Tao N J, Lindsay S M, Rupprecht A
Biopolymers. 1989 May;28(5):1019-30. doi: 10.1002/bip.360280509.
We have used Raman scattering to study the water O-H stretching modes at approximately 3450 and approximately 3220 cm-1 in DNA films as a function of relative humidity (r.h.). The intensity of the 3220-cm-1 band vanishes as the r.h. is decreased from 98% to around 80%, which indicates that the hydrogen-bond network of water is disrupted in the primary hydration shell (which therefore cannot have an "ice-like" structure). The number of water molecules in the primary hydration shell was determined from the intensity of the approximately 3200-cm-1 band as about 30 water molecules per nucleotide pair. The approximately 3400-cm-1 O-H stretch band was used for determining the total water content, and this band persists at 0% r.h., implying that 5-6 tightly bound water molecules per nucleotide pair remain. The frequency of the approximately 3400-cm-1 O-H stretch mode is lower by 30 to 45 cm-1 in the primary hydration shell compared to free water. The water content as a function of r.h. obtained from these experiments agrees with gravimetric measurements. The disappearance of the approximately 3200-cm-1 band and the shift of the approximately 3400-cm-1 O-H stretch band provide a reliable way of measuring the hydration number of DNA.
我们利用拉曼散射研究了DNA薄膜中在约3450和约3220 cm-1处的水O-H伸缩模式随相对湿度（r.h.）的变化。当r.h.从98%降至约80%时，3220-cm-1谱带的强度消失，这表明水的氢键网络在初级水化层中被破坏（因此不可能具有“冰状”结构）。根据约3200-cm-1谱带的强度确定初级水化层中的水分子数约为每核苷酸对30个水分子。约3400-cm-1的O-H伸缩谱带用于确定总含水量，该谱带在r.h.为0%时仍然存在，这意味着每核苷酸对仍有5 - 6个紧密结合的水分子。与自由水相比，初级水化层中约3400-cm-1的O-H伸缩模式频率低30至45 cm-1。从这些实验获得的含水量随r.h.的变化与重量法测量结果一致。约3200-cm-1谱带的消失和约3400-cm-1的O-H伸缩谱带的位移提供了一种可靠的测量DNA水合数的方法。
