Density Functional Theory (DFT) Study of Edaravone Derivatives as Antioxidants

Quantum chemical calculations at the B3LYP/6-31G* level of theory were employed for the structure-activity relationship and prediction of the antioxidant activity of edaravone and structurally related derivatives using energy (E), ionization potential (IP), bond dissociation energy (BDE), and stabilization energies(Delta E-iso). Spin density calculations were also performed for the proposed antioxidant activity mechanism. The electron abstraction is related to electron-donating groups (EDG) at position 3, decreasing the IP when compared to substitution at position 4. The hydrogen abstraction is related to electron-withdrawing groups (EDG) at position 4, decreasing the BDECH when compared to other substitutions, resulting in a better antioxidant activity. The unpaired electron formed by the hydrogen abstraction from the C-H group of the pyrazole ring is localized at 2, 4, and 6 positions. The highest scavenging activity prediction is related to the lowest contribution at the carbon atom. The likely mechanism is related to hydrogen transfer. It was found that antioxidant activity depends on the presence of EDG at the C-2 and C-4 positions and there is a correlation between IP and BDE. Our results identified three different classes of new derivatives more potent than edaravone.

A theoretical study of SnF2+, SnCl2+, and SnO2+ and their experimental search

We present a detailed theoretical study of the stability of the gas-phase diatomic dications SnF2+, SnCl2+, and SnO2+ using ab initio computer calculations. The ground states of SnF2+, SnCl2+, and SnO2+ are thermodynamically stable, respectively, with dissociation energies of 0.45, 0.30, and 0.42 eV. Whereas SnF2+ dissociates into Sn2+ + F, the long range behaviour of the potential energy curves of SnCl2+ and SnO2+ is repulsive and wide barrier heights due to avoided crossing act as a kind of effective dissociation energy. Their equilibrium internuclear distances are 4.855, 5.201, and 4.852 a(0), respectively. The double ionisation energies (T-e) to form SnF2+, SnCl2+, and SnO2+ from their respective neutral parents are 25.87, 23.71, and 25.97 eV. We combine our theoretical work with the experimental results of a search for these doubly positively charged diatomic molecules in the gas phase. SnO2+ and SnF2+ have been observed for prolonged oxygen (O-16(-)) ion beam sputtering of a tin metal foil and of tin (II) fluoride (SnF2) powder, respectively, for ion flight times of about 10(-5) s through a magnetic-sector mass spectrometer. In addition, SnCl2+ has been detected for O-16(-) ion surface bombardment of stannous (tin (II)) chloride (SnCl2) powder. To our knowledge, SnF2+ is a novel gas-phase molecule, whereas SnCl2+ had been detected previously by electron-impact ionization mass spectrometry, and SnO2+ had been observed before by spark source mass spectrometry as well as by atom probe mass spectrometry. We are not aware of any previous theoretical studies of these molecular systems. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4758475]

Low-energy electron collisions with glycine

We report cross sections for elastic electron scattering by gas phase glycine (neutral form), obtained with the Schwinger multichannel method. The present results are the first obtained with a new implementation that combines parallelization with OpenMP directives and pseudopotentials. The position of the well known pi* shape resonance ranged from 2.3 eV to 2.8 eV depending on the polarization model and conformer. For the most stable isomer, the present result (2.4 eV) is in fair agreement with electron transmission spectroscopy assignments (1.93 +/- 0.05 eV) and available calculations. Our results also point out a shape resonance around 9.5 eV in the A' symmetry that would be weakly coupled to vibrations of the hydroxyl group. Since electron attachment to a broad and lower lying sigma* orbital located on the OH bond has been suggested the underlying mechanism leading to dissociative electron attachment at low energies, we sought for a shape resonance around similar to 4 eV. Though we obtained cross sections with the target molecule at the equilibrium geometry and with stretched OH bond lengths, least-squares fits to the calculated eigenphase sums did not point out signatures of this anion state (though, in principle, it could be hidden in the large background). The low energy (similar to 1 eV) integral cross section strongly scales as the bond length is stretched, and this could indicate a virtual state pole, since dipole supported bound states are not expected at the geometries addressed here. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3687345]