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 H2O/g ds-DNA and 0.434 g H2O/g ss-DNA. The measurements were performed at 8 and 5.2 Å for the ds-DNA sample, and at 5.2 Å 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 Å, with a local diffusion coefficient of 2.2 × 10−5 cm2 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 H2O/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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机译：在ds-DNA和ss-DNA的水合样品中进行准弹性中子散射测量。将样品在较高的相对湿度气氛中水合，其最终水含量为0.559 g H2O / g ds-DNA和0.434 g H2O / g ss-DNA。对于ds-DNA样品，在8和5.2Å下进行测量，对于ss-DNA样品，在5.2Å下进行测量。两种情况下的温度均为298K。对所得数据的分析表明，在ds-DNA样品中，我们可以区分两种类型的质子-属于牢固附着于ds-DNA表面的水分子的质子和属于水的ds在半径为2.8的球体内各向同性扩散，局部扩散系数为2.2×10 −5 cm 2 s −1 。另一方面，对于ss-DNA，没有发现运动受限或受限的水的迹象。此外，正如我们中的一个人所研究的那样（GM），牢固附着在ds-DNA表面的质子部分相当于0.16 g H2O / g ds-DNA，等于热变性后ds-DNA释放的水量。 ）的差示扫描量热法。该值也等于ds-DNA和ss-DNA的临界水合值之间的差，其也由DSC确定。因此，这些结果代表了在临界水合作用值下ds-和ss-DNA中水的特性和行为的完全独立的测量，因此证实了量热法所得结果的先前建议/结论。
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