Molecular Materials Design Laboratory, Department of Chemistry , Indiana University , 800 East Kirkwood Avenue , Bloomington , Indiana 47405 , United States.
J Am Chem Soc. 2019 Nov 6;141(44):17588-17600. doi: 10.1021/jacs.9b06410. Epub 2019 Oct 23.
Anfinsen's dogma that sequence dictates structure is fundamental to understanding the activity and assembly of proteins. This idea has been applied to all manner of oligomers but not to the behavior of cyclic oligomers, aka macrocycles. We do this here by providing the first proofs that sequence controls the hierarchical assembly of nonbiological macrocycles, in this case, at graphite surfaces. To design macrocycles with one (AAA), two (AAB), or three (ABC) different carbazole units, we needed to subvert the synthetic preferences for one-pot macrocyclizations. We developed a new stepwise synthesis with sequence-defined targets made in 11, 17, and 22 steps with 25, 10, and 5% yields, respectively. The linear build up of primary sequence (1°) also enabled a thermal Huisgen cycloaddition to proceed regioselectively for the first time using geometric control. The resulting macrocycles are planar (2° structure) and form H-bonded dimers (3°) at surfaces. Primary sequences encoded into the suite of tricarb macrocycles were shown by scanning-tunneling microscopy (STM) to impact the next levels of supramolecular ordering (4°) and 2D crystalline polymorphs (5°) at solution-graphite interfaces. STM imaging of an AAB macrocycle revealed the formation of a new gap phase that was inaccessible using only -symmetric macrocycles. STM imaging of two additional sequence-controlled macrocycles (AAD, ABE) allowed us to identify the factors driving the formation of this new polymorph. This demonstration of how sequence controls the hierarchical patterning of macrocycles raises the importance of stepwise syntheses relative to one-pot macrocyclizations to offer new approaches for greater understanding and control of hierarchical assembly.
安芬森的序列决定结构的教条是理解蛋白质活性和组装的基础。这个想法已经应用于各种寡聚物,但不适用于环状寡聚物,又名大环的行为。我们通过提供第一个证据来做到这一点,证明序列控制非生物大环的分层组装,在这种情况下,是在石墨表面。为了设计具有一个(AAA)、两个(AAB)或三个(ABC)不同咔唑单元的大环,我们需要颠覆一锅法大环化的合成偏好。我们开发了一种新的逐步合成方法,具有序列定义的目标,分别在 11、17 和 22 步中以 25、10 和 5%的产率合成,线性构建一级序列(1°)还能够首次使用几何控制进行热 Huisgen 环加成,具有区域选择性。所得大环是平面的(2°结构),并在表面形成氢键二聚体(3°)。通过扫描隧道显微镜(STM)显示,一系列三咔唑大环中的一级序列编码影响了下一个层次的超分子有序性(4°)和在溶液-石墨界面的 2D 结晶多态性(5°)。对 AAB 大环的 STM 成像揭示了新的间隙相的形成,而仅使用 -对称大环是无法获得的。对两个额外的序列控制大环(AAD、ABE)的 STM 成像使我们能够确定驱动这种新多晶型形成的因素。这种序列控制大环分层图案的方式的演示提高了逐步合成相对于一锅法大环化的重要性,为更好地理解和控制分层组装提供了新的方法。