Chen G, Lean J T, Alcalá M, Mallouk T E
Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
J Org Chem. 2001 May 4;66(9):3027-34. doi: 10.1021/jo991054y.
Three neutral cyclophanes were synthesized, and their association with indole, an aromatic pi-donor, was studied. The cyclophanes were designed to contain a rigid, hydrophobic binding cavity with 1,4,5,8-naphthalenetetracarboxylic diimide or 1,5-dinitronaphthalene as the pi-acceptor. Two of the cyclophanes also contain a (S)-(valine-leucine-alanine) tripeptide unit to provide chiral hydrogen bonding interactions with guest molecules. Despite the fact that these cyclophanes contain a hydrophobic binding cavity of appropriate dimensions, their association with indole is very weak. In the case of cyclophanes derived from 1,5-dinitronaphthalene, steric interactions force the nitro groups out of the plane of the naphthalene ring, diminishing their effectiveness as pi-acceptors. A simple UV--visible titrimetric method, using N,N,N',N'-tetramethyl-1,4-phenylenediamine (TMPD) as a pi-donor, was used to rank the pi-acceptor strength of these and other aromatic units. These titrations show that 1,4,5,8-naphthalenetetracarboxylic diimide and 1,5-dinitronaphthalene derivatives are weaker pi-acceptors than viologens, which make good pi-acceptor cyclophanes. Methyl viologen is in turn a weaker pi-acceptor than anthaquinone disulfonate, suggesting that the latter may serve as a useful building block for pi-accepting cyclophane hosts.
合成了三种中性环番，并研究了它们与芳香π供体吲哚的结合情况。这些环番被设计成含有一个刚性的疏水结合腔，以1,4,5,8-萘四羧酸二酰亚胺或1,5-二硝基萘作为π受体。其中两种环番还含有一个（S）-（缬氨酸-亮氨酸-丙氨酸）三肽单元，以便与客体分子提供手性氢键相互作用。尽管这些环番含有尺寸合适的疏水结合腔，但它们与吲哚的结合非常弱。在由1,5-二硝基萘衍生的环番的情况下，空间相互作用迫使硝基偏离萘环平面，降低了它们作为π受体的有效性。使用N,N,N',N'-四甲基-1,4-苯二胺（TMPD）作为π供体的简单紫外-可见滴定法，用于对这些以及其他芳香单元的π受体强度进行排序。这些滴定表明，1,4,5,8-萘四羧酸二酰亚胺和1,5-二硝基萘衍生物作为π受体比紫精弱，紫精可形成良好的π受体环番。甲基紫精又是比蒽醌二磺酸盐弱的π受体，这表明后者可能是构建π受体环番主体的有用结构单元。
