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Small-angle x-ray scattering from 25 basepair DNA in 100 mM chloride salts. The background-subtracted scattering intensity, I(q), versus momentum transfer, q, is shown in semilog scale with absolute units (electrons2 per DNA molecule). The intensity at low angles depends on the cation type, indicated in the legend. (Inset) The extrapolated forward-scattering amplitude, I(q→0)1/2, varies linearly with the effective ion contrast, Zeff (see Eqs. 1 and 2).
