TY - DATA T1 - Isomer-Selected Photoelectron Spectroscopy of Isolated DNA Oligonucleotides: Phosphate and Nucleobase Deprotonation at High Negative Charge States PY - 2012/05/09 AU - Matthias Vonderach AU - Oli T. Ehrler AU - Katerina Matheis AU - Patrick Weis AU - Manfred M. Kappes UR - https://acs.figshare.com/articles/journal_contribution/Isomer_Selected_Photoelectron_Spectroscopy_of_Isolated_DNA_Oligonucleotides_Phosphate_and_Nucleobase_Deprotonation_at_High_Negative_Charge_States/2523739 DO - 10.1021/ja300619j.s001 L4 - https://ndownloader.figshare.com/files/4166668 KW - deprotonated phosphate backbone sites KW - GT KW - photoelectron spectra KW - PE KW - pentanucleotide tetraanions show evidence KW - PES KW - room temperature solutions KW - Isolated DNA Oligonucleotides KW - deprotonated DNA oligonucleotide multianions KW - deprotonated base N2 - Fractionation according to ion mobility and mass-to-charge ratio has been used to select individual isomers of deprotonated DNA oligonucleotide multianions for subsequent isomer-resolved photoelectron spectroscopy (PES) in the gas phase. Isomer-resolved PE spectra have been recorded for tetranucleotides, pentanucleotides, and hexanucleotides. These were studied primarily in their highest accessible negative charge states (3–, 4–, and 5–, respectively), as provided by electrospraying from room temperature solutions. In particular, the PE spectra obtained for pentanucleotide tetraanions show evidence for two coexisting classes of gas-phase isomeric structures. We suggest that these two classes comprise: (i) species with excess electrons localized exclusively at deprotonated phosphate backbone sites and (ii) species with at least one deprotonated base (in addition to several deprotonated phosphates). By permuting the sequence of bases in various [A5–xTx]4– and [GT4]4– pentanucleotides, we have established that the second type of isomer is most likely to occur if the deprotonated base is located at the first or last position in the sequence. We have used a combination of molecular mechanics and semiempirical calculations together with a simple electrostatic model to explore the photodetachment mechanism underlying our photoelectron spectra. Comparison of predicted to measured photoelectron spectra suggests that a significant fraction of the detected electrons originates from the DNA bases (both deprotonated and neutral). ER -