title: Gas-phase spectroscopy of protonated adenine, adenosine 5'-monophosphate and monohydrated ions.
abstract: Microsolvation of chromophore ions commonly has large effects on their electronic structure and as a result on their optical absorption spectra. Here spectroscopy of protonated adenine (AdeH(+)) and its complex with one water molecule isolated in vacuo was done using a home-built mass spectrometer in combination with a tuneable pulsed laser system. Experiments also included the protonated adenosine 5'-monophosphate nucleotide (AMPH(+)). In the case of bare AdeH(+) ions, one-photon absorption leads to four dominant fragment ions corresponding to ammonium and ions formed after loss of either NH3, HCN, or NH2CN. The yields of these were measured as a function of the wavelength of the light from 210 nm to 300 nm, and they were combined to obtain the total photoinduced dissociation at each wavelength (i.e., action spectrum). A broad band between 230 nm and 290 nm and the tail of a band with maximum below 210 nm (high-energy band) are seen. In the case of AdeH(+)(H2O), the dominant dissociation channel after photoexcitation in the low-energy band was simply loss of H2O while photodissociation of protonated AMP revealed two dominant dissociation channels associated with the formation of either AdeH(+) or loss of H3PO4. The action spectra of AdeH(+), AdeH(+)(H2O), and AMPH(+) are almost identical in the 230-290 nm region, and they resemble the absorption spectrum of protonated adenine in aqueous solution recorded at low pH. Hence from our work it is firmly established that the lowest-energy transitions are independent of the surroundings.
authors.affiliation: Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark. sbn@phys.au.dk.
authors.forename: Sara Øvad
authors.initials: SØ
authors.lastname: Pedersen
authors.forename: Kristian
authors.initials: K
authors.lastname: Støchkel
authors.forename: Camilla Skinnerup
authors.initials: CS
authors.lastname: Byskov
authors.forename: Lisbeth Munksgaard
authors.initials: LM
authors.lastname: Baggesen
authors.forename: Steen Brøndsted
authors.initials: SB
authors.lastname: Nielsen
mesh_terms: D000225:Adenine / Q000737:chemistry*; D000249:Adenosine Monophosphate / Q000737:chemistry*; D011522:Protons; D013057:Spectrum Analysis; D014867:Water / Q000737:chemistry*
chemical_list: D011522:Protons; D014867:Water; D000249:Adenosine Monophosphate; D000225:Adenine