Karle I L, Flippen-Anderson J L, Uma K, Balaram P
Laboratory for the Structure of Matter, Naval Research Laboratory, Washington, DC 20375-5000.
Biopolymers. 1990 Dec;29(14):1835-45. doi: 10.1002/bip.360291414.
Three crystalline polymorphs of the helical decapeptide, Boc-Aib-Ala-Leu-Ala-Leu-Aib-Leu-Ala-Leu-Aib-OMe, have been obtained. Antiparallel helix aggregation is observed in crystals grown from methanol (A), while completely parallel packing is observed in crystals from isopropanol (B) or an ethylene glycol-ethanol mixture (C). Crystals B and C are very similar in molecular conformation and packing. The packing motifs in crystals A and B consist of rows of parallel molecules, with an almost identical arrangement in both crystals. In crystal A, adjacent rows assemble with the helix axes pointed in opposite directions, whereas in crystal B all rows assemble with helix axes pointed in the same direction. Electrostatic interactions between helix dipoles do not appear to be a major determinant of packing modes. The structures also do not provide a ready rationalization of packing preferences in terms of side-chain interactions or solvation. The alpha-helix of the peptide in crystal A has seven 5----1 hydrogen bonds; the helix in crystal B is a mixed 3(10)/alpha-helix. The crystal parameters are as follows. Crystal A: C51H92N10O13.CH3OH, space group P2(1) with a = 10.498 (1) A, b = 18.189 (3) A, c = 16.475 (3) A, beta = 99.28 (1) degree, Z = 2, R = 9.6% for 1860 data. Crystal B: C51H92N10O13.C3H7OH, space group P2(1) with a = 10.534 (1) A, b = 28.571 (4) A, c = 11.055 (2) A, beta = 95.74 (1) degree, Z = 2, R = 6.5% for 3251 data. Crystal C: C51H92N10O13.C2H5OH, space group P2(1), with a = 10.450 (1) A, b = 28.442 (5) A, c = 11.020 (2) A, beta = 95.44(1) degree, Z = 2, R = 14.8% (isotropic) for 1948 data.
已获得螺旋十肽Boc-Aib-Ala-Leu-Ala-Leu-Aib-Leu-Ala-Leu-Aib-OMe的三种晶体多晶型物。在从甲醇中生长的晶体（A）中观察到反平行螺旋聚集，而在从异丙醇（B）或乙二醇 - 乙醇混合物中生长的晶体（C）中观察到完全平行堆积。晶体B和C在分子构象和堆积方面非常相似。晶体A和B中的堆积基序由平行分子的行组成，两种晶体中的排列几乎相同。在晶体A中，相邻行以螺旋轴指向相反方向的方式组装，而在晶体B中，所有行以螺旋轴指向相同方向的方式组装。螺旋偶极子之间的静电相互作用似乎不是堆积模式的主要决定因素。这些结构也没有根据侧链相互作用或溶剂化对堆积偏好提供现成的合理解释。晶体A中肽的α-螺旋有七个5----1氢键；晶体B中的螺旋是混合的3(10)/α-螺旋。晶体参数如下。晶体A：C51H92N10O13.CH3OH，空间群P2(1)，a = 10.498 (1) Å，b = 18.189 (3) Å，c = 16.475 (3) Å，β = 99.28 (1)°，Z = 2，对于1860个数据，R = 9.6%。晶体B：C51H92N10O13.C(3)H(7)OH，空间群P2(1)，a = 10.534 (1) Å，b = 28.571 (4) Å，c = 11.055 (2) Å，β = 95.74 (1)°，Z = 2，对于3251个数据，R = 6.5%。晶体C：C51H92N10O13.C(2)H(5)OH，空间群P2(1)，a = 10.450 (1) Å，b = 28.442 (5) Å，c = 11.020 (2) Å，β = 95.44(1)°，Z = 2，对于1948个数据，R = 14.8%（各向同性）。
