Abstract : Ø RRKM and KINETIC MONTE CARLO (KMC) SIMULATIONS : statistical reactivity. Ø INTRODUCTION-NH 3-HNCO Ensemble of trajectories V = V ion + V Ar-ion QM MM Potential energy function Ø QM-MM CHEMICAL DYNAMICS SIMULATIONS [1] : non-statistical mechanisms Collision system Ø RESULTS • Studying the reactivity of biomolecules in the gas phase allows to get rid of the effects of the environment: intrinsic properties of the molecule. • System: Uracil in DNA has cytotoxic and mutagenic potential. AM1, PM3 and DFT Collision gas Fragment ion Fragments ions (product ions) Activated fragment ion (continues to fragment) Fragmenting ion Activated ion Precursor ion Neutral loss Ø ESI-MS/MS: mass of the fragments. Collision cell Ø Our AIM • Explain non-statistical and statistical reactivity of protonated Uracil in the gas phase and obtain predictive MS-MS spectra. • For trajectories that did not react before IVR (intramolecular vibrational relaxation) takes place but have enough energy to react later on. • Following automatic protocol [3] to find all fragmentation pathways, TSs and minima. Then this is used as input fot RRKM and KMC simulations. (1) (6)-CO loss (m/z 85) (2) (3) (4) (5) from RRKM analysis: H + transfer ns (out of simulation time) NH 3 loss H 2 O loss React. <1%-no NH 3 loss All isomers: [5] mechanism (m/z 70 and m/z 44) [2] • As suggested by experiments, m/z 70 is obtained by a retro Diels-Alder (rDA) mechanism. • rDA reaction does not follow the minimum energy path along the reaction coordinate, while stepwise mechanisms do. In experiments, both mechanisms can co-exist. • Initial protonation state of the ion plays a crucial role in determining the fragmentation pathway. • NH 3 loss is a selective reaction, while H 2 O loss it is not. Ø CONCLUSIONS Refs. [1] Hase et al. JPCA (1999) [2] Rossich Molina et al. Example of NH 3 loss mechanism for isomer 4. Product yields of the different fragmentation channels of the C 4 H 5 N 2 O 2 + system obtained in the KMC simulation as a function of the excitation energy. a) Average final (internal) energies of [uracil]H + as a function of the collision energy (in the center of mass framework) for Ar + [uracil]H + collisional system. (b) Percent energy transfer values to [uracil]H + internal degrees of freedom. Symbols and solid lines correspond to the chemical dynamics simulation (CDS), and energy transfer model results, respectively.
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Submitted on : Tuesday, October 23, 2018 - 9:34:11 AM
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Estefania Rossich Molina, Jean-Yves Salpin, Riccardo Spezia, Emilio Martinez-Nuñez. STUDYING THE REACTIVITY OF URACIL IN THE GAS PHASE: STATISTICAL vs. NON-STATISTICAL APPROACH. CECAM Workshop: “Theoretical and Computational Studies of Non-Equilibrium and Non-Statistical Dynamics in Gas-Phase, Condensed-Phase, and Interfacial Reactions”, Apr 2016, Paris, France. 2016. 〈hal-01890967〉



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