Standard ion transfer potential at the water|butyronitrile interface

Butyronitrile is an organic solvent stable enough to be used in photochemical reactions at liquid/liquid interfaces. However, it provides a rather short polarisation window making the analysis of ion transfer across the water|butyronitrile interface challenging. Here, steady-state cyclic voltammetry, at microhole-supported micro-interfaces, was used to measure Gibbs energies of transfer. A linear relationship between the standard Gibbs energies of ion partition for the water|butyronitrile interface and the water|1,2-dichloroethane and water|nitrobencene interfaces was found, making easy to extrapolate the Gibbs energy of other ions from this empiric correlation.Fil: Riva, Julieta Soledad. Swiss Federal Institute Of Technology Epfl; Suiza. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Bassetto, V. C.. Swiss Federal Institute Of Technology Epfl; SuizaFil: Girault, Hubert. Swiss Federal Institute Of Technology Epfl; SuizaFil: Olaya, A. J.. Swiss Federal Institute Of Technology Epfl, Lausanne

On the numerical approximation of p-biharmonic and ∞-biharmonic functions

In [KP16] (arXiv:1605.07880) the authors introduced a second-order variational problem in L∞. The associated equation, coined the ∞-Bilaplacian, is a \emph{third order} fully nonlinear PDE given by Δ2∞u:=(Δu)3|D(Δu)|2=0. In this work we build a numerical method aimed at quantifying the nature of solutions to this problem which we call ∞-Biharmonic functions. For fixed p we design a mixed finite element scheme for the pre-limiting equation, the p-Bilaplacian Δ2pu:=Δ(|Δu|p−2Δu)=0. We prove convergence of the numerical solution to the weak solution of Δ2pu=0 and show that we are able to pass to the limit p→∞. We perform various tests aimed at understanding the nature of solutions of Δ2∞u and in 1-d we prove convergence of our discretisation to an appropriate weak solution concept of this problem, that of -solutions

Study of peptide on-line complexation with transition-metal ions generated from sacrificial electrodes in thin-chip polymer microsprays

A miniaturized polymer electrospray-type interface is used to study metal-ion chelation with model peptides. Taking advantage of the intrinsic electrochemical behavior of electrospray, a sacrificial electrode is used to generate at the same time electrospray and transition-metal ions coming from the anodic dissolution of the electrode. The microspray interface provides enhanced mass transport due to its small dimensions, increasing the yield of possible reactions, in particular complex formation. Transition-metal electrodes, e.g. copper, zinc, nickel, iron and silver, are used to obtain on-line complexation with model peptides. It is demonstrated that the use of in-reservoir sacrificial electrodes is an efficient way to generate metal ions in order to form and study complexes with peptides, avoiding the addition of metallic salts

Probing Cysteine Reactivity in Proteins by Mass Spectrometric EC-Tagging

The on-line electrochemical tagging (EC-tagging) of cysteine residues in proteins during mass spectrometry is studied to probe the cysteine environment. Benzoquinone probes electrogenerated at a microspray electrode react with the thiol functions of the proteins within a microchannel and the products are analyzed by mass spectrometry. The fundamentals of the technique are discussed, with a focus on the kinetic aspects. The EC-tagging efficiency of the cysteine residues in proteins is used to probe their environment. Experiments with unmodified proteins and their chemically reduced forms highlight the strong effect of the cysteine site reactivity on the tagging efficiencies. This study highlights relevant parameters for such on-line electrochemical derivatization/MS detection strategies

Size Dependence of Investigations of Hot Electron Cooling Dynamincs in Metal/Adsorbates Nanoparticles

The size dependence of electron-phonon coupling rate has been investigated by femtosecond transient absorption spectroscopy for gold nanoparticles (NPs) wrapped in a shell of sulfate with diameter varying from 1.7 to 9.2 nm. Broad-band spectroscopy gives an overview of the complex dynamics of nonequilibrium electrons and permits the choice of an appropriate probe wavelength for studying the electron-phonon coupling dynamics. Ultrafast experiments were performed in the weak perturbation regime (less than one photon in average per nanoparticle), which allows the direct extraction of the hot electron cooling rates in order to compare different NPs sizes under the same conditions. Spectroscopic data reveals a decrease of hot electron energy loss rates with metal/adsorbates nanosystem sizes. Electron-phonon coupling time constants obtained for 9.2 nm NPs are similar to gold bulk materials (a. 1 ps) whereas an increase of hot electron cooling time up to 1.9 ps is observed for sizes of 1.7 nm. This is rationalized by the domination of surface effects over size (bulk) effects. The slow hot electron cooling is attributed to the adsorbates-induced long-lived nonthermal regime, which significantly reduces the electron-phonon coupling strength (average rate of phonon emission)

First-Order System Least Squares and the Energetic Variational Approach for Two-Phase Flow

This paper develops a first-order system least-squares (FOSLS) formulation for equations of two-phase flow. The main goal is to show that this discretization, along with numerical techniques such as nested iteration, algebraic multigrid, and adaptive local refinement, can be used to solve these types of complex fluid flow problems. In addition, from an energetic variational approach, it can be shown that an important quantity to preserve in a given simulation is the energy law. We discuss the energy law and inherent structure for two-phase flow using the Allen-Cahn interface model and indicate how it is related to other complex fluid models, such as magnetohydrodynamics. Finally, we show that, using the FOSLS framework, one can still satisfy the appropriate energy law globally while using well-known numerical techniques.Comment: 22 pages, 8 figures submitted to Journal of Computational Physic