Preparation And Application Of Optically Active Core-Shell Composite Microspheres Constructed By Helical Substituted Polyacetylene

Synthetic helical polymers have received a great deal of attention owing to their distinctive helical structures and the corresponding properties that cannot be found in usual polymers. Helical polymers have visually elegant structures and possess fascinating optical activity, chiral amplification effect, etc. Because a conjugated structure of alternating single and double bonds exists in the main chain of polyacetylene, it exhibits special properties, such as electroconductivity and paramagnetism. Polyacetylene has also encountered some restrictions in the application; for instances, it is hard to dissolve, manufacture and its stability is relatively low. To overcome these drawbacks, scientists synthesized substituted polyacetylene nanoparticles. Recently, researchers synthesized substituted polyacetylenes microspheres from nanometers to micrometers by emulsion polymerization, precipitation polymerization and suspension polymerization methods. The substituted polyacetylene microspheres were successfully applied to chiral recognition.Core/shell structured composite particles, which excellently combine the advantages of the core and the shell components, are gathering rapidly increasing interest, because their composition, morphology, and properties are easy to control. Composite particles which have a magnetic core and an organic shell may have unique applications and properties: biocompatibility, catalysts, superparamagnetic properties. In the present study, we synthesized optically active, magnetic core/shell microspheres structured by Fe3O4@substituted polyacetylene (defined as Fe3O4@PA MPs) which comprise magnetic Fe3O4 NPs as core and helical substituted polyacetylene as shell. The Fe3O4@PA MPs integrated the magneticity of the Fe3O4 core and the intriguing optical activity of the helical polymer shell. We further employed the resulting MPs for chiral recognition.The major contents are as follows:1. Triton X-100 was used as emulsifier to emulsify alkynyl-Fe3O4 NPs, and then monomer and catalyst were added in the emulsion system. After polymerization at room temperature for 3 hours, Fe3O4@polyacetylene microspheres (approximately 1 μm in diameter) were obtained. The core-shell structure and surface morphology of the microspheres were observed by scanning electron microscopy and transmission electron microscopy. The optical properties of core-shell microspheres were characterized by circular dichroism and UV-vis absorption measurements. The magnetic properties of core-shell microspheres were characterized by hysteresis loop test. The resulting composite microspheres were further used as chiral additive to perfrom enantioselective crystallization processes. After enantioselectively crystallizing twice, the e.e. of the induced L-threonine reached 90%. SEM and optical rotation technique were taken to observe the changes of L-threonine crystal morphology and ee values, respectively.2. Through copolymerization of N-propargylamide monomer 1 with monomer 3 which contains catechol moieties, optically active helical N-propargylamide copolymers containing functional catechol groups in side chains were obtained. The PA@Au core-shell composite NPs were obtained by the complexation of gold particles with the catechol groups. Based on TEM images, the average size of the obtained core-shell microspheres is about 500 nm, with obvious core-shell structure. PA@Au core/shell composite NPs were found to be optically active, accordingly to circular dichroism and UV-vis absorption spectroscopy.