DISTRIBUTION OF CONFORMATIONAL STATES AS COMMON SOURCE OF G-STRAIN AND A-STRAIN IN THE ESR-SPECTRA OF PROTEINS AND GLASSES

Additional experimental evidence on the structural and dynamical similarity between proteins and glasses is provided by the analysis conducted on the ESR spectra, at different temperatures, of some copper proteins and of some Cu++-doped glass formed by water and a second component (NaOH, DMSO, alcohols). All the spectra taken at temperatures below approximately 210 K display a significant g- and A-strain that consists in a progressive broadening and decrease in the intensity of the copper hyperfine lines as the order of m1 increases (I = 3/2 is the Cu nuclear spin). These spectral features are taken into account by using a theoretical model which attributes the random distribution of the electric ligand fields around the copper ions to a distribution of the conformational substate energies both in the proteins and in the amorphous materials.