Desorption/Ionization on self-Assembled Monolayer Surface (DIAMS) Evaluation of a New Matrix-Free Laser Desorption/Ionization method

Date du colloque&nbsp;: 06/2008</p

Evaluation of a new matrix-free laser desorption/ionization method through statistic studies: comparison of the DIAMS (desorption/ionization on self-assembled monolayer surface) method with the MALDI and TGFA-LDI techniques

This work demonstrates that the desorption/ionization on self-assembled monolayer surface (DIAMS) mass spectrometry, a recent matrix-free laser desorption/ionization (LDI) method based on an organic target plate, is as statistically repeatable and reproducible as matrix assisted laser desorption ionization (MALDI) and thin gold film-assisted laser desorption/ionization (TGFA-LDI) mass spectrometries. On lipophilic DIAMS of target plates with a mixture of glycerides, repeatability/reproducibility has been estimated at 15 and 30% and the relative detection limit has been evaluated at 0.3 and 3 pmol, with and without NaI respectively. Salicylic acid and its d6-isomer analysis confirm the applicability of the DIAMS method in the detection of compounds of low molecular weight

Desorption/ionization on self-assembled monolayer surfaces (DIAMS): a new matrix-free laser desorption/ionization promising for the analysis of vegetal extracts

Rapid analysis of small molecular weight compounds is one of the most widespread applications of mass spectrometry. The high throughput analyses of vegetal extracts are relatively difficult to perform in MALDI mass spectrometry, since preparation of the sample involves the co-crystallization of the matrix with the analyte. Moreover irradiation of the matrix ion produces many low-m/z vs high-intensity ions preventing the detection of low molecular weight molecules such as secondary metabolites.Our work aims at developing a matrix free alternative to MALDI analysis by the means of an original desorption/ionization on self-assembled monolayers surfaces (DIAMS) technique. We have focused our attention on a monolayer constituted by a 2,2\u27-bithiophene 5-substituted by an alkylthio linked to the gold surface [1]. With the example of salicylate derivatives, we show that the DIAMS method is suitable to the detection and quantification of the low molecular weight compounds. Indeed, the technique is as statistically repeatable and reproducible as other mass spectrometries [2]. This DIAMS method could be suitable to the qualitative and quantitative studies of polar and apolar vegetal extracts without any preliminary chromatographic resolution

A Poly(cobaloxime)/Carbon Nanotube Electrode: Freestanding Buckypaper with Polymer-Enhanced H2-Evolution Performance.

A freestanding H2-evolution electrode consisting of a copolymer-embedded cobaloxime integrated into a multiwall carbon nanotube matrix by π-π interactions is reported. This electrode is straightforward to assemble and displays high activity towards hydrogen evolution in near-neutral pH solution under inert and aerobic conditions, with a cobalt-based turnover number (TON(Co)) of up to 420. An analogous electrode with a monomeric cobaloxime showed less activity with a TON(Co) of only 80. These results suggest that, in addition to the high surface area of the porous network of the buckypaper, the polymeric scaffold provides a stabilizing environment to the catalyst, leading to further enhancement in catalytic performance. We have therefore established that the use of a multifunctional copolymeric architecture is a viable strategy to enhance the performance of molecular electrocatalysts.We acknowledge support by the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and National Foundation for Research, Technology and Development), the OMV Group, the EPSRC, the BBSRC (Grant BB/K010220/1) and the Woolf Fisher Trust in New Zealand and the Cambridge Trusts. We also thank the National EPSRC XPS User’s Service (NEXUS) at Newcastle University, UK.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/anie.20151137

Supramolecular electrode assemblies for bioelectrochemistry

For more than three decades, the field of bioelectrochemistry has provided novel insights into the catalytic mechanisms of enzymes, the principles that govern biological electron transfer, and has elucidated the basic principles for bioelectrocatalytic systems. Progress in biochemistry, bionanotechnology, and our ever increasing ability to control the chemistry and structure of electrode surfaces has enabled the study of ever more complex systems with bioelectrochemistry. This feature article highlights developments over the last decade, where supramolecular approaches have been employed to develop electrode assemblies that increase enzyme loading on the electrode or create more biocompatible environments for membrane enzymes. Two approaches are particularly highlighted: the use of layer-by-layer assembly, and the modification of electrodes with planar lipid membranes

Développement de dispositifs moléculaires fonctionnalisés par un sidérophore pour la reconnaissance moléculaire spécifique en diagnostic clinique

Siderophores wich are naturally complexin iron ( III ) are synthesized and secreted by microorganisms against iron. In bacteria and some yeast, siderophores can be actively transported across the cell membrane through receptors and transport proteins with high activity and specificity. The synthesis of an analogue of ferrichrome ( trihydroxamate siderophore ) was recently reported by Ouchetto et al. which highlighted the active transport of this type of siderophores in C. albicans. In this context, we initiated the development of electrode with surfaces of gold functionalized by a siderophore, and involving self-assembled monolayers, in order to develop molecular devices for potential applications in biological media. One of these goals is to develop a sensor of iron ( III ) with a simple detection and real-time electrochemical type. From a medical point of view, the demand from industries to commerziale diagnostic disposable sensors of iron ( III ) is important : the aim is to develop a mobile device to diagnose excess of iron deficiency in patient. Currently, this essays is done in the laboratory by colorimetric method which is non-transportable and unreliable. Compared to optical methods, electrochemical systems using the self-assembled monolayers on gold surface have a number of advantages such as ease of implementation, speed, low cost of finite systems. In this context, this work revolves around two axes : the synthesis and physicochemical study of complexes of iron ( III )-siderophore. In this study, the ligands are associated with different electroactive units in order to set the surface of sensing applications. Our research has therefore developed in three step : * Development of a molecular engineering to synthesize new siderophores immobilsable with specific steric requirements; * Behavioral analysis and/or structure of these complexes in solution, from measurements of UV-Visible and cyclic voltammetry; * The develompent and characterization of electrode materials for electrochemical and piezoelectric technologies. In this work, we first synthesized two series of siderophores with several substituents. Initially, the first synthesis was performed by peptidic coupling of desferrioxamine B with various activated esters to afford various desferrioxamine B analogues for which optical and electrochemical properties are expected to be different. In the second step, we developed synthesis pathways which give access to two immobilisable ferrichrome analogues functionalized by bithiophene probe and a alkanethiol chain. Then the optical and the electrochemical properties of the obtained ligands were characterized and compared in the presence of Fe ( III ). Finally, we conducted a preliminary study of development of self-assembled monolayer to develop the right conditions of post- functionalization.Les sidérophores sont des complexants naturels du fer(III), synthétisés et sécrétés par les microorganismes pour s'approvisionner en fer. Chez les bactéries et certaines levures, les sidérophores peuvent être activement transportés à travers la membrane cellulaire via des récepteurs et des protéines de transport à haute activité et spécificité. La synthèse d'un analogue du ferrichrome (sidérophore trihydroxamate) a été récemment été décrite au laboratoire1 et permis de mettre en évidence le transport actif de ce type de sidérophore chez C. albicans. Dans ce contexte, nous avons entrepris d'élaborer des électrodes ou surfaces d'or fonctionnalisées par un sidérophore, et mettant en jeu des monocouches auto-assemblées, dans le but de développer des dispositifs moléculaires pour des applications potentielles en milieu biologique. Un de ces objectifs est d'élaborer un capteur du fer (III) muni d'une détection simple et en temps réel de type électrochimique. D'un point de vue médical, la demande de la part des industries du diagnostic pour commercialiser des capteurs jetables du fer (III) est importante : la finalité étant de doter d'un dispositif mobile pour diagnostiquer un excès ou une carence en fer chez un patient. Actuellement, ce dosage se fait en laboratoire par des techniques colorimétriques non transportables et peu fiables. Par rapport aux méthodes optiques, les systèmes électrochimiques faisant appel aux monocouches auto-assemblées sur surface d'or2 présentent un certain nombre d'avantages tel que la facilité de mise en oeuvre, la rapidité, le faible coût des systèmes finis. Dans ce contexte, ce travail s'articule autour deux axes : la synthèse et l'étude physicochimique des complexes de fer(III)-sidérophore. Dans cette étude, les ligands sont associés à différentes unités électroactives afin de les fixés à la surface de transducteurs physiques. Notre travail de recherche s'est donc développé selon trois étapes : Le développement d'une ingénierie moléculaire pour synthétiser de nouveaux sidérophores immobilisables ayant des exigences stériques particulières L'analyse du comportement et/ou de la structure de ces complexes en solution, à partir des mesures de l'UV-Visible et la voltampérométrie cyclique L'élaboration et caractérisation les matériaux d'électrode par des techniques électrochimiques et piézoélectriques. Au cours de ce travail, nous avons tout d'abord synthétisé deux séries de sidérophores sur lesquels plusieurs substituant ont été greffés. Dans un premier temps, les premières synthèses ont été réalisées par couplage peptidique de la desferrioxamine B à différents esters activés pour obtenir des analogues de la desferrioxamine B dont les propriétés optiques et électrochimiques sont différentes. Dans un deuxième temps, nous avons mis au point une méthode de synthèse qui a permis d'accéder à deux analogues du ferrichrome immobilisables fonctionnalisés par une sonde bithiophènique et une chaine alcanethiol. Ensuite, les propriétés optiques et électrochimiques des ligands obtenus ont été caractérisées et comparées en présence du Fe(III). Enfin, nous avons réalisé une étude préliminaire d'élaboration de monocouche auto-assemblée pour mettre au point les conditions de la post-fonctionnalisation