title: Effect of substituents on the excited-state dynamics of the modified DNA bases 2,4-diaminopyrimidine and 2,6-diaminopurine.
abstract: To explore the excited state dynamics of pyrimidine derivatives, we performed a combined experimental and theoretical study. We present resonant two-photon ionization (R2PI) and IR-UV double resonance spectra of 2,4-diaminopyrimidine and 2,6-diaminopurine seeded in a supersonic jet by laser desorption. For 2,4-diaminopyrimidine (S(0)-->S(1) 34,459 cm(-1)), we observed only the diamino tautomer with an excited state lifetime bracketed between experimental limits of 10 ps and 1 ns. For 2,6-diaminopurine, we observed two tautomers, the 9H- (S(0)-->S(1) 34,881 cm(-1)) and 7H- (S(0)-->S(1) 32,215 cm(-1)) diamino forms, with excited state lifetimes of 6.3±0.4 ns and 8.7±0.8 ns, respectively. We investigated the nature of the excited state of 2,4-diaminopyrimidine by means of multi-reference ab initio methods. The calculations of stationary points in the ground and excited states, minima on the S(0)/S(1) crossing seam and connecting reaction paths show that several paths with negligible barriers exist, allowing ultrafast radiationless deactivation if excited at energies slightly higher than the band origin. The sub-nanosecond lifetime found experimentally is in good agreement with this finding.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA.
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Gengeliczki
authors.forename: Michael P
authors.initials: MP
authors.lastname: Callahan
authors.forename: Nathan
authors.initials: N
authors.lastname: Svadlenak
authors.forename: Csaba István
authors.initials: CI
authors.lastname: Pongor
authors.forename: Bálint
authors.initials: B
authors.lastname: Sztáray
authors.forename: Leo
authors.initials: L
authors.lastname: Meerts
authors.forename: Dana
authors.initials: D
authors.lastname: Nachtigallová
authors.forename: Pavel
authors.initials: P
authors.lastname: Hobza
authors.forename: Mario
authors.initials: M
authors.lastname: Barbatti
authors.forename: Hans
authors.initials: H
authors.lastname: Lischka
authors.forename: Mattanjah S
authors.initials: MS
authors.lastname: de Vries
mesh_terms: D015075:2-Aminopurine / Q000031:analogs & derivatives* / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D008962:Models, Theoretical; D056951:Photoelectron Spectroscopy; D011743:Pyrimidines / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D011743:Pyrimidines; C017205:2,4-diaminopyrimidine; D015075:2-Aminopurine; C007300:2,6-diaminopurine; D004247:DNA