Electron photodetachment dissociation of DNA anions with covalently or noncovalently bound chromophores

Double stranded DNA multiply charged anions coupled to chromophores were subjected to UV-Vis photoactivation. in a quadrupole ion trap mass spectrometer. The chromophores included noncovalently bound minor groove binders (activated in the near UV), noncovalently bound intercalators (activated with visible light), and covalently linked fluorophores and quenchers (activated at their maximum absorption wavelength). We found that the activation of only chromophores having long fluorescence lifetimes did result in efficient electron photodetachment from the DNA complexes. In the case of ethidium-dsDNA complex excited at 500 nm, photodetachment is a multiphoton process. The MS3 fragmentation of radicals produced by photodetachment at lambda = 260 nm (DNA excitation) and by photodetachment at lambda > 300 nm (chromophore excitation) were compared. The radicals keep no memory of the way they were produced. A weakly bound noncovalent ligand (m-amsacrine) allowed probing experimentally that a fraction of the electronic internal energy was converted into vibrational internal energy. This fragmentation channel was used to demonstrate that excitation of the quencher DABSYL resulted in internal conversion, unlike the fluorophore 6-FAM. Altogether, photodetachment of the DNA complexes upon chromophore excitation can be interpreted by the following mechanism: (1) ligands with sufficiently long excited-state lifetime undergo resonant two-photon excitation to reach the level of the DNA excited states, then (2) the excited-state must be coupled to the DNA excited states for photodetachment to occur. Our experiments also pave the way towards photodissociation probes of biomolecule conformation in the gas-phase by Forster resonance energy transfer (FRET)

Formation and characterization of thioglycolic acid–silver cluster complexes

Gas phase reactivity observed in an ion trap was used to produce silver clusters protected with thioglycolic acid. Fragmentation pathways as well as optical properties were explored experimentally and theoretically. Sequential losses of SCH2 and CO2 in the ion trap lead to redox reactions with charge transfers between the metal part and the carboxylate and thiolate groups. This allows us to control the number of electrons in the metallic subunit and thus optical properties of the complexes. The presented formation process can be used as a prototype for tuning optical and chemical properties of ligated metal clusters by varying the number of confined electrons within the metallic subunit

Resonant Raman Scattering by quadrupolar vibrations of Ni-Ag Core-shell Nanoparticles

Low-frequency Raman scattering experiments have been performed on thin films consisting of nickel-silver composite nanoparticles embedded in alumina matrix. It is observed that the Raman scattering by the quadrupolar modes, strongly enhanced when the light excitation is resonant with the surface dipolar excitation, is mainly governed by the silver electron contribution to the plasmon excitation. The Raman results are in agreement with a core-shell structure of the nanoparticles, the silver shell being loosely bonded to the nickel core.Comment: 3 figures. To be published in Phys. Rev.

Ag31(SG)19 and Ag15(SG)11

We report a simple synthesis of silver:glutathione (Ag:SG) clusters using a cyclic reduction under oxidative conditions. Two syntheses are described which lead to solutions containing well-defined Ag31(SG)19 and Ag15(SG)11 clusters that have been characterized by mass spectrometry. The optical properties of silver:glutathione (Ag:SG) cluster solutions have been investigated experimentally. In particular, the solution containing Ag15(SG)11 clusters shows a bright and photostable emission. For Ag31(SG)19 and Ag15(SG)11 clusters, the comparison of experimental findings with DFT and TDDFT calculations allowed us to reveal the structural and electronic properties of such low nuclearity liganded silver clusters

Ag31(SG)19 and Ag15(SG)11

We report a simple synthesis of silver:glutathione (Ag:SG) clusters using a cyclic reduction under oxidative conditions. Two syntheses are described which lead to solutions containing well-defined Ag31(SG)19 and Ag15(SG)11 clusters that have been characterized by mass spectrometry. The optical properties of silver:glutathione (Ag:SG) cluster solutions have been investigated experimentally. In particular, the solution containing Ag15(SG)11 clusters shows a bright and photostable emission. For Ag31(SG)19 and Ag15(SG)11 clusters, the comparison of experimental findings with DFT and TDDFT calculations allowed us to reveal the structural and electronic properties of such low nuclearity liganded silver clusters

Ion-Induced Dipole Interactions and Fragmentation Times : Cα\alpha -Cβ\beta Chromophore Bond Dissociation Channel

The fragmentation times corresponding to the loss of the chromophore (C$\alpha$-- C$\beta$ bond dissociation channel) after photoexcitation at 263 nm have been investigated for several small peptides containing tryptophan or tyrosine. For tryptophan-containing peptides, the aromatic chromophore is lost as an ionic fragment (m/z 130), and the fragmentation time increases with the mass of the neutral fragment. In contrast, for tyrosine-containing peptides the aromatic chromophore is always lost as a neutral fragment (mass = 107 amu) and the fragmentation time is found to be fast (\textless{}20 ns). These different behaviors are explained by the role of the postfragmentation interaction in the complex formed after the C$\alpha$--C$\beta$ bond cleavage

A historical transplantation in the child: the kidney

C'est à dessein que la transplantation rénale figure dans ce programme sous la mention de transplantation historique. En effet, avec la transplantation rénale on peut suivre pas à pas la véritable histoire des transplantations d'organes. C'est elle qui a ouvert la voie aux autres greffes. Il s'agit d'une histoire passionnante où les médecins et les chercheurs français ont joué un rôle très important

Propriétés optiques de nanoparticules uniques de métaux nobles

Dans la gamme de tailles nanométriques, les propriétés optiques de particules uniques d or et d argent sont celles du solide massif modifiées par le confinement diélectrique : en particulier les Résonances de Plasmon de Surface. L interaction lumièrenanoparticule étant très faible, l étude d une particule unique a pu être réalisée grâce au développement d une technique optique originale en champ lointain basée sur la modulation spatiale de l échantillon. Cette technique a permis la détection et la caractérisation optique géométrique de nanoparticules uniques d environ 10 nm de diamètre, à l aide de sources laser ou d un continuum. L utilisation d une lampe blanche et d un montage proche UltraViolet visible proche InfraRouge a permis l étude de plus grosses particules et donc du mode quadrupolaire du plasmon ainsi que l analyse de valeurs publiées des fonctions diélectriques des métaux nobles. L étude de particules en fonction de leur taille a permis de vérifier le passage au mode quasi-statique d oscillation collective des électrons de conduction. La corrélation des mesures optiques à la microscopie électronique à transmission a montré l influence de la forme et des interactions entre particules sur cette réponse optiqueIn the range of nanometric sizes, the optical properties of single gold and silver particles are those of the massive solid modified by dielectric confinment: in particular Surface Plasmon Resonances. The light-nanoparticle interaction being very weak, the study of a single particle could be carried out thanks to the development of an original optical technique in far field based on the spatial modulation of the sample. This technique allowed the detection and the geometrical optical characterization of single nanoparticles of approximately 10 nm diameter, using laser sources or a conitnuum. The use of a white lamp and a Near UltraViolet - visible - Near InfraRed setup allowed the study of larger particles and thus of the quadrupolar mode of the plasmon as well as the analysis of published values of the dielectric functions of noble metals. The study of particles according to their size made it possible to check the changeover to the quasi-static mode of collective oscillation of the conduction electrons. The correlation of the optical measurements to transmission electron microscopy showed the influence of the form and the interactions between particles on this optical responseLYON1-BU.Sciences (692662101) / SudocSudocFranceF