Positron and electron scattering by glycine and alanine: Shape resonances and methylation effect

Abstract

We report integral cross sections (ICSs) for both positron and electron scattering by glycine and alanine amino acids. These molecules differ only by a methyl group. We computed the scattering cross sections using the Schwinger multichannel method for both glycine and alanine in different levels of approximation for both projectiles. The alanine ICSs are greater in magnitude than the glycine ICSs for both positron and electron scattering, probably due to the larger size of the molecule. In electron scattering calculations, we found two resonances for each molecule. Glycine presents one at 1.8 eV, and another centered at around 8.5 eV, in the static-exchange plus polarization (SEP) approximation. The ICS for alanine shows one resonance at 2.5 eV and another at around 9.5 eV, also in SEP approximation. The results are in good agreement with most of the data present in the literature. The comparison of the electron scattering ICSs for both molecules indicates that the methylation of glycine destabilizes the resonances, shifting them to higher energies.

Shape and core-excited resonances in electron scattering from alanine

“…"Ch" indicates the character: "S", shape; "M", mixed shape-core-excited; "CE", core-excited; "F" Feshbach. Also listed are the theoretical results from Panosetti et al 4 , Fujimoto et al 6 and Nunes et al 7 and the experimental results of (a) Aflatooni et al 3 , (b) Ptasińska et al 8 , (c) Vasil'ev et al 9 and (d) Scheer et al. 10 For the DEA results, we have followed Ptasińska et al and grouped those peaks for different anion yields that are sufficiently close to potentially correspond to a single resonance.…”

“…A third resonance, lying energetically between these two, was identified for the conformers with the largest dipole moment, but not discussed. More recently, Nunes et al 7 used the SMC method to study both positron and electron elastic scattering from alanine. They also identified two resonances for the lowest energy conformer, with positions in excellent agreement with Fujimoto et al. DEA experiments were carried out for alanine by Ptasińska et al 8 , Vasil'ev et al 9 and Scheer et al 10 .…”

Electron scattering from molecules and molecular aggregates of biological relevance

“…With regards to amino acids, elastic cross sections were determined computationally for scattering from glycine (Tashiro 2008, Panosetti et al 2010, dos Santos et al 2012, Nunes et al 2016, alanine (Panosetti et al 2010, Fujimoto et al 2014, Nunes et al 2016, Fujimoto et al 2016, proline and valine (Panosetti et al 2010). The 2012, both with Born-dipole correction (the dashed blue line is the uncorrected calculation).…”

“…Experimental total and positronium formation cross sections for scattering from pyrimidine as well as theoretical ECS and DCS have been determined (Palihawadana et al 2013, Sanz et al 2013, Barbosa et al 2015. Finally, ECS have been determined for scattering from glycine and alanine (Nunes et al 2016).…”

Positive and negative ions of the amino acid histidine formed in low‐energy electron collisions

“…The formation of negative ions from amino acids upon resonant attachment of free electrons was previously studied as a function of the electron energy for glycine, proline, tryptophan, and methionine. [19][20][21][22][23][24][25][26][27][28] In contrast, for His, the electron energy dependence was neither studied nor discussed to the authors' knowledge. Voigt and Schmid studied negative ion mass spectroscopy of His in the gas phase, 29 where they used a low-temperature plasma source to generate low-energy electrons with approximate kinetic energies between 2 and 4 eV.…”