Precursor carboxy‐silica for functionalization with interactive ligands. I. Carbodiimide‐assisted preparation of silica‐bonded stationary phases with octadecyl, naphthyl, and anthracenyl ligands: Comparison of their selectivity and retentivity

Abstract

A precursor carboxy-silica support was introduced for grafting retentive ligands for use in high-performance liquid chromatography. This support was prepared by sequentially reacting 5 μm silica particles with vinyltrimethoxysilane and then thioglycolic acid. The carboxy-silica thus obtained was subsequently functionalized with octadecylamine, 2-naphthylamine, or 2-aminoanthracene by oncolumn reactions via a carbodiimide conjugation reaction. The carbodiimide with its zero-length carboxyl-to-amine coupling ability works by activating the surface carboxyl groups of the precursor support for direct reaction with the primary amines of octadecylamine, 2-naphthylamine, or 2-aminoanthracene via amide bond formation. These reactions series, which are applied for the first time in high-performance liquid chromatography column fabrication, yielded the octadecyl-, naphthyl-, and anthracenyl-silica columns. The three columns were evaluated for their reversed-phase chromatography retention properties with alkylbenzenes, alkylphenyl ketones, nitroalkanes, benzene and toluene derivatives, polyaromatic hydrocarbons, and nitro-substituted amino acids. The naphthyl-and anthracenyl-silica exhibited a good selectivity and efficiency toward most of the aromatic analytes when compared to the octadecyl-silica. Nitro-substituted amino acids containing electron withdrawing groups showed greater selectivity than other analytes on the aromatic-based columns than the C 18 column. This is because of the ability of the π electron system of the analyte to accept electrons from the aromatic-based stationary phase (a Lewis base).

Revisiting carboxylic group functionalization of silica sol–gel materials

“…74 Paranama et al used a thermal-radical initiated reaction using 2,2 0 -azobis(isobutyronitrile) between vinyl-modified SiO 2 and thioglycolic acid for anchoring glucamine. 113,114 Anionic type thiol-ene addition was also used to incorporate COOH groups onto mesoporous SiO 2 using a thiosuccinic moiety as shown in Scheme 10. 115 This molecular group enhanced the affinity of the mesoporous framework for oxaliplatin, a chemotherapeutic agent, and controlled its release via an acid mediated hydrolysis, as cancer cells have typically an acidic environment.…”

“…Paranama et al used a thermal-radical initiated reaction using 2,2′-azobis(isobutyronitrile) between vinyl-modified SiO 2 and thioglycolic acid for anchoring glucamine. 113,114…”