The nature of the radicals contributing to the room temperature spectrum of irradiated “dry” DNA, with special reference to the central structure, is discussed, and the thesis of their ionic origin tested by irradiation experiments with intercalators. The mechanism of spin transfer protein→DNA has been investigated through a comparative ESR study on the DNA-histones complex, the structureless random molecular mixture of the DNA-histones and the neat components. The yield of spin transfer is enhanced in the random mixture, presumably because of the greater efficiency of molecular contacts. Evidence of the scavenging of electrons by the thymine and cytosine bases, as a key mechanism for the spin transfer, has been obtained.
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