New Radical Detected by HF-EPR, ENDOR, and Pulsed EPR in a Room Temperature Irradiated Single Crystal of Glycine

Abstract

Single crystals of room temperature γ-irradiated glycine have been studied with electron nuclear double resonance (ENDOR) and X-band and high-frequency continuous wave electron paramagnetic resonance (EPR) spectroscopies and electron spin echo spectroscopy. EchoEPR spectroscopy was used to distinguish the radicals with different phase memory relaxation times. Three radicals have been detected, which have been identified as −CH−COO- (radical A), CH2−COO- (radical B), and CH2−NH2 (radical C). Whereas radicals A and B had been observed by other authors in the past, radical C was not detected previously. The hyperfine tensors of the two CH2 protons and of one of the NH2 protons were determined by ENDOR. ESEEM (electron spin echo envelope modulation) and HYSCORE (hyperfine sublevel correlation spectroscopy) experiments were performed in order to obtain the relative signs of the hyperfine coupling constants of the three protons. The principal values and the principal directions of the hyperfine tensors are in agreement with the hypothesis of a nonplanar structure of the radical. Unrestricted Hartree−Fock calculations have been carried out for different conformations of radical C. The calculated hyperfine coupling constants are compared with the experimental results.

Dissociative electron attachment to gas-phase glycine

“…Thus a number of theoretical [13,14,15,16,17] and experimental [14,15,18,19,20] investigations on glycine have been published in recent years. For glycine and other amino acids a tautomeric equilibrium between neutral and zwitterionic forms exists that is of fundamental importance in biochemistry.…”

Formation of anion fragments from gas-phase glycine by low energy (0–15 eV) electron impact

“…In that context a number of theoretical [1][2][3][4][5] and experimental 4 -8 investigations have appeared within the last years concerning glycine in the gas phase or in condensed phases. Furthermore, recent studies have shown that 1-20 eV electrons are able to induce substantial damage in various complex biomolecules, 9 including DNA ͑without its proteins͒.…”

Cluster or periodic, static or dynamic—the challenge of calculating the g tensor of the solid-state glycine radical

“…Recently, Barone and Causa`2 8 reported that a larger 8-Clustercontaining two glycine molecules in addition to the 6-Cluster-would yield g values for the glycine radical that are in better accordance with the experiment of Brustolon et al 20 Unfortunately, they misinterpreted the experimental results and compared their calculated isotropic g values with the non-diagonal g value measured along the crystallographic hci axis. Comparing their calculated principal values-(2.0048, 2.0041, 2.0028) for the 8-Cluster, (2.0042, 2.0037, 2.0022) for the 6-Cluster-with the experimental data of Collins and Whiffen, 21 it turns out that the former actually leads to an overall worse agreement with experiment.…”