Karle I L
Int J Pept Protein Res. 1986 Jul;28(1):6-14. doi: 10.1111/j.1399-3011.1986.tb03224.x.
Crystals of [Phe4 Val6] antamanide (cyclic [ValProProPhePhe]2) grown from dioxane/H2O, with space group P21212 and cell parameters a = 15.099(4), b = 22.008(5) and c = 11.024(3) A, are almost identical to crystals grown from H2O/acetone, the structure of which was determined a number of years ago. Per peptide molecule there are the equivalent of 12 water molecules occupying 16 sites in both crystals; however, in the new investigation a number of water molecules present at one-half occupancy have been found in different positions than in the earlier analysis. The interpretation of the hydrogen bonding between peptide/water and between water/water is much more satisfactory. Pentagonal water assemblies are present in the solvent channel. There is a distinct indication of the occurrence of a bifurcated bond between two water molecules, as well as the presence of three-center hydrogen bonds joining three water molecules. This may be the first experimental example of a bifurcated bond between two water molecules.
从二氧六环/水体系中生长出的[苯丙氨酸⁴缬氨酸⁶]抗毒蕈环肽（环[缬氨酸-脯氨酸-脯氨酸-苯丙氨酸-苯丙氨酸]₂）晶体，其空间群为P2₁2₁2，晶胞参数a = 15.099(4) Å、b = 22.008(5) Å和c = 11.024(3) Å，与从水/丙酮体系中生长出的晶体几乎相同，后者的结构已于多年前确定。每个肽分子有相当于12个水分子占据两种晶体中的16个位点；然而，在新的研究中发现，一些占据率为一半的水分子所处位置与早期分析不同。肽/水之间以及水/水之间氢键的解释更加令人满意。五角形水簇存在于溶剂通道中。有明显迹象表明两个水分子之间存在分叉键，以及存在连接三个水分子的三中心氢键。这可能是两个水分子之间存在分叉键的首个实验实例。
