title: Low-Energy Electron Interaction with Melatonin and Related Compounds.
abstract: The electron attaching properties and fragmentation of temporary negative ions of melatonin and its biosynthetic precursor tryptophan are studied in vacuo using dissociative electron attachment (DEA) spectroscopy. The experimental findings are interpreted in silico with the support of Hartree-Fock and density functional theory calculations of empty orbital energies and symmetries, and evaluation of the electron affinities of the indolic molecules under investigation. The only fragment anions formed by DEA to melatonin at incident electron energies below 2 eV are associated with the elimination of a hydrogen atom (energetically favored from the NH site of the pyrrole ring, leaving the ring intact) or a CH3·radical from the temporary molecular negative ion. Opening of the pyrrole ring of melatonin is not detected over the whole electron energy range of 0-14 eV. The DEA spectra of l- and d-tryptophan are almost identical under the present experimental conditions. The adiabatic electron affinity of melatonin is predicted to be -0.49 eV at the B3LYP/6-31+G(d) level, indicating that the DEA mechanism in melatonin is likely to be present in most life forms given the availability of low energy electrons in living systems in both plant and animal kingdoms. In particular, H atom donation usually associated with free-radical scavenging activity can be stimulated by electron attachment and N-H bond cleavage at electron energies around 1 eV.
authors.affiliation: Institute of Molecule and Crystal Physics, Ufa Research Centre, Russian Academy of Sciences , Prospeκt Oktyabrya 151, 450075 Ufa, Russia.|St. Petersburg State University , Universitetskaya nab. 7/9, 199034 St. Petersburg, Russia.
authors.forename: Stanislav A
authors.identifier: 0000-0001-5318-3638
authors.initials: SA
authors.lastname: Pshenichnyuk
authors.affiliation: Dipartimento di Chimica "G. Ciamician″, Università di Bologna , via Selmi 2, 40126 Bologna, Italy.|Centro Interdipartimentale di Ricerca in Scienze Ambientali , via S. Alberto 163, 48123 Ravenna, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Modelli
authors.affiliation: ISOF, Istituto per la Sintesi Organica e la Fotoreattività , C.N.R., via Gobetti 101, 40129 Bologna, Italy.
authors.forename: Derek
authors.initials: D
authors.lastname: Jones
authors.affiliation: St. Petersburg State University , Universitetskaya nab. 7/9, 199034 St. Petersburg, Russia.
authors.forename: Eleonora F
authors.initials: EF
authors.lastname: Lazneva
authors.affiliation: St. Petersburg State University , Universitetskaya nab. 7/9, 199034 St. Petersburg, Russia.
authors.forename: Alexei S
authors.initials: AS
authors.lastname: Komolov
mesh_terms: D004583:Electrons; D006859:Hydrogen / Q000737:chemistry; D008550:Melatonin / Q000737:chemistry*; D008958:Models, Molecular; D011789:Quantum Theory; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D006859:Hydrogen; D014364:Tryptophan; D008550:Melatonin