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 CH 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.

Melatonin Synthesis and Function: Evolutionary History in Animals and Plants

“…After its isolation and identification in the pineal gland of the cow, in subsequent years melatonin was identified in a wide variety of animals and plants (1–7). The extensive distribution of melatonin, especially in the primitive bacteria (cyanobacteria and α-proteobacteria) indicates that the chemical is an ancient molecule that has been retained throughout the evolution of all organisms (8, 9) (Figure 1). It is speculated that melatonin evolved in bacteria prior to the process referred to as endosymbiosis.…”

Melatonin Mitigates Mitochondrial Meltdown: Interactions with SIRT3

“…The repeated independent verification of the capability of melatonin to function as a free radical scavenger [50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68] and to hold oxidative stress in check has solidified the idea that this intrinsically-produced indole is a legitimate in vivo agent that limits oxidative damage. An additional small percentage of the total number of published reports substantiating the ability of melatonin to limit oxidative stress under conditions that would have otherwise had disastrous consequences are summarized in Table 1 [69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100].…”

Melatonin Confers Heavy Metal Tolerance of a Dark Septate Endophyte (DSE) Exophiala Pisciphila Via Lowering Oxidative Stress and Heavy Metal Accumulation

“…Although various functions of melatonin in varied animals and plants, and partial microorganisms have been studied via regulating endogenous melatonin levels, little investigation in lamentous fungi is available [13]. Melatonin originated from the primitive bacteria (cyanobacteria and α-proteobacteria) and has been retained throughout the evolution of all organisms [14,15]. Therefore, it can't be ignored that lamentous fungi have a signi cant position in the melatonin evolution process [5].…”