EPR investigation of the gamma-ray-irradiated natural and tanned collagen

Free radicals produced in natural and tanned collagen by gamma-ray irradiation within 1–15 kGy absorbed dose ranges were investigated by EPR spectroscopy. Tanned collagen was prepared using formaldehyde as well as aluminum basic salts [Al(OH)SO4] tanning processes. Both natural and formaldehyde-tanned irradiated collagen show the same kind of EPR spectrum consisting of a single broad, slightly asymmetric line. Irradiated collagen tanned by aluminum basic salts process displayed a complex EPR spectrum consisting of a superposition of broad and narrow lines. A computer simulation of this spectrum allowed to evidence the presence of seven different kinds of paramagnetic centers, including those observed in the irradiated natural collagen. Corresponding Spin Hamiltonian parameters (g-factor, hyperfine splitting constant) as well as relative concentrations of these centers were calculated. Experimentally determined relative concentrations display a positive correlation with the absorbed dose described by a linear-type dependence. After three weeks of storage at room temperature, the concentration of some centers diminished by about 50%. The possible nature of these centers is discussed in connection with the local structure of the tanned collagen.