Enantioselective recognition of a fluorescence-labeled phenylalanine by self-assembled chiral nanostructures

Article abstract of DOI:10.1039/c5cc00261c

Self-assembled chiral nanostructures such as nanofibers and nanotubes formed by a pyridylpyrazole-conjugated l-glutamide showed an enantioselective recognition toward a fluorescence labeled chiral amino acid.

Full text of DOI:10.1039/c5cc00261c

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DOI: 10.1039/C5CC00261C
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Enantioselective recognition of a fluorescence-labeled phenylalanine by
self-assembled chiral nanostructures
Li Zhanga, Qingxian Jina,b, Kai Lva, Long Qina and Minghua Liua,c*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
Self-assembled chiral nanostructures such as nanofibers,
nanotubes formed by pyridylpyrazole-conjugated L-
50
The synthesis, gelation properties of the gelator molecule,
PPLG, was reported previously.22 The structure of DNSP (Dansyl
linked phenylalanine, abbreviated as DNSP, the reaction was
shown in the Supporting Information), PPLG and PPLGOEt were
shown in Figure 1.
a
glutamide showed an enantioselective recognition to
fluorescence labeled chiral amino acid.
a
10
Chiral recognition is a fundamental phenomenon widely
observed in biological systems because these systems are not
isotropic and two enantiomers of a chiral active substance may
have dramatically different effects. Apart from molecular
55
15 interactions between the enantiomers and a chiral biological
system, the chiral recognition in organism strongly relies on the
encapsulation the chiral substance into the hydrophobic receptor
pockets in proteins.1ꢀ3 Thus the chiral selfꢀassembled
supramolecular host formed by various nonꢀcovalent interactions
20 provides an idea model for mimicking natural biopolymer to
recognize the chiral guest. These chiral architectures can present
a cavity with a high degree of chiral recognition that can
selectively host the analytes to be encapsulated and can amplify
the sensing ability through synchronized changes of the building
25 block.4ꢀ9 Therefore, instead of the chiral recognition between
molecules10ꢀ12, the interaction between the chiral architecture and
the chiral molecules becoming an important issue.13ꢀ21 It is
expected how supramolecular assembling can be used to show
enhanced enantioselective recognition. Here, we report a new
30 chiral recognition system using the chiral nanostructure as the
host, which showed enantioselective recognition to the chiral
amino acids.
Figure 1. (A) The molecular structure of PPLG, PPLGOEt and DNSP;
the fluorescence of (B) enantiomer of DNSP solution in waterꢀethanol
(9:1); (C) dispersion of DNSP enantiomer with PPLG assemblies in
60 waterꢀethanol (9:1). The concentration of DNSP is 1×10ꢀ4M, the PPLG
is 4mg/mL.
In the experiment, various nanostructures of PPLG were obtained
through gelation with different organic solvents. Then PPLG was
65 fabricated into xerogels, the nanostructure of which is verified
The chiral nanostructures were fabricated through an
22
from the SEM observation.
Figure 1B shows the emission
organogelation from
a
pyridylpyrazoleꢀlinked glutamide
spectrum of enantiomeric DNSP (10mM) measured in 90:10
H2Oꢀethanol solutions. Both LꢀDNSP and DꢀDNSP show an
emission peak at 550 nm and a yellow luminance is observed
70 while excited at 330nm. The PPLG xerogels obtained from
ethanol, which exhibited as the nanofiber structures, was
dispersed into the DNSP solution. It is observed that the LꢀDNSP
remains the yellow fluorescence with the emission band at 550
nm when PPLG nanofiber is added, which is the same as that of
75 the LꢀDNSP in waterꢀethanol. However, it is interesting to note
that the λmax blue shifts dramatically to 490nm when the PPLG
xerogels is dispersed into DꢀDNSP solution. This emission band
shows a large blue shift compared with the band of DꢀDNSP
solution or the dispersion of LꢀDNSP with PPLG. It is well
80 known that the DNS exhibits faint yellow emission in water and
shows blue shifts when the solvent polarity decreases.23,25 Herein,
35 amphiphile (PPLG), which can form diverse nanostructures from
nanofiber, nanotwist to nanotube and microtubes depending on
the solvents.22 In order to express the recognition using
fluorescence, we modified the amino acids with a Dansyl group.
Dansyl group is a typical fluorescence probe and is very sensitive
40 to the environment and exhibits different fluorescence in a
hydrophobic or hydrophilic environment.23ꢀ25 We have found
that the chiral nanostructures of PPLG showed a clearly different
fluorescence toward Dꢀ and Lꢀamino acids. While the Lꢀamino
acid attached a dansyl group (LꢀDNSP) remains a yellow
45 fluorescence with the emission band at 550 nm when meet with
PPLG nanofibers, it shows a dramatically blue shift to 490nm
when DꢀDNSP solution is used. The results provided a simple
way to recognize chiral species through the visualized emission
difference.
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the blue shift of λmax of Dꢀisomer binding with PPLG
assemblies was interpreted on the basis of decreased
micropolarity at the binding site of DNSP. The emission
difference for enantiomeric DNSP in PPLG xerogels confirmed
that the PPLG assemblies can enantiomerically recognize the
amino acid derivatives.
5
In order to make it clear the differences of the PPLG
assemblies with the L/DꢀDNSP, the UV spectra, CD spectra and
SEM pictures were investigated. The SEM images of PPLG in
Figure 3. The UVꢀvis spectra (A) and CD spectra (B) of DNSP solution
50 and after removing DNSP binding on PPLG assemblies by filtering. a)
DꢀDNSP solution; b) LꢀDNSP solution; c) and d) represents the filter
liquor of DꢀDNSP and LꢀDNSP system after interacting with PPLG
assemblies. The concentration of DNSP is 1×10ꢀ4M, the PPLG is
4mg/mL.
10 the absence and the presence of enantiomeric DNSP are shown in
Figure 2. The nanofiber structures with the width of 100ꢀ200nm
and the length of several micrometers were found for the PPLG
xerogels obtained from ethanol. After dispersing in the LꢀDNSP
solution, most of the nanofiber structures were kept. However,
15 when dispersed in DꢀDNSP solution, the long nanofiber
structures were cut into short nanorod structures, indicating that
PPLG nanostructure was strongly reacted with DꢀDNSP.
55
FTIR spectra were recorded to explore molecular interactions
between DNSP and PPLG, as shown in Fig S1 in the Supporting
Information. For the PPLG xerogels, the occurrence of the amide
I and amide II bands at 1645 and 1545 cmꢀ1, respectively,
60 indicated that the amide groups formed strong hydrogen bonds.26
Bands at 1725 and 1590 cmꢀ1 for DNSP sample suggested the
existence of carboxylic group and carboxylate. The FTIR
spectrum of the PPLG/DꢀDNSP mixture (1:4) displayed two new
broad vibration bands at around 2360 and 2105 cmꢀ1, which are
20 Figure 2. The SEM image of PPLG assemblies (A) PPLG xerogel
obtained from ethanol; (B) PPLG xerogels was dispersed into LꢀDNSP
solution; (C) dispersed into DꢀDNSP solution.
65 typical of carboxylic acid
– pyridine hydrogenꢀbond
interactions.27,28 In the case of LꢀDNSP/PPLG, there was no these
two peaks, indicating that the PPLG assemblies prefer to interact
with Dꢀenantiomer.
It is suggested that such chiral recognition could be due to the
25 different interaction between the PPLG assemblies and the
enantiomeric DNSP. The DꢀDNSP was interacted with PPLG
and entered into the hydrophobic microenvironment of PPLG
assemblies. Thus, the DꢀDNSP interacted with PPLG might be
more effective than that of LꢀDNSP. In order to confirm this,, the
30 dispersion of DNSP with PPLG was filtered to remove the DNSP
which adsorbed onto the PPLG assemblies and then the UV and
CD spectra of the solution were recorded, as shown in Figure 3.
The almost same spectra profile was observed for the Dꢀand Lꢀ
DNSP solution, whereas, an obvious difference was found when
35 PPLG was interacted with the enantiomer of DNSP. As for Lꢀ
DNSP, the intensity of absorption band kept constant, and the
adsorption intensity of DꢀDNSP/PPLG dropped remarkably.
More evidence came from CD spectra measurements. The CD
spectra of DꢀDNSP and LꢀDNSP solutions showed as mirror
40 image. However, when PPLG nanostructures were introduced,
the CD intensity of DꢀDNSP system exhibited much lower
intensity than that of LꢀDNSP system. All these results indicated
that the PPLG assemblies interacted more efficient with DꢀDNSP
than with LꢀDNSP. Hence, more DꢀDNSP was adsorbed in the
45 assembly of PPLG than that of Lꢀisomer. Thus, after remove
PPLG and DꢀDNSP bound on PPLG, the intensity of adsorption
band and CD band of DꢀDNSP decreased obviously.
It should be noted that the analog of PPLG, PPLGOEt without
70 long hydrophobic chain, could not show such chiral recognition.
The PPLGOEt cannot selfꢀassemble into organized
nanostructures. After PPLGOEt was dispersed into the solution
of DNSP, the fluorescence spectra of dispersion containing
DNSP and PPLGOEt was measured. The emission band of DNSP
75 in PPLGOEt dispersion was the same as that of in the
water/ethanol solution. The Dꢀ and Lꢀ enantiomer showed the
same emission as yellow one, as shown in Figure S2. This result
suggested that the PPLGOEt failed to recognize enantiomeric
DNSP. Further, if the PPLG sample was directly dispersed into
80 the DNSP waterꢀethanol solution without forming the
nanostructures, there is also no differences in the fluorescence for
LꢀDNSP and DꢀDNSP. The failure of PPLG without assembling
and PPLGOEt on the chiral recognition to DNSP indicated that
the chiral recognition indeed occurred at the supramolecular level.
85
Previously, we have found that PPLG formed various
nanostructures in different organic solvents such as nanofibers,
nanotwists, nanotubes and macrotubes.22 We have further
investigated the effect of various nanostructures of PPLG on the
chiral recognition for DNSP. The different nanostructures were
90 prepared according to their solvent which PPLG gelled. The
nanofiber, nanotwist, nanotube and microtube, and nanofiber
structures were prepared from toluene, pyridine, DMF, DMSO
and ethanol, respectively. Then the PPLG xerogels vacuum dried
from various solvents were dispersed into the DNSP solution and
95 monitored by fluorescence spectra, as shown in Figure S3. All
nanostructures formed by PPLG through supramolecular gelation
can show the recognition on the enantiomer of DNSP, because Lꢀ
DNSP and DꢀDNSP exhibited different emission after interacting
2
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with PPLG assemblies. The dispersion of PPLG assemblies with 45 Foundation of China (Nos. 21473219, 21321063, 91427302) and
LꢀDNSP showed the same yellow emission as that of PPLG
xerogels obtained from ethanol, which exhibited an emission
band at 550nm. This band is the same as that of LꢀDNSP solution,
indicating that the PPLG nanostructures have no obvious
interaction with LꢀDNSP. While the DꢀDNSP interacted with
various nanostructures, blueꢀgreen emission was all observed
with a slight change. For example, the nanofiber structure of
PPLG made the emission band showing at 501nm, the nanotwist
10 structures lead the emission band blue shift to 500 nm. When the
nanotube and microtube PPLG was used, the emission band blue
shifted to 498nm. Meanwhile, it is obvious that the shoulder peak
at 550nm, which is ascribed to the emission band of DNSP
located in polar microenvironment decreased. These results
15 indicated that the chiral recognition occurred between the PPLG
nanostructures and enantiomer DNSP.
the Fund of the Chinese Academy of Sciences (No.
XDB12020200)..
5
Notes and references
a
50
Beijing National Laboratory for Molecular Science, CAS Key
Laboratory of Colloid Interface and Chemical Thermodynamics, Institute
of Chemistry, Chinese Academy of Sciences, Beijing, 100190 (P.R. China),
E-mail: liumh@iccas.ac.cn
b
Henan Provincial Key Laboratory of Surface & Interface Science,
55 Zhengzhou University of Light Industry, Zhengzhou, Henan 450002, (P.R.
China)
c.
Collaborative Innovation Center of Chemical Science and Engineering
(Tianjin, P.R. China)
†Electronic Supplementary Information (ESI) available: [Experimental
60 part and FT-IR spectra]. See DOI: 10.1039/b000000x/
1. I. Vayá, V. LhiaubetꢀVallet, M. C. Jiménez and M. A. Miranda,
Chem. Soc. Rev., 2014, 43, 4102ꢀ4122.
2. C. J. Hastings, M. D. Pluth, S. M. Biros, R. G. Bergman, K. N.
Raymond, Tetrahedron, 2008, 64, 8362–8367.
3. J. L. Brumaghim, M. Michels, and K. N. Raymond, Eur. J. Org.
Chem. 2004, 4552ꢀ4559.
4. M. Wanderley, C. Wang, C. Wu and W. Lin, J. Am. Chem. Soc.,
2012, 134, 9050ꢀ9053.
Given the structure of the DNSP and PPLG molecule, the
hydrogen bonding between the pyridine and phenylalanine
20 resulted in the DNSP closing to PPLG assembly and being
captured in the hydrophobic cavity. The PPLG are more
favorable DꢀDNSP closing than LꢀDNSP owing to the steric
hindrance, as shown in Scheme 1. The more favorable
65
interaction will be greatly amplified in the chiral supramolecular 70 5. J. Rebek,Jr. Acc. Chem. Res. 2009, 42, 1660ꢀ1668.
6. W. Xuan, M. Zhang, Y. Liu, Z., Chen, Y. Cui, J. Am. Chem. Soc.,
25 assembly, leading to the fluorescent enantioselective response.
2012, 134,6904ꢀ6907.
7. W. Huang, P. Y. Zavalij and L. Isaacs, Angew. Chem., Int. Ed., 2007,
46, 7425ꢀ7427.
75 8. K. Kodama, Y. Kobayashi, and K. Saigo, Chem. Eur. J. 2007, 13,
2144ꢀ2152.
9. T. Liu, Y. Liu, W. Xuan and Y. Cui, Angew. Chem., Int. Ed., 2010,
49, 4121ꢀ4124.
10. L. Pu, Acc. Chem. Res., 2012, 45, 150ꢀ163.
80 11. Y. Zhou and J. Yoon, Chem. Soc. Rev., 2012, 41, 52ꢀ67.
12. F. Song, N. Fei, F. Li, S. Zhang, Y. Cheng and C. Zhu, Chem.
Commun., 2013, 49, 2891ꢀ2893.
13. T. Tu, W. Fang, X. Bao, X. Li and K. H. Doetz, Angew. Chem., Int.
Ed., 2011, 50, 6601ꢀ6605.
85 14. Q. Jin, L. Zhang, X. Zhu, P. Duan and M. Liu, Chem. Eur. J., 2012,
18, 4916ꢀ4922.
15. H. Jintoku, M. Takafuji, R. Oda and H. Ihara, Chem. Commun., 2012,
48, 4881ꢀ4883.
16. X. Chen, Z. Huang, S. Chen, K. Li, X. Yu and L. Pu, J. Am. Chem.
90
95
Soc., 2010, 132, 7297ꢀ7299.
Scheme 1. The enantiomer of DNSP can be selectively trapped into the
chiral assemblies and showing different emission.
17. W. Edwards, D. K. Smith, J. Am. Chem. Soc., 2014, 136, 1116ꢀ1124.
18. H. Cao, X. Zhu and M. Liu, Angew. Chem. Int. Ed. 2013, 52, 4122ꢀ
4126.
19. W. Miao, L. Zhang, X. Wang, L. Qin, and M. Liu, Langmuir, 2013,
29, 5435−5442.
20. N. Liu, S. Song, D. Li and Y. Zheng, Chem. Commun., 2012, 48,
4908–4910.
21. T. Tu, W. Fang and Z. Sun, Adv. Mater., 2013, 25, 5304ꢀ5313.
22. Q. Jin, L. Zhang and M. Liu, Chem. Eur. J., 2013, 19, 9234ꢀ9241.
30
Conclusions
In summary, a chiral supramolecular based on PPLG assemblies
formed by organogelating procedure, can be functioned as an
enantioselective system. The obvious fluorescence color change
35 between the DNSP isomer with PPLG assembly demonstrated
that the chiral supramolecular assemblies are potentially useful
for visual chiral recognition. An interesting point is that the
chiral recognition of PPLG on DNSP depended on the
nanostructures of PPLG assembly. The study of PPLG
40 supermolecules used as chiral separation system is ongoing.
100 23. H. Nagatani, T. Sakamoto, T. Torikai and T. Sagara, Langmuir, 2010,
26, 17686ꢀ17694.
24. R. Corradini, A. Dossena, G. Galaverna, R. Marchelli, A. Panagia, G.
Sartor, J. Org. Chem. 1997, 62, 6283ꢀ6289.
25. M. Vasilescu, A. Caragheorgheopol, H. Caldararu, R. Bandula, H.
Lemmetyinen, H. Joela,. J. Phys. Chem. B 1998, 102, 7740ꢀ7751.
26. M. Masuda, T. Shimizu, Langmuir, 2004, 20, 5969ꢀ5977.
27. J. Y. Lee, P. C. Painter, M. M. Coleman, Macromolecules 1988, 21,
954ꢀ960.
28. J. Gao, Y. N. He, F. Liu, X. Zhang, Z. Q. Wang, X. G. Wang, Chem.
Mater. 2007, 19, 3877ꢀ3881.
105
110
Acknowledgements
This work was supported by the Basic Research Development
Program (2013CB834504), the National Natural Science
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5
Selfꢀassembled chiral nanostructures formed by a pyridylpyrazoleꢀconjugated Lꢀglutamide showed an enantioselectivity for a
fluorescence labeled chiral amino acid.
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