Resonant Formation of DNA Strand Breaks by Low-Energy (3 to 20 eV) Electrons

J. F. Ward in Advances in Radiation Biology 5 J. T. Lett and H. Adler Eds. (Academic Press New York 1977) pp. 181–239.

O. Yamamoto in Aging Carcinogenesis and Radiation Biology K. Smith Ed. (Plenum New York 1976) pp. 165–192.

A. F. Fuciarelli and J. D. Zimbrick Eds. Radiation Damage in DNA: Structure/Function Relationships at Early Times (Battelle Columbus OH 1995).

C. von Sonntag The Chemical Basis for Radiation Biology (Taylor and Francis London 1987).

International Commission on Radiation Units and Measurements ICRU Report 31 (ICRU Washington DC 1979).

S. M. Pimblott and J. A. LaVerne in (3) pp. 3–12.

10.1016/S0969-806X(97)00096-0

D. Srdoc et al. in IAEA CRP Atomic and Molecular Data for Radiotherapy and Radiation Research M. Inokuti Ed. (IAEA Press Vienna 1995) chapter 8.

The only previous low-energy work concerned DNA damage by 25- to 4000-eV electrons [see

10.1080/09553009314551891

]. In that study the samples were exposed to high background gas pressures (10 −5 to 10 −6 torr) and contained salt (EDTA ratio of DNA to EDTA = 1:1 by weight) during electron irradiation; the latter was reported to shield the DNA toward low-energy electrons.

10.1063/1.466329

10.1016/S0009-2614(97)01026-9

10.1063/1.475503

L. Sanche unpublished data.

10.1021/jp990686l

For a review see

10.1007/s004110050125

Each sample consisted of 500 ng of purified DNA in 10 μl of nanopure water which was deposited on a tantalum substrate over a measured area of ∼6 mm average diameter. After lyophilization this results in a pure solid calculated to have an average thickness of 10 nm at a known density of 1.7 g cm −3 assuming minimal clustering of the plasmids in the solid.

Desiccation leaves plasmid DNA with its structural water of about 2.5 water molecules per base pair [

10.2307/3578034

] with the plasmid solids containing a mixture of A and C conformations. Removal of this intrinsic hydration water is believed to lead to substantial conformational changes and DSBs which are not observed in our unirradiated control samples held under UHV.

10.1021/j100203a039

10.1080/09553009414551631

B. D. Michael et al. in (3) pp. 251–258.

For a review see

Sanche L., Scanning Microsc. 9, 619 (1995).

10.1063/1.460090

10.1021/j100165a054

10.1063/1.477530

10.1063/1.479078

For vertical electron attachment energies in gas-phase nucleobases below 5 eV see

10.1021/jp980865n

; for detachment energies in solvated uracil cluster anions see

10.1063/1.475360

10.1038/29015

L. G. Christophorou E. Illenberger W. Schmidt Eds. Linking the Gaseous and Condensed Phases of Matter: The Behavior of Slow Electrons (Plenum New York 1994).

Sample exposure-response curves can be seen at Science Online (www.sciencemag.org/feature/data/1044957.shl).

We thank A. J. Waker for helpful comments and suggestions. Supported by the Medical Research Council of Canada.