Novel Smart Polymer-Brush-Modified Magnetic Graphene Oxide for Highly Efficient Chiral Recognition and Enantioseparation of Tryptophan Enantiomers

Abstract

Multifunctional graphene oxide nanocomposites simultaneously possessing high enantioselectivity, excellent thermosensitivity, and magnetism demonstrate great application potentials in direct enantioseparation. We herein report one novel smart graphene oxide nanocomposite (MGO@PNG-CD) with high enantioselectivity, excellent thermosensitivity, and magnetism for highly efficient chiral identification and enantioseparation of tryptophan enantiomers. The MGO@PNG-CD is composed of graphene oxide nanosheets with immobilized superparamagnetic Fe 3 O 4 nanoparticles and grafted PNG-CD smart polymer brushes. The PNG-CD is made up of poly(N-isopropylacrylamide-co-glycidyl methacrylate) (PNG) chains with numerous appended β-cyclodextrin (β-CD) units, which play a significant role in effective chiral discrimination and resolution of DL-tryptophan (DL-Trp). The β-CD units serve as chiral selectors capable of selectively recognizing and binding L-tryptophan (L-Trp) into their cavities to form stable host−guest inclusion complexes of β-CD/L-Trp. The PNIPAM chains in PNG act as a microenvironmental adjustor for the inclusion constants of β-CD/L-Trp complexes. The resulted MGO@PNG-CD demonstrates high thermosensitive enantioselectivity toward L-Trp over D-Trp based on the chiral discrimination ability of β-CD toward L-Trp and the thermosensitive volume phase transition of PNIPAM chains. Operating temperature and initial concentrations of DL-Trp are two significant factors affecting the separation efficiency of DL-Trp enantiomers. Moreover, the MGO@PNG-CD also displays satisfactory recycling and convenient magnetic separability from enantiomeric solution. Such a multifunctional graphene oxide nanocomposite developed in this study can serve as a high-performance nanoselector for highly efficient chiral recognition and enantioseparation of various chiral compounds.

Thermosensitive Microgels-Decorated Magnetic Graphene Oxides for Specific Recognition and Adsorption of Pb(II) from Aqueous Solution

“…Moreover, the characteristic peaks at 592 cm –1 for the Fe–O stretching vibration, the asymmetric stretching vibrations of −SO 3 – groups at 1213 cm –1 , and the C=O asymmetric stretching vibrations of COO – in PSSMA at 1407 and 1581 cm –1 are also observed, indicating a successful anchoring of Fe 3 O 4 NPs and PSSMA molecules onto the GO. 47−50 After immobilizing PNB onto the MGO, the typical double peaks at 1363 and 1392 cm –1 for isopropyl group and the characteristic peak of C=O stretching vibrations at 1648 cm –1 from PNIPAM are all found in the FT-IR spectra of MGO@PNB. 51 Meanwhile, the peaks of benzo-18-crown-6, including a strong peak at 1521 cm –1 (shoulder peak) for C=C skeletal stretching vibration in the phenyl ring, a peak at 1230 cm –1 for C–O asymmetric stretching vibration in Ar–O–R groups, 51 and a peak at 1128 cm –1 for C–O symmetric stretching vibration in R–O–R groups, are also observed in the FT-IR spectra of MGO@PNB, indicating the successful fabrication of MGO@PNB.…”

“…First, MGO are prepared by a versatile one-step solvothermal method (Figure 2a). 47−50 Then, PNB are synthesized by a simple precipitation copolymerization method using N -isopropylacrylamide (NIPAM) and acrylamide-modified benzo-18-crown-6 (B18C6Am) as the functional monomers (Figure 2b). 51 The PNB are immobilized onto the MGO via self-polymerization of bio-adhesive dopamine (DA) at a weak alkaline condition (pH 8.5, Figure 2c), finally causing the formation of MGO@PNB.…”

Chiral Graphene Hybrid Materials: Structures, Properties, and Chiral Applications

“…To enhance the amount of cyclodextrins attached on GO sheets and simultaneously to prepare smart and pH‐sensitive chiral hybrids, Cheng and co‐workers created a distinctive route for grafting cyclodextrin units on GO, as presented in Figure . [ 105 ] The produced chiral hybrids were composed of GO, Fe 3 O 4 nanoparticles, poly(NIPAM‐ co ‐GMA) and β ‐CD. The preparation of the target chiral hybrids can be divided into four major steps: 1) deposition of Fe 3 O 4 nanoparticles on GO to fabricate magnetic GO (MGO); 2) grafting active sites for subsequently initiating free radical polymerization on MGO, thereby forming MGO@PDA‐Br; 3) surface‐initiating atom transfer radical polymerization (ATRP) of NIPAM and GMA monomers to generate MGO@PNG (poly(NIPAM‐ co ‐GMA)); 4) grafting β ‐CD units along the copolymer chains via epoxide ring‐opening reaction to finally form the chiral hybrid, MGO@PNG‐CD.…”

Enantiomeric Recognition and Separation by Chiral Nanoparticles

“…Finally, the surfaces of rGO@SiO 2 were physically coated with cellulose tris-(3,5-dimethylphenylcarbamate) to prepare the CSP. Most recently, a smart multifunctional graphene oxide nanocomposite was prepared which showed exceptionally good selectivity, thermosensitivity and magnetic separability for the identification and enantiomeric separation of Trp enantiomers [111]. The synthesized nanocomposite was composed of GO nanosheets, immobilized superparamagnetic Fe 3 O 4 nanoparticles, poly( N -isopropylacrylamide-co-glycidyl methacrylate) (PNG) chains and β-CD which was fabricated through a combination of surface-initiated atom transfer radical polymerization (SI-ATRP) and a ring-opening reaction, as shown in Figure 10.…”

“…(A) As the temperature is below the LCST of PNIPAM chains (T1), the β-CD units in PNG-CD can selectively recognize and accommodate l -enantiomers to form stable host-guest inclusion complexes, while as the temperature is above the LCST of PNIPAM chains (T2), the loaded l -enantiomers can desorb from the β-CD cavities automatically because of the reduction in the inclusion constants of β-CD/ l -enantiomers complexes; (B) The MGO@PNG-CD is added in the AAs enantiomeric solution at T1 and the PNIPAM chains are swollen, and then l -enantiomers are recognized by β-CD; (C) Through an external magnetic field l -enantiomers are loaded on the MGO@PNG-CD, and d -enantiomers are remained in the enantiomeric solution for subsequent separation; (D) while the operating temperature is above the LCST of PNIPAM (T2), the PNIPAM chains occur to collapse, and the loaded l -enantiomers are released, and the MGO@PNG-CD is recycled; (E and F) the regenerated MGO@PNG-CD is recovered using a magnet and reused. The figure and the caption have been adapted with permission from [111], Copyright © 2018 American Chemical Society.…”