One-pot synthesis of N,N-bis[2-methylbutyl] imidazolium hexafluorophosphate–TiO2 nanocomposites and application for protein isolation

Abstract

A novel one-pot procedure for the synthesis of ionic liquid N,N-bis[2-methylbutyl] imidazolium hexafluorophosphate (PPimPF₆/TiO₂) nanocomposites is reported for the first time. During the in situ formation of TiO₂ nanoparticles via hydrolysis of tetrabutyl titanate (TBOT), the ionic liquid PPimPF₆ is simultaneously incorporated into the TiO₂ nanostructure via H-bonding. The PPimPF₆/TiO₂ nanocomposites are characterized by means of TEM, FT-IR and XRD, showing that they possess the structure of anatase and exhibit selective adsorption for neutral proteins, hemoglobin (Hb) in this particular case, under controlled experimental conditions. At pH 8, an adsorption efficiency of 88.3% for 150 μg mL⁻¹ Hb is achieved by 2.0 mg of PPimPF₆/TiO₂ nanocomposites, while virtually no adsorption is observed for the basic protein cytochrome c (cyt-c) and the acidic protein bovine serum albumin (BSA). An adsorption capacity of 122.3 μg mg⁻¹ is obtained for Hb by calculation on the amount of the incorporated ionic liquid, corresponding to a 5-fold improvement with respect to that achieved by pure PPimPF₆. The retained Hb on the PPimPF₆/TiO₂ nanocomposites could be readily collected by stripping with 0.5% SDS, giving rise to a recovery of ca. 73%. The circular dichroism (CD) spectra indicate no conformational change of Hb after the adsorption/elution process. The selective isolation of Hb from human whole blood is achieved by the nanocomposites.