T. Lavere et al., YIELDS OF (OH)-O-CENTER-DOT IN GAMMA-IRRADIATED DNA AS A FUNCTION OF DNA HYDRATION - HOLE TRANSFER IN COMPETITION WITH (OH)-O-CENTER-DOT FORMATION, Radiation research, 145(6), 1996, pp. 673-680
In this work, we report the yields of hydroxyl radicals, as G values a
nd ''destruction constants,'' in the DNA hydration shell as a function
of the level of hydration. Electron spin resonance spectroscopy of ga
mma-irradiated DNA at low temperatures is employed for detection of th
e hydroxyl radical. Due to the glassy nature of the DNA hydration laye
r at low temperature, the hydroxyl radical gives a broad ESR resonance
which is easily distinguished from the hydroxyl radical in a polycrys
talline ice phase; thus (OH)-O-. in both glassy and ice regions is qua
ntified. Three regimes of radiological behavior for waters of hydratio
n in DNA are found. For the first approximately 9 waters/nucleotide (w
hich are glassy), no significant amounts of (OH)-O-. are found, sugges
ting hole transfer to DNA. The second regime of hydration waters compr
ises up to about 12 additional glassy waters/nucleotide (Gamma = 21).
In this regime, substantial amounts of glassy (OH)-O-. are found, sugg
esting that only a few holes which escape recombination in spurs charg
e-transfer to the DNA. In these two glassy regimes no trapped electron
s are found, which is in accord with previous work that has reported t
hat all electrons which do not undergo recombination in spurs transfer
to DNA. The third regime of hydration water is comprised of bulk (or
bulk-like) polycrystalline ice which forms when levels of hydration ov
er 21 waters/nucleotide are reached. These waters form a separate phas
e from the DNA/glassy-water system, and neither hole nor substantial e
lectron transfer to the DNA occurs; (OH)-O-. in this ice phase is obse
rved with G values that vary slightly with the amount of water in the
ice phase, but which are close to the values found for pure ice. (C) 1
996 by Radiation Research Society.