Integrative self-sorting is a programming language for high level self-assembly

Abstract

Starting from the basis of a simple 4-component self-sorting system of crown ethers and ammonium ions, we design 6 building blocks in which 2 identical or different binding sites are incorporated. These building blocks can be mixed in many different ways to yield quite distinctly different pseudorotaxane assemblies. The self-sorting process integrates all building blocks in specific places so that this approach permits us to exert positional control and can widely influence the resulting assemblies with respect to the details of their structures. At maximum, we report quadruply interlocked species with up to 5 subunits that form specific assemblies. Although NMR methods are limited to the analysis of simpler complexes, ESI-MS and, in particular, tandem mass spectrometry is highly useful to analyze the assemblies' connectivities.interlocked molecules ͉ pseudorotaxanes ͉ supramolecular chemistry ͉ tandem mass spectrometry ͉ crown ether T he ''bottom-up'' approach to the construction of molecular devices and machines through molecular self-assembly has attracted extensive attention in the past 2 decades (1-4). Molecular self-assembly (5-7) harnesses noncovalent interactions to organize discrete components into well-organized architectures. To achieve this, the necessary instructions must be written into the structures of the building blocks by chemical synthesis. Most artificial self-assembled architectures known today incorporate multiple copies of the same building blocks and thus are often highly symmetrical structures.In the macroscopic world, however, devices and machines are assembled from many different components cooperating with each other to perform complex functions. The same holds true for most biomolecules. Nature efficiently uses the principles of noncovalent self-assembly together with self-sorting (8, 9) phenomena to generate complex, functional architectures. DNA may serve as a prominent example whose function is information storage. Four bases (adenine (A), thymine (T), guanine (G), and cytosine (C)) self-sort to form base pairs (AT and GC) in their mixture. Integrating these bases to the polymer backbones of DNA in a specific sequence not only stores information but also allows the cell to replicate and transcribe the stored information.When complex functions are to be achieved in artificial molecular devices or machines, the self-assembly of highly symmetrical architectures from multiple identical building blocks is a severe restriction that can be overcome by applying the same strategy used by nature: The integration of different subunits into the architecture with precise positional control by combining the principles of self-assembly and self-sorting. We very recently coined this strategy, integrative self-sorting (10), and are convinced that it will not only enrich the world of supramolecular architectures from the point of view of structural variability but will also form the basis for the implementation of high-level functions in future assemblies.Herein, we present several strategies abou...

Tandem mass spectrometry for the analysis of self‐sorted pseudorotaxanes: the effects of Coulomb interactions

“…Pseudorotaxanes 5-2H· 2 PF 6 and 6-2H· 2 PF 6 which differ only with respect of the length of the axle center piece, behave very similarly. [8] In the ESI mass spectra, the sole intense signals correspond to the two pseudorotaxane monocations ] + and [6-2H· PF 6 ] + , respectively, which again fragment in the same sequence as described above for 4-2H· 2 PF 6 .…”

“…The syntheses of C7, [16] 1-2H· 2 PF 6 , 2-2H· 2 PF 6 , 3-2H· 2 PF 6 and 7-2H· 2 PF 6 and the preparation of hetero [3]pseudorotaxanes 4-2H· 2 PF 6 , 5-2H· 2 PF 6 ,6-2H· 2 PF 6 , 20-4H· 4 PF 6 and 21-4H· 4 PF 6 have been reported elsewhere. [7,8] All mixtures for supramolecular assemblies were sonicated or stored at room temperature until reaching equilibrium before any NMR or MS experiments. 1 H NMR and 1 H-1 H COSY spectra were recorded on a Jeol Eclipse 500 MHz NMR spectrometer.…”

“…This study aims at a more profound understanding of the gas-phase reactivity of supramolecules and how MS methods can be used for structure assignment. The solution structures of those few assemblies which have not been characterized previously [7,8] have been established by nuclear magnetic resonance (NMR) experiments. The data are given in the supporting information.…”

“…[13 -15] The methodological arsenal of tandem mass spectrometry has been quite successful in characterizing the pseudorotaxanes in Scheme 1. [7,8] It provides detailed information on their non-covalent connectivities through fragmentation reactions in the gas phase. However, the application of mass spectrometry to structural studies in supramolecular chemistry requires a detailed understanding of several points: (1) the transfer of supramolecules from solution to the gas phase significantly affects their properties and may even compromise the complex integrity due to the drastic changes in the environment.…”

“…[7,8] All the architectures are based on a simple self-sorting scheme. The smaller crown ether benzo-21-crown-7 (C7) is too small to slip over a phenyl group, [9] so that site A of axles 1-2H· 2 PF 6 to 3-2H· 2 PF 6 can only be occupied by dibenzo-24-crown-8 (C8).…”