Molecular self-sorting

Scheme 4.6 Self-sorting behavior of C-shaped molecular clips 13 and ( )-14.

Wu AX, Chakraborty A, Eettinger JC, Elowers RA, Isaacs L. Molecular clips that undergo heterochiral aggregation and self-sorting. Angew Chem Int Ed 2002 41 4028-4031. 

Since the original definition of supramolecular chemistry was coined by Lehn several corollaries have emerged. One that has risen to great importance is the idea of a dynamic combinatorial library of molecular components that self-sort to generate supramolecules with reactive termini which are then predisposed to form covalent bonds. The effects of weak interactions together with geometric and steric constraints lead to the formation of far fewer products than would be predicted by pure statistics. This development will be discussed in greater detail later. 

We therefore considered addressing in the first part of this review some of most representative examples in which specific molecular architectures and materials are constitutionally self-sorted in the presence of different biomolecular targets or... 

In this context the supramolecular crystalline [15-22] or hybrid materials [23-35] can be prepared and constitutionally self-sorted by using an irreversible kinetic process like crystallization or sol-gel polymerization. The self-selection is based on constitutional internal interactions of library components, resulting in the dynamic amplification of self-optimized architectures, during the phase change process. With all this in mind, the second part will be devoted to sol-gel resolution of dynamic molecular supramolecular libraries, emphasizing recent developments, especially as pursued in our laboratory. 

VI. Interlude. Molecular clips Capable of Enantiomeric Self-Recognition, Heterochiral Recognition, and Self-Sorting... 

Remarkably, the H NMR spectrum of the mixture is simply equal to the sum of the H NMR spectra of its components. This spectroscopic earmark indicates that this mixture of molecules undergoes self-sorting. Self-sorting refers to the ability of a molecule or entity to efficiently distinguish between self and non-self even within a complex mixture. Self-sorting is commonly observed in Nature (e.g. the immune system) but is still relatively rare in designed supramolecular systems. The molecular clips described here represent a well-defined model system for studies of self-sorting. 

In the formation of complexes via self-sorting, no external template is used. Instead, the molecular structure of the host can be considered as the template for the preparation of a host-guest complex. In this case, the ampHfication of the most stable complex takes place via intermolecular interactions, such as hydrogen bonding, metal coordination, or ionic interactions, between the different components in the mixture. Since the strength of these supramolecular interactions is known to be influenced by substituents, a dynamic library can be obtained-not... 

The validity of the complete molecular code was tested in a more complex [2 -1- 2] self-sorting experiment in which two different axles and two different wheels are mutually competing. As shown in Fig. 30.18, a total of 20 possible homo- and heteropseudo[3]rotaxanes can form with symmetrical axles. 

These results undoubtedly confirm the validity of the molecular code even for a more complex [2 + 2] self-sorting system, in which only 2 out of 20 possible pseudo [3]rotaxanes are stereospecifically formed [34]. 

Ajami D, Hou JL, Dale TJ, Barrett E, Rebek J Jr (2009) Disproportionation and self-sorting in molecular encapsulation. Proc Natl Acad Sci U S A 106 10430-10434... 

In a recent experiment, translational and rotational motion of a single molecule was driven and monitored by the STM tip at 7 K in a sort of rack-and-pinion device.67 The pinion consists of a 1.8 nm diameter molecule acting as a six-toothed wheel interlocked at the edge of a self-assembled molecular island functioning as a rack. The rotation of the pinion molecule tooth by tooth along the rack could be monitored owing to the presence of a chemical tag attached to one of its cogs. 

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