Amino-terminated supramolecular cucurbit [6] uril pseudorotaxane complexes immobilized on magnetite@silica nanoparticles: A highly efficient sorbent for salvianolic acids

In this study, a novel amino-terminated supramolecular cucurbit [6] uril (CB [6]) pseudorotaxane motif coated magnetic nanoparticles (MNPs) was successfully fabricated through cucurbit [6] uril promoted azide-alkyne cycloaddition. The physicochemical properties of the obtained functional MNPs were investigated by scanning electron microscope, transmission electron microscope, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffractometer, vibrating sample magnetometer, thermal gravimetric-derivative thermogravimetric analysis, and Zeta potential analyzer. Due to the abundant carboxyl groups in the structure of CB [6] and amino residue on the surface of the pseudorotaxane motif MNPs, the prepared materials were employed to extract salvianolic acids (SAs) for the first time. A series of significant parameters in the extraction and elution process, including sample pH, acetonitrile percentage, ionic strength and extraction temperature, as well as eluent type and desorption time, were examined systematically. Based on the results, the electrostatic interaction, van der Waals interaction, hydrophilic interaction and hydrogen bonding formation between the analytes and sorbent were speculated. The equilibrium state of static adsorption study indicated the outstanding adsorption capacity of pseudorotaxane motif MNPs toward six SAs to be 15-80 mg/g, providing much better adsorption affinity for SAs compared with MNPs only modified with amino, and their adsorption behaviors were all fitted with Freundlich adsorption isotherm model. In addition, the developed pseudorotaxane motif MNPs offered good recyclability and stability. Taking advantage of these merits, four SAs from Salvia miltiorrhiza Bunge were successfully extracted using the prepared pseudorotaxane motif MNPs with relative recovery in the range from 95.1% to 106.5% and RSDs below 9.7%. These results demonstrated that the synthesized pseudorotaxane motif MNPs showed potential as a candidate in the extraction of SAs.