Johnson Ross S, Yamazaki Takeshi, Kovalenko Andriy, Fenniri Hicham
National Institute for Nanotechnology, Department of Chemistry, University of Alberta, 11421 Saskatchewan Drive, Edmonton, Alberta, Canada.
J Am Chem Soc. 2007 May 2;129(17):5735-43. doi: 10.1021/ja0706192. Epub 2007 Apr 7.
Helical rosette nanotubes (RNTs) are obtained through the self-assembly of the GwedgeC motif, a self-complementary DNA base analogue featuring the complementary hydrogen bonding arrays of both guanine and cytosine. The first step of this process is the formation of a 6-membered supermacrocycle (rosette) maintained by 18 hydrogen bonds, which then self-organizes into a helical stack defining a supramolecular sextuple helix whose chirality and three-dimensional organization arise from the chirality, chemical structure, and conformational organization of the GwedgeC motif. Because a chiral GwedgeC motif is predisposed to express itself asymmetrically upon self-assembly, there is a natural tendency for it to form one chiral RNT over its mirror image. Here we describe the synthesis and characterization of a chiral GwedgeC motif that self-assembles into helical RNTs in methanol, but undergoes mirror image supramolecular chirality inversion upon the addition of very small amounts of water (<1% v/v). Extensive physical and computational studies established that the mirror-image RNTs obtained, referred to as chiromers, result from thermodynamic (in water) and kinetic (in methanol) self-assembly processes involving two conformational isomers of the parent GwedgeC motif. Although derived from conformational states, the chiromers are thermodynamically stable supramolecular species, they display dominant/recessive behavior, they memorize and amplify their chirality in an achiral environment, they change their chirality in response to solvent and temperature, and they catalytically transfer their chirality. On the basis of these studies, a detailed mechanism for supramolecular chirality inversion triggered by specific molecular interactions between water molecules and the GwedgeC motif is proposed.
螺旋玫瑰花结纳米管（RNTs）是通过G楔形C基序的自组装获得的，G楔形C基序是一种自互补的DNA碱基类似物，具有鸟嘌呤和胞嘧啶的互补氢键阵列。该过程的第一步是形成由18个氢键维持的六元超大环（玫瑰花结），然后自组装成螺旋堆叠，形成超分子六重螺旋，其手性和三维结构源于G楔形C基序的手性、化学结构和构象组织。由于手性G楔形C基序在自组装时倾向于不对称地表达自身，因此它自然倾向于形成一种手性RNT而不是其镜像。在这里，我们描述了一种手性G楔形C基序的合成和表征，该基序在甲醇中自组装成螺旋RNTs，但在加入极少量水（<1% v/v）后会发生镜像超分子手性反转。广泛的物理和计算研究表明，获得的镜像RNTs，称为手性异构体，是由涉及母体G楔形C基序的两种构象异构体的热力学（在水中）和动力学（在甲醇中）自组装过程产生的。尽管手性异构体源自构象状态，但它们是热力学稳定的超分子物种，它们表现出显性/隐性行为，它们在非手性环境中记忆并放大其手性，它们响应溶剂和温度改变其手性，并且它们催化转移其手性。基于这些研究，提出了由水分子与G楔形C基序之间的特定分子相互作用引发的超分子手性反转的详细机制。
