Hymidity-induced phase transition of nucleotide hydrates

用X射线衍射和拉曼光谱研究了核酸重复单元核苷酸在湿度作用下的一级相变。主要结果如下：1.核苷酸在晶体中形成分子层。在分子层之间有一个由结晶水分子和阳离子组成的区域，结晶水分子的数量是湿度的函数。晶体水分子的增减伴随着钠离子层间距的变化、氢键网络和配位模式的转换。在Na_2CMP中观察到了类马氏体相变。2.在Na_2CMP中观察到了沿着倒易晶格垂直于分子平面的行的漫散射。20.结晶水分子数目的静态或动态波动会引起层无序. 3.在低水合状态下，分子层内的分子间相互作用是可逆转变的必要条件. 4.拉曼光谱的声子区。S-模式的特征与核酸的集体模式的特征相同，通过逐步转变而保持不变。根据偏振拉曼谱确定了S模的不可约表示。5.量热测量表明，S模的跃迁可分为两类。对于第一组，所观察到的焓变与水的潜热处于同一数量级。对于第二组，焓变约为一半。后一组分子层的转变是相当小的。

Humidity-induced first order phase transition of nucleotides, which are repeating units of nucleic acid, was examined by X-ray analysis and Raman spectroscopy. Main results are as follows :1.In crystals, nucleotides make a molecular layr. Between molecular layrs, there is a region which consists of crystal water molecules and cations.Number of crystal water molecules is a function of humidity. Increase or decrease of crystal water molecules accompanies change of inter layr distances and switching of hydrogen-bond networks and coordination scheme around sodium ions. Amartensite-like transformation was observed in the casa of Na_2CMP.2.Diffused scattering along rows of the reciprocal lattice normal to the molecular plane was observed in the case of Na_2CMP.9H_2O.Static or dynamic fluctuation of number of crystal water molecules should cause layr disorder.3.Intermolecular interactions within a molecular layr in a low hydrated state was found to be essential for reversible transition.4.Rman spectra of a phonon region were measured. S-mode, whose character is common to that of the collective mode of nucleic acid, was conserved through the stepwise transition. The irreducible representation of S-mode was determined based on the polarized Raman spectra.5.Calorimetric measureements revealed that the transition is classified into two groups. For the first group, the observed enthalpy change is in the same order to the latent heat of water. For the second group, the enthalpy change is about a half. Transformation of molecular layrs of the latter group is fairly small.