Theoretical Study On The Fragmentation Mechanism Of Deprotonated Asparagine

The H₂O-,NH₃-and CO₂-loss fragmentation reactions of amino acids are still the important aspects which are focused on experiment and theory,involving not only the biochemical mechanism of the amono acids in organisms but the structure indentify of the amino acids.In this study,the fragmentation mechanism of the deprotonated asparagine（[Asn–H]^–）was investigated in detail using density functional theory.The fragmentation reaction profile constructed by the relative Gibbs free energies of the reactants,intermediates,transitionstates,andproductscomputedatthe BHandHLYP/6-311++G（2df,2pd）level of theory was used to analyze the preferred pathways of the H₂O-,NH₃-and CO₂-loss fragmentation reactions and the structures of the resulting molecular ion products.Furthermore,we also examined the dependence of thermodynamics and kinetics of relevant dissociation reactions on temperature.The results detailedly revealed the isomeric structures of asparagine and deprotonated asparagine.For the asparagine isomers,they are in coexist because of low barriers to interversions,and we further provided their thermodynamic equilibrium.For the deprotonated asparagine isoemers,after locating their molecular geometries we classified them into several types based on their characteristics in structure.Also,we computed and analyzed their thermodynamics and kinetics.Furthermore,the H₂O-,NH₃-and CO₂-loss channels of the dissociation reactions of[Asn–H]^–were explored.The resulting molecular ion and dissociation fragments were assigned in detail.On the basis of the computed thermodynamical and kinetic data,we envaluated the factors controlling these fragmentations and the energy requirement for these processes.Additionally,we analyzed the temperature-dependent preferred dissociation pathways.This study offered a gross data support of building the fragmentation model of deprotonated amino acids.