new film assists the localised electrodissolution of copper. A complex reaction pathway for copper anodisation in these media for the low and high potential range is advanced.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Revision and analysis of the chromosome variability in the speciose genus Akodon (Rodentia, Sigmodontinae), including new data from Argentina

Abstract Rodentia has a high species number and chromosomal variability. The South American genus Akodon is one of the most speciose muroids, with more than 40 species included in several species groups. Here, we characterize cytogenetically specimens of Akodon from central-western Argentina. Subsequently, we reviewed and analyzed the cytogenetic data for this genus, build a phylogeny and mapped chromosome changes to interpret its evolution. Specimens of A. dolores from central-western Argentina have 2n=42-44/FNa=44 (46, 48) due to a Robertsonian rearrangement. Our data expand the distribution range known for this polymorphism and confirm its geographic structure. Other specimens had 2n=40/FNa=40, representing populations of A. oenos, A. polopi, and A. spegazzinii. All karyotypes have a low amount of heterochromatin, concentrated in centromeres and sex chromosomes, as in other rodents. The complement with 2n=40/FNa=40 is the most frequent in Akodon and is shared by most species in some groups. Chromosome numbers are very diverse. The FNa shows less variability; FNa=42 was recovered as ancestral, excluding A. mimus, which was connected at the base of the Akodon tree and has FNa=44. This indicates a complex chromosome evolution in Akodon, and suggests that reductions and increases in the 2n and FNa evolved independently in some lineages

Chromosomal localization of the 18S-28S and 5S rRNA genes and (TTAGGG)n sequences of butterfly lizards (Leiolepis belliana belliana and Leiolepis boehmei, Agamidae, Squamata)

Chromosomal mapping of the butterfly lizards Leiolepis belliana belliana and L. boehmei was done using the 18S-28S and 5S rRNA genes and telomeric (TTAGGG)n sequences. The karyotype of L. b. belliana was 2n = 36, whereas that of L. boehmei was 2n = 34. The 18S-28S rRNA genes were located at the secondary constriction of the long arm of chromosome 1, while the 5S rRNA genes were found in the pericentromeric region of chromosome 6 in both species. Hybridization signals for the (TTAGGG)n sequence were observed at the telomeric ends of all chromosomes, as well as interstitially at the same position as the 18S-28S rRNA genes in L. boehmei. This finding suggests that in L. boehmei telomere-to-telomere fusion probably occurred between chromosome 1 and a microchromosome where the 18S-28S rRNA genes were located or, alternatively, at the secondary constriction of chromosome 1. The absence of telomeric sequence signals in chromosome 1 of L. b. belliana suggested that its chromosomes may have only a few copies of the (TTAGGG)n sequence or that there may have been a gradual loss of the repeat sequences during chromosomal evolution