maria vela - Academia.edu (original) (raw)
Papers by maria vela
Microscopy and Microanalysis, 2020
Surface Review and Letters, 1997
The structures resulting from 1-dodecanethiol, 1-butanethiol and 1,9-nonanedithiol films produced... more The structures resulting from 1-dodecanethiol, 1-butanethiol and 1,9-nonanedithiol films produced on highly oriented pyrolytic graphite (HOPG) and gold(111) have been comparatively studied by scanning probe microscopies. Molecular resolution images resulting from atomic force microscopy (AFM) and scanning tunneling microscopy (STM) of different thiol films show the formation of arrays of molecules parallel to the HOPG surface. The electrochemical response of the ferro-ferricyanide reaction was used to test the characteristics of electron transfer processes in thiol-covered HOPG as compared to the bare substrate. The decrease in the heterogeneous rate constant for the test reaction appears to be directly related to the degree of film thickness uniformity. For comparison, films with the same kind of thiols were produced on Au(111). Although the electrochemical characteristics of these films appear to be the same irrespective of the substrate nature, the structure of the films on Au(11...
Langmuir, 1998
The structure and dynamics of dodecanethiol and butanethiol monolayers adsorbed on Au(111) at 298... more The structure and dynamics of dodecanethiol and butanethiol monolayers adsorbed on Au(111) at 298 K have been followed by in situ and ex situ scanning tunneling microscopy (STM). Results show that a gaslike initial adsorption stage where monatomic deep pit clustering occurs is followed by an advanced adsorption stage in which adlayer structural changes p(n×1) w (x3×x3)R30°S c(4×2) take place. The first change is interpreted as the motion of adsorbed molecules from fcc to hcp sites, and the second one is explained by the fluctuations of adsorbed molecules from hollow to bridge sites. The structural fluctuations at adsorbate domains occur simultaneously with fluctuations in the size of monatomic deep pits. These processes reveal the complexity of surface dynamics of alkanethiol adlayers on Au(111) at 298 K.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2014
α-Hemolysin (HlyA) is a protein toxin, a member of the pore-forming Repeat in Toxin (RTX) family,... more α-Hemolysin (HlyA) is a protein toxin, a member of the pore-forming Repeat in Toxin (RTX) family, secreted by some pathogenic strands of Escherichia coli. The mechanism of action of this toxin seems to involve three stages that ultimately lead to cell lysis: binding, insertion, and oligomerization of the toxin within the membrane. Since the influence of phase segregation on HlyA binding and insertion in lipid membranes is not clearly understood, we explored at the meso-and nanoscale-both in situ and in real-time-the interaction of HlyA with lipid monolayers and bilayers. Our results demonstrate that HlyA could insert into monolayers of dioleoylphosphatidylcholine/ sphingomyelin/cholesterol (DOPC/16:0SM/Cho) and DOPC/24:1SM/Cho. The time course for HlyA insertion was similar in both lipidic mixtures. HlyA insertion into DOPC/16:0SM/Cho monolayers, visualized by Brewster-angle microscopy (BAM), suggest an integration of the toxin into both the liquid-ordered and liquid-expanded phases. Atomic-force-microscopy imaging reported that phase boundaries favor the initial binding of the toxin, whereas after a longer time period the HlyA becomes localized into the liquid-disordered (Ld) phases of supported planar bilayers composed of DOPC/16:0SM/Cho. Our AFM images, however, showed that the HlyA interaction does not appear to match the general strategy described for other invasive proteins. We discuss these results in terms of the mechanism of action of HlyA.
Electrochimica Acta, 1998
The dynamics of 1-dodecanethiol self-assembled monolayers (SAMs) on Au(111) produced by contactin... more The dynamics of 1-dodecanethiol self-assembled monolayers (SAMs) on Au(111) produced by contacting pure thiol was followed by in situ STM at 298 K. Initially, these SAMs constituted a heterogeneous surface consisting of disordered and ordered adsorbate domains at terraces, step edges and pits, forming a p(6  1) superlattice which later changed to the ( 3 p  3 p )R308 structure. Subsequently, the c(4  2) superlattice was also observed. Surface dynamics involves the coalescence and Ostwald ripening phenomena at pits occurring simultaneously with adsorbate ordering at dierent surface domains. The dierence in surface mobility between adsorbate-free and 1dodecanethiol-covered Au(111) can be explained taking into account both gold lattice relaxation due to adsorption and alkyl chain interaction at SAM. Data analysis in terms of clustering theory allowed us to conclude that a single mechanism is likely involved in the overall surface phenomena in which the mass transport is either a nonsteady state surface diusion or an interface transfer along step edges as rate-determining step. #
Surface Review and Letters, 1997
The structures resulting from 1-dodecanethiol, 1-butanethiol and 1,9-nonanedithiol films produced... more The structures resulting from 1-dodecanethiol, 1-butanethiol and 1,9-nonanedithiol films produced on highly oriented pyrolytic graphite (HOPG) and gold(111) have been comparatively studied by scanning probe microscopies. Molecular resolution images resulting from atomic force microscopy (AFM) and scanning tunneling microscopy (STM) of different thiol films show the formation of arrays of molecules parallel to the HOPG surface. The electrochemical response of
Langmuir, 1998
... F. Terán Arce, ME Vela, RC Salvarezza, and AJ Arvia*. Instituto de Investigaciones Fisicoquím... more ... F. Terán Arce, ME Vela, RC Salvarezza, and AJ Arvia*. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Sucursal 4, Casilla de Correo 16, 1900 La Plata, Argentina. Langmuir , 1998, 14 (25), pp 72037212. ...
This work reports on the features that Ni-W nanostructured alloys, electrodeposited on carbon ste... more This work reports on the features that Ni-W nanostructured alloys, electrodeposited on carbon steel by different current pulse programs, may present depending on their surface morphology and surface composition. The Ni-W nanostructured coating, with a cauliflower structure, lack of fragility, and high WO 3 /W surface composition ratio, is a stable electrode to catalyze hydrogen evolution reaction, exceeding bulk and electrodeposited Ni catalytic activity. Also, the nanostructured alloys must have a low WO 3 /W surface composition ratio for Ni and its oxides to provide protection and improve corrosion resistance in sulfate media.
Microscopy and Microanalysis, 2020
Surface Review and Letters, 1997
The structures resulting from 1-dodecanethiol, 1-butanethiol and 1,9-nonanedithiol films produced... more The structures resulting from 1-dodecanethiol, 1-butanethiol and 1,9-nonanedithiol films produced on highly oriented pyrolytic graphite (HOPG) and gold(111) have been comparatively studied by scanning probe microscopies. Molecular resolution images resulting from atomic force microscopy (AFM) and scanning tunneling microscopy (STM) of different thiol films show the formation of arrays of molecules parallel to the HOPG surface. The electrochemical response of the ferro-ferricyanide reaction was used to test the characteristics of electron transfer processes in thiol-covered HOPG as compared to the bare substrate. The decrease in the heterogeneous rate constant for the test reaction appears to be directly related to the degree of film thickness uniformity. For comparison, films with the same kind of thiols were produced on Au(111). Although the electrochemical characteristics of these films appear to be the same irrespective of the substrate nature, the structure of the films on Au(11...
Langmuir, 1998
The structure and dynamics of dodecanethiol and butanethiol monolayers adsorbed on Au(111) at 298... more The structure and dynamics of dodecanethiol and butanethiol monolayers adsorbed on Au(111) at 298 K have been followed by in situ and ex situ scanning tunneling microscopy (STM). Results show that a gaslike initial adsorption stage where monatomic deep pit clustering occurs is followed by an advanced adsorption stage in which adlayer structural changes p(n×1) w (x3×x3)R30°S c(4×2) take place. The first change is interpreted as the motion of adsorbed molecules from fcc to hcp sites, and the second one is explained by the fluctuations of adsorbed molecules from hollow to bridge sites. The structural fluctuations at adsorbate domains occur simultaneously with fluctuations in the size of monatomic deep pits. These processes reveal the complexity of surface dynamics of alkanethiol adlayers on Au(111) at 298 K.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2014
α-Hemolysin (HlyA) is a protein toxin, a member of the pore-forming Repeat in Toxin (RTX) family,... more α-Hemolysin (HlyA) is a protein toxin, a member of the pore-forming Repeat in Toxin (RTX) family, secreted by some pathogenic strands of Escherichia coli. The mechanism of action of this toxin seems to involve three stages that ultimately lead to cell lysis: binding, insertion, and oligomerization of the toxin within the membrane. Since the influence of phase segregation on HlyA binding and insertion in lipid membranes is not clearly understood, we explored at the meso-and nanoscale-both in situ and in real-time-the interaction of HlyA with lipid monolayers and bilayers. Our results demonstrate that HlyA could insert into monolayers of dioleoylphosphatidylcholine/ sphingomyelin/cholesterol (DOPC/16:0SM/Cho) and DOPC/24:1SM/Cho. The time course for HlyA insertion was similar in both lipidic mixtures. HlyA insertion into DOPC/16:0SM/Cho monolayers, visualized by Brewster-angle microscopy (BAM), suggest an integration of the toxin into both the liquid-ordered and liquid-expanded phases. Atomic-force-microscopy imaging reported that phase boundaries favor the initial binding of the toxin, whereas after a longer time period the HlyA becomes localized into the liquid-disordered (Ld) phases of supported planar bilayers composed of DOPC/16:0SM/Cho. Our AFM images, however, showed that the HlyA interaction does not appear to match the general strategy described for other invasive proteins. We discuss these results in terms of the mechanism of action of HlyA.
Electrochimica Acta, 1998
The dynamics of 1-dodecanethiol self-assembled monolayers (SAMs) on Au(111) produced by contactin... more The dynamics of 1-dodecanethiol self-assembled monolayers (SAMs) on Au(111) produced by contacting pure thiol was followed by in situ STM at 298 K. Initially, these SAMs constituted a heterogeneous surface consisting of disordered and ordered adsorbate domains at terraces, step edges and pits, forming a p(6  1) superlattice which later changed to the ( 3 p  3 p )R308 structure. Subsequently, the c(4  2) superlattice was also observed. Surface dynamics involves the coalescence and Ostwald ripening phenomena at pits occurring simultaneously with adsorbate ordering at dierent surface domains. The dierence in surface mobility between adsorbate-free and 1dodecanethiol-covered Au(111) can be explained taking into account both gold lattice relaxation due to adsorption and alkyl chain interaction at SAM. Data analysis in terms of clustering theory allowed us to conclude that a single mechanism is likely involved in the overall surface phenomena in which the mass transport is either a nonsteady state surface diusion or an interface transfer along step edges as rate-determining step. #
Surface Review and Letters, 1997
The structures resulting from 1-dodecanethiol, 1-butanethiol and 1,9-nonanedithiol films produced... more The structures resulting from 1-dodecanethiol, 1-butanethiol and 1,9-nonanedithiol films produced on highly oriented pyrolytic graphite (HOPG) and gold(111) have been comparatively studied by scanning probe microscopies. Molecular resolution images resulting from atomic force microscopy (AFM) and scanning tunneling microscopy (STM) of different thiol films show the formation of arrays of molecules parallel to the HOPG surface. The electrochemical response of
Langmuir, 1998
... F. Terán Arce, ME Vela, RC Salvarezza, and AJ Arvia*. Instituto de Investigaciones Fisicoquím... more ... F. Terán Arce, ME Vela, RC Salvarezza, and AJ Arvia*. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Sucursal 4, Casilla de Correo 16, 1900 La Plata, Argentina. Langmuir , 1998, 14 (25), pp 72037212. ...
This work reports on the features that Ni-W nanostructured alloys, electrodeposited on carbon ste... more This work reports on the features that Ni-W nanostructured alloys, electrodeposited on carbon steel by different current pulse programs, may present depending on their surface morphology and surface composition. The Ni-W nanostructured coating, with a cauliflower structure, lack of fragility, and high WO 3 /W surface composition ratio, is a stable electrode to catalyze hydrogen evolution reaction, exceeding bulk and electrodeposited Ni catalytic activity. Also, the nanostructured alloys must have a low WO 3 /W surface composition ratio for Ni and its oxides to provide protection and improve corrosion resistance in sulfate media.