Glasser L, Scheraga H A
Baker Laboratory of Chemistry, Cornell University, Ithaca, NY 14853-1301.
J Mol Biol. 1988 Feb 5;199(3):513-24. doi: 10.1016/0022-2836(88)90622-5.
Crystal packing calculations have been carried out on a substantial number of conformations of Leu-enkephalin; namely, those obtained both from crystal structures and from energy minimizations on isolated molecules, and with and without waters of crystallization. The known crystal structures represent the most energetically stable packings found. The conformations of the enkephalin molecules in the crystal are not the most stable for an isolated molecule; i.e. intermolecular interactions force the isolated molecule to change conformation in order to achieve a small packing volume and an optimal packing energy in the crystal. It is found that the packing energy of an enkephalin molecule is a reasonably smooth function of its molecular volume in the unit cell, if structures with intermolecular hydrogen bonding are excluded, and is substantially independent of other details of the molecular conformation or of the crystal packing. Hydrogen bonding provides additional stabilization of the crystal structure, and would likely permit crystallization of the system if it is sufficiently dense. Solvent molecules further stabilize the structure when they can also provide intermolecular hydrogen bonds.
已对亮氨酸脑啡肽的大量构象进行了晶体堆积计算；也就是说，这些构象既来自晶体结构，也来自对孤立分子的能量最小化，且考虑了有无结晶水的情况。已知的晶体结构代表了所发现的能量上最稳定的堆积。晶体中脑啡肽分子的构象对于孤立分子而言并非最稳定的；即分子间相互作用迫使孤立分子改变构象，以便在晶体中获得较小的堆积体积和最佳的堆积能量。研究发现，如果排除具有分子间氢键的结构，脑啡肽分子的堆积能量是其在晶胞中分子体积的合理平滑函数，并且基本上与分子构象或晶体堆积的其他细节无关。氢键为晶体结构提供了额外的稳定性，并且如果体系足够致密，可能会使该体系结晶。当溶剂分子也能提供分子间氢键时，它们会进一步稳定结构。
