Thiol-ene photo-click immobilization of a chiral chromatographic ligand on silica particles.

This work reports procedures for the immobilization of vinyl ligands on silica particles by UV-initiated thiol-ene radical addition reaction (photo-click immobilization). tert‑Butylcarbamoyl quinine was the functional ligand (ene component) for the synthesis of chiral stationary phases. Two distinct surface chemistries were evaluated. In one approach, the ligand was directly attached to 3-mercaptopropyl-silica triggered by radicals generated by UV irradiation from a photoinitiator. In another approach, the ligand was immobilized onto vinyl silica via poly(3-mercaptopropyl-methylsiloxane) (PMPMS) as crosslinker by a photoinitiated double click reaction in which functionalization with chiral ligand and crosslinking to vinylsilica occurred simultaneously in one synthesis step. PMPMS-bonded CSPs were prepared from suspension (slurry method) or solventless after coating of the polythiol onto the vinylsilica surface (film method). Optimization by a design of experiment approach showed that the reaction time is the prime variable to optimize the surface coverage of chiral selector which also increased with PMPMS concentration. When the film formation of the latter approach was assisted by a minute volume of toluene during photo-click immobilization, selector coverage could be significantly increased to 0.73 µmol/m

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.