Steacie Institute for Molecular Sciences, National Research Council of Canada, 100 Sussex Dr., Ottawa, Ontario K1A 0R6, Canada.
J Chem Phys. 2011 Mar 28;134(12):121104. doi: 10.1063/1.3574393.
Single crystal x-ray crystallography is used to detect guest-host hydrogen bonding in structure II (sII) binary clathrate hydrate of 1-propanol and methane. X-ray structural analysis shows that the 1-propanol oxygen atom is at a distance of 2.749 and 2.788 Å from the closest clathrate hydrate water oxygen atoms from a hexagonal face of the large sII cage. The 1-propanol hydroxyl hydrogen atom is disordered and at distances of 1.956 and 2.035 Å from the closest cage water oxygen atoms. These distances are compatible with guest-water hydrogen bonding. The C-C-C-O torsional angle in 1-propanol in the cage is 91.47° which corresponds to a staggered conformation for the guest. Molecular dynamics studies of this system demonstrated guest-water hydrogen bonding in this hydrate. The molecular dynamics simulations predict most probable distances for the 1-propanol-water oxygen atoms to be 2.725 Å, and the average C-C-C-O torsional angle to be ~59° consistent with a gauche conformation. The individual cage distortions resulting from guest-host hydrogen bonding from the simulations are rather large, but due to the random nature of the hydrogen bonding of the guest with the 24 water molecules making up the hexagonal faces of the large sII cages, these distortions are not observed in the x-ray structure.
采用单晶 X 射线晶体学检测了 1-丙醇和甲烷结构 II（sII）二元笼状水合物中的主体-客体氢键。X 射线结构分析表明，1-丙醇的氧原子距离大 sII 笼的六边形面的最接近笼状水合物氧原子的距离分别为 2.749 和 2.788 Å。1-丙醇羟基氢原子无序，距离最接近笼状水氧原子的距离分别为 1.956 和 2.035 Å。这些距离与客体-水氢键相兼容。1-丙醇在笼中的 C-C-C-O 扭转角为 91.47°，这对应于客体的交错构象。该体系的分子动力学研究表明，这种水合物中存在客体-水氢键。分子动力学模拟预测 1-丙醇-水氧原子的最可能距离为 2.725 Å，平均 C-C-C-O 扭转角约为 59°，与 gauche 构象一致。由于构成大 sII 笼六边形面的 24 个水分子的客体与主体之间氢键的随机性，模拟中产生的单个笼变形相当大，但这些变形在 X 射线结构中未被观察到。
