Melittin Adsorption and Lipid Monolayer Disruption at Liquid-Liquid Interfaces

Hubert Girault, Yu Lu, Manuel Alejandro Méndez Agudelo, Zahra Nazemi
American Chemical Society, 2011
Journal paper

Abstract

Melittin, a membrane-active peptide with antimicrobial activity, was investigated at the interface formed between two immiscible electrolyte solutions (ITIES) supported on a metallic electrode. Ion-transfer voltammetry showed well-defined semi-reversible transfer peaks along with adsorptive peaks. The reversible adsorption of melittin at the liquid-liquid interface is qualitatively discussed from voltammetric data and experimentally confirmed by real-time image analysis of video snapshots. It is also demonstrated that polarization of the water/1,2-DCE interface results in drastic drop shape variations caused by large variations of the interfacial tension. The experimental data also confirmed that maximum adsorption occurs near the ion transfer potential. Finally, the interaction of melittin with a monolayer of L-alpha-dipalmitoyl phosphatidylcholine (DPPC) was also investigated showing that melittin destabilizes the lipidic monolayer facilitating its desorption. The non-covalent complex formation between melittin and DPPC was confirmed by mass spectrometry.

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Hubert Girault, Yu Lu, Manuel Alejandro Méndez Agudelo, Zahra Nazemi
American Chemical Society, 2011
Journal paper

Abstract

Official source

https://infoscience.epfl.ch/record/170754?ln=en

About this result

Related concepts (8)

Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a mass spectrum, a plot of intensity as a function of the mass

Voltammetry is a category of electroanalytical methods used in analytical chemistry and various industrial processes. In voltammetry, information about an analyte is obtained by measuring the current

In chemistry, a non-covalent interaction differs from a covalent bond in that it does not involve the sharing of electrons, but rather involves more dispersed variations of electromagnetic interactio

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Interactions and Reactivity at Liquid-Liquid Interfaces

Manuel Alejandro Méndez Agudelo

The interface between two immiscible electrolyte solutions (ITIES) provides a well-defined platform for fundamental studies of adsorption processes and molecular reactivity in general. Two bio-inspired systems are considered in the present work: adsorbed phospholipid monolayers at the classical water-1,2-dichloroethane interface and photosensitized reduction of carbon dioxide at the novel water-supercritical CO2 interface. In first instance, theoretical modeling of adsorption processes at an ideally polarizable ITIES was carried out. In this part of the work, extension of previous models was performed in order to account for the ionic partition of the surface-active molecule. For the sake of simplicity, only a potential-dependent Langmuir isotherm was considered. A general model was then obtained in which prediction of triangular-shaped adsorptive peaks in voltammetric measurements arises naturally. Additionally, the interplay between the Gibbs energies of adsorption and ion-transfer was shown to be especially important for intermediate values between -20 to -40 kJ·mol-1. Adsorbed phospholipid monolayers at the ITIES were employed as a model for mimicking half of a cell membrane. Interactions between peptides and L-α-dipalmitoylphosphatidylcholine (DPPC), the most abundant phospholipid in cell membranes, were proven to occur by voltammetry. Further confirmation of the existence of non-covalent complexes was obtained by the complementary use of biphasic electrospray ionization mass spectrometry (BESI-MS); a technique recently developed in the Laboratoire d'Electrochimie Physique et Analytique (LEPA). Cationization of neutral peptides was equally observed to induce the complex formation with DPPC observed as a net current across the ITIES. Antimicrobial peptides were also considered given their high affinity to cell membranes. Therefore, melittin, selected as model antimicrobial peptide, exhibited a well-defined ion-transfer process accompanied by adsorptive signals. Contact angle estimation of supported interfaces over a platinum electrode indicated that these signals are reversible and induce deformation of deposited aqueous droplets. Earlier desorption of phospholipids was equally observed in presence of the antimicrobial peptide, confirming its membrane-disrupting ability by cyclic voltammetry. Finally, reduction of carbon dioxide was studied at the water-supercritical interface, in an attempt to mimic natural photosynthetic systems. As a first approach, the reduction of CO2 to formate was obtained in presence of decamethylferrocene, an organometallic compound which is capable of reducing protons under anaerobic conditions in 1,2-dichloroethane. However, the reaction follows a different pathway in presence of supercritical CO2 and formate is detected as the most abundant product. Taking one step further the application of water-supercritical CO2 interfaces, the photosensitized reduction of CO2 was conducted. In this approach, nickel(II)-1,4,8,11-tetraazacyclotetradecane (Ni(II)cyclam) was employed as catalyst, ruthenium(II)tris(2,2'-bipyridyl) ([Ru(bpy)3]2+) as photosensitizer and sodium ascorbate as sacrificial electron donor. All the components of the catalytic cycle are dissolved in water. Hence, the presence of supercritical CO2 provides with adsorption sites in which intermediates are hypothesized to be adsorbed, leading to increased efficiency and selectivity simultaneously. Adsorption of the catalyst was observed at the air-water interface and further corroborated by pendant drop shape analysis at the water-supercritical CO2 interface. In what is considered as a very promising approach, modification of the supercritical phase with co-solvents opens the route for the study of many different systems in presence of large amounts of CO2 with the long-term goal of conceiving an efficient artificial leave.

EPFL2011

This thesis is devoted to the study of oxygen reduction reaction catalysed by porphyrins at the interface between two immiscible electrolyte solutions (ITIES). Electrochemical and spectrophotometric techniques are introduced to these interfaces in order to gather more information about the transfer mechanism. Furthermore, the reduction of oxygen and the oxidation of decamethylferrocene (DMFc) in 1,2-DCE and production of hydrogen peroxide (H2O2) in the aqueous phase, on the basis of the two-phase reaction controlled by a common ion are investigated. Mass spectrometric measurements were carried out for the 1,2-DCE phase before and after two-phase reaction with an aqueous phase containing acid to indicate the stability of DMFc and the DMFc+ over the course of the two-phase reaction. Density function theory (DFT) computations have been performed based on developed a reaction pathway. Catalytic effect of 5,10,15,20-tetraphenylporphyrinatocobalt(II) [Co(tpp)], 2,3,7,8,12,13,17,18-Octaethyl-porphyrin cobalt(II) (CoOEP) and two free-base porphyrins 5,10,15,20-meso-tetraphenylporphyrin (H2TPP) and 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin (H2OEP) have been investigated as a catalyst for a two electron reduction of O2 in presence of an electron donor at various pH values at the polarized water|1,2-DCE interface. Using voltammetry, it is possible to drive this catalytic reduction at the interface as a function of the applied potential difference, where aqueous protons and organic electron donors combine to reduce O2. The signal observed corresponds to a proton-coupled electron transfer (PCET) reaction, as no current and no reaction can be observed in the absence of either catalyst, acid or O2. [Co(tpp)] and CoOEP catalysis work like conventional cobalt porphyrins, activating O2 via coordination by the formation of a superoxide structure. The advantages of the present system is that, by controlling the interfacial potential difference, the proton transfer from water to 1,2-DCE can be accurately controlled. Accordingly, the driving force for proton-coupled electron transfer reactions is also effectively harnessed. Assisted proton transfer (APT) reactions were studied across the water|1,2-DCE interface facilitated by two free-base porphyrins such as H2TPP and H2OEP. At a water|1,2-DCE interface, the interfacial formation of di-acid H4TPP2+ and H4OEP2+ are observed by ion-transfer voltammetry and UV-Visible spectroscopy, due to the double protonation of H2TPP and H2OEP at the tertiary nitrogens in the ring. Additionally, "Ionic Partition Diagram" of neutral and ionisable H2TPP compounds is plotted to illustrate the various contributions of H2TPP.

EPFL2010

Interactions and Reactivity at Liquid-Liquid Interfaces

Manuel Alejandro Méndez Agudelo

EPFL2011

EPFL2010