NEW RADICAL DETECTED BY HF-EPR, ENDOR, AND PULSED EPR IN A ROOM-TEMPERATURE IRRADIATED SINGLE-CRYSTAL OF GLYCINE

Single crystals of room temperature gamma-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 spectrosco py was used to distinguish the radicals with different phase memory re laxation times. Three radicals have been detected, which have been ide ntified as NH3+-CH-COO- (radical A), CH2-COO- (radical B), and CH2-NH2 (radical C). Whereas radicals A and B had been observed by other auth ors 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 dete rmined by ENDOR, ESEEM (electron spin echo envelope modulation) and HY SCORE (hyperfine sublevel correlation spectroscopy) experiments were p erformed in order to obtain the relative signs of the hyperfine coupli ng constants of the three protons. The principal values and the princi pal directions of the hyperfine tensors are in agreement with the hypo thesis of a nonplanar structure of the radical. Unrestricted Hartree-F ock calculations have been carried out for different conformations of radical C. The calculated hyperfine coupling constants are compared wi th the experimental results.