title: Ionization of dimethyluracil dimers leads to facile proton transfer in the absence of hydrogen bonds.
abstract: Proton transfer is ubiquitous in chemistry and biology, occurring, for example, in proteins, enzyme reactions and across proton channels and pumps. However, it has always been described in the context of hydrogen-bonding networks ('proton wires') acting as proton conduits. Here, we report efficient intramolecular ionization-induced proton transfer across a 1,3-dimethyluracil dimer, a model π-stacked system with no hydrogen bonds. Upon photoionization by tunable vacuum ultraviolet synchrotron radiation, the dimethyluracil dimer undergoes proton transfer and dissociates to produce a protonated monomer. Deuterated dimethyluracil experiments confirm that proton transfer occurs from the methyl groups and not from the aromatic C-H sites. Calculations reveal qualitative differences between the proton transfer reaction coordinate in the π-stacked and hydrogen-bonded base pairs, and that proton transfer in methylated dimers involves significant rearrangements of the two fragments, facilitating a relatively low potential energy barrier of only 0.6 eV in the ionized dimer.
authors.affiliation: Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Amir
authors.initials: A
authors.lastname: Golan
authors.forename: Ksenia B
authors.initials: KB
authors.lastname: Bravaya
authors.forename: Romas
authors.initials: R
authors.lastname: Kudirka
authors.forename: Oleg
authors.initials: O
authors.lastname: Kostko
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Leone
authors.forename: Anna I
authors.initials: AI
authors.lastname: Krylov
authors.forename: Musahid
authors.initials: M
authors.lastname: Ahmed
mesh_terms: D003903:Deuterium / Q000737:chemistry; D019281:Dimerization; D006860:Hydrogen Bonding; D007477:Ions / Q000737:chemistry*; D013058:Mass Spectrometry; D011522:Protons; D014498:Uracil / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D007477:Ions; D011522:Protons; D014498:Uracil; C002451:1,3-dimethyluracil; D003903:Deuterium