Mechanostereochemistry and the mechanical bond

Abstract

The chemistry of mechanically interlocked molecules (MIMs), in which two or more covalently linked components are held together by mechanical bonds, has led to the coining of the term mechanostereochemistry to describe a new field of chemistry that embraces many aspects of MIMs, including their syntheses, properties, topologies where relevant and functions where operative. During the rapid development and emergence of the field, the synthesis of MIMs has witnessed the forsaking of the early and grossly inefficient statistical approaches for template-directed protocols, aided and abetted by molecular recognition processes and the tenets of self-assembly. The resounding success of these synthetic protocols, based on templation, has facilitated the design and construction of artificial molecular switches and machines, resulting more and more in the creation of integrated functional systems. This review highlights (i) the range of template-directed synthetic methods being used currently in the preparation of MIMs; (ii) the syntheses of topologically complex knots and links in the form of stable molecular compounds; and (iii) the incorporation of bistable MIMs into many different device settings associated with surfaces, nanoparticles and solid-state materials in response to the needs of particular applications that are perceived to be fair game for mechanostereochemistry.

Computationally forecasting the effect of dibenzylammonium substituents on pseudorotaxane formation with dibenzo[24]crown-8

“…[9][10][11][12][13] One of the most outstanding templates which has been developed for MIM synthesis is the hydrogenbonded dibenzylammonium (DBA)/dibenzo- [24] crown-8 (DB24C8) recognition motif whose remarkable stability 14 has inspired the use of a variety of appropriately-sized crown ethers for DBA ion recognition in numerous intriguing studies. 7, 15 Ashton and co-workers published an interesting keynote article 16 in which they determined the stabilities of several paraand meta-substituted DBA/DB24C8 pseudorotaxanes and found good correlation between experimental binding energies and the Hammett substituent constants 17 (r) associated with the para-groups on the DBA phenyl rings. This relationship allows the relative stability of these analogous complexes to be predicted, prior to their synthesis, by considering the electronic properties of the substituted DBA threads-effectively allowing the synthetic chemist to 'fine-tune' the strength of complexation at the initial design stage-resulting not only in considerable time-and cost-savings, but also improved control during the final stages of MIM assembly.…”

“…Since Stoddart's initial discovery 1 of the first threaded donor/acceptor complex, we have not only seen the assembly of a myriad of other pseudorotaxanes, but also witnessed their usefulness as precursors to a variety of topologically-fascinating mechanically interlocked molecules (MIMs) [2][3][4][5][6][7][8] and functional molecular machinery. [9][10][11][12][13] One of the most outstanding templates which has been developed for MIM synthesis is the hydrogenbonded dibenzylammonium (DBA)/dibenzo- [24] crown-8 (DB24C8) recognition motif whose remarkable stability 14 has inspired the use of a variety of appropriately-sized crown ethers for DBA ion recognition in numerous intriguing studies.…”

Molecular machines – a new dimension of biological sciences

“…The macromolecular device is powered by chemical energy (hydrolysis of ATP Brownian ratchet (A) and power stroke modes (B) demonstrated in the example of active transport of polymer though biological membrane equipped with a specific and selective pore system such as TOM-TIM23 complexes in the inner mitochondrial membrane. The protein transfer is powered by the association with HSP70 family proteins residing in the lumen of endoplasmic reticulum (BiP) and in the matrix of mitochondria (mtHSP70) [43].…”

An Introduction to the Mechanical Bond

“…16,17 Without a doubt, the mechanical bond will continue to evolve. We believe that the publication of this book is timely because the evolution of MIMs appears to be approaching a turning point.…”

“…Catenanes and rotaxanes are a subset of a family of molecules known [13][14][15][16][17] as Mechanically Interlocked Molecules, or MIMs, for short. Not all MIMs necessarily possess mechanical bonds because entanglements are possible in molecules that lack distinguishable component parts, such as molecular knots.…”