Francisco Prieto Dapena - Academia.edu (original) (raw)

Papers by Francisco Prieto Dapena

Langmuir, 2002

We report the use of scanning electrochemical microscopy (SECM) to control the generation of Tl(I... more We report the use of scanning electrochemical microscopy (SECM) to control the generation of Tl(I) at a mercury substrate and detect this species at a mercury-coated tip to study the transport of these ions through ion channels. The transport of Tl(I) across gramicidin D half-channels imbedded in a dioleoylphosphatidylcholine (DOPC) monolayer supported on a Tl amalgam hanging mercury drop electrode (HMDE) was studied using the substrate generation-tip collection mode of SECM. A Hg/Pt "submarine" electrode, used as the SECM tip, was made through simple contact of the Pt ultramicroelectrode with the HMDE. The tip transient response for the collection of generated Tl(I) at the amalgam HMDE was recorded for several tip to substrate distances. This collection-generation experiment was repeated with a DOPCmodified Tl/HMDE and a gramicidin-DOPC-modified Tl/HMDE. An apparent heterogeneous rate constant (khet) 2.8 ((0.1) × 10-4 cm/s) for the transport of Tl(I) through the gramicidin to the tip was extracted.

AAPS PharmSciTech, 2019

Liposomes with their capacity to anchor gold nanoparticles (AuNPs) onto their surface are used in... more Liposomes with their capacity to anchor gold nanoparticles (AuNPs) onto their surface are used in the treatment of several pathologies such as cancer. The objective of this work was the optimization of the vesicle composition by using cationic agents in order to reinforce the anchoring process of AuNPs, and for the study of the influence of local temperature and vesicle size on drug release. A Plackett-Burman design was conducted to determine the optimal composition for the anchoring of AuNPs. A comprehensive study of the influence of lipid bilayer composition on the surface charge, size, and polydispersity index (PdI) of liposomes was carried out. Afterwards, in vitro release studies by dialysis were performed and several release parameters were evaluated as a function of temperature. Cholesterol was fixed as the rigid agent and Didodecyldimethylammonium bromide (DDAB) was selected as the cationic lipid into the liposome bilayer. Photomicrographs revealed that DDAB facilitated the anchoring of AuNPs onto the liposomal surface. The anchoring of AuNPs also enhanced the amount and rate of calcein released, especially in extruded samples, at several incubating temperatures. In addition, it was observed that both the anchoring of AuNPs and the calcein release were improved by increasing the surface of the vesicles. The contributions of liposome composition (DDAB inclusion, incubation temperature, anchoring of AuNPs) and size and surface availability of the vesicles on calcein release could be used to design improved lipid nanostructures for the controlled release of anticancer drugs.

Electrochimica Acta, 2016

The adsorption of thymine on gold electrodes has been studied by ATR-SEIRAS in situ spectroscopy ... more The adsorption of thymine on gold electrodes has been studied by ATR-SEIRAS in situ spectroscopy at three pH values (1, 7 and 12), in order to analyse the tautomeric equilibrium of deprotonated thymine in the adsorbed state. The anionic form which is deprotonated in nitrogen N1 (N1 tautomer) and the one deprotonated in nitrogen N3 (N3 tautomer) are considered. The spectroscopic results have been interpreted in the light of DFT ab-initio calculations of both tautomeric forms adsorbed on gold surfaces. The basis sets 6-311 + +G(d,p) for C, H, O and N atoms and LANDL2DZ for Au atoms have been used. The electrode surface has been simulated as an unreconstructed Au(111) surface of 19 atoms. The preponderance of each tautomer of adsorbed thymine as a function of pH has been inferred from the analysis of the spectral signals in the 1500-1800 cm À1 wavenumber region related mostly to stretching modes of the carbonyl groups. It has been found that the adsorbed N3 tautomer predominates in the case of adsorption from acid media while the N1 tautomer predominates in the adsorption from basic media but the adsorption of both forms have been distinguished in the experiments from neutral media. Moreover, the plausible changes in the orientation of the two adsorbed tautomers with the electric field have been determined by analysing the relative intensities of the characteristic CH stretching signals in the 2800-3300 cm À1 spectral region. It is proposed that the N3 tautomer undergoes changes in the interaction sites with the metal and in the molecular plane orientation on the electrode as the electric potential is increased, but the N1 tautomer molecule keeps the interaction sites while the molecular plane slightly rotates to facilitate the electrostatic interaction with the field.

Journal of Electroanalytical Chemistry, 1999

The reduction of nitromethane has been studied by impedance voltammetry at various water activiti... more The reduction of nitromethane has been studied by impedance voltammetry at various water activities using NaClO 4 as the base electrolyte. The impedance analysis conforms well to an EC-C-eee mechanism, and the rate constants for the three rate determining steps are obtained together with the standard potential for the first reduction process (EC). On the other hand, the results obtained for the reduction of deuterated nitromethane in 1 M NaCl+ D 2 O solutions are compared with the ones obtained for nitromethane in 1 M NaCl aqueous solutions. A special role played by the solvent on the first chemical step shows up in both kinds of experiments, thus suggesting that it consists of a nitro-aci tautomerism reaction.

Electrochimica Acta, 2012

In situ external reflection infrared reflection spectroscopy (IRRAS) and surface-enhanced infrare... more In situ external reflection infrared reflection spectroscopy (IRRAS) and surface-enhanced infrared reflection absorption spectroscopy under attenuated total reflection conditions (ATR-SEIRAS) have been used to study the adsorption of adenine at Au(1 1 1) and gold thin-film electrodes in 0.1 M HClO 4 solutions in deuterium oxide and in water. The existence of protonated and deprotonated adenine molecules at the electrode surface has been proved from the comparison of the spectra for adsorbed adenine with those obtained for dissolved adenine. In all cases, characteristic band frequencies are observed for the enhanced ring stretching band in D 2 O and also the bending band of the amino group in H 2 O. Both signals appear at higher wavenumbers for the protonated species. In acid media, deprotonation of adsorbed adenine is induced by increasing positive potentials and/or adenine coverage leading to the same adsorbed species as previously reported in basic media, namely chemically adsorbed adenine with a tilted orientation of the molecular plane on the electrode. Co-adsorption of water and perchlorate anions is detected in the case of the acid media, indicating the involvement of these species in the stabilization of the organic film. Time-resolved experiments at negative potentials and low adenine concentrations have shown also the physical adsorption of protonated adenine and have allowed the monitoring of the adsorption of the protonated and unprotonated forms as a function of time. Adsorption of unprotonated adenine is slower but is favored at the equilibrium at the electrode surface even if the pH of the media is three units lower than the pK a of adenine in solution.

Electrochemistry Communications, 2013

The co-adsorption of complementary DNA bases adenine and thymine on gold thin-film electrodes fro... more The co-adsorption of complementary DNA bases adenine and thymine on gold thin-film electrodes from 0.1 M HClO 4 solutions in H 2 O and D 2 O is studied by surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS). The comparison of the spectra in the range 1750-1550 cm −1 for co-adsorbed adenine and thymine at controlled potentials to those of the individual adsorbed bases shows the enhancement of the signals associated to the vibration modes of adenine and the inhibition of those of thymine. The results can be explained by invoking the rearrangement of both molecules on the electrode surface in order to facilitate the Watson-Crick (W-C) and/or Hoogsteen (HG) interactions between the bases. The co-adsorption seems to be a cooperative process in which a low surface concentration of each base can induce the rearrangement of the complementary base molecules on the surface.

Electroanalysis, 1998

2-Dimensional amperometry” using arrays of gold channel microband electrodes is applied to the ox... more 2-Dimensional amperometry” using arrays of gold channel microband electrodes is applied to the oxidation of 2,3,7,8-tetramethoxythianthrene (TMT) and to the characterization of the follow-up kinetics of the resulting radical cation with pyridine. In the absence of pyridine the reaction is consistent with an E mechanism and a value of 1.3 × 10−5 cm2 s−1 is obtained for the diffusion coefficient of TMT. In the presence of pyridine the experimental results are consistent with a DISP2 mechanism where the values of the rate constant have a first order dependence on the concentration of pyridine. The following mechanism is proposed: and a value of 5.8 × 104 M−2s−1 is found for the rate constant for the regeneration of TMT.

Analytical Chemistry, 1998

A channel electrode array, with electrodes ranging in size from the millimeter to the submicromet... more A channel electrode array, with electrodes ranging in size from the millimeter to the submicrometer scale, is used for the amperometric interrogation of mechanistically complex electrode processes. In this way, the transportlimited current, measured as a function of both electrode size and electrolyte flow rate (convection), is shown to provide a highly sensitive probe of mechanism and kinetics. The application of "two-dimensional voltammetry" to diverse electrode processes, including E, ECE, ECEE, EC′, and DISP2 reactions, is reported.

Electroanalysis, 2004

ABSTRACT

International Journal of Pharmaceutics, 2022

Pharmaceutics, 2021

Stimulus-responsive liposomes (L) for triggering drug release to the target site are particularly... more Stimulus-responsive liposomes (L) for triggering drug release to the target site are particularly useful in cancer therapy. This research was focused on the evaluation of the effects of cholesterol levels in the performance of gold nanoparticles (AuNPs)-functionalized L for controlled doxorubicin (D) delivery. Their interfacial and morphological properties, drug release behavior against temperature changes and cytotoxic activity against breast and ovarian cancer cells were studied. Langmuir isotherms were performed to identify the most stable combination of lipid components. Two mole fractions of cholesterol (3.35 mol% and 40 mol%, L1 and L2 series, respectively) were evaluated. Thin-film hydration and transmembrane pH-gradient methods were used for preparing the L and for D loading, respectively. The cationic surface of L allowed the anchoring of negatively charged AuNPs by electrostatic interactions, even inducing a shift in the zeta potential of the L2 series. L exhibited nanomet...

Electrochimica Acta, 2021

Abstract Chronocoulometry was applied to determine charge in a monolayer of nucleolipid (1,2-dipa... more Abstract Chronocoulometry was applied to determine charge in a monolayer of nucleolipid (1,2-dipalmitoyl-sn‑glycero-3-(cytidine diphosphate)) deposited at a gold electrode surface. The immersion method was used to measure the potential of zero charge of the interface (Epzci), which is a sum of charge on the monolayer of the nucleolipid and charge on the gold surface. Photon polarization infrared reflection absorption spectroscopy (PM-IRRAS) was used to determine formation of the Watson-Crick complex between terminal cytidine moiety of the nucleolipid and guanine (its complementary base) added to the solution. The combination of electrochemical and spectroscopic studies allowed one to demonstrate that the Watson-Crick complex is formed when the interface is positively charged. The potential applied to the electrode affects not only the complex formation but also orientation of the cytosine moiety. The complex is formed when the cytosine moiety is oriented assuming a small angle with respect to the electrode surface.

Collection of Czechoslovak Chemical Communications, 2011

The application of Electrochemical Impedance Spectroscopy to the study of surface electrode proce... more The application of Electrochemical Impedance Spectroscopy to the study of surface electrode processes is reviewed. The impedance expressions and the physical meaning of the parameters included in them are shown for three surface processes: adsorption kinetics, diffusion towards partially blocked electrodes and surface confined redox reactions. The models are applied to selected examples, showing the capability of Electrochemical Impedance Spectroscopy to obtain fundamental kinetic information of these processes. A review with 83 references.

Journal of Electroanalytical Chemistry

Electrochemistry Communications, 2013

An Electrochemical Scanning Tunneling Microscopy (EC-STM) study of the adsorption of adenine on A... more An Electrochemical Scanning Tunneling Microscopy (EC-STM) study of the adsorption of adenine on Au(111) electrodes was undertaken in the pH range between 1 and 7, aiming at achieving a deeper knowledge on the structure and organization of adenine chemisorbed on gold, and at confirming previous conclusions obtained from combined electrochemical and insitu IR spectroscopy measurements. This study confirms that chemisorption of adenine induces the lifting of the Au(111) surface reconstruction. Furthermore, the 4% excess gold atoms of the reconstructed surface which are expelled during lifting of the reconstruction do not diffuse away from the reconstruction rows. We observe, in contrast, the formation of nanometric islands arranged forming chains along the directions previously followed by the reconstruction solitons. Chemisorbed adenine adlayers consist of short chains of adenine molecules roughly aligned along the three main crystallographic directions of the substrate and stabilized by  stacking. These chains tend to align parallel to each other, forming very small domains and yielding an adlayer with a very short-range order. The same adlayer structure is observed at all the studied pH values. The STM results also confirm that, in very acidic media, and at low potentials, adenine adsorbs very weakly on the reconstructed Au(111) surface.

Electrochemistry Communications, 2013

An Electrochemical Scanning Tunneling Microscopy (EC-STM) study of the adsorption of adenine on A... more An Electrochemical Scanning Tunneling Microscopy (EC-STM) study of the adsorption of adenine on Au(111) electrodes was undertaken in the pH range between 1 and 7, aiming at achieving a deeper knowledge on the structure and organization of adenine chemisorbed on gold, and at confirming previous conclusions obtained from combined electrochemical and insitu IR spectroscopy measurements. This study confirms that chemisorption of adenine induces the lifting of the Au(111) surface reconstruction. Furthermore, the 4% excess gold atoms of the reconstructed surface which are expelled during lifting of the reconstruction do not diffuse away from the reconstruction rows. We observe, in contrast, the formation of nanometric islands arranged forming chains along the directions previously followed by the reconstruction solitons. Chemisorbed adenine adlayers consist of short chains of adenine molecules roughly aligned along the three main crystallographic directions of the substrate and stabilized by  stacking. These chains tend to align parallel to each other, forming very small domains and yielding an adlayer with a very short-range order. The same adlayer structure is observed at all the studied pH values. The STM results also confirm that, in very acidic media, and at low potentials, adenine adsorbs very weakly on the reconstructed Au(111) surface.

Langmuir, 2002

We report the use of scanning electrochemical microscopy (SECM) to control the generation of Tl(I... more We report the use of scanning electrochemical microscopy (SECM) to control the generation of Tl(I) at a mercury substrate and detect this species at a mercury-coated tip to study the transport of these ions through ion channels. The transport of Tl(I) across gramicidin D half-channels imbedded in a dioleoylphosphatidylcholine (DOPC) monolayer supported on a Tl amalgam hanging mercury drop electrode (HMDE) was studied using the substrate generation-tip collection mode of SECM. A Hg/Pt "submarine" electrode, used as the SECM tip, was made through simple contact of the Pt ultramicroelectrode with the HMDE. The tip transient response for the collection of generated Tl(I) at the amalgam HMDE was recorded for several tip to substrate distances. This collection-generation experiment was repeated with a DOPCmodified Tl/HMDE and a gramicidin-DOPC-modified Tl/HMDE. An apparent heterogeneous rate constant (khet) 2.8 ((0.1) × 10-4 cm/s) for the transport of Tl(I) through the gramicidin to the tip was extracted.

AAPS PharmSciTech, 2019

Liposomes with their capacity to anchor gold nanoparticles (AuNPs) onto their surface are used in... more Liposomes with their capacity to anchor gold nanoparticles (AuNPs) onto their surface are used in the treatment of several pathologies such as cancer. The objective of this work was the optimization of the vesicle composition by using cationic agents in order to reinforce the anchoring process of AuNPs, and for the study of the influence of local temperature and vesicle size on drug release. A Plackett-Burman design was conducted to determine the optimal composition for the anchoring of AuNPs. A comprehensive study of the influence of lipid bilayer composition on the surface charge, size, and polydispersity index (PdI) of liposomes was carried out. Afterwards, in vitro release studies by dialysis were performed and several release parameters were evaluated as a function of temperature. Cholesterol was fixed as the rigid agent and Didodecyldimethylammonium bromide (DDAB) was selected as the cationic lipid into the liposome bilayer. Photomicrographs revealed that DDAB facilitated the anchoring of AuNPs onto the liposomal surface. The anchoring of AuNPs also enhanced the amount and rate of calcein released, especially in extruded samples, at several incubating temperatures. In addition, it was observed that both the anchoring of AuNPs and the calcein release were improved by increasing the surface of the vesicles. The contributions of liposome composition (DDAB inclusion, incubation temperature, anchoring of AuNPs) and size and surface availability of the vesicles on calcein release could be used to design improved lipid nanostructures for the controlled release of anticancer drugs.

Electrochimica Acta, 2016

The adsorption of thymine on gold electrodes has been studied by ATR-SEIRAS in situ spectroscopy ... more The adsorption of thymine on gold electrodes has been studied by ATR-SEIRAS in situ spectroscopy at three pH values (1, 7 and 12), in order to analyse the tautomeric equilibrium of deprotonated thymine in the adsorbed state. The anionic form which is deprotonated in nitrogen N1 (N1 tautomer) and the one deprotonated in nitrogen N3 (N3 tautomer) are considered. The spectroscopic results have been interpreted in the light of DFT ab-initio calculations of both tautomeric forms adsorbed on gold surfaces. The basis sets 6-311 + +G(d,p) for C, H, O and N atoms and LANDL2DZ for Au atoms have been used. The electrode surface has been simulated as an unreconstructed Au(111) surface of 19 atoms. The preponderance of each tautomer of adsorbed thymine as a function of pH has been inferred from the analysis of the spectral signals in the 1500-1800 cm À1 wavenumber region related mostly to stretching modes of the carbonyl groups. It has been found that the adsorbed N3 tautomer predominates in the case of adsorption from acid media while the N1 tautomer predominates in the adsorption from basic media but the adsorption of both forms have been distinguished in the experiments from neutral media. Moreover, the plausible changes in the orientation of the two adsorbed tautomers with the electric field have been determined by analysing the relative intensities of the characteristic CH stretching signals in the 2800-3300 cm À1 spectral region. It is proposed that the N3 tautomer undergoes changes in the interaction sites with the metal and in the molecular plane orientation on the electrode as the electric potential is increased, but the N1 tautomer molecule keeps the interaction sites while the molecular plane slightly rotates to facilitate the electrostatic interaction with the field.

Journal of Electroanalytical Chemistry, 1999

The reduction of nitromethane has been studied by impedance voltammetry at various water activiti... more The reduction of nitromethane has been studied by impedance voltammetry at various water activities using NaClO 4 as the base electrolyte. The impedance analysis conforms well to an EC-C-eee mechanism, and the rate constants for the three rate determining steps are obtained together with the standard potential for the first reduction process (EC). On the other hand, the results obtained for the reduction of deuterated nitromethane in 1 M NaCl+ D 2 O solutions are compared with the ones obtained for nitromethane in 1 M NaCl aqueous solutions. A special role played by the solvent on the first chemical step shows up in both kinds of experiments, thus suggesting that it consists of a nitro-aci tautomerism reaction.

Electrochimica Acta, 2012

In situ external reflection infrared reflection spectroscopy (IRRAS) and surface-enhanced infrare... more In situ external reflection infrared reflection spectroscopy (IRRAS) and surface-enhanced infrared reflection absorption spectroscopy under attenuated total reflection conditions (ATR-SEIRAS) have been used to study the adsorption of adenine at Au(1 1 1) and gold thin-film electrodes in 0.1 M HClO 4 solutions in deuterium oxide and in water. The existence of protonated and deprotonated adenine molecules at the electrode surface has been proved from the comparison of the spectra for adsorbed adenine with those obtained for dissolved adenine. In all cases, characteristic band frequencies are observed for the enhanced ring stretching band in D 2 O and also the bending band of the amino group in H 2 O. Both signals appear at higher wavenumbers for the protonated species. In acid media, deprotonation of adsorbed adenine is induced by increasing positive potentials and/or adenine coverage leading to the same adsorbed species as previously reported in basic media, namely chemically adsorbed adenine with a tilted orientation of the molecular plane on the electrode. Co-adsorption of water and perchlorate anions is detected in the case of the acid media, indicating the involvement of these species in the stabilization of the organic film. Time-resolved experiments at negative potentials and low adenine concentrations have shown also the physical adsorption of protonated adenine and have allowed the monitoring of the adsorption of the protonated and unprotonated forms as a function of time. Adsorption of unprotonated adenine is slower but is favored at the equilibrium at the electrode surface even if the pH of the media is three units lower than the pK a of adenine in solution.

Electrochemistry Communications, 2013

The co-adsorption of complementary DNA bases adenine and thymine on gold thin-film electrodes fro... more The co-adsorption of complementary DNA bases adenine and thymine on gold thin-film electrodes from 0.1 M HClO 4 solutions in H 2 O and D 2 O is studied by surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS). The comparison of the spectra in the range 1750-1550 cm −1 for co-adsorbed adenine and thymine at controlled potentials to those of the individual adsorbed bases shows the enhancement of the signals associated to the vibration modes of adenine and the inhibition of those of thymine. The results can be explained by invoking the rearrangement of both molecules on the electrode surface in order to facilitate the Watson-Crick (W-C) and/or Hoogsteen (HG) interactions between the bases. The co-adsorption seems to be a cooperative process in which a low surface concentration of each base can induce the rearrangement of the complementary base molecules on the surface.

Electroanalysis, 1998

2-Dimensional amperometry” using arrays of gold channel microband electrodes is applied to the ox... more 2-Dimensional amperometry” using arrays of gold channel microband electrodes is applied to the oxidation of 2,3,7,8-tetramethoxythianthrene (TMT) and to the characterization of the follow-up kinetics of the resulting radical cation with pyridine. In the absence of pyridine the reaction is consistent with an E mechanism and a value of 1.3 × 10−5 cm2 s−1 is obtained for the diffusion coefficient of TMT. In the presence of pyridine the experimental results are consistent with a DISP2 mechanism where the values of the rate constant have a first order dependence on the concentration of pyridine. The following mechanism is proposed: and a value of 5.8 × 104 M−2s−1 is found for the rate constant for the regeneration of TMT.

Analytical Chemistry, 1998

A channel electrode array, with electrodes ranging in size from the millimeter to the submicromet... more A channel electrode array, with electrodes ranging in size from the millimeter to the submicrometer scale, is used for the amperometric interrogation of mechanistically complex electrode processes. In this way, the transportlimited current, measured as a function of both electrode size and electrolyte flow rate (convection), is shown to provide a highly sensitive probe of mechanism and kinetics. The application of "two-dimensional voltammetry" to diverse electrode processes, including E, ECE, ECEE, EC′, and DISP2 reactions, is reported.

Electroanalysis, 2004

ABSTRACT

International Journal of Pharmaceutics, 2022

Pharmaceutics, 2021

Stimulus-responsive liposomes (L) for triggering drug release to the target site are particularly... more Stimulus-responsive liposomes (L) for triggering drug release to the target site are particularly useful in cancer therapy. This research was focused on the evaluation of the effects of cholesterol levels in the performance of gold nanoparticles (AuNPs)-functionalized L for controlled doxorubicin (D) delivery. Their interfacial and morphological properties, drug release behavior against temperature changes and cytotoxic activity against breast and ovarian cancer cells were studied. Langmuir isotherms were performed to identify the most stable combination of lipid components. Two mole fractions of cholesterol (3.35 mol% and 40 mol%, L1 and L2 series, respectively) were evaluated. Thin-film hydration and transmembrane pH-gradient methods were used for preparing the L and for D loading, respectively. The cationic surface of L allowed the anchoring of negatively charged AuNPs by electrostatic interactions, even inducing a shift in the zeta potential of the L2 series. L exhibited nanomet...

Electrochimica Acta, 2021

Abstract Chronocoulometry was applied to determine charge in a monolayer of nucleolipid (1,2-dipa... more Abstract Chronocoulometry was applied to determine charge in a monolayer of nucleolipid (1,2-dipalmitoyl-sn‑glycero-3-(cytidine diphosphate)) deposited at a gold electrode surface. The immersion method was used to measure the potential of zero charge of the interface (Epzci), which is a sum of charge on the monolayer of the nucleolipid and charge on the gold surface. Photon polarization infrared reflection absorption spectroscopy (PM-IRRAS) was used to determine formation of the Watson-Crick complex between terminal cytidine moiety of the nucleolipid and guanine (its complementary base) added to the solution. The combination of electrochemical and spectroscopic studies allowed one to demonstrate that the Watson-Crick complex is formed when the interface is positively charged. The potential applied to the electrode affects not only the complex formation but also orientation of the cytosine moiety. The complex is formed when the cytosine moiety is oriented assuming a small angle with respect to the electrode surface.

Collection of Czechoslovak Chemical Communications, 2011

The application of Electrochemical Impedance Spectroscopy to the study of surface electrode proce... more The application of Electrochemical Impedance Spectroscopy to the study of surface electrode processes is reviewed. The impedance expressions and the physical meaning of the parameters included in them are shown for three surface processes: adsorption kinetics, diffusion towards partially blocked electrodes and surface confined redox reactions. The models are applied to selected examples, showing the capability of Electrochemical Impedance Spectroscopy to obtain fundamental kinetic information of these processes. A review with 83 references.

Journal of Electroanalytical Chemistry

Electrochemistry Communications, 2013

An Electrochemical Scanning Tunneling Microscopy (EC-STM) study of the adsorption of adenine on A... more An Electrochemical Scanning Tunneling Microscopy (EC-STM) study of the adsorption of adenine on Au(111) electrodes was undertaken in the pH range between 1 and 7, aiming at achieving a deeper knowledge on the structure and organization of adenine chemisorbed on gold, and at confirming previous conclusions obtained from combined electrochemical and insitu IR spectroscopy measurements. This study confirms that chemisorption of adenine induces the lifting of the Au(111) surface reconstruction. Furthermore, the 4% excess gold atoms of the reconstructed surface which are expelled during lifting of the reconstruction do not diffuse away from the reconstruction rows. We observe, in contrast, the formation of nanometric islands arranged forming chains along the directions previously followed by the reconstruction solitons. Chemisorbed adenine adlayers consist of short chains of adenine molecules roughly aligned along the three main crystallographic directions of the substrate and stabilized by  stacking. These chains tend to align parallel to each other, forming very small domains and yielding an adlayer with a very short-range order. The same adlayer structure is observed at all the studied pH values. The STM results also confirm that, in very acidic media, and at low potentials, adenine adsorbs very weakly on the reconstructed Au(111) surface.

Electrochemistry Communications, 2013

An Electrochemical Scanning Tunneling Microscopy (EC-STM) study of the adsorption of adenine on A... more An Electrochemical Scanning Tunneling Microscopy (EC-STM) study of the adsorption of adenine on Au(111) electrodes was undertaken in the pH range between 1 and 7, aiming at achieving a deeper knowledge on the structure and organization of adenine chemisorbed on gold, and at confirming previous conclusions obtained from combined electrochemical and insitu IR spectroscopy measurements. This study confirms that chemisorption of adenine induces the lifting of the Au(111) surface reconstruction. Furthermore, the 4% excess gold atoms of the reconstructed surface which are expelled during lifting of the reconstruction do not diffuse away from the reconstruction rows. We observe, in contrast, the formation of nanometric islands arranged forming chains along the directions previously followed by the reconstruction solitons. Chemisorbed adenine adlayers consist of short chains of adenine molecules roughly aligned along the three main crystallographic directions of the substrate and stabilized by  stacking. These chains tend to align parallel to each other, forming very small domains and yielding an adlayer with a very short-range order. The same adlayer structure is observed at all the studied pH values. The STM results also confirm that, in very acidic media, and at low potentials, adenine adsorbs very weakly on the reconstructed Au(111) surface.