Biological encapsulants, such as viral capsids and ferritin protein cages, use many identical subunits to tile the surface of a polyhedron. Inspired by these natural systems, synthetic chemists have prepared artificial nanocages with well-defined shapes and cavities. Rational control over the self-assembly of discrete, nanometre-scale, hollow coordination cages composed of simple components remains challenging as a result of the entropic costs associated with binding many subunits together, difficulties in the error-correction processes associated with assembly and increasing surface energy as their size grows. Here we demonstrate the construction of nanocages of increasing size derived from a single pentatopic pyrrole-based subcomponent. Reasoned shifts in the preferred coordination number of the metal ions used, along with the denticity and steric hindrance of the ligands, enabled the generation of progressively larger cages. These structural changes of the cages are reminiscent of the differences in the folding of proteins caused by minor variations in their amino acid sequences; understanding how they affect capsule structure and thus cavity size may help to elucidate the construction principles for larger and functional capsules, capable of binding and carrying large biomolecules as cargoes.

生物封装剂，例如病毒衣壳和铁蛋白蛋白笼，使用许多相同的亚基来平铺多面体的表面。受这些自然系统的启发，合成化学家制备了具有明确形状和空腔的人造纳米笼。由于与许多亚基结合在一起相关的熵成本、与组装相关的纠错过程中的困难以及增加表面，对由简单组件组成的离散、纳米级、空心协调笼的自组装进行合理控制仍然具有挑战性随着他们的规模增长的能量。在这里，我们展示了从单个基于五位吡咯的子组件中获得的尺寸不断增加的纳米笼的构造。所用金属离子的优选配位数的合理变化，连同配体的密度和空间位阻，能够生成逐渐变大的笼子。笼子的这些结构变化让人想起由氨基酸序列的微小变化引起的蛋白质折叠差异；了解它们如何影响胶囊结构，从而影响空腔大小，可能有助于阐明更大的功能性胶囊的构造原理，能够结合和携带大的生物分子作为货物。