Ciaccia Maria, Tosi Irene, Baldini Laura, Cacciapaglia Roberta, Mandolini Luigi, Di Stefano Stefano, Hunter Christopher A
Dipartimento di Chimica and IMC/CNR , Università La Sapienza , P.le A. Moro 5 , 00185 Rome , Italy . Email:
Department of Chemistry , University of Sheffield , Sheffield , S3 7HF , UK.
Chem Sci. 2015 Jan 1;6(1):144-151. doi: 10.1039/c4sc02347a. Epub 2014 Sep 29.
A new strategy for determining thermodynamic effective molarities (EM) for macrocylisation reactions using dynamic combinatorial chemistry under dilute conditions is presented. At low concentrations, below the critical value, Dynamic Libraries (DLs) of bifunctional building blocks contain only cyclic species, so it is not possible to quantify the equilibria between linear and cyclic species. However, addition of a monofunctional chain stopper can be used to promote the formation of linear oligomers allowing measurement of EM for all cyclic species present in the DL. The effectiveness of this approach was demonstrated for DLs generated from mixtures of 1,3-diimine calix[4]arenes, linear diaminoalkanes and monoaminoalkanes. For macrocycles deriving from one bifunctional calixarene and one diamine, there is an alternating pattern of EM values with the number of methylene units in the diamine: odd numbers give significantly higher EMs than even numbers. For odd numbers of methylene units, the alkyl chain can adopt an extended all conformation, whereas for even numbers of methylene units, conformations are required for cyclisation, and the associated strain reduces EM. The value of EM for the five-carbon linker indicates that this macrocycle is a strainless ring.
本文提出了一种在稀溶液条件下利用动态组合化学测定大环化反应热力学有效摩尔浓度（EM）的新策略。在低于临界值的低浓度下，双功能构建单元的动态库（DLs）仅包含环状物种，因此无法量化线性和环状物种之间的平衡。然而，添加单功能链终止剂可用于促进线性低聚物的形成，从而能够测量DL中存在的所有环状物种的EM。该方法的有效性在由1,3 - 二亚胺杯[4]芳烃、线性二氨基烷烃和单氨基烷烃混合物生成的DLs中得到了证明。对于由一种双功能杯芳烃和一种二胺衍生的大环，EM值随着二胺中亚甲基单元数量呈现交替模式：奇数个亚甲基单元对应的EM值显著高于偶数个亚甲基单元对应的EM值。对于奇数个亚甲基单元，烷基链可以采取伸展的全反式构象，而对于偶数个亚甲基单元，环化需要特定构象，并且相关的应变会降低EM。五碳连接基的EM值表明该大环是一个无应变环。
