We present the results of density functional calculations of 1 H, 13 C, and 14 N hyperfine coupling constants (hfcc's) in radicals derived from the simple amino acid L-alanine. The calculations are performed using the B3LYP functional in combination with Pople basis sets (6-31G(d) and 6-311G(d)) and the IGLO-III basis set. Both isotropic and anisotropic hfcc's show good agreement with available experimental data. Detailed study of the isotropic hfcc's allows for investigation of specific geometrical features of the various radical structures. The scope and limitations of this type of calculations both for elucidation of experimental electron paramagnetic resonance spectra and investigation of radical structure are briefly discussed.

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Polycrystalline samples of the amino acid L-alpha-alanine have been irradiated with X rays at both room temperature and higher temperatures. The electron paramagnetic resonance (EPR) spectra of alanine powder irradiated at room temperature are dominated by the well-known room-temperature-stable alanine radical CH3C*HCOOH. Upon heating of room-temperature-irradiated alanine powder, a strong decay of the signal was observed, and the features of the spectrum recently ascribed to a second stable radical in alanine irradiated at room temperature become more pronounced, providing an experimental isolation of this second alanine radical. In combination with the high-temperature experiments, a multivariate statistical decomposition method, maximum likelihood common factor analysis, was used to determine the number of components in irradiated alanine powder which behave differently as a function of temperature. The EPR components found in the present study are compared with simulations using earlier EPR and ENDOR single-crystal data.

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