Hymidity-induced phase transition of nucleotide hydrates

用X射线分析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.在晶体中，核苷酸形成了分子层。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。结晶水分子的增加或减少伴随着层间距的变化、氢键网络的切换和钠离子周围配位方案的改变。在Na_2CMP中观察到类阿马氏体型转变。2在Na_2CMP中观察到垂直于分子平面的倒易晶格的扩散散射。9H_2O中结晶水分子数的静态或动态波动可能会引起Layr无序。3.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.测量了声子区的Rman光谱。S模具有与核酸集体模相同的性质，它是通过逐步跃迁而保守的。根据偏振拉曼光谱确定了S模的不可约表象。5.量热测量表明，跃迁分为两类。对于第一组，观测到的热变与水的潜热的变化顺序相同。对于第二组，热变大约是一半。后一类分子层的转变较小。

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.