An integrated experimental-theoretical approach to understand the electron transfer mechanism of adsorbed ferrocene-terminated alkanethiol monolayers

In this work, the electron transfer mechanism of self-assembled monolayers of 6-ferrocenyl-1-hexanethiol (FcC6SH) on Au(111) substrates is addressed from two perspectives. To acquire a complete overview of the involved pathways, cyclic voltammetry and scanning electrochemical microscopy (SECM) were combined using an integrated experimental-theoretical approach. In the first case, the electrochemical behaviour is evaluated in the light of computer simulations of the experimental voltammetric response measured at successive potential scans in different supporting electrolytes. Successive potential scans change the lateral interactions between adsorbed Fc molecules that affect the oxidation of the electroactive monolayer. Furthermore, ion-pair formation between the oxidized ferrocene moieties and the anions of the supporting electrolyte controls the electron transfer process as well as the type of the lateral interactions. In the second case, a thin-layer cell based formalism is used to develop a new model to understand feedback SECM experiments carried out with an additional redox mediator in solution. Since these experiments sense the parallel pathways of the electron transfer mechanism (pinholes and direct electron tunnelling and mediated electron transfer through the monolayer), the results are processed by using the new developed model for the analysis of the multipathway electron transfer mechanism. On that sense, the experimental results are processed by using the new SECM model accounting for the parallel electron transfer via the monolayer and the pinholes simultaneously.Fil: Stragliotto, María Fernanda. Universidad Nacional de Córdoba. Instituto de Investigación y Desarrollo en Ingeniería de Procesos y Química Aplicada. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación y Desarrollo en Ingeniería de Procesos y Química Aplicada; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; ArgentinaFil: Fernandez, Jose Luis. Universidad Nacional del Litoral. Instituto de Química Aplicada del Litoral. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Química Aplicada del Litoral.; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: Dassie, Sergio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; ArgentinaFil: Giacomelli, Carla Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; Argentin

Facilitated anion transfer reactions across oil∣water interfaces

In this paper we present the general equations for a model of anion transfer reactions across the oil{divides}water interface assisted by a neutral ligand. Our analysis mainly focuses on the effect of water autoprotolysis. The equations reported here allow us to simulate the system under a variety of possible conditions. The formation of complex with j:k anion-to-ligand stoichiometry is analyzed. Three different models are compared: buffered solutions (BASA model) and unbuffered solutions with and without considering water autoprotolysis (UBASA and UBAS model respectively). Moreover, the analytical relationships for the BASA model between half-wave potential and the initial concentration of anion and ligand are developed. © 2010 Elsevier B.V. All rights reserved.Fil: Dassie, Sergio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

An electroanalytical method for monitoring acid hydrolysis reactions using thick-film modified electrodes

Many organic compounds of pharmaceutical interest undergo unwanted reactions that reduce their effectivity or even generate harmful products. One of the many possible mechanisms for these degradation reactions is acid hydrolysis. We propose the use of the thick-film modified electrode setup to follow the acid hydrolysis reaction of water-soluble compounds that contain protonatable sites. We focus on the determination of the first order or pseudo-first order kinetic constant in the aqueous phase. The developed procedure is presented using a model for the transfer of protonated species at liquid|liquid interfaces coupled with an electron transfer process at the solid|liquid interface. Moreover, we experimentally validate this strategy by determining the kinetic constant for the degradation of tylosin A in acidic solutions.Fil: Zanotto, Franco Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Florida State University; Estados UnidosFil: Fernández, Ricardo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Dassie, Sergio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Thermodynamic model for the analysis of calorimetric data of oligomeric proteins

The thermodynamic parameters for the process of protein unfolding can be obtained through differential scanning calorimetry. However, the unfolding process may not be a two-state one. Between the native and the unfolded state, there may be association or dissociation processes or the formation of an intermediate state. As a consequence of this, the precise interpretation of the calorimetric data should be done with a specific thermodynamic model. In this work, we present two general models for the unfolding process of an oligomeric protein: Nn ⇌ nN ⇌ nD (model A) and Nn ⇌ In ⇌ nD (model B). In model A, the first step represents the dissociation of the oligomer into the monomeric native species, and the second step represents the denaturation process. In model B, the first step represents the conformational change of the oligomer, and the second step represents the dissociation of this species with the concomitant unfolding process. A canonical ensemble was employed to describe these systems, by considering that the total protein concentration remains constant. In the present work, we show and analyze the behavior of these systems in different conditions and how this analysis could help with the identification of the unfolding mechanism experimentally observed.Fil: Burgos, Martha Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Dassie, Sergio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Fidelio, Gerardo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentin

The effect of denaturants on protein thermal stability analyzed through a theoretical model considering multiple binding sites

A novel mathematical development applied to protein ligand binding thermodynamics is proposed, which allows the simulation, and therefore the analysis of the effects of multiple and independent binding sites to the Native and/or Unfolded protein conformations, with different binding constant values. Protein stability is affected when it binds to a small number of high affinity ligands or to a high number of low affinity ligands. Differential scanning calorimetry (DSC) measures released or absorbed energy of thermally induced structural transitions of biomolecules. This paper presents the general theoretical development for the analysis of thermograms of proteins obtained for n-ligands bound to the native protein and m-ligands bound to their unfolded form. In particular, the effect of ligands with low affinity and with a high number of binding sites (n and/or m > 50) is analyzed. If the interaction with the native form of the protein is the one that predominates, they are considered stabilizers and if the binding with the unfolded species predominates, it is expected a destabilizing effect. The formalism presented here can be adapted to fitting routines in order to simultaneously obtain the unfolding energy and ligand binding energy of the protein. The effect of guanidinium chloride on bovine serum albumin thermal stability, was successfully analyzed with the model considering low number of middle affinity binding sites to the native state and a high number of weak binding sites to the unfolded state.Fil: Burgos, Martha Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Dassie, Sergio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; ArgentinaFil: Fidelio, Gerardo Daniel. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentin

Effect of aggregation on the simple ion transfer across oil|water interfaces

The theory of cyclic voltammetry of simple ion transfer across a liquid|liquid (L|L) interface including the effect of aggregation is developed. We focus on two different situations: ion transfer followed by an aggregation process in the organic phase, and a disaggregation process in the aqueous phase followed by ion transfer. We use parameters typical of the areas of study of molecular aggregation and polymer formation, namely average aggregate size and polydispersity index. These parameters allow us to analyse, in a simple and rigorous way, the interconversion between monomer and aggregate species, both at the aqueous or organic side of the L|L interface and in the interfacial region during the potential scan. Our results show that aggregation occurring in the organic phase facilitates ion transfer across the L|L interface. In contrast, when the aggregates are present in the aqueous phase, they must be disaggregated so that the monomers can be transferred, hence the transfer energy increases. Both processes significantly alter the shape of voltammograms. The peak current and mid-peak potential are analysed as a function of initial concentrations, aggregation constants and maximum number of monomers forming each aggregate. These results are compared with approximate analytical equations, which can be used to guide further experiments and extract information from experimental responses.Fil: Zanotto, Franco Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Florida State University; Estados UnidosFil: Fernández, Ricardo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Dassie, Sergio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Hanging meniscus rotating disk electrode: A theoretical perspective

The hanging meniscus rotating disk has been proposed as a useful experimental configuration for enhancing mass transfer in electrochemical reactions mainly involving monocrystalline electrodes. Notwithstanding its common use, few authors have focused on the study of hydrodynamics in this system and its effect on mass transport. Using computational simulations based on the finite element method, a theoretical study of this configuration is presented. The effect of mass transport in the hanging meniscus on the electrochemical signal is evaluated. The reduction of the accessible electroactive area of the electrode due to the hydrodynamic conditions of the fluid near the electrode surface is presented as the explanation for the different experimentally observed phenomena. In addition, the effect of the shape of the meniscus formed on the electrochemical signal is analysed.Fil: Zanotto, Franco Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Lopez Teijelo, Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Dassie, Sergio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Role of metal contacts in the mechanical properties of molecular nanojunctions: Comparative ab initio study of Au/1,8-octanedithiol and Au/4,4-bipyridine

A comparative study of the mechanical properties of Au/4, 4 ′ -bipyridine (4, 4′ BPD) and Au/1,8-octanedithiol (1,8 ODT) molecular nanojunctions is developed using different metal wires and small clusters to represent the metal contact. Rupture of the junction at different bonds is analyzed. While in the case of 1,8 ODT, rupture at Au-Au bonds is always found; in the case of 4, 4′ BPD, rupture of a N-Au bond also appears as possible. Comparison of rupture forces, maximum elongations and force constants with the experimental values lead to the conclusion that the most common geometrical arrangement in scanning tunneling microscopy break junctions should be that where the number of Au atoms is of the order of 4. Activation energies for the rupture of these structures are calculated at sample elongations.Fil: Velez, Patricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Dassie, Sergio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Leiva, Ezequiel Pedro M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Ion transfer across liquid|liquid interface under forced hydrodynamic conditions. I: Digital simulations

In this paper, we present the general equations for a model that describes ion transfer reactions across the oil|water interface assisted by a ligand, under forced hydrodynamic conditions. Our analysis is mainly focused on the effect of mechanical stirring of the aqueous or organic phase during the potential sweep, and its influence on the limiting diffusion currents. The model was solved numerically using explicit finite difference; the results of digital simulations are obtained for simple and facilitated ion transfer. The corresponding transfer mechanism was analyzed in terms of the current-potential profiles, concentration profiles and interfacial distributions, obtained from digital simulations.Fil: Ovejero, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Fernández, Ricardo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Dassie, Sergio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Facilitated proton transfer via water autoprotolysis-electron transfer coupled reactions at thick-film modified electrodes

We present the derivation of a general mathematical model for facilitated proton transfer (FPT) reactions across a liquid|liquid (L|L) interface assisted by a protonatable neutral weak base at a thick organic film modified electrode setup. The effect of the explicit consideration of water autoprotolysis is analysed. The model reported in this paper allows us to simulate the system under different experimental conditions, such as initial pH, organic phase to aqueous phase volume ratio and concentration of redox probe and transferring protonated species. This model for the FPT reactions via water autoprotolysis in a system with two polarized interfaces is compared to our previous results calculated for a single polarizable interface [J. Electroanal. Chem. 578 (2005) 159–170]. We simulate a system with a single redox probe with two reversible non-simultaneous reduction processes with the goal of obtaining detailed mechanistic information of the facilitated proton transfer via water autoprotolysis process at thick-film modified electrodes. Our conclusions can be straightforwardly applied in experiments. We focus on a system consisting of 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a redox probe and 2,9-dimethyl-1,10-phenanthroline (2,9-DMP) as a neutral weak base.Fil: Zanotto, Franco Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Fernández, Ricardo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Dassie, Sergio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin