In the realm of molecular engineering, creating an aluminum-based rotaxane and polyrotaxane is a breakthrough for researchers. These complex shapes with their exceptional mechanical interlocking properties are very promising for a broad range of applications from materials science to nanotechnology.
Unraveling The Properties Of Molecular Circles
The design of rotaxanes has intrigued the scientific field for decades, due to their unique structure consisting in mechanically interlocked axles and macrocycles. These interesting molecular assemblies are constructed by a variety of organic macrocycles such as crown ethers, cyclodextrins, and cucurbiturils as reported by researchers.
Nevertheless, the unique electronic nature of inorganic metal ions has facilitated novel strategies to the emergence at molecular level of macrocycles. This paper, led by Prof. Zhang Jian and Prof. Fang Weihui of the Chinese Academy of Sciences, illustrates a new kind of bottom-up approach to piecewise synthesis of polymeric rotaxanes following an inverse “ring-donor···axle-acceptor” method with Al8 molecular rings as the core.
All in with the Al8 Macrocycle
The structure of macrocycle Al8 in Figure 1 is something else; it is essentially a hydrophilic Al8(OH)8 ring with two hydrophobic ports: The macrocycle features unique binding of a “ring-H/axle-acceptor”-type due to the presence of inward-oriented OH groups that can offer multiple interaction sites for various acceptors, such as anions, metal cations or organic ligands.
The Al8 macrocycle has been shown to encapsulate a range of aromatic compounds including single-site carboxylic acids and dual-site bipyridine. All of these aromatic guests have metal coordination sites that point toward the Al8(OH)8 plane, thereby providing the possibility of forming an axle structure by addition of a metal cation. We sought Ag+ and Na+ as competent cations with linear coordination geometry in order to fabricate a family of [2]-rotaxanes containing inner linear complex axles.
Conclusion
This study exemplifies the ground-breaking discoveries that are possible with aluminum rotaxanes and polyrotaxanes. The researchers have exploited the distinctive “ring-donor···axle-acceptor” mode thereby establishing a universal assembly strategy, which presents an increased configurability and adaptability over these molecular constructs We believe the Ag(NA)2– embedded [2]-rotaxane represents a new benchmark in host-guest complexes showing highly enhanced nonlinear optical properties, which may find broad applications in areas from optoelectronics to energy storage and beyond. This way of thinking about molecular engineering — as with nanotechnologics — is likely to inspire new developments and the coming of a macro-scale era driven by an understanding that only occurs on the scale below.
