title: Vibrational signatures of Watson-Crick base pairing in adenine-thymine mimics.
abstract: The vibrational fingerprints of hydrogen-bonding associated with the adenine-thymine (A-T) Watson-Crick (WC) base pair have been identified in an infrared study of the A-T mimics 4-aminopyrimidine-1-methylthymine (4APM-1MT) and 4-aminopyrimidine-6-methyl-4-pyrimidinone (4APM-M4PMN) in the gas-phase. The IR vibrational spectra were measured via a double resonance scheme utilizing femtosecond multiphoton ionization. The changes in the molecular structure, anharmonic vibrational parameters, and the assignment of the observed vibrational spectra in the NH/CH stretch region were investigated by carrying out high-level theoretical calculations of the anharmonic spectra. The experimental observations and theoretical calculations indicate that the hydrogen bonds associated with WC base-pairing are relatively stronger than those associated with reverse WC (rWC) base pairing. This is manifested in a more pronounced red-shift of the H-bonded vibrational modes associated with the WC as compared with the rWC base-pairing. An analysis of the factors contributing to the anharmonicity of the vibrational modes associated with H-bonding reveals that the magnitude of the off-diagonal anharmonic coupling of the H-bonded -NH2 stretch and the -NH2 bend is much smaller in WC base-pairing than in the corresponding rWC base-pairing. The chemical and biological implications of these results, especially in the context of using vibrational spectroscopy as a tool for identifying the signatures of nucleotide base vibrations is addressed.
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Goethe-Universität, Max-von-Laue-Straße 7, 60438 Frankfurt/Main, Germany. nosenko@chemie.uni-kl.de
authors.forename: Yevgeniy
authors.initials: Y
authors.lastname: Nosenko
authors.forename: Maksim
authors.initials: M
authors.lastname: Kunitski
authors.forename: Tina
authors.initials: T
authors.lastname: Stark
authors.forename: Michael
authors.initials: M
authors.lastname: Göbel
authors.forename: Pilarisetty
authors.initials: P
authors.lastname: Tarakeshwar
authors.forename: Bernhard
authors.initials: B
authors.lastname: Brutschy
mesh_terms: D020029:Base Pairing; D011743:Pyrimidines / Q000737:chemistry*; D011744:Pyrimidinones / Q000737:chemistry*; D013941:Thymine / Q000031:analogs & derivatives* / Q000737:chemistry; D014732:Vibration
chemical_list: D011743:Pyrimidines; D011744:Pyrimidinones; C030630:1-methylthymine; C034821:4-aminopyrimidine; D013941:Thymine