Radicals formed by the reaction of electrons with amino acids and peptides in a neutral aqueous glass

Abstract

= 0.5 eV, a quantum of vibrational stretching, then the rate constant for reaction 2 is V2 106 sec™1 and therefore disallowed. If Ey = £2 0 and both involve translational energy alone it can be estimated that vy = Ay exp(-EyfkT) with Ay s 1013 sec-1 and vy < 1013 sec"1. Since vy = 21r2 for H20, V2 < 5 X 1011 sec-1. This is less than H+-transfer frequency between nearest neighbor acid and base, e.g., by Raman line broadening.7 These considerations indicate that £1 = £2 = 0 and, if so, then H-atom transfer by reaction 2 occurs on the first nearest approach. The average time required is half the vibrational period, or the rate is twice the O-H vibrational stretching frequency.That is, V2 = 2.2 X 1014 sec"1 in H20 and 1.6 x 1014 sec"1 in D20. Since ¡q/V2 is 21 in H20 and 25 in D20, vy = 4.6 X 1015 sec"1 in H20 and 4.0 X 1015 sec"1 in D20. The ratios ¡q/r2, in terms of the model, are the numbers of molecules visited (some twice) by a migrating hole. These values approximate those calculated previously.8The isotope effect on vy suggests interaction of the migrating hole with molecular vibrations. If the hole migrates from oxygen to oxygen along H bridges, the frequency should depend upon the phase angle and, to some extent, upon the vibrational frequency.Acknowledgment. The authors are indebted to Professor Gideon Czapski for helpful comments. References and Notes(1) The Radiation Laboratory of the University of Notre Dame is operated under contract with the U. S. Atomic Energy Commission. This Is AEG Document No. COO-38-904.(2) M.

A Density-Functional Theory Investigation of the Radiation Products of l-α-Alanine

“…[16][17][18] Also in several spintrapping studies 19,20 of alanine radicals formed in polycrystalline samples, only R1 was detected. However, it has been suggested 3,13,[16][17][18]21,22 that the spectra of several radicals could be overlapping. This hypothesis was proven by Sagstuen et al 2 In their study, two new radicals were clearly detected by a combination of EPR (electron paramagnetic resonance), ENDOR (electron-nuclear double resonance), and EIE (ENDOR-induced EPR) techniques.…”

Excess electron reactivity in amino acid aqueous solution revealed by ab initio molecular dynamics simulation: anion-centered localization and anion-relayed electron transfer dissociation

“…Thus, it is of great interest to understand the interactions of low energy excess electrons (EEs) with biomolecules such as nucleotides/nucleosides/DNA, and amino acids/peptides/proteins. Numerous studies have been carried out to reveal the behavior of an EE interacting with biomolecules, [1][2][3][4][5][6][7][8][9][10][11][12][13] with some focused on radiation damage to DNA. [1][2][3] It has been shown that low energy (down to 0 eV) EEs are capable of producing single and double strand breaks in plasmids or isolated DNA at the phosphate-sugar C-O bond, after EE attachment to nucleotides.…”

“…Different from desolvated proteins, even with a little structural water, where an EE can localize at some electron-binding sites and also transfer through-space, or through-bond, amino acids and oligopeptides in water or physiological medium could exhibit complicated thermodynamic characteristics because solvent water also behaves as a good EE carrier, and solvent fluctuations could considerably affect the states and dynamics of the injected EE. Indeed, previous studies have demonstrated the reactivity of EEs with amino acids and N-acetyl amino acids in neutral aqueous 11 and alkaline glasses, 12 and shown that the injected EEs induce a number of fragmentation reactions in these aqueous systems to form various radical species. In particular, it was experimentally reported that after attachment, EEs are found to add to the peptide bond or to the carboxyl group, [13][14][15] which is distinctly different from the EE-binding modes in the gas phase.…”

Valence anions of N-acetylproline in the gas phase: Computational and anion photoelectron spectroscopic studies

“…1, 2 For this reason the interactions between solvated electrons and small molecules mimicking peptides have received extensive study. [3][4][5] Upon capturing an excess electron, otherwise stable peptides backbones may lose their structural stability. [6][7][8][9][10][11][12][13] Here, it is worth mentioning that proline seems to be quite an unusual amino acid as far as electron-induced N-C α bond breaking is concerned.…”

“…14 As a matter of fact, the pulse radiolysis experiments on amino acids and simple peptides in an aqueous glass, carried out in the 1970's, demonstrated that immediate deamination follows the formation of anion radicals only if the N-terminal amino group is protonated. 5 Thus, presence of a proton donating group in the close vicinity to a center accepting an excess electron appears to govern the reactivity of nascent radicals which resulted from electron attachment to peptide based systems. In this paper, we report photoelectron spectroscopic (PES) and quantum chemical modeling results pertaining to N-acetylproline (N-AcPro) anions, which results from electron attachment to the neutral N-AcPro.…”