Manuel A. Méndez
École Polytechnique Fédérale de Lausanne
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Publication
Featured researches published by Manuel A. Méndez.
Journal of the American Chemical Society | 2009
Imren Hatay; Bin Su; Fei Li; Manuel A. Méndez; Tony Khoury; Claude P. Gros; Jean-Michel Barbe; Mustafa Ersoz; Zdenek Samec; Hubert H. Girault
Cobalt porphine (CoP) dissolved in the organic phase of a biphasic system is used to catalyze O(2) reduction by an electron donor, ferrocene (Fc). Using voltammetry at the interface between two immiscible electrolyte solutions (ITIES), 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 O(2). The current 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 the aqueous acid, CoP, Fc, or O(2).
Journal of the American Chemical Society | 2010
Imren Hatay; Bin Su; Manuel A. Méndez; Clémence Corminboeuf; Tony Khoury; Claude P. Gros; Mélanie Bourdillon; Michel Meyer; Jean-Michel Barbe; Mustafa Ersoz; Stanislav Záliš; Zdeněk Samec; Hubert H. Girault
The diprotonated form of a fluorinated free base porphyrin, namely 5-(p-aminophenyl)-10,15,20-tris(pentafluorophenyl)porphyrin (H(2)FAP), can catalyze the reduction of oxygen by a weak electron donor, namely ferrocene (Fc). At a water/1,2-dichloroethane interface, the interfacial formation of H(4)FAP(2+) is observed by UV-vis spectroscopy and ion-transfer voltammetry, due to the double protonation of H(2)FAP at the imino nitrogen atoms in the tetrapyrrole ring. H(4)FAP(2+) is shown to bind oxygen, and the complex in the organic phase can easily be reduced by Fc to produce hydrogen peroxide as studied by two-phase reactions with the Galvani potential difference between the two phases being controlled by the partition of a common ion. Spectrophotometric measurements performed in 1,2-dichloroethane solutions clearly evidence that reduction of oxygen by Fc catalyzed by H(4)FAP(2+) only occurs in the presence of the tetrakis(pentafluorophenyl)borate (TB(-)) counteranion in the organic phase. Finally, ab initio computations support the catalytic activation of H(4)FAP(2+) on oxygen.
Physical Chemistry Chemical Physics | 2010
Manuel A. Méndez; Raheleh Partovi-Nia; Imren Hatay; Bin Su; Peiyu Ge; Astrid J. Olaya; Nathalie Younan; Mohamad Hojeij; Hubert H. Girault
The fundamental aspects of electrochemistry at liquid-liquid interfaces are introduced to present the concept of molecular electrocatalysis. Here, a molecular catalyst is adsorbed at the interface to promote a proton coupled electron transfer reaction such as hydrogen evolution or oxygen reduction using lipophilic electron donors.
Chemical Communications | 2011
Joonas J. Nieminen; Imren Hatay; Peiyu Ge; Manuel A. Méndez; Lasse Murtomäki; Hubert H. Girault
Aqueous protons reduction by decamethylferrocene in 1,2-dichloroethane can be catalyzed efficiently by platinum and palladium nanoparticles electrogenerated in situ at the liquid-liquid interface.
Analytical Chemistry | 2010
Rune A. Hartvig; Manuel A. Méndez; Marco van de Weert; Lene Jorgensen; Jesper Østergaard; Hubert H. Girault; Henrik Jensen
The interaction between an intact protein and two lipophilic ions at an oil-water interface has been investigated using cyclic voltammetry, impedance based techniques and a newly developed method in which the biphasic oil-water system is analyzed by biphasic electrospray ionization mass spectrometry (BESI-MS), using a dual-channel electrospray emitter. It is found that the protein forms interfacial complexes with the lipophilic ions and that it specifically requires the presence of the oil-water interface to be formed under the experimental conditions. Furthermore, impedance based techniques and BESI-MS with a common ion to polarize the interface indicated that the Galvani potential difference across the oil-water interface significantly influences the interfacial complexation degree. The ability to investigate protein-ligand complexes formed at polarized liquid-liquid interfaces is thus a new analytical method for assessing potential dependent interfacial complexation using a structure elucidating detection principle.
Angewandte Chemie | 2011
Manuel A. Méndez; Patrick Voyame; Hubert H. Girault
Not just a solvent anymore: CO2 reduction under supercritical conditions was achieved in a biphasic water–supercritical CO2 system using an aqueous soluble catalyst (see picture). The introduction of such an interface provides a suitable reaction medium where adsorption, CO2 binding, and protonation of intermediates are intimately linked.
Chemical Communications | 2010
Bin Su; Imren Hatay; Pei Yu Ge; Manuel A. Méndez; Clémence Corminboeuf; Zdenek Samec; Mustafa Ersoz; Hubert H. Girault
Experimental studies and density functional theory (DFT) computations suggest that oxygen and proton reduction by decamethylferrocene (DMFc) in 1,2-dichloroethane involves protonated DMFc, DMFcH(+), as an active intermediate species, producing hydrogen peroxide and hydrogen in aerobic and anaerobic conditions, respectively.
Metallomics | 2010
Yu Lu; Michel Prudent; Liang Qiao; Manuel A. Méndez; Hubert H. Girault
Copper-β-amyloid 16 (Aβ16) complexes were investigated by electrospray ionization mass spectrometry (ESI-MS). Copper(i) and (ii) complexes were formed on-line in a microchip electrospray emitter by using a sacrificial copper electrode as the anode in positive ionization mode. In the presence of ascorbic acid in the peptide solution, the amount of Cu(i)-Aβ16 generated electrochemically was even higher. A kinetic model is proposed to account for the generation of copper complexes. The structure of Cu(i)-Aβ16 was investigated by tandem mass spectrometry (MS/MS), and the binding site of Cu(i) to Aβ16 was identified at the His13, His14 residues. Cu(ii)-Aβ16 was also investigated by MS/MS and, based on the unusual observations of a-ions, the two binding residues of His13 and His14 of Aβ16 to Cu(ii) were also confirmed. This approach provides direct information on Cu(i)-Aβ16 complexes generated in solution from metallic copper and gives evidence that both His13 and His14 are involved in the coordination of both Cu(i)- and Cu(ii)-Aβ16 complexes.
Inorganic Chemistry | 2013
Patrick Voyame; Kathryn E. Toghill; Manuel A. Méndez; Hubert H. Girault
The reduction of CO2 in a biphasic liquid-condensed gas system was investigated as a function of the CO2 pressure. Using 1-benzyl-1,4-dihydronicotinamide (BNAH) as sacrificial electron donor dissolved in a dimethylformamide-water mixture and [Ru(bpy)2(CO)L](n+) as a catalyst and [Ru(bpy)3](2+) as a photosensitizer, the reaction was found to produce a mixture of CO and formate, in total about 250 μmol after just 2 h. As CO2 pressure increases, CO formation is greatly favored, being four times greater than that of formate in aqueous systems. In contrast, formate production was independent of CO2 pressure, present at about 50 μmol. Using TEOA as a solvent instead of water created a single-phase supercritical system and greatly favored formate synthesis, but similarly increasing CO2 concentration favored the CO catalytic cycle. Under optimum conditions, a turnover number (TON) of 125 was obtained. Further investigations of the component limits led to an unprecedented TON of over 1000, and an initial turnover frequency (TOF) of 1600 h(-1).
Analytical Chemistry | 2008
Manuel A. Méndez; Michel Prudent; Bin Su; Hubert H. Girault
Two peptides known to interact with receptors embedded in cell membranes, angiotensin III (Ang III) and Leu-enkephalin (LeuEnk), were studied electrochemically at the interface formed between two immiscible electrolyte solutions modified by an adsorbed monolayer of dipalmitoylphosphatidylcholine (DPPC). The results indicate that cationic angiotensin III transfer can be facilitated by the interfacial formation of a complex with DPPC. The complexation constant was determined by voltammetry and found to be equal to 5.2 x 10(4) M(-1). For neutral Leu-enkephalin, a current only observable in the presence of the lipidic monolayer results from the formation of a complex between the lithium cation, LeuEnk or LeuEnk dimer and the phospholipid. For both peptides, the peptide-lipid complexes were identified by biphasic electrospray ionization mass spectrometry using a setup consisting of a dual-channel microchip, which puts in contact two immiscible phases at the Taylor cone and makes possible the study of interfacial complexes. The stability of the 1:1 complexes between lysine, diphenylalanine, Ang III, and LeuEnk and DPPC were evaluated by varying the temperature of the heated capillary of the mass spectrometer. Finally, from the complementary use of voltammetry and mass spectrometry, a mechanism for the interaction between these two biologically relevant peptides and DPPC monolayers is formulated.