Abstract:

Hybrid core/shell composites, in which an organic core was surrounded by a layer of inorganic material, have been widely investigated both to improve the stability and surface chemistry of the core materials and chemical properties that are not possible from one material alone. This article reports a category of hybrid core/shell composite consist of an organic core(composed of an optically active polyaniline) and a shell(composed of silica dioxide) and thus exhibit optical activities. Chiral polyaniline[(+)-PANI] was synthesized with aniline as monomer and D-camphorsulfonic acid[D-(+)-CSA] as chiral dopant. The silica dioxide was coated on the surface of (+)-PANI by sol-gel approach, thus to obtain the chiral polyaniline/silica dioxide core/shell composite[(+)-PANI@SiO₂]. (+)-PANI and (+)-PANI@SiO₂ were characterized by optical activity and regular morphology. The UV-Vis absorption spectra, circular dichroism and specific rotation demonstrated that the (+)-PANI and(+)-PANI@SiO₂ endowed with optical activity. Fourier transform infrared spectroscopy was used to verify the surface groups and the scanning electron microscopy was used to verify the core/shell conformation. The (+)-PANI and (+)-PANI@SiO₂ were used as chiral selectors for the enantioselective crystallization of alanine racemates, respectively. L-alanine was preferable induced from the racemic solution. More times of inducing, e. e.% value is bigger. The shells could be further cross-linked for improving the properties of organic core. The investigations are of importance not only in chiral studies but also in materials due to the integration of organic helical polymers and inorganic materials in one single material.

Key words: Polyaniline, Silica dioxide, Hybrid core/shell composite, Enantioselective crystallization, Alanine