Laboratory of Macromolecular and Organic Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
J Am Chem Soc. 2010 Jan 20;132(2):620-6. doi: 10.1021/ja9080875.
By systematic variation of the chemical structure of benzene-1,3,5-tricarboxamide (BTA) derivatives, the effect of chemical structure on the amplification of chirality was studied and quantified. In combination with temperature-dependent amplification experiments, the limits of the majority-rules principle were also investigated. For all BTA derivatives a high, constant helix reversal penalty was determined, which is related to the intermolecular hydrogen bonds that are present in all studied derivatives. For asymmetrically substituted BTA derivatives an odd-even effect was found in the degree of chiral amplification when changing the position of the stereogenic center with respect to the amide functionality. It was found that the mismatch penalty could be directly related to the number of stereocenters present in the molecules. Increasing this number from one to three resulted in an increase in this energy penalty while leaving the helix reversal penalty unaffected. For the majority-rules principle this implies that a single stereocenter present in the molecule contains sufficient chiral information at the molecular level to result in a chirally amplified state at the supramolecular level. Further evidence that the mismatch penalty is directly related to the number of stereocenters was obtained from mixed majority-rules experiments where two BTA derivatives with different numbers of stereocenters with opposite stereoconfiguration were studied in a majority-rules experiment. Finally, the ultimate limits of chiral amplification for the majority-rules principle were investigated, revealing that, given a certain helix reversal penalty, there is an optimum to which the mismatch penalty can be reduced while also enhancing the degree of chiral amplification. Temperature-dependent majority-rules experiments could indeed confirm these simulations. These findings show the relevance of both energy penalties when trying to enhance the degree of chiral amplification for the majority-rules principle in a one-dimensional helical supramolecular polymer.
通过系统地改变苯-1,3,5-三羧酸酰胺（BTA）衍生物的化学结构，研究并量化了化学结构对手性放大的影响。结合温度依赖性放大实验，还研究了多数规则原理的极限。对于所有的 BTA 衍生物，确定了一个高且恒定的螺旋反转罚分，这与所有研究的衍生物中存在的分子间氢键有关。对于不对称取代的 BTA 衍生物，当相对于酰胺官能团改变手性中心的位置时，在手性放大程度上发现了奇数-偶数效应。发现失配罚分可以直接与分子中存在的手性中心数量相关。将这个数量从一个增加到三个，在不影响螺旋反转罚分的情况下，增加了这个能量罚分。对于多数规则原理，这意味着分子中存在一个手性中心就包含了足够的手性信息，从而导致在超分子水平上呈现手性放大状态。从混合多数规则实验中获得了更多证据，证明失配罚分与手性中心数量直接相关，在多数规则实验中研究了具有相反立体构型的两个具有不同手性中心数量的 BTA 衍生物。最后，研究了多数规则原理的手性放大的极限，结果表明，在给定一定的螺旋反转罚分的情况下，存在一个最佳值，可以在增强手性放大程度的同时降低失配罚分。温度依赖性的多数规则实验确实可以证实这些模拟。这些发现表明，在一维螺旋超分子聚合物中增强多数规则原理的手性放大程度时，这两个能量罚分都很重要。
