Covalent Organic Frameworks with Chirality Enriched by Biomolecules for Efficient Chiral Separation

Article abstract of DOI:10.1002/anie.201810571

The separation of racemic compounds is important in many fields, such as pharmacology and biology. Taking advantage of the intrinsically strong chiral environment and specific interactions featured by biomolecules, here we contribute a general strategy is developed to enrich chirality into covalent organic frameworks (COFs) by covalently immobilizing a series of biomolecules (amino acids, peptides, enzymes) into achiral COFs. Inheriting the strong chirality and specific interactions from the immobilized biomolecules, the afforded biomolecules?COFs serve as versatile and highly efficient chiral stationary phases towards various racemates in both normal and reverse phase of high-performance liquid chromatography (HPLC). The different interactions between enzyme secondary structure and racemates were revealed by surface-enhanced Raman scattering studies, accounting for the observed chiral separation capacity of enzymes?COFs.

Full text of DOI:10.1002/anie.201810571

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
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Accepted Article
Title: Covalent Organic Frameworks with Chirality Enriched by
Biomolecules for Efficient Chiral Separation
Authors: Sainan Zhang, Yunlong Zheng, Hongde An, Briana Aguila,
Cheng-Xiong Yang, Yueyue Dong, Wei Xie, Peng Cheng,
Zhenjie Zhang, Yao Chen, and Shengqian Ma
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201810571
Angew. Chem. 10.1002/ange.201810571
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Angewandte Chemie International Edition
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COMMUNICATION
Covalent Organic Frameworks with Chirality Enriched by
Biomolecules for Efficient Chiral Separation
[
a],[c]
[a],[c]
[a],[c]
[b]
[d]
Sainan Zhang,
Yunlong Zheng,
Hongde An,
Briana Aguila, Cheng-Xiong Yang, Yueyue
[d]
[d]
[d]
* [a],[d]
* [a],[c]
* [b]
Dong, Wei Xie, Peng Cheng, Zhenjie Zhang,
Yao Chen,
Shengqian Ma
Abstract: The separation of racemic compounds has long been of
great significance given its importance in many fields such as
pharmacology and biology. The development of new materials or
strategies for efficient resolution of enantiomers is highly desirable.
Taking advantage of the intrinsically strong chiral environment and
specific interactions featured by biomolecules, here we contribute a
general strategy to enrich chirality into covalent organic frameworks
chiral stationary phases (CSPs) in chromatography if they can
be immobilized on some solid-state materials. Herein, we
contribute a general approach to immobilize biomolecules into a
new class of solid-state materials, covalent organic frameworks
(COFs) and the afforded BiomoleculesCOFs can serve as
versatile and highly efficient CSPs towards various racemates in
both normal phase and reverse phase of high-performance
liquid chromatography.
(COFs) via covalently immobilizing a series of biomolecules
including amino acids, peptides, and enzymes into achiral COFs.
Inheriting the strong chirality and specific interactions from the
immobilized biomolecules, the afforded BiomoleculesCOFs can
serve as versatile and highly efficient chiral stationary phases
towards various racemates in both normal and reverse phase of
high-performance liquid chromatography (HPLC). The different
interactions between enzyme’s secondary structure and racemates
have been unveiled by surface-enhanced Raman scattering studies,
accountable for the observed chiral separation capacity of
enzymesCOFs. This study established a general and efficient
strategy to introduce chirality into COFs thereby promoting the
applications of COFs in chiral separation and related fields.
Emerged as a new class of crystalline solid-state materials,
COFs feature high surface area, low mass density, tunable pore
size, high stability, and facilely tailored functionality,[
12-14]
which
make them hold promise for applications in many fields such as
gas storage,[ photoelectricity,
15]
[16]
catalysis,[17-19] environmental
remediation,[20] drug delivery,[21] and functional devices.[22] The
development of COFs for chiral separation is still in the infancy
stage,[23-25] primarily relying on the construction of chiral COFs
based on chiral monomers. On the basis of our recent success
in immobilizing enzymes into COFs,[26] in this work we present
an alternative strategy to create chirality into COFs via
covalently anchoring a series of biomolecules including amino
acids, peptides, and enzymes onto the channel walls of achiral
COFs to form BiomoleculesCOFs (Scheme 1).[27-29] We
postulate that inheriting the strong chirality and specific
interactions from the anchored biomolecules, the resultant
BiomoleculesCOFs are anticipated to demonstrate high
Chiral resolution is an important tool in the production of
pharmaceutical and biologically active compounds, since the
biological behavior, metabolism, and toxicity of pure
enantiomers are often quite different.[ The separation of
racemic compounds has long been of great significance
especially for pharmaceutical and medicinal applications,[2,3]
which has spurred continuous interest in the exploration of new
materials/approaches for efficient separation of enantiomers.[4-7]
To achieve efficient separation of enantiomers, it is essential the
material possess both strong chiral environment and preferable
binding ability through some specific interactions (e.g. hydrogen
bonding, van der Waals interactions, electrostatic interactions
and electrostatic interactions).[8-10] Biomolecules such as
enzymes that are created by nature,[11] can well discriminate
enantiomers due to their natural conformations composed of
chiral subunits (i.e. amino acids) as well as amphiphilic and
zwitterionic features capable of providing specific interactions.
This makes them appealing for chiral separation particularly as
1]
efficiency for chiral separation; in addition, the protective
environments provided by COFs[
26]
and the strong covalent
bonding between the biomolecules and COF channel walls thus
to prevent the denaturing and leaching of biomolecules make
BiomoleculesCOFs ideal chiral stationary phases in both
normal and reverse phase of HPLC.
To demonstrate the generality of our strategy as well as to
investigate the effect of structural complexity of biomolecules on
the chiral separation performance, enzymes, peptides, and
amino acids were covalently anchored on the channel walls of
COFs to form BiomoleculesCOFs. Lysozyme is
a good
candidate protein for chiral recognition and separation due to its
low cost, high thermal stability, relatively small size (3.0 × 3.0 ×
30]
4
.5 nm), and facile modification.[ To compare with lysozyme,
we also used tripeptide Lys-Val-Phe (similar arrangement with
NH -terminal of lysozyme) and L-lysine (abundance in lysozyme)
2
as controls.
[
a] S. Zhang, Y. Zheng, H. An, Prof. Z. Zhang, Prof. Y. Chen
State Key Laboratory of Medicinal Chemical biology, Nankai
University, Tianjin 300071, China
E-mail: zhangzhenjie@nankai.edu.cn; chenyao@nankai.edu.cn
[
b] B. Aguila, Prof. S. Ma
Department of Chemistry, University of South Florida, 4202 E. Fowler
Avenue, Tampa, Florida 33620, United States
E-mail: sqma@usf.edu
[
c] S. Zhang, Y. Zheng, H. An, Prof. Y. Chen
College of Pharmacy, Nankai University, Tianjin, 300071, China
d] Prof. C.-X. Yang, Y. Dong, Prof. W. Xie, Prof. P. Cheng, Prof. Z.
Zhang
[
Scheme 1. Illumination of covalently immobilizing biomolecules into COFs.
College of Chemistry, Nankai University, Tianjin, 300071, China
A new mesoporous COF, 1, was designed and synthesized
Supporting information and the ORCID identification number(s) for
via a condensation reaction to immobilize biomolecules (Figure
the
author(s)
of
this
article
can
be
found
under:
1a and S1). The powder X-ray diffraction (PXRD) pattern of COF
https://dx.doi.org/10.1002/anie.201xxxxxx.
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Angewandte Chemie International Edition
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COMMUNICATION
1
(
1
agrees with the simulated structure with AA layer packing
Figure 1b). The characteristic FT-IR peaks at 1778 cm-1 and
721 cm-1 can be attributed to the asymmetric and symmetric
vibrations of C=O groups of the imide rings of COF 1. The peak
1352 cm-1 revealed the successful formation of imidized
~
networks (Figure S2).[31] More specific structural information of
COF 1 was confirmed by 13C CP/MAS NMR spectra (Figure S3).
COF 1 showed a broad resonance signal overlapping from
1
27.8 ppm to 141.4 ppm, which corresponds to the phenyl
Scheme 2. Graphic view of tested biomolecules: (a) Lysozyme, (b) tripeptide
Lys-Val-Phe, (c) Lysine; (d) Illumination of the covalent strategy to bond
various biomolecules with COFs.
carbons. The peak at 157.7 ppm was assigned to the carbonyl
carbon of the imide rings. COF 1 possesses 1D hexagonal
channels with a pore size of ~3.6 nm after subtracting van der
Waals radius (measured between two nitrogen atoms along the
diagonal), which is large enough to accommodate biomolecules
such as lysozyme. The N atoms in triazine and O atoms in imide
groups are potential hydrogen bonding acceptors to interact with
In order to efficiently enrich chirality into COFs using
biomolecules, we employed
a covalent coupling strategy
(Scheme 2) to immobilize biomolecules via a coupling reaction
of -NH2 (from the biomolecules) and -COOH (from the COF)
using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and
biomolecules. Moreover, COF
1
not only demonstrated
N-hydroxysuccinimide (NHS). This reaction is widely applied for
immobilization of biomolecules.[
36,37]
We first compared this
extraordinary stability in various organic solvents (Figure S4),
but also exhibited excellent water stability (e.g. pH 6.0 MES
buffer or hot water, Figure S5), which is critical for bio-related
applications. The structural features together with the high
strategy with traditional adsorption methods. Lysozyme,
tripeptide Lys-Val-Phe, and L-lysine (Scheme 2) were loaded by
adsorption in COF 1 to form Biomolecules@COF 1 (‘@’ here
means ‘adsorbed in’) in comparison with covalently bonded
BiomoleculesCOF 1 (‘’ here means ‘covalently bonded with’).
The loading amount of lysozyme with the covalent
immobilization method (Figure 2a, ~22 μmol/g) was almost
double that with the adsorption method (~12 μmol/g). Inversely,
the leakage of lysozyme for the covalent method was far lower
than that for the adsorption method (Figure 2b). In the covalently
loaded systems, we observed nearly no leaching of lysozyme
from LysozymeCOF 1. However, in the adsorption systems,
the leakage of lysozyme came up to ~90% from
Lysozyme@COF 1. Similarly, the loading amounts of peptide
and L-lysine with the covalent method were much higher than
the amount with adsorption method (Figure S8). The leakages of
peptide and L-lysine that were covalently immobilized in COF 1
were as low as 6% and 7%, which were far lower than the
adsorption systems (~90% and ~91% leaching for
Peptide@COF 1 and Lysine@COF 1, respectively) (Figure S8).
These results reveal that there are strong binding interactions
between biomolecules and COF 1 in BiomoleculeCOF 1
systems. In contrast, in Biomolecule@COF 1 systems, the
absence of a strong interaction between the host matrix and
guest molecules leads to low loading efficiency and high leakage
of biomolecules. We also compared the performance of COF 1
with other porous materials (e.g. MOFs and MCM-41).[38-41]
Overall, covalent immobilization of biomolecules using COF 1 is
superior to all the other tested porous materials (Figure 2).
water-stability make COF
accommodate biomolecules.
1
a
promising platform to
Figure 1. (a) Graphic view of COF 1. (b) PXRD patterns of COF 1,
BiomoleculeCOF 1 and the simulated pattern of COF 1.
The condensation reaction of an anhydride and a primary
amine possesses a two-step mechanism (Scheme S1).[32] First,
the anhydride can react with the primary amine to form amic
acid intermediates via a spontaneous ring opening process.
Second, while the synthesis temperature rises to >150°C, this
amic acid group can dehydrate to form an imide group.
Carboxylate groups (-COOH) can exist as residuals during this
condensation reaction. To determine the amount of accessible -
COOH residues, analysis methods including Toluidine blue O
(
TBO) dye assay and acid-base titration method were
employed.[
33-35]
The results revealed synthesis temperature and
reactants’ ratio played critical roles to the amount of accessible -
COOH in COF 1 (Figure S6). Finally, we employed COF 1 that
was synthesized at 200 °C using reactants of stoichiometric
mole ratio as the major focus of further study because it
exhibited the best crystallinity (Figure S7) as well as a good
amount of –COOH residues (5.1% and 5.7% determined by
TBO assay and acid-base titration, respectively). The accessible
–
COOH is potential to react with -NH
which make COF perfect platform to immobilize
biomolecules via covalent bonding.
2
residues in biomolecules,
1
a
Figure 2. Loading profiles (a) and releasing profiles (b) of lysozyme into COF
1
and other tested porous supports. LysozymeCOF
lysozyme@COF 1 (red), lysozyme@PCN-600 (dark yellow), lysozyme@MCM-
1 (blue).
1
(black),
4
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COMMUNICATION
We
conducted
various
characterizations
on
BiomoleculesCOF 1 systems, including scanning electron
microscopy (SEM), PXRD, confocal laser scanning microscopy
1
3
(
CLSM), FT-IR, C CP/MAS NMR and gas sorption. SEM
images
(Figure
S9)
displayed
that
particles
of
BiomoleculesCOF
1
retained the same filamentous
morphology as pristine COF 1. In addition, PXRD patterns
revealed that these BiomoleculeCOF 1 complexes possessed
the same structure as parent COF 1 (Figure 1), which indicated
that COF 1 is a robust platform for post-modification with
biomolecules. To confirm the covalent reaction occurred
between the biomolecules and COF 1, two florescence marks,
fluorescein amine and 5-carboxylfluorescein, were used to react
with COF 1 and lysozyme, respectively, via the same reaction
procedure as the formation of BiomoleculeCOF 1. After the
reactions, the samples were thoroughly washed to remove the
unreacted florescence marks, and then scanned by CLSM. We
observed that florescence marks were uniformly dispersed in
both the modified lysozyme and COF 1 samples (Figure S10),
Figure 3. CLSM images of fluorescein-labelled lysozyme covalently
immobilized in COF 1: (a) optical image, (b) fluorescent and (c) overlap of
optical and fluorescent images; (d) N
LysozymeCOF 1 (red), PeptideCOF 1 (dark yellow) and LysineCOF 1
blue).
2
sorption isotherms of COF 1 (black),
(
The afforded LysozymeCOF
1 maintained > 90% of
2
which proved the coupling reaction of -NH and -COOH indeed
enzymatic activity (Figure S13, Table S1), which validated the
designed immobilization strategy presents no influence on
biomolecules’ activity. In addition, Circular Dichroism (CD)
spectroscopic analysis indicated no significant structural change
of lysozyme after covalent immobilization into COF 1 (Figure
S14, Table S2).[43] We further tested the stability and recyclability
of LysozymeCOF 1 under various treatments including heating,
sonication, and various solvent treatments (Figure S15, S16).
The results unveiled excellent stability of LysozymeCOF 1 (>85%
of activity) after all the treatments, while the free lysozymes
nearly lost all the activities after the same treatments. In the
reusability test, LysozymeCOF 1 retained >90% of activity after
five catalytic cycles of chitosan hydrolysis (Figure S17). In
contrast, Lysozyme@COF 1 prepared via the adsorption method
completely lost its activity after five catalytic cycles because of
the severe leaching of lysozyme (Figure S17). The excellent
loading and non-leaching performance, together with COF 1’s
high porosity and extraordinary stability, make them good
candidates for the preparation of highly efficient and durable
CSPs.
happened. Fluorescein amine labelled lysozyme was also
immobilized into COF 1 to determine the distribution of lysozyme
in COF 1, and CLSM results indicated that lysozyme is not just
attached on the surface of COF 1, but uniformly distributed in
COF 1 (Figure 3a-c). Due to the existence of amide groups in
lysozyme and peptide, we selected AminofluoresceinCOF 1
and LysineCOF 1 as representatives to study the formation of
covalent bonds (i.e. amide) between the framework and
biomolecules. The characteristic FT-IR peaks at ~1240 and
3400 cm-1 were observed, which can be ascribed to C-N and
~
N-H bond stretching vibrations of amide groups formed by
(Figure S11).[
42] 13
reaction of -COOH and -NH
2
C CP/MAS NMR
spectrum of AminofluoresceinCOF 1 and LysineCOF 1 both
showed the characteristic carbonyl carbon peaks of amide at
~170 ppm (Figure S3). All these results verified the coupling
reactions indeed occurred between -NH and -COOH of COF 1.
2
To further confirm the biomolecules are located inside the
channels of COF 1, we compared COF 1’s porosity before and
after covalent immobilization. COF 1 possesses a BET and
2
2
Langmuir surface areas of 714 m /g and 1100 m /g, respectively
(
(
Figure 3d and S12). The nonlocal density functional theory
NLDFT) pore size distribution analysis indicates that COF 1 has
a pore size distribution centered at 3.7 nm, which is consistent
with the simulated structure with hexagonal channels (3.6 nm).
After immobilization of biomolecules, the BET and Langmuir
2
surface areas of LysozymeCOF 1 decreased to 103 m /g and
2
2
39 m /g, respectively. Based on NLDFT pore size distribution
analysis, LysozymeCOF 1 has a pore size centered at ~1.5 nm,
which is much smaller than COF 1 due to the blockage of
channels by lysozyme. For PeptideCOF 1 and LysineCOF 1,
we also observed similar trend as LysozymeCOF 1 that the
surface area and pore size decreased after the immobilization of
biomolecules. All these results revealed the efficient covalent
immobilization of biomolecules into the channels of COF 1.
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COMMUNICATION
Figure 4. (a) Illumination of LysozymeCOF
1 based CSPs for chiral
with L-tryptophan exhibited the absence of the amide I band at
1
separation; Enantiomer separate chromatograms of (b) DL-threonine, (c) DL-
leucine, (d) DL-tryptophan, (e) Ofloxacin, (f) Metoprolol, and (g)
Chlorpheniramine.
651 cm-1 , which is assigned to the random coil structure of
lysozyme (Figure S29a). Moreover, the amide I band at 1623
cm-1 assigned to α-helical structure and amide III band at 1241
cm-1 assigned to random coil structure of lysozyme were blue
The afforded BiomoleculeCOF 1 materials were anticipated
to inherit the intrinsic chirality from biomolecules, which will
-1
shifted to 1596 and 1231 cm , respectively. By contrast, after
mixing lysozyme with D-tryptophan, we only observed the
absence of amide I band at 1651 cm-1 assigned to the random
coil structure, without observation of any band shift (Figure
S29a). These results indicated that the interaction between the
secondary structure of lysozyme and L-tryptophan is more
profound than that of D-tryptophan, which can interpret the
HPLC results that the L-tryptophan was eluted later than the D-
enantiomer. In contrast, after mixing with tryptophan, peptide’s
Raman spectra presented no change (Figure S29b), implying no
interaction between peptide and the racemates possibly due to
the lack of secondary structure. These results highlighted that
the resolution abilities of biomolecules are related to their
secondary or higher order structures.
facilitate
chiral
separation.
Thereby,
the
formed
BiomoleculeCOF 1 were employed as biomolecule-based
CSPs for chiral separation (Figure 4). They were examined by
HPLC towards various racemates including DL-tryptophan, DL-
leucine, DL-threonine, DL-lysine, DL-aspartic acid, ofloxacin, (+/-
)
-propranolol hydrochloride, metoprolol tartrate, alanyl glutamine,
chlorpheniramine, and benzoin (Figure S18). The separation
factors (α) and resolution (Rs) results demonstrate
LysozymeCOF 1 exhibits high chiral separation efficiency for
all the tested racemates (Figure 4, S19-S21 and Table S3). The
racemates' elution order was confirmed through testing pure
enantiomer (Figure S21). It is notable that the dimensions of all
the tested racemates are smaller than the pore size of
LysozymeCOF
1 (15 Å), implying the chiral separation
The interaction between lysozyme and enantiomers mainly
manifests as hydrophobic and electrostatic interactions.[47] Due
to the amphipathicity of the protein, and the excellent solvent
stability of COF 1, LysozymeCOF 1 can act as versatile CSPs
for both reverse and normal phase HPLC tests (Figure S19 and
S20) with high efficiency, which results in its ability to separate a
large range of chiral compounds. In addition, lysozyme is
covalently immobilized and protected by COF 1, which leads to
good reusability and extended service life (Table S5).
LysozymeCOF 1 CSP demonstrated high efficiency for >120
separation runs during the tested period (2 months) (Figure S30).
Such excellent performance of LysozymeCOF 1 entitled its
great potential to serve as a versatile and durable protein-based
CSP.
occurred inside the pores of LysozymeCOF 1. Moreover, we
observed broader and overlapping peaks, and tailing in the
HPLC chromatograms of Lysozyme@COF 1 (Figure S22),
which indicated its lower separation efficiency compared to
LysozymeCOF 1. This difference is probably due to a lower
loading amount and severe leaching of lysozyme in
Lysozyme@COF 1, implying the correlation between loading
amount of lysozyme and separation efficiency of the formed
CSPs. As for Lysozyme@MCM-41, even though MCM-41 can
load a small amount of lysozyme, the protein was completely
leached out even before the baseline was stable in the HPLC
test, and thus showed no separation effect (Figure S23). In
addition, blank COF 1 and MCM-41 exhibited no separation
effect on any of the tested racemates (Table S4). These results
indicate the strategy to covalently immobilize biomolecules into
In summary, we demonstrated for the first time the successful
anchoring of a series of biomolecules (lysozyme, tripeptide and
porous
matrix
surpasses
the
traditional
adsorption
L-lysine) into
a newly synthesized polyimide achiral COF
immobilization strategy toward chiral separation performance.
The influences of different biomolecules on the chiral
(
BiomoleculeCOF 1) through covalent immobilization to enrich
chirality of COF. Inheriting the strong chirality and specific
interactions from the anchored biomolecules, the afforded
LysozymeCOF 1 exhibited versatile and high chiral separation
efficiency for various racemates in both normal phase and
reverse phase HPLC, and demonstrated good reusability and
reproducibility due to the protection of COFs. Surface-enhanced
Raman scattering studies unveiled that the different interactions
between lysozyme’s secondary structure and racemates
account for the observed chiral separation capacity. Furthermore,
separation performance of BiomoleculesCOF
studied. The separation performance of PeptideCOF 1 and
LysineCOF 1 were tested under the same conditions as the
1 was also
LysozymeCOF
1 column (Figure S24 and S28). The
PeptideCOF 1 only exhibited separation effect towards some
of the tested racemates with low separation efficiency (Figure
S24, S25). This is probably due to the structural simplicity of the
peptide (NH -Lys-Val-Phe-COOH), which is supported by CD
2
spectroscopic analysis: the structure of the selected peptide was
mainly sheet, turn, and unordered structures (37%, 21.6%, and
by
evaluating
the
chiral
separation
capacities
of
BiomoleculeCOF 1, we discovered that the resolution abilities
are likely related to the structural complexity, number of chiral
centers, and amphipathicity of biomolecules. This study will
promote the wide applications of COFs in chiral separation, and
provide valuable guidance on design of highly efficient and
durable biomolecule-based CSPs.
2
9.4%, respectively, Figure S26, S27). LysineCOF 1 failed to
separate any of the tested racemates (Figure S28), which
highlighted the importance of higher order structure of
biomolecules (e.g. lysozyme) in chiral recognition and resolution.
It is likely that the resolution abilities of BiomoleculeCOFs are
related to the secondary or higher order structures and the
number of chiral centers.[11,44] Therefore, surface-enhanced
Raman scattering (SERS) spectra were collected to probe the
specific interactions between racemic substrates and lysozyme
Acknowledgements
The authors acknowledge the Young 1000-Plan program and
financial support from the National Natural Science Foundation
of China (21601093) and Tianjin Natural Science Foundation of
Tryptophan was selected as a representative substrate).[45,46]
(
Compared with lysozyme, Raman spectra of lysozyme mixed
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COMMUNICATION
China (17JCZDJC37200). Financial support from NSF (DMR-
[24] X. Han, J. Huang, C. Yuan, Y. Liu, Y. Cui, J. Am. Chem. Soc. 2018, 140,
8
92-895.
25] H. L. Qian, C. X. Yang, W. L. Wang, C. Yang, X. P. Yan, J. Chromatogr. A
018, 1542, 1-18.
26] Q. Sun, C. W. Fu, B. Aguila, J. Perman, S. Wang, H. Y. Huang, F. S. Xiao,
1
352065) is also acknowledged.
Keywords: Covalent organic framework
Biomolecules • Chiral stationary phases • Chiral separation
[
•
Chirality
•
2
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This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201810571
COMMUNICATION
COMMUNICATION
Text for Table of Contents
Sainan Zhang, Yunlong Zheng, Hongde
An, Briana Aguila, Cheng-Xiong Yang,
Yueyue Dong, Wei Xie, Peng Cheng,
*
*
Zhenjie Zhang, Yao Chen, Shengqian
Ma*
Covalent Organic Frameworks with
Chirality Enriched by Biomolecules
for Efficient Chiral Separation
A general and efficient strategy has been developed to introduce chirality into
covalent organic frameworks (COFs) via covalently immobilizing biomolecules into
achiral COFs and the afforded BiomoleculesCOFs can serve as chiral stationary
phases for efficient chiral separation towards a broad range of racemates.
This article is protected by copyright. All rights reserved.