Roy & Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.
J Am Chem Soc. 2014 May 14;136(19):7169-85. doi: 10.1021/ja5035107. Epub 2014 May 2.
A library of dendronized cyclotriveratrylene (CTV) crowns substituted with chiral, racemic, or achiral peripheral alkyl chains, including enantiopure R and S branched alkyls, "racemic by mixture", "racemic by synthesis", n-octyl, and n-dodecyl groups was synthesized. In solvophobic solvents and in bulk they self-assemble in helical columns. Their solution and bulk shape-persistent supramolecular structures were determined by a complementary combination of circular dichroism (CD) and UV in solution and thin film, microspot CD in thin film, differential scanning calorimetry combined with fiber X-ray diffraction, computer simulation, and molecular models. In solution, self-assembly via a cooperative mechanism generates single-handed columns from enantiopure CTVs and mixtures of right- and left-handed columns from racemic by mixture, racemic by synthesis, other combinations of R and S, and even from achiral compounds. In bulk state all supramolecular columns form a 3D hexagonal crystalline phase, Φ(h)(k) (P6₃ symmetry), that can be obtained only from single-handed columns and a columnar hexagonal 2D liquid crystal, Φ(h). The highest order Φ(h)(k) consists of enantiopure single-handed columns that are slightly distorted 12-fold triple helices. The "hat-shaped" dendronized CTV assembles in bent-branch pine-tree columns that allow interdigitation of alkyl groups in adjacent columns regardless of their direction. Enantiomerically rich, racemic, and achiral compositions undergo deracemization in the crystal state by transfer of the transient disc-like conformer of dendronized CTV from column to column during crown inversion. Solid state NMR experiments identified motional processes that allow such transfer. This unprecedented supramolecular chiral self-sorting will impact the creation of functions in complex systems.
合成了一系列取代手性、外消旋或非手性外围烷基链的树枝状轮烷（CTV）冠的库，包括手性纯 R 和 S 支化烷基、“混合物外消旋”、“合成外消旋”、正辛基和正十二烷基。在疏溶剂和亲溶剂中，它们会自组装成螺旋柱。通过圆二色性（CD）和紫外在溶液和薄膜中的互补组合、薄膜中的微斑点 CD、差示扫描量热法与纤维 X 射线衍射相结合、计算机模拟和分子模型，确定了它们的溶液和本体形状保持超分子结构。在溶液中，通过协同机制的自组装会从手性纯 CTV 中生成单手性的螺旋柱，从混合物外消旋、合成外消旋、R 和 S 的其他组合，甚至从非手性化合物中生成左右手混合的螺旋柱。在本体状态下，所有超分子螺旋柱都形成一个 3D 六方晶相，Φ(h)(k)（P6₃对称），只能从单手性螺旋柱和柱状六方 2D 液晶Φ(h)中获得。最高阶的Φ(h)(k)由手性纯单手性螺旋柱组成，这些螺旋柱略有扭曲的 12 重三重螺旋。“帽子状”树枝状 CTV 组装成弯曲分支的松树柱，允许相邻柱中的烷基相互交错，而不管它们的方向如何。手性丰富的外消旋和非手性组成在晶体状态下通过手性纯 CTV 的瞬态盘状构象在冠反转期间从一个螺旋柱转移到另一个螺旋柱来发生外消旋化。固态 NMR 实验确定了允许这种转移的动态过程。这种前所未有的超分子手性自分类将影响复杂系统中功能的创造。
