title: Universal mechanism for breaking amide bonds by ionizing radiation.
abstract: The photodissociation of the amide bond by UV light and soft x-rays is investigated by x-ray absorption spectroscopy at the C, N, and O 1s edges. Irradiation leaves a clear and universal signature for a wide variety of amides, ranging from oligopeptides to large proteins and synthetic polyamides, such as nylon. As the π∗ peak of the amide bond shrinks, two new π∗ peaks appear at the N 1s edge with a characteristic splitting of 1.1 eV. An additional characteristic is the overall intensity reduction of both the π∗ and σ∗ features at the O 1s edge, which indicates loss of oxygen. The spectroscopic results are consistent with the release of the O atom from the amide bond, followed by the migration of the H atom from the N to one of its two C neighbors. Migration to the carbonyl C leads to an imine, and migration to the C(α) of the amino acid residue leads to a nitrile. Imine and nitrile produce the two characteristic π∗ transitions at the N 1s edge. A variety of other models is considered and tested against the N 1s spectra of reference compounds.
authors.affiliation: Department of Physics, University of Wisconsin-Madison 1150 University Ave., Madison, Wisconsin 53706, USA.
authors.forename: Phillip S
authors.initials: PS
authors.lastname: Johnson
authors.forename: Peter L
authors.initials: PL
authors.lastname: Cook
authors.forename: Xiaosong
authors.initials: X
authors.lastname: Liu
authors.forename: Wanli
authors.initials: W
authors.lastname: Yang
authors.forename: Yiqun
authors.initials: Y
authors.lastname: Bai
authors.forename: Nicholas L
authors.initials: NL
authors.lastname: Abbott
authors.forename: F J
authors.initials: FJ
authors.lastname: Himpsel
mesh_terms: D000577:Amides / Q000737:chemistry*; D008956:Models, Chemical; D010782:Photolysis; D014466:Ultraviolet Rays; D056928:X-Ray Absorption Spectroscopy; D014965:X-Rays
chemical_list: D000577:Amides