Enantioselective Separation Using Chiral Amino Acid Functionalized Polyfluorene Coated on Mesoporous Anodic Aluminum Oxide Membranes

Abstract

Homochiral mesoporous anodic aluminum oxide membranes (AAO) were prepared by coating protected chiral D/L aspartic acid appended polyfluorene in the pores. These chiral AAO membranes successfully demonstrated enantioselective recognition and separation of a range of amino acids from their aqueous racemic mixture by simple filtration. Enantioselective separation was achieved by selective adsorption of one enantiomer from the aqueous racemic mixture into the chiral pores of the AAO membrane leaving the filtrate enriched with the other enantiomer. Extraction and quantification of the adsorbed amino acid (glutamic acid) demonstrated that 1 mg of homochiral polyfluorene could effectively extract about 3.5 mg of glutamic acid with 95% enantiomeric excess in 24 h. This is one of the highest enantiomeric excesses (ee %) and yields reported so far in the literature for a racemic mixture of glutamic acid. The pore size of the AAO membrane influenced the efficiency of separation with a reduction in pore size from 200 to 20 nm leading to reduced ee % (∼95% to ∼28%). These results raise the possibility for a facile method to carry out enantioselective separation.

Recent Progress of Fabrication, Characterization, and Applications of Anodic Aluminum Oxide (AAO) Membrane: A Review

“…One enantiomer was absorbed within the chiral pores, and the other enantiomer was left in the filtrate. This study revealed that the modulation of polymer-coated membrane and pore size can effectively enhance the separation process [108]. Various other applications of AAO membranes for filtration purposes have been reported in the literature and are also given in Table 4 AAO based 3D microchannels 50 Microchannels for molecular separation [109] Two nano-porous AAO membranes sandwiched in between PDMS layers 30 80 Two AAO membranes sandwiched between PDMS for Exosomes Isolation [106] AAO membrane in micro hydraulic mechanical system 50 Vibro-active nano filter for filtration, separation, and transportation of particles, using standing surface acoustic waves (SSAW) [110] Optical gas sensing package covered with AAO membrane 40 Filtration interface to let air and other gases pass and prevent contaminations in forms of particles for an optical gas sensor [111] AAO tubular membrane 20 Potential application for hemodialysis [112] AAO membrane and polydimethylsiloxane (PDMS) microwells with through holes 25 Microwell-assisted filtration of algal solution [113] (Continued)…”

“…Two-layered AAO membrane structures have been used for effective dialysis and to sieve exosomes, potential biomarkers for the early detection of cancerous cells [106]. Functionalized AAO membranes for purification of contaminated water and enantioselective separation have also been reported in the literature [107,108]. Figs.…”

Coordination-Assistant Chiral Agent Anchoring on Amphiphilic Graphitic Phase Carbon Nitride Membrane for Multiple Molecular Separation

“…Amino acids, as the basic components of proteins, play a vital role in the life activities of organisms, while amino acids with different chiralities have completely different physiological effects. − Therefore, it is of great significance for the separation of chiral amino acids and their derivatives. , In our work, enantiopure DPE (1 S ,2 S -(−)-1,2-diphenyl-1,2-ethanediamine) as a chiral spacer is introduced into the GCN interlayers through the coordination anchoring of copper ions (Cu 2+ ); hence, a chiral environment is created in the interlayer space to allow enantioselective permeation from racemate molecules. Herein, we used a GCN-Cu-DPE membrane 900 nm in thickness on a PES substrate to conduct isobaric enantioselective permeation tests for various chiral amino acid enantiomers with molecular weights ranging from 89 to 204 for 12 h (Figures S22–S25, Tables S5 and S6).…”

Advances in Micro/Nanoporous Membranes for Biomedical Engineering

“…TH membrane materials are mainly classified as inorganic, organic, and composite materials. [ 35 ] Inorganic materials mainly include anodic aluminum oxide (AAO) [ 36–41 ] and silicon‐based materials (Silicon nitride, SiN, and SiO 2 , for example). [ 42–47 ] The pore sizes of these inorganic membranes are typically at the nanoscale, ranging from a few nanometers to several hundred nanometers, and involve biochemical sensing applications.…”