A stand-alone magnetic guide for producing tuneable radical beams

Radicals are prevalent in gas-phase environments such as the atmosphere, combustion systems and the interstellar medium. To understand the properties of the processes occurring in these environments, it is helpful to study radical reaction systems in isolation—thereby avoiding competing reactions from impurities. There are very few methods for generating a pure beam of gas-phase radicals, and those that do exist involve complex set-ups. Here, we provide a straightforward and versatile solution. A magnetic radical filter (MRF), composed of four Halbach arrays and two skimming blades, can generate a beam of velocity selected low-field-seeking hydrogen atoms. As there is no line-of-sight through the device, all species that are unaffected by the magnetic fields are physically blocked; only the target radicals are successfully guided around the skimming blades. The positions of the arrays and blades can be adjusted, enabling the velocity distribution of the beam (and even the target radical species) to be modified. The MRF is employed as a stand-alone device-filtering radicals directly from the source. Our findings open up the prospect of studying a range of radical reaction systems with a high degree of control over the properties of the radical reactants

Inverse kinetic isotope effects in the charge transfer reactions of ammonia with rare gas ions

In the absence of experimental data, models of complex chemical environments rely on predicted reaction properties. Astrochemistry models, for example, typically adopt variants of capture theory to estimate the reactivity...</p

Transcriptome and genome sequencing uncovers functional variation in humans

Summary Genome sequencing projects are discovering millions of genetic variants in humans, and interpretation of their functional effects is essential for understanding the genetic basis of variation in human traits. Here we report sequencing and deep analysis of mRNA and miRNA from lymphoblastoid cell lines of 462 individuals from the 1000 Genomes Project – the first uniformly processed RNA-seq data from multiple human populations with high-quality genome sequences. We discovered extremely widespread genetic variation affecting regulation of the majority of genes, with transcript structure and expression level variation being equally common but genetically largely independent. Our characterization of causal regulatory variation sheds light on cellular mechanisms of regulatory and loss-of-function variation, and allowed us to infer putative causal variants for dozens of disease-associated loci. Altogether, this study provides a deep understanding of the cellular mechanisms of transcriptome variation and of the landscape of functional variants in the human genome

Étude de la stabilité d’ions moléculaires solvatés en phase gazeuse : refroidissement et irradiation

Radiation can damage our biological environment, but it can also be beneficial under certain controlled conditions. Initial action at microscopic scale consists of electronic excitation in molecules. The redistribution of this excitation energy to the environment is the primary process to be understood to describe the radiation effect on biomolecular system. Isolated molecular clusters in gas-phase are a promising model system to study the molecular interaction under radiation.The first part of this work describes the construction and the validation of a beamline which can produce bunches of cold molecular cluster ions to be injected in the RIKEN cryogenic electrostatic (RICE} storage ring. The beamline is composed of an electrospray ion source, a quadrupole mass filter, ion guides and an acceleration tube; with the main part being a cryogenic ion trap cool down to SK. The cold ion bunches, in which the ions have been mass selected and accelerated to 20keV, was probed with a laser. The beamline was successfully taken into operation and a measurement of the methylene blue action spectrum in gas-phase was carried out. The second part of this work rely on experiment realized with the dispositif d'irradiation d'agrégats moléculaires (DIAM-IPNL}. The COINTOF-VMI method allows the measurement of the velocity distributions of evaporated molecules from a cluster after high velocity collisions with an argon atom. The velocity distribution measured for mixed clusters protonated pyridine and water has two components: a low velocity part which corresponds to the evaporation of a water molecule after energy redistribution in the cluster, and a high velocity part in which the molecule is evaporated before total energy redistribution. Comparison with the distribution calculated by statistic molecular dynamic simulation shows that the low velocity part can be interpreted as the contribution of two possible excitations induced by collision: excitation on protonated pyridine and excitation on a water moleculeLes radiations peuvent endommager notre environnement biologique mais elles peuvent aussi être bienfaisantes si elles sont contrôlées. L'action initiale des radiations à l'échelle microscopique consiste en une excitation électronique dans une molécule. L'observation de la redistribution de l'énergie dans l'environnement de cette molécule excitée est primordiale à la compréhension et à la description de l'effet des rayonnements dans les systèmes biomoléculaires. Les agrégats de molécules isolés en phase gazeuse constituent des systèmes modèles prometteurs pour étudier les interactions entre molécules sous irradiation. La première partie de ce travail décrit la construction et la validation d'une ligne de faisceau permettant la production de paquets d'agrégats moléculaires froid injectables dans l'anneau de stockage RICE à RIKEN. La ligne de faisceau est composée d'une source electrospray, d'un filtre en masse quadripolaire, de guides d'ions d'un tube d'accélération, la pièce centrale étant un piège à ions cryogénique refroidi à 4 K. Le paquet d'ions froids, dont les ions ont été sélectionnés en masse et accélérés jusqu'à 20 keV, a été sondé avec un laser. La ligne a été validée par la mesure d'un spectre d'action du bleu de méthylène. La seconde partie de ce travail s'appuie sur les expériences réalisées auprès du dispositif d'irradiation d'agrégats moléculaires (DIAM-IPNL). La méthode COINTOF-VMI permet la mesure de la distribution de vitesse des molécules d'eau évaporées à partir d'un agrégat après collision à haute vitesse avec un atome d'argon. Les distributions de vitesse mesurées pour des agrégats mixtes pyridine protonée et eau présentent deux composantes : une partie à basse vitesse qui correspond à une évaporation après redistribution de l'énergie dans l'agrégat, et une partie à haute vitesse où la molécule d'eau est évaporée avant redistribution de l'énergie. La comparaison des résultats avec les distributions calculées par dynamique moléculaire statistique montre que la partie basse vitesse peut être interprétée comme la contribution des deux possibilités d'excitation induites par la collision : l'excitation de la pyridine protonée ou l'excitation d'une des molécules d'ea

Inverse kinetic isotope effects in the charge transfer reactions of ammonia with rare gas ions

In the absence of experimental data, models of complex chemical environments rely on predicted reaction properties. Astrochemistry models, for example, typically adopt variants of capture theory to estimate the reactivity...</p

Glycine Peptide Chain Formation in the Gas Phase via Unimolecular Reactions

International audiencePeptide chain formation from amino acids such as glycine is a key step in the emergence of life. Unlike their synthesis by living systems, how peptide chains grow under abiotic conditions is an open question given the variety of organic compounds discovered in various astrophysical environments, comets and meteorites. We propose a new abiotic route in the presence of protonated molecular dimers of glycine in a cold gaseous atmosphere without further need for a solid catalytic substrate. The results provide evidence for the preferential formation of mixed protonated dimers of glycine consisting of a dipeptide and a glycine molecule instead of pure protonated glycine dimers. Additional measurements mimicking a cosmic-ray impact in terms of internal excitation show that a single gas-phase collision induces polymerization via dehydration in both the mixed and pure dimer ions. Peptide chain growth is thus demonstrated to occur via a unimolecular gas-phase reaction in an excited cluster ion

Glycine Peptide Chain Formation in the Gas Phase via Unimolecular Reactions

International audiencePeptide chain formation from amino acids such as glycine is a key step in the emergence of life. Unlike their synthesis by living systems, how peptide chains grow under abiotic conditions is an open question given the variety of organic compounds discovered in various astrophysical environments, comets and meteorites. We propose a new abiotic route in the presence of protonated molecular dimers of glycine in a cold gaseous atmosphere without further need for a solid catalytic substrate. The results provide evidence for the preferential formation of mixed protonated dimers of glycine consisting of a dipeptide and a glycine molecule instead of pure protonated glycine dimers. Additional measurements mimicking a cosmic-ray impact in terms of internal excitation show that a single gas-phase collision induces polymerization via dehydration in both the mixed and pure dimer ions. Peptide chain growth is thus demonstrated to occur via a unimolecular gas-phase reaction in an excited cluster ion

Impact of a hydrophobic ion on the early stage of atmospheric aerosol formation

International audienceAtmospheric aerosols are one of the major factors affecting planetary climate, and the addition of anthropogenic molecules into the atmosphere is known to strongly affect cloud formation. The broad variety of compounds present in such dilute media and their specific underlying thermalization processes at the nanoscale make a complete quantitative description of atmospheric aerosol formation certainly challenging. In particular, it requires fundamental knowledge about the role of impurities in water cluster growth, a crucial step in the early stage of aerosol and cloud formation. Here, we show how a hydrophobic pyridinium ion within a water cluster drastically changes the thermalization properties, which will in turn change the corresponding propensity for water cluster growth. The combination of velocity map imaging with a recently developed mass spectrometry technique allows the direct measurement of the velocity distribution of the water molecules evaporated from excited clusters. In contrast to previous results on pure water clusters, the low-velocity part of the distributions for pyridinium-doped water clusters is composed of 2 distinct Maxwell–Boltzmann distributions, indicating out-of-equilibrium evaporation. More generally, the evaporation of water molecules from excited clusters is found to be much slower when the cluster is doped with a pyridinium ion. Therefore, the presence of a contaminant molecule in the nascent cluster changes the energy storage and disposal in the early stages of gas-to-particle conversion, thereby leading to an increased rate of formation of water clusters and consequently facilitating homogeneous nucleation at the early stages of atmospheric aerosol formation.</jats:p