Valence anions in complexes of adenine and 9-methyladenine with formic acid - stabilization by intermolecular proton transfer

Journal Article · Wed Feb 07 04:00:00 EST 2007 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja066229h· OSTI ID:903455

Mazurkiewicz, Kamil; Haranczyk, Maciej; Gutowski, Maciej S; Rak, Janusz; Radisic, Dunja; Eustis, Soren; Wang, Di; Bowen, Kit H

The photoelectron spectra of the adenine-formic acid (AFA)- and 9-methyladenine-formic acid (MAFA)- anionic complexes have been recorded with 2.540 eV photons. These spectra reveal broad features with maxima at 1.5-1.4 eV that indicate formation of stable valence anions in the gas phase. The neutral and anionic complexes of adenine/9- methyladenine and formic acid were also studied computationally at the B3LYP, second order Møller-Plesset and coupled clusters levels of theory, with the 6-31++G** and aug-cc-pVDZ basis sets. The neutral complexes form cyclic hydrogen bonds and the most stable dimers are bound by 17.7 and 16.0 kcal/mol for AFA and MAFA, respectively. The theoretical results indicate that the excess electron in both (AFA)- and (MAFA)- occupies a p* orbital localized on adenine/9-methyladenine and the adiabatic stability of the most stable anions amounts to 0.67 and 0.54 eV for AFA- and MAFA-, respectively. The excess electron attachment to the complexes induces a barrierfree proton transfer (BFPT) from the carboxylic group of formic acid to a N atom of adenine or 9-mathyladenine. As a result, the most stable structures of the anionic complexes can be characterized as neutral radicals of hydrogenated adenine(9-methyladenine) solvated by a deprotonated formic acid. The BFPT to the N atoms of adenine may be biologically relevant because some of these sites are not involved in the Watson-Crick pairing scheme and are easily accessible in the cellular environment. We suggest that valence anions of purines might be as important as those of pyrimidines in the process of DNA damage by low energy electrons. The calculations were performed at the Academic Computer Center in Gdansk (TASK) and at the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the U.S. Department of Energy's Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory, which is operated by Battelle for the US Department of Energy. The MSCF resources were available through a Computational Grand Challenge Application grant.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 903455
• Report Number(s): PNNL-SA-52542; 20901; KC0302010
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 5 Vol. 129; ISSN JACSAT; ISSN 0002-7863
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
ADENINES
ANIONS
ATOMS
DIMERS
DNA DAMAGES
ELECTRON ATTACHMENT
ELECTRONS
Environmental Molecular Sciences Laboratory
FORMIC ACID
HYDROGEN
PHOTONS
PROTONS
PURINES
PYRIMIDINES
RADICALS
SPECTRA
STABILIZATION
VALENCE
intermolecular protron transfer