Radiation induced

electron transfer between nucleohistone and caffeic acid and the radiation protection effect by caffeic acid have been studied. A series of binary molecular aggregates of nucleohistone and caffeic acid with weight ratios varied from 1:1 to 60:1 at pH9 were irradiated and observed at 77K using ESR spectrometer. The ESR spectra recorded at 77K indicate that ΔHpp (0.83~0.95 mT) of central peak from mixed aggregates with several moleoular ratios are close to ΔHpp(0.94mT) of caffeic acid alone and quite different from ΔHpp (2.5mT) of nucleohistone. It is suggested that caffeic acid anion radic al is the main radical product. P

ST

(%) defined as the percentage of the spin concentration of caffeic acid arising from transfer of captured electron by nucleohistone in the total spin concentration of caffeic acid could be obtained by resolution of composite ESR spectra. It is obvious that P

ST

increased with the increase of nucleohistone content and reaches more than 90% from weight ratios 10:1 to 60:1. The results indicates that electron transfer from nucleohistone to caffeic acid occurred within the mixed aggregtes.