Adsorption and Recovery of Polyphenolic Flavonoids Using TiO2-Functionalized Mesoporous Silica Nanoparticles

M Arif Khan; William T Wallace; Syed Z Islam; Suraj Nagpure; Joseph Strzalka; John M Littleton; Stephen E Rankin; Barbara L Knutson

doi:10.1021/acsami.7b09510

Adsorption and Recovery of Polyphenolic Flavonoids Using TiO₂-Functionalized Mesoporous Silica Nanoparticles

ACS Appl Mater Interfaces. 2017 Sep 20;9(37):32114-32125. doi: 10.1021/acsami.7b09510. Epub 2017 Sep 5.

Authors

M Arif Khan¹, William T Wallace¹, Syed Z Islam¹, Suraj Nagpure¹, Joseph Strzalka², John M Littleton³, Stephen E Rankin¹, Barbara L Knutson¹

Affiliations

¹ Department of Chemical and Materials Engineering, University of Kentucky , Lexington, Kentucky 40506, United States.
² X-ray Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
³ Naprogenix Inc. , Lexington, Kentucky 40506, United States.

PMID: 28825464
DOI: 10.1021/acsami.7b09510

Abstract

Exploiting specific interactions with titania (TiO₂) has been proposed for the separation and recovery of a broad range of biomolecules and natural products, including therapeutic polyphenolic flavonoids which are susceptible to degradation, such as quercetin. Functionalizing mesoporous silica with TiO₂ has many potential advantages over bulk and mesoporous TiO₂ as an adsorbent for natural products, including robust synthetic approaches leading to high surface area, and stable separation platforms. Here, TiO₂-surface-functionalized mesoporous silica nanoparticles (MSNPs) are synthesized and characterized as a function of TiO₂ content (up to 636 mg TiO₂/g). The adsorption isotherms of two polyphenolic flavonoids, quercetin and rutin, were determined (0.05-10 mg/mL in ethanol), and a 100-fold increase in the adsorption capacity was observed relative to functionalized nonporous particles with similar TiO₂ surface coverage. An optimum extent of functionalization (approximately 440 mg TiO₂/g particles) is interpreted from characterization techniques including grazing incidence X-ray scattering (GIXS), high-resolution transmission electron microscopy (HRTEM), and nitrogen adsorption, which examined the interplay between the extent of TiO₂ functionalization and the accessibility of the porous structures. The recovery of flavonoids is demonstrated using ligand displacement in ethanolic citric acid solution (20% w/v), in which greater than 90% recovery can be achieved in a multistep extraction process. The radical scavenging activity (RSA) of the recovered and particle-bound quercetin as measured by a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay demonstrates greater than 80% retention of antioxidant activity by both particle-bound and recovered quercetin. These mesoporous titanosilicate materials can serve as a synthetic platform to isolate, recover, and potentially deliver degradation-sensitive natural products to biological systems.

Keywords: adsorption; flavonoid; functionalization; silica nanoparticles; stability.