title: Benchmarking Electronic Excitation Energies and Transitions in Peptide Radicals.
abstract: Excited electronic states in several radical chromophores representing photochemically active groups in peptide and protein radicals and cation radicals were investigated computationally using equation-of-motion coupled cluster (EOM-CCSD) and time-dependent density functional theory (TD-DFT) methods. The calculations identified the main transitions responsible for photodissociations of gas-phase peptide cation radicals in the near-UV region of the spectrum. Analysis of the EOM-CCSD benchmarks showed that no TD-DFT method was universally accurate across the various radical motifs that included Cα-amide, aminoketyl, formamidyl, guanidyl, carbamyl, benzyl, phenoxy, and tautomeric dihydrophenyl and imidazolyl radicals. Overall, the ωB97XD, M06-2X, and LC-BLYP hybrid functionals showed acceptable performance when benchmarked against EOM-CCSD calculations. However, the performance of these TD-DFT methods depended on the nature of the radical chromophore, emphasizing the need for benchmarking and careful analysis.
authors.affiliation: Department of Chemistry, University of Washington , Bagley Hall, Box 351700, Seattle, Washington 98195-1700, United States.
authors.forename: František
authors.initials: F
authors.lastname: Tureček
mesh_terms: D004583:Electrons; D005609:Free Radicals / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D008958:Models, Molecular; D008962:Models, Theoretical; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry*; D044367:Phase Transition; D013816:Thermodynamics
chemical_list: D005609:Free Radicals; D005740:Gases; D010455:Peptides