In 2016, researchers Ben Feringa, Fraser Stoddart, and Jean-Pierre Savage received the Nobel Prize in Chemistry “for the design and synthesis of molecular machines.” Molecular machines are nanometric entities based on molecules that can perform controlled movements when stimulated with an energy source (heat, pH, light). This discovery has very important consequences in the development of new technologies, since, if there is a process associated with technological development in the 21st century, it is undoubtedly that of miniaturization. Molecular machines are the smallest technological devices that can be built, so that their rational design (which is aimed at subsequently fulfilling the function for which it was designed) constitutes one of the great challenges for a chemical researcher.
The mechanical link
The root of the works of Feringa, Stoddart and Savage is found in what is currently known as a mechanical link. Normally, molecules are made up of associations of atoms that are linked by covalent bonds, that is, by sharing electrons. Mechanical bonds are established when two or more molecules intertwine, as a consequence of their topology.
The existence of mechanical bonds allows the components of the molecule to move relative to each other, thus facilitating the movement that turns it into a molecular machine. For example, a ‘catenane’ (Figure 1) is made up of two (or more) cyclic components that are intertwined in the same way as two consecutive links in a chain. The existence of the mechanical link allows one of the components (link) to rotate with respect to the other.
Along with catenans, rotaxanes and molecular knots constitute the three types of mechanically intertwined molecules known to date (Figure 1). These three types of molecules have in common that they are based on cyclic structures, since it can be inferred that closed systems are the ones that most easily give interlocking structures.
The development of this new molecular engineering is today a field in continuous progress since the number of molecules capable of forming sophisticated molecular topologies is almost unimaginable. The development of new molecular machines provides a scenario comparable to the extraordinary versatility that we would have to design three-dimensional puzzles or architectures by combining Lego pieces. Precisely, Fraser Stodart, undoubtedly one of the greatest exponents in the design of molecular machines, recounts his addiction to puzzles during his childhood, and how this enhanced his creativity when designing molecular assemblies
Some mechanically interlocked molecules similar to those shown in Figure 1 have been used to build amazing molecular assemblies that simulate the process executed by a molecular elevator, the contraction of a muscle or a moving nanocar. All this, with the singularity of operating on the nanometric scale.
In this context, the preparation of more complex mechanically interlocked structures should allow the molecule to carry out a greater number of movements through the mechanical bonds and, therefore, be capable of performing increasingly sophisticated functions.
For all of the above, designing new types of mechanically intertwined molecules and, above all, finding new molecular topologies is of great importance to accelerate the development of this new field of chemical research. This would eventually open the window to new technological applications.
New molecular topology with non-cyclic components
In the search for new molecules with compatible characteristics for the formation of mechanical bonds, our group at the Universitat Jaume I has designed a new type of mechanically intertwined molecule based on the association of two molecules in the form of a clamp or clip (Figure 2).
When these molecules intertwine with each other, they form a novel molecular topology that we have baptized with the name of clypans (see Figure 2). It should be noted that, while the molecular topologies known so far (catenane, rotaxane and molecular knots) are based on cyclic structures, what is unique about clipane is that it is made up of two open (non-cyclic) components, in the form of a clip.
For the mechanical bond to occur, the components of the clipane must be in perfect harmony in terms of size, shape and position of functional groups along its molecular skeleton, which implies a great effort in the design and adjustment of the clipane. synthetic procedure.
The fact that this molecule could not be imagined until now opens up a wide range of possibilities, with applications that we are unable to imagine today. The results, which have been published in the prestigious chemical journal Angewandte Chemie International Edition, have had a great media echo in the scientific community, and have even been highlighted in the journal Science.
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