Centro Interdipartimentale Of Ricerca In Science Ambientali

Ravenna, Italy

Centro Interdipartimentale Of Ricerca In Science Ambientali

Ravenna, Italy
SEARCH FILTERS
Time filter
Source Type

Pshenichnyuk S.A.,Saint Petersburg State University | Modelli A.,University of Bologna | Modelli A.,Centro Interdipartimentale Of Ricerca In Science Ambientali | Jones D.,CNR Institute for Organic Syntheses and Photoreactivity | And 2 more authors.
Journal of Physical Chemistry B | Year: 2017

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. © 2017 American Chemical Society.


Pshenichnyuk S.A.,Russian Academy of Sciences | Modelli A.,University of Bologna | Modelli A.,Centro Interdipartimentale Of Ricerca In Science Ambientali
Journal of Chemical Physics | Year: 2014

Gas-phase formation of temporary negative ion states via resonance attachment of low-energy (0-6 eV) electrons into vacant molecular orbitals of salicylic acid (I) and its derivatives 3-hydroxy- (II) and 4-hydroxybenzoic acid (III), 5-cloro salicylic acid (IV) and methyl salicylate (V) was investigated for the first time by electron transmission spectroscopy. The description of their empty-level structures was supported by density functional theory and Hartree-Fock calculations, using empirically calibrated linear equations to scale the calculated virtual orbital energies. Dissociative electron attachment spectroscopy (DEAS) was used to measure the fragment anion yields generated through dissociative decay channels of the parent molecular anions of compounds I-V, detected with a mass filter as a function of the incident electron energy in the 0-14 eV energy range. The most intense negative fragment produced by DEA to isomers I-III is the dehydrogenated molecular anion [M-H]-, mainly formed at incident electron energies around 1 eV. The vertical and adiabatic electron affinities were evaluated at the B3LYP/6-31+G(d) level as the anion/neutral total energy difference. The same theoretical method was also used for evaluation of the thermodynamic energy thresholds for production of the negative fragments observed in the DEA spectra. The gas-phase DEAS data can provide support for biochemical reaction mechanisms in vivo. © 2014 AIP Publishing LLC.


Pshenichnyuk S.A.,Saint Petersburg State University | Modelli A.,University of Bologna | Modelli A.,Centro Interdipartimentale Of Ricerca In Science Ambientali | Lazneva E.F.,Saint Petersburg State University | Komolov A.S.,Saint Petersburg State University
Journal of Physical Chemistry A | Year: 2016

Electron-accepting properties, and in particular resonance dissociative electron attachment (DEA) to ascorbic acid (AA), are investigated by means of DEA spectroscopy in vacuo. The experimental features are assigned in silico and discussed in relation to expected dissociative electron transfer processes in vivo with the support of density functional theory calculations and the polarizable continuum model. It is shown that formation of the two most abundant AA metabolites in living cells, namely monodehydroascorbic acid and dehydroascorbic acid, can be stimulated by cellular electron transfer to AA under reductive conditions. Prooxidant effects caused by AA are suggested to be mediated by hydroxyl radicals formation via the DEA mechanism. The involvement of excited electronic states under UV-irradiation in plants could open additional DEA channels leading to specific AA activity forbidden under dark state conditions. © 2016 American Chemical Society.


Modelli A.,University of Bologna | Modelli A.,Centro Interdipartimentale Of Ricerca In Science Ambientali | Pshenichnyuk S.A.,Russian Academy of Sciences
Physical Chemistry Chemical Physics | Year: 2013

The gas-phase empty-level structures and formation of anion states via resonance attachment of low-energy electrons to the flavonoids naringenin (III), quercetin (IV) and myricetin (V) and the smaller reference molecules chromone (I) and flavone (II) are investigated experimentally for the first time. Dissociative electron attachment spectroscopy (DEAS) is used to measure the fragment anion currents generated through dissociative decay channels of the molecular anions of compounds I-V, detected with a mass filter as a function of the incident electron energy in the 0-14 eV energy range. Due to the insufficient volatility of flavonoids III-V, the energies of vertical electron attachment associated with temporary occupation of the lower-lying virtual orbitals are measured with electron transmission spectroscopy (ETS) only in the smaller reference molecules I and II. The experimental findings are interpreted with the support of appropriate density functional theory calculations with the B3LYP functional. The experimental vertical electron attachment energies measured in the ET spectra of I and II are compared with the orbital energies of the neutral molecules scaled using an empirically calibrated linear equation. The vertical and adiabatic electron affinities are evaluated at the B3LYP/6-31+G(d) level as the anion/neutral total energy difference. The latter theoretical method is also used for evaluation of the most stable conformers of the neutral molecules, O-H bond dissociation energies and thermodynamic energy thresholds for production of the anion fragments observed in the DEA spectra. A possible role played by loss of an H2 molecule from the parent molecular anion in vivo in the mitochondrial respiratory chain is briefly discussed. © 2013 the Owner Societies.


Burrow P.D.,University of Nebraska - Lincoln | Modelli A.,University of Bologna | Modelli A.,Centro Interdipartimentale Of Ricerca In Science Ambientali
SAR and QSAR in Environmental Research | Year: 2013

Calculated energies of lowest unoccupied molecular orbitals (LUMOs) are frequently employed as descriptors in studies of quantitative structure-activity relationships and linear free energy relationships involving electron transfer. However, the quantum chemical programs with which these are carried out, whether Hartree-Fock or density functional theory, do not treat orbitals of different character, for example, C=C π* and C-Cl σ*, consistently, nor is there consistency among different families of compounds. These problems can be ameliorated with the use of the experimental equivalent of the LUMO energy, the vertical attachment energy (VAE), or by shifting and scaling LUMO energies to a training set of available VAEs in similar compounds. Examples from the literature are used to illustrate these points. © 2013 Copyright Taylor and Francis Group, LLC.


Modelli A.,University of Bologna | Modelli A.,Centro Interdipartimentale Of Ricerca In Science Ambientali | Pshenichnyuk S.A.,Russian Academy of Sciences
Journal of Physical Chemistry A | Year: 2012

The energy and nature of the gas-phase temporary anion states of tert-butylperoxybenzoate in the 0-6 eV energy range are determined for the first time by means of electron transmission spectroscopy (ETS) and appropriate theoretical calculations. The first anion state, associated with electron capture into a delocalized π * MO with mainly ring and carbonyl character, is found to lie close to zero energy, i.e., sizably more stable (about 2 eV) than the ground (σ *) anion state of saturated peroxides. Dissociative decay channels of the unstable parent molecular anions are detected with dissociative attachment spectroscopy (DEAS), as a function of the incident electron energy, in the 0-14 eV energy range. A large DEA cross-section, with maxima at zero energy, 0.7 and 1.3 eV, is found for production of the (m/e = 121) PhCOO - anion fragment, together with the corresponding tert-butoxy neutral radical, following cleavage of the O-O bond. Although with much smaller intensities, a variety of other negative currents are observed and assigned to the corresponding anion fragments with the support of density functional theory calculations. © 2012 American Chemical Society.


Modelli A.,University of Bologna | Modelli A.,Centro Interdipartimentale Of Ricerca In Science Ambientali | Jones D.,CNR Institute for Organic Syntheses and Photoreactivity | Pshenichnyuk S.A.,Russian Academy of Sciences
Journal of Physical Chemistry C | Year: 2010

The energies of electron attachment associated with temporary occupation of π* and σ ;* virtual orbitals of the pentaheterocyclic rhodanine molecule are measured in the gas phase with electron transmission spectroscopy. The corresponding orbital energies of the neutral molecule, supplied by B3LYP/6-31G(d) calculations and scaled using an empirically calibrated linear equation, are compared with the experimental vertical attachment energies. The same computational procedure is applied to rhodanine-3-acetic acid, proposed as a possible component of dye-sensitized solar cells. In addition, the (positive) vertical and adiabatic electron affinities are evaluated at the B3LYP/6-31+G(d) level. The calculations also indicate a thermodynamic tendency toward dissociation of the ring H 2C-S bond of the molecular anion. Dissociative electron attachment spectroscopy is used to measure the total anion current, as a function of the incident electron energy, and detect with a mass filter the negative fragments generated through the dissociative decay channels of the molecular anion in the 0-4 eV energy range. In rhodanine, only two intense negative fragments are observed due to loss of a hydrogen atom or a neutral ketene (H2C=C=O) molecule from the molecular anion. In the -CH2COOH derivative, in addition to these two dissociative channels, a great number of negative fragments are observed, mainly at zero electron energy, which often imply the occurrence of multiple bond cleavage and complex atomic rearrangements. These results cast serious doubts upon the stability of dyes containing rhodanine-3-acetic acid under conditions of excess negative charge. Copyright © 2010 American Chemical Society.

Loading Centro Interdipartimentale Of Ricerca In Science Ambientali collaborators
Loading Centro Interdipartimentale Of Ricerca In Science Ambientali collaborators