Hydration of ds-DNA and ss-DNA by neutron quasielastic scattering.
Quasielastic neutron scattering measurements were performed in hydrated samples of ds-DNA and ss-DNA. The samples were hydrated in a high relative humidity atmosphere, and their final water content was 0.559 g H(2)O/g ds-DNA and 0.434 g H(2)O/g ss-DNA. The measurements were performed at 8 and 5.2 A for the ds-DNA sample, and at 5.2 A for the ss-DNA sample. The temperature was in both cases 298 K. Analysis of the obtained data indicates that in the ds-DNA sample we can distinguish two types of protons-those belonging to water molecules strongly attached to the ds-DNA surface and another fraction belonging to water that diffuses isotropically in a sphere of radius 2.8 A, with a local diffusion coefficient of 2.2 x 10(-5) cm(2) s(-1). For ss-DNA, on the other hand, no indication was found of motionally restricted or confined water. Further, the fraction of protons strongly attached to the ds-DNA surface corresponds to 0.16 g H(2)O/g ds-DNA, which equals the amount of water that is released by ds-DNA upon thermal denaturation, as studied by one of us (G.M.) by differential scanning calorimetry. This value also equals the difference between the critical hydration values of ds-DNA and ss-DNA, also determined by DSC. These results represent, thus, a completely independent measurement of water characteristics and behavior in ds- and ss-DNA at critical hydration values, and therefore substantiate the previous suggestions/conclusions of the results obtained by calorimetry.
Bastos
M
M
Centro de Investigacao em Quimica (Universidade do Porto), Department of Chemistry, Faculty of Sciences, University of Porto, P-4169-007 Porto, Portugal. mbastos@fc.up.pt
Castro
V
V
Mrevlishvili
G
G
Teixeira
J
J
D004247:DNA / Q000737:chemistry*; D004277:DNA, Single-Stranded / Q000737:chemistry*; D008968:Molecular Conformation; D009502:Neutrons; D014867:Water / Q000737:chemistry*
D004277:DNA, Single-Stranded; D014867:Water; D004247:DNA