Yatsushiro National College of Technology, Yatsushiro 866-8501, Japan.
J Mol Graph Model. 2010 Sep;29(2):290-4. doi: 10.1016/j.jmgm.2010.05.003. Epub 2010 Jun 1.
Clathrate hydrates formed from binary gas mixtures of methane and other small lipophilic molecules change from the sI phase to sII and back depending on the concentration of methane in the mixtures. In contrast, pure methane hydrate under increasing pressure transforms first from sI to sII and then finally to sH. But the mechanism of the transformation from sI to sII or sH has not yet been identified. Here we present a fundamental cluster unit in the transformation from a structural point of view, which consists of 48 cages of 624 waters, called a 624W-cluster. In the solid state, the 48 cages of 14-hedron in the 624W-cluster of sI would be transformed to 24 cages of 16-hedron and 24 cages of 12-hedron in sII. The 624W-clusters in the sI hydrate each would work as a nucleus in the transformation of sI to sII. Hence, the transformation could occur throughout the solid according to the symmetry of the crystalline hydrate.
由甲烷和其他小疏水分子组成的二元气体混合物形成的包合物根据混合物中甲烷的浓度从 sI 相转变为 sII 相和 sII 相再转变为 sI 相。相比之下，纯甲烷水合物在压力增加下首先从 sI 相转变为 sII 相，然后最终转变为 sH 相。但是，从 sI 相转变为 sII 相或 sH 相的机制尚未确定。在这里，我们从结构的角度提出了一个基本的团簇单元，它由 48 个 624 个水分子的笼组成，称为 624W-团簇。在固态下，sI 相中 14-面体的 48 个笼将转变为 sII 相中 24 个 16-面体笼和 24 个 12-面体笼。sI 水合物中的 624W-团簇每个团簇都可以作为 sI 相到 sII 相转变的核。因此，根据水合物晶体的对称性，转变可以在整个固体中发生。
