title: Pairing of isolated nucleobases: double resonance laser spectroscopy of adenine-thymine.
abstract: The vibronic spectrum of the adenine-thymine (A-T) base pair was obtained by one-color resonant two-photon ionization (R2PI) spectroscopy in a free jet of thermally evaporated A and T under conditions favorable for formation of small clusters. The onset of the spectrum at 35,064 cm-1 exhibits a large red shift relative to the pi-pi* origin of 9H-adenine at 36,105 cm-1. The IR-UV spectrum was assigned to cluster structures with HNH...O=C/N...HN hydrogen bonding by comparison with the IR spectra of A and T monomers and with ab initio calculated vibrational spectra of the most stable A-T isomers. The Watson-Crick A-T base pair is not the most stable base-pair structure at different levels of ab initio theory, and its vibrational spectrum is not in agreement with the observed experimental spectrum. Experiments with methylated A and T were performed to further support the structural assignment.
authors.affiliation: Institut für Physikalische Chemie und Elektrochemie I Heinrich Heine Universität Düsseldorf 40225 Düsseldaof, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Plützer
authors.forename: Isabel
authors.initials: I
authors.lastname: Hünig
authors.forename: Karl
authors.initials: K
authors.lastname: Kleinermanns
authors.forename: Eyal
authors.initials: E
authors.lastname: Nir
authors.forename: Mattanjah S
authors.initials: MS
authors.lastname: de Vries
mesh_terms: D000225:Adenine / Q000737:chemistry*; D006860:Hydrogen Bonding; D008745:Methylation; D008956:Models, Chemical; D017785:Photons; D013053:Spectrophotometry / Q000379:methods*; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013941:Thymine / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D000225:Adenine; D013941:Thymine