Over the years

Over the years, mechanically interlocked molecular structures have been synthesized, they received much attention due to their unique non-trivial topology and dynamic behavior. Despite the increased report of complex supramolecular topologies, their synthesis remains laborious and expensive through the kinetically controlled multi-step pathways. Two of these structures, rotaxanes and catenanes, received attention recently as new syntheses are being discovered on a regular basis (Martijn 2017).. Ranging from laboratory bench to the real world, however, finding applications for these molecules remain a difficult task. Many applications of rotaxanes and catenanes have been described in recent literature, ranging from chemical applications which includes; catalysts and sensor to polymers. In biological application, they find application such as drug delivery agents or as in optical bio-imaging agents. Molecular motors and switches are the most pronounced applications of these supramolecules in materials research, which has attracted a lot of current research being a hot item. (Martijn 2017). The 2016 Nobel Prize in chemistry was awarded in this area, this show the high potential of these molecules for future application.
Significant developments in fundamental supramolecular concepts such as self-organisation, self-assembly, molecular recognition, template-direct synthesis and dynamic covalent synthesis have unlocked access to more elaborate interlocked architectures including knots, suitanes, Borromean rings and ravels (Bruns & Fraser 2010, Twyman & Sanders 1999, Kieran, A. L et. al., 2003, Kieran, A. L et. al., 2005 ). These unique molecular architectures have shown promise in the areas of sensing, catalysis, and even artificial molecular machines, hence, facile synthetic routes to these complex systems are of great interest.
In literature, 5 primary routes have been adopted in synthesizing rotaxanes which include; Capping, Snapping, Clipping, Slipping and active metal template. With these methods, supramolecular chemists have synthesized numerous rotaxanes. The major challenges in supramolecular chemistry however are the formation of rotaxanes and catenanes polymer with special characteristic and finding applications to it in the real life. Chak-Shink et. al., (2018) developed a facile synthetic approach of type III-B rotaxanes dendrimers, demonstrated their potential applications in guest binding by molecular shuttling in 3D manner. Although, the author quoted that higher generation T3B-RDs is currently underway in their laboratory, they recommend further development of different versions and higher generations of RDs with various properties and potential applications in smart-molecular machines, materials, and nanotechnology.
The desire to contribute scientifically to enhance the properties of polymeric supramolecules and finding practical applications to these materials is pushing the search of novel mechanically interlocked supramolecules materials that can be applied in the area of materials and engineering as molecular machines, there is rising need of approaches that can be used to supplement movement in living organism; movement is one of the central attributes of life and key feature in many technological processes. Also, there are specific situations that require artificial muscles capable of macroscopic actuation. Skeletal muscles shows that motion can be amplified from molecular to macroscopic scale if molecular motors are appropriately organized and integrated within polymeric structures (Schliwa M. 2003, Goodsell D.S 2004, Jones R.A 2004). The concept of artificial molecular machines can be applied in polymer science to develop mechanically active materials. In the same vein, concept and system pertaining to artificial molecular machines can be applied in supramolecules polymer science to develop mechanically active materials. Literature in this direction have shown that incorporated large numbers of artificial molecular machines in polymer can be collected, leading to macroscopic actuation (Goujon A. et. al., 2017, J.T Foy et. al., 2017).
Although, the prospects of synthesizing a polymeric supramolecules are budding, there have been under-reporting of research going on in this area. Most researchers have focused on writing review papers on the potential synthesis and application of polymeric supramolecules as molecular machines and not necessarily carrying out the research work in the laboratory. This is a big gap that this research work hopes to cover. The few ones that have been strategic enough to undertake laboratory works on polymeric supramolecules have not emphasized on the use as molecular machines “artificial muscles” and optimization of the properties of such materials in response to external stimuli.
This research apart from paving pathways and solutions will work more in ensuring that these developed methods find more relevant applications to supramolecular polymers.
Research Methodology
This research work will apply the following approaches in generation of data and creation of necessary tools:
• Review existing synthetic methods.
• Laboratory synthesis of rotaxanes and its polymer.
• Use of analytical instruments to characterize synthesized supramolecules.
• Laboratory experiments and designs; cutting across transducer techniques, chemical modifications and automation.
• Testing of the molecular machine to find suitable application.
Research Significance
The impact of this research work will be very useful to Hong Kong and will assist in alleviating the molecular machines application issues that are needed for developed technology in Hong Kong, neighbouring Mainland China. Findings that will also be developed from this research project will open more frontiers for further use of various supramolecular polymers in robotic technology applications. The challenges to finding applications to synthesized polymeric supramolecules in real life are on the very lookout by world supramolecular scientist. The desire to ensure solutions are provided scientifically to this challenge very soon is the main motivation behind this project and hence, the research effect will not only be applicable to Hong Kong alone; but the global materials scientist and engineer.
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Chak-Shing Kwan, Rundong Zhao, Michel A. Van Hove, Zongwei Cai and Ken Cham-Fai Leung. Higher-generation type III-B rotaxane dendrimers with controlling particle size in three-dimensional molecular switching. Nature Communication.9:497 (2018).
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