UV/Vis Action Spectroscopy and Structures of Tyrosine Peptide Cation Radicals in the Gas Phase

Abstract

We report the first application of UV/Vis photodissociation action spectroscopy for the structure elucidation of tyrosine peptide cation radicals produced by oxidative intramolecular electron transfer in gas‐phase metal complexes. Oxidation of Tyr‐Ala‐Ala‐Ala‐Arg (YAAAR) produces Tyr‐O radicals by combined electron and proton transfer involving the phenol and carboxyl groups. Oxidation of Ala‐Ala‐Ala‐Tyr‐Arg (AAAYR) produces a mixture of cation radicals involving electron abstraction from the Tyr phenol ring and N‐terminal amino group in combination with hydrogen‐atom transfer from the Cα positions of the peptide backbone.

Cytosine Radical Cations: A Gas‐Phase Study Combining IRMPD Spectroscopy, UVPD Spectroscopy, Ion–Molecule Reactions, and Theoretical Calculations

“…Another set of excitation energies was obtained with equation-of-motion calculations with coupled clusters and single and double excitations (EOM-CCSD) [42] using the 6-31 + G(d,p) basis set and, for structures 4 and 8 also using the 6-311 + G(2d,p) basis set, to benchmark the TD-DFT energies. Ac omparison of the TD-DFT and EOM-CCSD data showed ac loser agreement between the M06-2X and EOM-CCSD benchmark computations for most of the cytosine structures (Table S2), and MO6-2X was therefore used to further compute the vibronically broadened absorption spectra at 300 K. [44] Vibronically broadened spectra were generated with Newton-X (version 1.4, www.newtonx.org), [45] PuTTY 0.67 SSH suite (Simon Ta tham, 1997-2016), Xming (Colin Harrison, 2005, and WinSCP (Martin Prikryl, 2000-2016 programs. The smaller 6-31 + G(d,p) basis set was then used in EOM-CCSD calculations of all cytosine cation radicals.…”

“…The smaller 6-31 + G(d,p) basis set was then used in EOM-CCSD calculations of all cytosine cation radicals. Ac omparison of the TD-DFT and EOM-CCSD data showed ac loser agreement between the M06-2X and EOM-CCSD benchmark computations for most of the cytosine structures (Table S2), and MO6-2X was therefore used to further compute the vibronically broadened absorption spectra at 300 K. [44] Vibronically broadened spectra were generated with Newton-X (version 1.4, www.newtonx.org), [45] PuTTY 0.67 SSH suite (Simon Ta tham, 1997-2016), Xming (Colin Harrison, 2005, and WinSCP (Martin Prikryl, 2000-2016 programs. Optimized Cartesian atomic coordinates and harmonic frequencies obtained with M06-2X/6-31 + G(d,p) were used to generate random configurations that were weighted according to their Boltzmann factors at 300 K. At otal of 12 excited electronic states and 500 configurations were used to produce each spectrum.…”