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.

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Previously presented models of collagen-DNA (7) and collagen-siRNA (8) complexes point to a general description of delivery systems and indicate to what specific topology that system should be equipped with to effectively deliver the gene into the living body via in vivo and in vitro injection. We focused our interest on the nature of collagen-DNA complex structure and the molecular and environmental determinants of the self-association processes of collagen with the presence of DNA. In this aspect, the self-association of collagen-DNA complex offers an opportunity to characterize a unique system, which may be related to the general mechanisms of self-association of fiber macromolecules by water bridges. For characterizing the collagen-DNA interaction, we used FTIR-ATR, NMR, and AFM experiments done on a separate collagen film, DNA film, and on the peptide-DNA aqueous solution. We demonstrate that collagen-DNA spontaneously forms self-assembling complex systems in aqueous solution. Such self-association of the complex could be induced by electrostatic interactions between neutral collagen cylinders, having strong dipole moment, and negatively charged DNA cylinders. A final complex could be formed by hydrogen bonds between specified donor groups of collagen and phosphate acceptor groups of DNA. According to FTIR measurements, a collagen triple helix should not change global conformation during collagen-DNA complex formation.

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