Deprotonated Cytosine Anions:  A Theoretical Prediction of Photoelectron Spectra

Abstract

Predictions on the photoelectron spectra of deprotonated cytosine anions (cytosinate, Cye(-)) have been made with ab initio electron propagator methods. Two imino-oxo forms are most stable, but four other isomers have energies within 10 kcal/mol. The first vertical electron detachment energies (VEDEs) for the three most stable Cye(-) isomers are approximately 3.4 eV. Imino-oxy VEDEs are about 0.3 eV smaller. For each anion, the lowest VEDE corresponds to a pi Dyson orbital. The order of higher final states is changed when relaxation and correlation effects are considered. Considerable mixing between lone-pair and bonding lobes occurs in the sigma Dyson orbitals.

Tautomer‐Specific Resonant Photoelectron Imaging of Deprotonated Cytosine Anions

“…Theo bserved ion abundance suggests the order of stability for the three anions as tKAN3H8b À > cKAN3H8a À > KAN1 À ,c onsistent with the theoretical predictions for the deprotonated cytosine anions both from the current study (Table S1) and the previous calculation by Vµzquez et al [22] It is interesting that the three observed anions could all stem from direct deprotonation of the KAN3H tautomer (Scheme S2), which is the second most stable tautomer in solution. Thet KAN3H8b À and cKAN3H8a À anions can also stem from direct deprotonation of the rare trans-a nd cis-keto-imino tautomers,r espectively.…”

“…Relative energies (below the structures) are given in kcal mol À1 . spectrum was assigned to the KAN1 À anion with ameasured EA of 3.037(15) eV for the neutral KAN1 radical, compared with the theoretical values of 3.00 eV by Lou et al [21] and 3.37 eV by Vµzquez et al [22] However,n oo ther tautomeric forms of the [CyÀH] À anion have been disclosed.…”

“…[15] Additionally,v arious tautomeric forms of the radical anion and cation of cytosine as well as the protonated cytosine have been studied. [16][17][18][19][20] However,r elatively little is known of the deprotonated cytosine anion ([CyÀH] À ), [21][22][23] despite its potential role in DNAd amage.T he ionization of DNAb ases by low-energy electrons is ac rucial process for DNAd amage after radiation. [24] Dissociative-electron-attachment experiments have shown that [CyÀH] À is the most abundant anion fragment [25] and it can pair with guanine to form anionic complexes.…”

“…[26] Thecytosine tautomers can be deprotonated at different sites to produce ap lethora of negative ions (Scheme S2). Luo et al [21] calculated the structures of five different [CyÀH] À anions generated by deprotonation of the canonical KAN1H tautomer and computed the electron affinities (EAs) of the corresponding neutral [CyÀH] radicals.C onsidering the deprotonation of other rare tautomers and searching for 95 initial structures,Vµzquez et al [22] found that the six most stable [CyÀH] À anions were,i nt he order of stability,t KAN3H8b À > cKAN3H8a À > KAN1 À > cEAOH8a À > cKAN1H8a À > tEAOH8a À (Table S1).…”

Electron Momentum Spectroscopy and Its Applications to Molecules of Biological Interest

“…Rapid development of synchrotron sourced spectroscopic techniques ensures one to measure larger biological molecules from valence space to core space (e.g., Plekan Vazquez et al, 2006). Rapid development of synchrotron sourced spectroscopic techniques ensures one to measure larger biological molecules from valence space to core space (e.g., Plekan Vazquez et al, 2006).…”