Fragmentation of adenine under energy control

Abstract

We present results on the fragmentation of adenine dication as a function of the excitation energy. The adenine molecule is charged and excited in a single collision with Cl(+) ion at 3 keV and the excitation energy distribution is obtained for each fragmentation channel by measuring the kinetic energy loss of the projectile. This method named collision induced dissociation under energy control is based on the formation of a negative scattered projectile as a result of double electron capture from the target molecule. Comparison between the main dissociation channels of singly and doubly charged adenine shows that fragmentation patterns are very similar consisting mainly of the successive emission of neutral HCN or H(2)CN(+). The energy distributions of the parent adenine dication and the kinetic energy release of the fragments measured for the most abundant fragmentation channels confirms the assumption of successive emission dynamics. A specific fragmentation pathway of the adenine requiring less energy than the usual successive emission of neutral HCN could be identified. It consists of the emission of a charged H(2)CN(+) following on by the emission of a dimer of HCN (precisely HC(2)N(2)). This new channel, measured for a mean excitation energy of 8.4 eV for the adenine dication is very closed to the emission of HCN monomer measured at 7.9 eV. The implications of these results concern the formation of adenine in the sealed-tube reaction of HCN with liquid ammonia as well as the possible formation of the adenine molecule in the interstellar medium. This last point is briefly discussed in relation to astrobiology and exobiology interests.

Elucidation of Electron Ionization Induced Fragmentations of Adenine by Semiempirical and Density Functional Molecular Dynamics

“…In the following years, mechanistic studies involving selectively isotope-labeled A were conducted [5][6][7][8] and subsequently the fragmentation patterns of A + , HA + , and A 2+ using various ionization techniques were reported. [9][10][11][12][13][14] The protonated and doubly charged species showed similar reactivity patterns to the singly charged one. Jochims et al determined appearance energies of certain decomposition products of A by photo-ionization mass spectrometry and assigned fragment structures entirely without theoretical support.…”

Electron impact fragmentation of adenine: partial ionization cross sections for positive fragments

“…Doubly-charged adenine has been clearly observed by Alvarado et al [38] in adenine mass spectra after collisions with 14 keV projectiles (H + and H, He + and He, and C + and C), and by Bredy et al [39,40] after impact with 3 keV Cl + ions and 36 keV F 2+ ions. We have examined the mass spectra of the other nucleobases measured in our laboratory, but do not observe any clear indications for the formation of doubly charged parent ions in these.…”

Fragmentation of singly charged adenine induced by neutral fluorine beam impact at 3 keV

“…3 The fragmentation of adenine has been studied intensively during the last decades. Electron, 4 photon, [5][6][7] and atom or ion collision [8][9][10] induced fragmentation spectra have shown common features characterized by the dominant population of ions H n C n N n q+ (n = 2, 3, 4, 5; q = 1, 2) in the mass spectra. The locations of the expulsed fragments from Ad + parent ions have been identified using 15 N, 13 C, and 2 D labeled adenine in some early works.…”