Electron spin resonance study of electron and hole transfer in DNA: Effects of hydration, aliphatic amine cations, and histone proteins

In this work, we employ election spin resonance spectroscopy to investigate the effects of hydration, and various cationic complexing agents, such as, aliphatic amine cations and histone proteins, on electron and hole transfer in DNA. Electrons and holes generated by irradiation at 77 K are trapped on DNA and transfer to a randomly interspersed intercalator, mitoxantrone (MX). Monitoring the changes of ESR signals of MX radicals, one electron oxidized guanine (G(.+)), one-electron reduced cytosine [C(N3)H-.], and thymine anion radicals (T.-) with time at 77 K allows for the direct observation of electron and hole transfer. The apparent transfer distance (D-a) in bps is derived from the change in radicals with time and is a measure of the total number of bps within the tunneling range. In all solid DNA samples in which tunneling from electrons and holes to an intercalator was investigated, we find that the distance between DNA duplexes is the dominant factor in the degree of transfer observed. Tn hydrated DNA samples intercalated with MX, the apparent distances and rates of hole and electron transfer to MX decrease as hydration level increases mainly because the distance between DNA duplexes increases with hydration. DNA complexing agents such as poly-lysine, polyethylenimine, nucleohistone, and cationic lipids also reduce the apparent transfer rates by reducing the amount of transfer between duplexes. Transfer rates in DNA complexed with spermine, however, are similar to those in equivalently hydrated MX-DNA. A double layer of cationic lipids is found to nearly isolate DNA duplexes from electron or hole transfer to adjacent duplexes. Our modeling of rates and distances of electron transfer in DNA-complexes allow for estimates of the spacing between DNA duplexes in each complex.