Vacuum-Ultraviolet Photoionization Studies of the Microhydration of DNA Bases (Guanine, Cytosine, Adenine, and Thymine)

Belau, Leonid; Wilson, Kevin R.; Leone, Stephen R.; Ahmed, Musahid

doi:10.1021/jp0705929

Cited by 96 publications

(168 citation statements)

References 43 publications

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“…These results are consistent with the experimentally observed onsets of PT, which are independent of the cluster size (see Fig. 2E), in stark contrast to the lowest IE of microhydrated nucleobases which show notable dependence on the number of hydrated waters (∼ 0.1 eV drop in IE per water molecule) [20,24,25]. respectively.…”

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confidence: 91%

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Proton Transfer in Nucleobases is Mediated by Water

et al. 2013

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Water plays a central role in chemistry and biology by mediating the interactions between molecules, altering energy levels of solvated species, modifying potential energy profiles along reaction coordinates, and facilitating efficient proton transport through ion channels and interfaces. This study investigates proton transfer in a model system comprising dry and microhydrated clusters of nucleobases. With mass spectrometry and tunable vacuum ultraviolet (VUV) synchrotron radiation, we show that water shuts down ionization-induced proton transfer between nucleobases, which is very efficient in dry clusters. Instead, a new pathway opens up in which protonated nucleobases are generated by proton transfer from the ionized water molecule and elimination of a hydroxyl radical. Electronic structure calculations reveal that the shape of the potential energy profile along the proton transfer coordinate depends strongly on the character of the molecular orbital from which the electron is removed, i.e., the proton transfer from water to nucleobases is barrierless when an ionized state localized on water is accessed. The computed energetics of proton transfer is in excellent agreement with the experimental appearance energies. Possible adiabatic passage on the ground electronic state of the ionized system, while energetically accessible at lower energies, is not efficient. Thus, proton transfer is controlled electronically, by the character of the ionized state, rather than statistically, by simple energy considerations.Excited-state proton transfer (PT) is ubiquitous in chemistry [1-3] and biology, occurring, for example, in photoactive proteins such as green fluorescent [4] and photoactive yellow proteins [5]. In DNA, excited-state proton transfer between the nucleobases is a pathway contributing to photoprotection [6,7]. The driving force for excited-state proton transfer in

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confidence: 91%

“…The experiments were performed on a molecular beam apparatus [24] on the Chemical Dynamics Beamline at the Advanced Light Source (Fig. S1 SM).…”

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Proton Transfer in Nucleobases is Mediated by Water

et al. 2013

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“…The gas-phase NABs are prepared by thermal desorption (T= 495 K for A and T, T= 582 K for C and T= 698 K for G), and cooled in a supersonic beam. The thermal vaporization source has been described recently in a publication detailing the microsolvation of DNA bases [53]. In the current experiments, the backing pressure of Ar expanded through a 100 µm diameter nozzle was 35 kPa.…”

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Electronic Structure and Spectroscopy of Nucleic Acid Bases: Ionization Energies, Ionization-Induced Structural Changes, and Photoelectron Spectra

et al. 2010

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We report high-level ab initio calculations and single-photon ionization mass spectrometry study of ionization of adenine (A), thymine (T), cytosine (C) and guanine (G). For thymine and adenine, only the lowest-energy tautomers were considered, whereas for cytosine and guanine we characterized five lowest-energy tautomeric forms. The first adiabatic and several vertical ionization energies were computed us-

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“…A thermal vaporization technique coupled with supersonic molecular beams, which provides a gentle way to generate these species in the gas phase, was developed at the beamline. 43 This source allows for detailed investigations of the micro-solvation of individual DNA bases with small water clusters. 43 relative to the monomer occur in asymmetric hydrogen-bonded and symmetric-stacked isomers, whereas in the lowest-energy symmetric hydrogen-bonded dimer the shift in IEs is much smaller (0.1 eV).…”

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“…43 This source allows for detailed investigations of the micro-solvation of individual DNA bases with small water clusters. 43 relative to the monomer occur in asymmetric hydrogen-bonded and symmetric-stacked isomers, whereas in the lowest-energy symmetric hydrogen-bonded dimer the shift in IEs is much smaller (0.1 eV). The origin of the shift and the character of the ionized states are different in asymmetric hydrogen-bonded and symmetric stacked isomers.…”

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confidence: 99%