Mass Spectrometric Investigation of Anions Formed upon Free Electron Attachment to Nucleobase Molecules and Clusters Embedded in Superfluid Helium Droplets

Abstract

Here we report the first mass spectrometric study of negative ions formed via free electron attachment (EA) to nucleobases (NBs) embedded in helium clusters. Pure and mixed clusters of adenine and thymine have been formed by pickup of isolated NB molecules by cold helium droplets. In contrast to EA of isolated molecules in the gas phase we observe a long-lived parent anion NB- and, in addition, parent cluster ions NB-n up to size n=6. Moreover, we show that a low energy electron penetrating into a doped helium droplet causes efficient damage of the embedded nucleobases via resonant, site selective, dissociative electron attachment.

Electron attachment and electron ionization of acetic acid clusters embedded in helium nanodroplets

“…The apparatus and basic operating procedure has already been described elsewhere, so only a brief account will be given here. [16][17][18] The helium nanodroplets are formed by supersonic expansion at high pressure (20 bar) with high purity gaseous helium (499.9999%). Before expansion the helium passes through a liquid nitrogen-cooled trap, which helps to remove any remaining trace impurities.…”

“…The peak maximum is shifted to higher energies than in the gas phase because of the energy required for the electron to penetrate inside the helium droplet. 17,23 The peak at approximately 22 eV corresponds to the same excitation process but in combination with inelastic scattering (auto-scavenging) of the electron by a helium atom (electronic excitation to the 2 3 S state at 19.82 eV above the ground electronic state). Fig.…”

Gas-phase formation of large neutral alkaline-earth metal tryptophan complexes

“…(19]. But it has still remained a challenge to find reproducible methods for photoionizing biomolecules and complexes with masses exceeding 3000 u [17,20,21].The formation and photo-detection of small amino acid [22] and nucleotide clusters [23], both hydrated and solvent-free, were already reported for objects up to 1400 u. Ultracold small bioclusters can be formed by pick-up in helium nano-droplets [24]. Complexes formed between metal atoms and amino acids were also studied to understand their structure [25], their fragmentation pathways [26,27], and metal ion affinities [28].…”

Ultrafast Dynamics in Helium Nanodroplets Probed by Femtosecond Time-Resolved EUV Photoelectron Imaging

“…[1][2][3] Today, clusters of 4 He atoms are probably best known for their use as a superfluid host that enables spectroscopic studies on regular and exotic species at temperatures of ~0.4 K. [4][5][6][7][8][9][10][11][12] He droplets exhibit a unique combination of cryogenic temperatures, superfluidity, nanoscale dimensions, excellent dopant pickup capability, high effective heat capacity, and high electronic excitation energies. These properties continue to inspire a range of proven and proposed applications, from providing nano-scale reaction chambers 13,14 to hosting biological samples in ultrafast single shot diffractive imaging experiments at 4th…”