TY - JOUR

T1 - Low-Energy Electron Interaction with Melatonin and Related Compounds

AU - Pshenichnyuk, Stanislav A.

AU - Modelli, Alberto

AU - Jones, Derek

AU - Lazneva, Eleonora F.

AU - Komolov, Alexei S.

PY - 2017/4/27

Y1 - 2017/4/27

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85020209981&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcb.7b01408

DO - 10.1021/acs.jpcb.7b01408

M3 - Article

AN - SCOPUS:85020209981

VL - 121

SP - 3965

EP - 3974

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 16

ER -