MAGNETIC-FIELD EFFECTS ON THE BEHAVIOR OF RADICALS IN PROTEIN AND DNAENVIRONMENTS

We have examined the behavior of radical pairs derived by hydrogen abs traction of triplet benzophenone and some of its derivatives from bovi ne serum albumin, human serum albumin and calf thymus DNA, They have b een investigated by means of nanosecond laser flash photolysis techniq ues, The dynamics of radical pair behavior are shown to be sensitive t o external magnetic fields; these effects are interpreted using the es tablished model for the influence of magnetic fields on radical pairs in micellar aggregates, in which intersystem crossing of the radical p air is slowed by the external magnetic field. Our results indicate tha t proteins and DNA can confine the radicals for a sufficiently long pe riod of time for spin evolution to be affected by external fields, In proteins the radical pair retains its geminate character (i.e. remains confined) for about 0.5-1 mu s. Interestingly, the magnetic field eff ects observed in proteins and in DNA seem to occur in distinct timesca les; for example, for 2,3,4,5,6-pentafluorobenzophenone bound to DNA, the magnetic field alters the radical reactivity only over times less than or equal to 50 ns, suggesting poor confinement. The timescale for these effects can be increased by promoting Coulombic attraction betw een DNA and the radical precursor, Electron transfer interactions play a role in the case of DNA.