The solid-state radiation chemistry of simple amino acids, revisited.

Abstract

The solid-state radiation-induced free radical formation in simple amino acids like alpha-glycine (gly) and L-alpha-alanine (ala) has been the subject of investigations by EPR spectroscopy since the late 1950s. The EPR spectra from crystals of gly and ala generally are very complex due to the simultaneous trapping of several free radicals regardless of irradiation and observation temperatures. Untangling these complex spectra is necessary for understanding the mechanisms for the solid-state radiation chemistry of amino acids. Recently, radical formation in gly and ala after room-temperature irradiation has been reinvestigated in our laboratories using X-, K- and Q-band EPR and ENDOR spectroscopy, combined with the ENDOR-induced EPR (EIE) techniques as well as single-crystal and powder EPR and ENDOR spectrum simulations. Several new radical products have been detected and characterized, most prominently the gly species H2N - C x H - COOH and the ala species H3+N - C x (CH3) - COO and H2N - C x (CH3) - COOH. A short description of these radicals is given, and an overview of the solid-state radiation chemistry of the simple amino acids is presented, based on a review of the literature combined with these recent experimental results.