Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6, 14195 Berlin, Germany.
Department of Chemistry, School of Natural Science, Ulsan National Institute of Science and Technology , Ulsan 44919, South Korea.
J Am Chem Soc. 2016 Dec 21;138(50):16315-16321. doi: 10.1021/jacs.6b08700. Epub 2016 Dec 12.
Amphiphilic porphyrins are of great interest in the field of supramolecular chemistry because they can be fabricated into highly ordered architectures that are stabilized by π-π stacking of porphine rings as well as by non-covalent interactions between their hydrophilic substituents. Protoporphyrin IX (PPIX) has two flexible propionic acid tails and is one of the most common amphiphilic porphyrins. However, unlike other PPIX analogues, PPIX does not form stable extended nanostructures, and the reason for this is still not understood. Here, we employ ion mobility mass spectrometry in combination with infrared multiple photon dissociation spectroscopy to investigate early aggregates of PPIX. The ion mobility results show that growth occurs via single-stranded face-to-face stacking of PPIX. From the infrared spectroscopy on well-defined aggregates, it can be concluded that pairing of the carboxylic acid groups of the tails is a stabilizing element and that such a pairing occurs across a third residue from residue n to residue n+2. The tetramer appears to be especially stable, because all of its propionic acid tails are optimally paired and no free tails to promote further growth are present, which possibly prevents PPIX from forming larger, well-ordered assemblies.
两亲卟啉在超分子化学领域中备受关注，因为它们可以被构建成高度有序的结构，这些结构通过卟啉环的π-π堆积以及亲水性取代基之间的非共价相互作用得到稳定。原卟啉 IX（PPIX）具有两个柔性丙酸尾巴，是最常见的两亲卟啉之一。然而，与其他 PPIX 类似物不同，PPIX 不会形成稳定的扩展纳米结构，其原因尚不清楚。在这里，我们采用离子淌度质谱结合红外多光子解离光谱研究 PPIX 的早期聚集体。离子淌度结果表明，PPIX 通过单链面对面堆叠发生生长。从对明确定义的聚集体的红外光谱可以得出结论，尾巴羧酸基团的配对是一个稳定的因素，这种配对发生在从残基 n 到残基 n+2 的第三个残基上。四聚体似乎特别稳定，因为其所有丙酸尾巴都得到了最佳配对，没有游离的尾巴来促进进一步的生长，这可能阻止 PPIX 形成更大、更有序的组装体。
