Ionization of Purine Tautomers in Nucleobases, Nucleosides, and Nucleotides: From the Gas Phase to the Aqueous Environment

0358633 - ÚOCHB 2012 RIV US eng J - Journal Article
Pluhařová, Eva - Jungwirth, Pavel - Bradforth, S. E. - Slavíček, P.
Ionization of Purine Tautomers in Nucleobases, Nucleosides, and Nucleotides: From the Gas Phase to the Aqueous Environment.
Journal of Physical Chemistry B. Roč. 115, č. 5 (2011), s. 1294-1305. ISSN 1520-6106. E-ISSN 1520-5207
R&D Projects: GA MŠMT LC512; GA ČR GA203/08/0114
Grant - others:GA ČR(CZ) GA203/09/0422
Program: GA
Institutional research plan: CEZ:AV0Z40550506
Keywords : DNA bases * purines * ab initio
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 3.696, year: 2011

We have simulated ionization of purine nucleic acid components in the gas phase and in a water environment. The vertical and adiabatic ionization processes were calculated at the PMP2/aug-cc-pVDZ level with the TDDFT method applied to obtain ionization from the deeper lying orbitals. The water environment was modeled via microsolvation approach and using a nonequilibrium polarizable continuum model. We have characterized a set of guanine tautomers and investigated nucleosides and nucleotides in different conformations. The results, for guanine, i.e., the nucleic Acid base with the lowest vertical ionization potential, were also compared to those for the other purine base, adenine. The main findings of our study are the following: (i) Guanine remains clearly the base with the lowest ionization energy even upon aqueous solvation. (ii) Water solvent has a strong effect on the ionization energetics of guanine and adenine and their derivatives; the vertical ionization potential (VIP) is lowered by about, 1 eV for guanine while it is similar to 1.5 eV higher in the nucleotides, overall resulting in similar VIPs for GMP(-), guanosine and guanine in water. (iii) Water efficiently screens the electrostatic interactions between nucleic acid components. Consequently, ionization in water always originates from the base unit of the nucleic acid and all the information about conformational state is lost in the ionization energetics. (iv) The energy splitting between ionization of the two least bound electrons increases upon solvation. (v) Tautomerism does not contribute to the width of the photoelectron spectra in water. (vi) The effect of specific short-range interactions with individual solvent molecules is negligible for purine bases, compared to the long-range dielectric effects of the aqueous medium.
Permanent Link: http://hdl.handle.net/11104/0006407