Synthesis and characterization of s-histidine-derived poly (ionic liquid)/silica nanocomposites and their application in the enantioselective hydrolysis of a chiral ester

摘要

In this study, a new optically active monomer containing two chemically preformed imide rings was synthesized. The monomer was then used to synthesize optically active poly(amide imide)s (OAPAIs) and an optically active polyionic liquid (OAPIL), which were finally reacted with various amounts of silica nanoparticles in an in situ polymerization reaction to produce OAPAI/SiO _2 and OAPIL/SiO_2 hybrid materials containing sulfonic acid groups. The prepared monomers and the OAPAI and OAPIL nanocomposites were characterized by ~1H-NMR spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and differential scanning calorimetry. OAPIL/SiO_2 served as an excellent catalyst in water as a solvent for the hydrolysis of d,l-phenylglycine methyl ester with the advantage of a markedly enhanced enantioselectivity and activity. Also, the enantioselectivity was strongly dependent on the SiO_2 content in the OAPIL/SiO_2 systems; a favorable SiO_2 content was 20% (w/w). The enantioselectivity was 95.2% (substrate conversion = 62.3%).