Supramolecular Self-assembly And Molecular Recognition Behaviors Of Helical Receptors

Foldamers are artificial folded molecular architectures. The folded structures canbe formed through supramolecular interactions including hydrogen bonding,solvophobic effects, Ï€-Ï€ interactions, electrostatic interactions and Van der Walsforces. In particular, the formation of helical conformation is very interesting in thepresence of non-covalent interactions.Supramolecular self-assembly is a spontaneous process which resulted in theformation of ordered structures following the thermodynamics and kinetics rules. InNature, biomacromolecules adopt the nano-scaled high-level structures andthree-dimensional conformations by supramolecular self-assembly. It is believed thatbiomacromolecules carry out the biological features and functions due to thehigh-level structures. This observation inspires one to develop the approach ofcontrollable supramolecular self-assembly by using synthetic building blocks in orderto simulate the three-dimensional high-level structures.Molecular recognition is very interesting in supramolecular chemistry. Once thehost-guest complex was generated, the physical properties are significantly changed,such as UV-visible absorption, fluorescence, NMR signals and so on. By using thespectroscopic techniques, the resulting supramolecular complex can be fullycharacterized. To date, the design and synthesis of artificial receptors as well as theirapplications for biological analysis are still an important research area.Herein, we successfully synthesized the receptor molecule and characterized thestructure and purity of the compound by various spectroscopic techniques such as¹HNMR,¹³C NMR, and mass spectrometry. We demonstrated that the synthetic receptors have helical conformation via computer simulation.As expected, helical receptors have the cavity for binding guest moleculesthrough hydrogen bonding interactions. The analysis indicated that the helicalreceptor have an association constant of5orders of magnitude for bromide ion asmeasured by fluorescence spectroscopy.Small helical molecules can form aggregates by self-assembly between oneanother. Helical receptor is a rigid structure with the self-assembly capacity ofcolumnar arrangement via inherent Ï€-Ï€ stacking, which was proved by UV-visiblespectroscopy, fluorescence spectroscopy and¹H NMR. More interestingly, thecolumnar strand can further self-assemble into tube-like structure. The nanotubemorphology can be clearly confirmed and observed by fluorescence opticalmicroscopy, transmission electron microscopy, scanning electron microscopy,intelligent powder X-ray diffraction （XRD）.In conclusion, we synthesized a new type of small helical receptors. The helicalmolecules can self-assemble into nanotube with a relatively controllable way. Thisstudy provides a new opportunity to develop foldamer-based controllablesupramolecular self-assembly and to design foldamer-based channels.