title: Non-standard base pairing and stacked structures in methyl xanthine clusters.
abstract: We present resonant two-photon ionization and IR-UV double resonance spectra of methylated xanthine derivatives including 7-methylxanthine dimer and theobromine dimer seeded in a supersonic jet by laser desorption. For 7-methylxanthine, theophylline and theobromine monomer we assign the lowest energy tautomer based on comparison with IR-UV double resonance spectra and calculated IR frequencies. For the 7-methylxanthine dimer, we observe hydrogen bonding on the N3H position suggesting 3 possible combinations, one that is reverse Watson-Crick type and two that are reverse Hoogsteen type. For the theobromine dimer, we observe a stacked structure. For trimethylxanthine dimers we infer a stacked structure as well.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106-9510, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Callahan
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Gengeliczki
authors.forename: Nathan
authors.initials: N
authors.lastname: Svadlenak
authors.forename: Haydee
authors.initials: H
authors.lastname: Valdes
authors.forename: Pavel
authors.initials: P
authors.lastname: Hobza
authors.forename: Mattanjah S
authors.initials: MS
authors.lastname: de Vries
mesh_terms: D019281:Dimerization; D013058:Mass Spectrometry; D015394:Molecular Structure; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D014970:Xanthines / Q000737:chemistry*
chemical_list: D014970:Xanthines; C008514:methylxanthine