Elsevier

Journal of Chromatography A

Volume 1600, 30 August 2019, Pages 209-218
Journal of Chromatography A

Graphene quantum dots functionalized β-cyclodextrin and cellulose chiral stationary phases with enhanced enantioseparation performance

https://doi.org/10.1016/j.chroma.2019.04.053Get rights and content

Highlights

  • GQDs functionalized β-CD and cellulose chiral stationary phases were prepared.

  • The enhancement performance of GQDs for chiral separation was stated.

  • GQDs had unique advantages as chiral enhancement material.

  • Molecular modeling was applied to investigate the enhancement mechanism.

Abstract

Graphene quantum dots (GQD) functionalized β-cyclodextrin (β-CD) and cellulose silica composites were first prepared and applied in HPLC as chiral stationary phases (CSP) to investigate the effect of GQDs on chiral separation. Through comparing the enantioseparation performance of GQDs functionalized β-CD or cellulose CSPs and unmodified β-CD or cellulose CSPs, we found GQDs enhanced the enantioseparation performance of nature β-CD, β-CD-3,5-dimethylphenylcarbamate derivative and cellulose-3,5-dimethylphenylcarbamate derivative. Molecular modeling was applied to understand and theoretically study the enhancement mechanism of GQDs for enantioseparation. According to molecular simulation results, GQDs provide extra interactions such as hydrophobic, hydrogen bond and π-π interaction when chiral selector interacts with enantiomers, which enhances the chiral recognition ability indirectly. The molecular simulation results showed a good agreement with the experimental results. Our work reveals the enhancement performance of GQDs for chiral separation, it can be expected that GQDs-based chiral composites and chiral GQDs have great prospect in chiral separation and other research fields such as asymmetric synthesis, chiral catalysis, chiral recognition and drug delivery.

Introduction

Chirality is an essential attribute of nature. The separation of enantiomers of chiral compounds continues to be of great interest due to their prevalence in the pharmaceutical industry, agrochemicals and food additives [1]. The task of enantioseparation is extremely challenging, because enantiomers are identical in most regards: they have the same densities and solubilities, boiling and melting points, electronic and vibrational frequencies, reactivities and refractivities, etc [2]. Chiral separation materials are the core to achieve enantioseparation. Cyclodextrins (CD) and their derivatives as well as cellulose derivatives are the most commonly used chiral selectors at present [[3], [4], [5], [6]]. With the rapid development of pharmaceutical industry and more and more attention to life safety, higher demands will be put forward for chiral separation. It can be expected that developing novel and effective chiral separation materials has great significance.

Carbon nanomaterials (CNM) with good physical and chemical characteristics have been widely used in various disciplines [[7], [8], [9], [10], [11], [12]]. With the development of CNMs in separation science, various CNMs have been applied to enantioseparation in recent years. Chiral single-walled carbon nanotubes and multi-walled carbon nanotubes have been directly applied for the enantioseparation of pharmaceuticals and biologicals by using them as stationary or pseudostationary phases in chromatographic separation techniques including high performance liquid chromatography (HPLC), capillary electrochromatography (CEC) and gas chromatography (GC) [13]. Collectively, functionalized carbon nanotubes have been indirectly applied in separation science by enhancing the enantioseparation of different chiral selectors [13,14]. Chiral selectors functionalized graphene oxide (GO) composites have been applied in CEC enantioseparation [[15], [16], [17], [18], [19]], however, their application in HPLC enantioseparation was relatively scarce [20,21]. In CEC, Qiu and coworkers prepared a series of chiral selectors functionalized GO nanocomposites [[15], [16], [17]] as chiral stationary phases (CSP) for chip-based open-tubular CEC. Li, Ji and coworkers prepared three types of GO-functionalized chiral affinity capillary silica monoliths [18]. Du and coworkers established a GO-modification CEC system for enantioseparation with methyl-β-CD as chiral mobile phase additives [19]. Research results demonstrated that GO possessed large surface area and abundant functional groups which were necessary for chiral selectors immobilization and could provide various interactions for enantioseparation with improved performance. In HPLC, Li and coworkers prepared cellulose derivative coated rGO-bonded silica CSP [21]. Due to the existence of rGO on the CSP, this CSP obtained stronger interaction with the analytes leading to better enantioseparation performance compared with cellulose derivative modified silica CSP. According to previous research, we may find that CNMs have great prospect in chiral separation.

Graphene quantum dots (GQD), as a new type of CNM, have been widely used in bioimaging and fluorescent sensing because of good water solubility, biocompatibility and unique fluorescence stability [22]. Recently, great efforts have been devoted to explore potential applications of GQDs in separation science, GQDs are gradually applied in GC [23], CEC [24] and HPLC [[25], [26], [27], [28], [29]] showing satisfactory separation performance. As chromatographic material, GQDs have some unique characteristics such as small dimension, high thermostability and good dispersibility, which make them easier to be immobilized on the silica support. Moreover, GQDs possess highly delocalized conjugate system of π-electron and abundant oxygen-containing groups, which enables them to provide various interactions including π-π, hydrophobic, hydrogen-bonding and hydrophilic interactions and thus to be used as multifunctional separation material. It is reasonable to believe that GQDs have great prospect in separation science. Though the separation performance of GQDs for all kinds of achiral compounds has been investigated systematically, their application in chiral separation has not been explored. We wonder if GQDs, as good chromatographic material and biocompatible nanomaterial, could be the chiral enhancement material for nature chiral selectors.

Hence, GQDs functionalized β-CD and cellulose silica composites were first prepared and applied in HPLC as CSPs to investigate the effect of GQDs on chiral separation. Ten chiral compounds were chosen as probes to evaluate the enantioseparation performance of the prepared CSPs. β-CD CSP and cellulose CSP were prepared and used as references. Generally, 3,5-dimethylphenyl isocyanate is always used as hydroxyls derivatization reagent of β-CD and cellulose to enhance their enantioseparation ability [[3], [4], [5],30,31]. Especially for cellulose CSPs, the available cellulose CSPs are cellulose derivatives-based CSPs since the poor solubility of cellulose [32,33]. To investigate the difference between GQDs and 3,5-dimethylphenyl isocyanate in abilities to enhance chiral separation performance, the enantioseparation performance of GQDs functionalized β-CD CSP was also compared with that of 3,5-dimethylphenylcarbamate derived β-CD CSP. In addition, β-CD-3,5-dimethylphenylcarbamate CSP was also functionalized by GQDs to further explore the chiral enhancement effect of GQDs to β-CD-3,5-dimethylphenylcarbamate derivative.

Section snippets

Materials and instruments

Silica gel (70 Å, 800 Å, 5 μm in diameter) was supplied by Fuji Silysia Chemical Ltd (Japan). 3-aminopropyltriethoxysilane (APTES), 3-isocyanatopropyltriethoxysilane, 3,5-dimethylphenyl isocyanate, β-CD and microcrystalline cellulose were obtained from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China). 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were purchased from Meryer Chemical Technology Co. Ltd (Shanghai, China). All chiral chemicals

Characterization

Fig. 2 showed the FTIR spectra of Si-CD, Si-GQD-CD, Si-CDD, Si-GQD-CDD, Si-Cellulose and Si-GQD-Cellulose. Compared to Si-CD, the enhanced peak at 1731 cm−1 (Cdouble bondO in Osingle bondCdouble bondO) of Si-GQD-CD indicated the existence of GQDs since GQDs had COOH. In Si-CDD and Si-GQD-CDD, the enhanced peaks at 1731 cm−1, 1627 cm−1 and 1561/1442 cm−1 which was assigned to the characteristic absorption peak of Osingle bondCdouble bondO, Nsingle bondH and benzene ring demonstrated that β-CDs were derived with 3,5-dimethylphenyl isocyanate successfully.

Conclusions

To investigate the effect of GQDs on chiral separation, GQDs functionalized β-CD and cellulose silica composites were first prepared and applied in HPLC enantioseparation. Through comparing the enantioseparation performance of GQDs functionalized β-CD or cellulose CSPs and unmodified β-CD or cellulose CSPs, it was found GQDs could enhance the enantioseparation performance of nature β-CD, β-CD-3,5-dimethylphenylcarbamate derivative and cellulose-3,5-dimethylphenylcarbamate derivative. GQDs had

Conflicts of interest

There are no conflicts to declare.

Acknowledgement

This work was supported by the National Natural Science Foundation of China (Nos. 21405162, 21405161, 21675163 and 21702210).

References (41)

  • X. Zhang et al.

    Nanocellulose 3, 5-dimethylphenylcarbamate derivative coated chiral stationary phase: preparation and enantioseparation performance

    Chirality

    (2016)
  • B. Chankvetadze

    Recent developments on polysaccharide-based chiral stationary phases for liquid-phase separation of enantiomers

    J. Chromatogr. A

    (2012)
  • X. Li et al.

    Enantioseparation of single layer native cyclodextrin chiral stationary phases: effect of cyclodextrin orientation and a modeling study

    Anal. Chim. Acta

    (2017)
  • T.J. Ward et al.

    Chiral separations: a review of current topics and trends

    Anal. Chem.

    (2012)
  • I.D. Rukhlenko et al.

    Completely chiral optical force for enantioseparation

    Sci. Rep.

    (2016)
  • T. Ikai et al.

    Enantioseparation by HPLC using phenylcarbonate, benzoylformate, p-toluenesulfonylcarbamate, and benzoylcarbamates of cellulose and amylose as chiral stationary phases

    Chirality

    (2005)
  • Y. Okamoto et al.

    Chiral HPLC for efficient resolution of enantiomers

    Chem. Soc. Rev.

    (2008)
  • T. Ikai et al.

    Structure control of polysaccharide derivatives for efficient separation of enantiomers by chromatography

    Chem. Rev.

    (2009)
  • H. Zhang et al.

    Discriminative detection of glutathione in cell lysates based on oxidase-like activity of magnetic nanoporous graphene

    Anal. Chem.

    (2019)
  • L. Song, H. Zhang, T. Cai, J. Chen, Z. Li, M. Guan, H. Qiu, Porous graphene decorated silica as a new stationary phase...
  • Cited by (0)

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