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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* 5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x Self-assembled chiral nanostructures such as nanofibers, nanotubes formed by a pyridylpyrazole-conjugated Lglutamide showed an enantioselective recognition to a fluorescence labeled chiral amino acid.
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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 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.1-3 Thus the chiral self-assembled supramolecular host formed by various non-covalent interactions 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 block.4-9 Therefore, instead of the chiral recognition between molecules10-12, the interaction between the chiral architecture and the chiral molecules becoming an important issue.13-21 It is expected how supramolecular assembling can be used to show enhanced enantioselective recognition. Here, we report a new chiral recognition system using the chiral nanostructure as the host, which showed enantioselective recognition to the chiral amino acids. The chiral nanostructures were fabricated through an organogelation from a pyridylpyrazole-linked glutamide 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 to the environment and exhibits different fluorescence in a hydrophobic or hydrophilic environment.23-25 We have found that the chiral nanostructures of PPLG showed a clearly different fluorescence toward D- and L-amino acids. While the L-amino acid attached a dansyl group (L-DNSP) remains a yellow fluorescence with the emission band at 550 nm when meet with PPLG nanofibers, it shows a dramatically blue shift to 490nm when D-DNSP solution is used. The results provided a simple way to recognize chiral species through the visualized emission difference. This journal is © The Royal Society of Chemistry [year]
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.
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Figure 1. (A) The molecular structure of PPLG, PPLGOEt and DNSP; the fluorescence of (B) enantiomer of DNSP solution in water-ethanol (9:1); (C) dispersion of DNSP enantiomer with PPLG assemblies in water-ethanol (9:1). The concentration of DNSP is 1×10-4M, the PPLG is 4mg/mL.
In the experiment, various nanostructures of PPLG were obtained through gelation with different organic solvents. Then PPLG was fabricated into xerogels, the nanostructure of which is verified from the SEM observation. 22 Figure 1B shows the emission spectrum of enantiomeric DNSP (10mM) measured in 90:10 H2O-ethanol solutions. Both L-DNSP and D-DNSP show an emission peak at 550 nm and a yellow luminance is observed 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 L-DNSP remains the yellow fluorescence with the emission band at 550 nm when PPLG nanofiber is added, which is the same as that of the L-DNSP in water-ethanol. However, it is interesting to note that the λmax blue shifts dramatically to 490nm when the PPLG xerogels is dispersed into D-DNSP solution. This emission band shows a large blue shift compared with the band of D-DNSP solution or the dispersion of L-DNSP with PPLG. It is well known that the DNS exhibits faint yellow emission in water and shows blue shifts when the solvent polarity decreases.23,25 Herein, [journal], [year], [vol], 00–00 | 1
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the blue shift of λmax of D-isomer 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. In order to make it clear the differences of the PPLG assemblies with the L/D-DNSP, the UV spectra, CD spectra and SEM pictures were investigated. The SEM images of PPLG in the absence and the presence of enantiomeric DNSP are shown in Figure 2. The nanofiber structures with the width of 100-200nm and the length of several micrometers were found for the PPLG xerogels obtained from ethanol. After dispersing in the L-DNSP solution, most of the nanofiber structures were kept. However, when dispersed in D-DNSP solution, the long nanofiber structures were cut into short nanorod structures, indicating that PPLG nanostructure was strongly reacted with D-DNSP.
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Figure 2. The SEM image of PPLG assemblies (A) PPLG xerogel obtained from ethanol; (B) PPLG xerogels was dispersed into L-DNSP solution; (C) dispersed into D-DNSP solution.
It is suggested that such chiral recognition could be due to the different interaction between the PPLG assemblies and the enantiomeric DNSP. The D-DNSP was interacted with PPLG and entered into the hydrophobic microenvironment of PPLG assemblies. Thus, the D-DNSP interacted with PPLG might be more effective than that of L-DNSP. In order to confirm this,, the 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 D-and LDNSP solution, whereas, an obvious difference was found when PPLG was interacted with the enantiomer of DNSP. As for LDNSP, the intensity of absorption band kept constant, and the adsorption intensity of D-DNSP/PPLG dropped remarkably. More evidence came from CD spectra measurements. The CD spectra of D-DNSP and L-DNSP solutions showed as mirror image. However, when PPLG nanostructures were introduced, the CD intensity of D-DNSP system exhibited much lower intensity than that of L-DNSP system. All these results indicated that the PPLG assemblies interacted more efficient with D-DNSP than with L-DNSP. Hence, more D-DNSP was adsorbed in the assembly of PPLG than that of L-isomer. Thus, after remove PPLG and D-DNSP bound on PPLG, the intensity of adsorption band and CD band of D-DNSP decreased obviously.
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Figure 3. The UV-vis spectra (A) and CD spectra (B) of DNSP solution and after removing DNSP binding on PPLG assemblies by filtering. a) D-DNSP solution; b) L-DNSP solution; c) and d) represents the filter liquor of D-DNSP and L-DNSP system after interacting with PPLG assemblies. The concentration of DNSP is 1×10-4M, the PPLG is 4mg/mL.
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 cm-1, respectively, indicated that the amide groups formed strong hydrogen bonds.26 Bands at 1725 and 1590 cm-1 for DNSP sample suggested the existence of carboxylic group and carboxylate. The FTIR spectrum of the PPLG/D-DNSP mixture (1:4) displayed two new broad vibration bands at around 2360 and 2105 cm-1, which are typical of carboxylic acid – pyridine hydrogen-bond interactions.27,28 In the case of L-DNSP/PPLG, there was no these two peaks, indicating that the PPLG assemblies prefer to interact with D-enantiomer. It should be noted that the analog of PPLG, PPLGOEt without long hydrophobic chain, could not show such chiral recognition. The PPLGOEt cannot self-assemble 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 in PPLGOEt dispersion was the same as that of in the water/ethanol solution. The D- and L- 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 the DNSP water-ethanol solution without forming the nanostructures, there is also no differences in the fluorescence for L-DNSP and D-DNSP. 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. 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 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 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 LDNSP and D-DNSP exhibited different emission after interacting This journal is © The Royal Society of Chemistry [year]
ChemComm Accepted Manuscript
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Given the structure of the DNSP and PPLG molecule, the hydrogen bonding between the pyridine and phenylalanine resulted in the DNSP closing to PPLG assembly and being captured in the hydrophobic cavity. The PPLG are more favorable D-DNSP closing than L-DNSP owing to the steric hindrance, as shown in Scheme 1. The more favorable interaction will be greatly amplified in the chiral supramolecular assembly, leading to the fluorescent enantioselective response.
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Foundation of China (Nos. 21473219, 21321063, 91427302) and the Fund of the Chinese Academy of Sciences (No. XDB12020200)..
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a
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: [email protected] b Henan Provincial Key Laboratory of Surface & Interface Science, 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 part and FT-IR spectra]. See DOI: 10.1039/b000000x/ 1. 2.
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Scheme 1. The enantiomer of DNSP can be selectively trapped into the chiral assemblies and showing different emission.
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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 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 supermolecules used as chiral separation system is ongoing.
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Acknowledgements This work was supported by the Basic Research Development Program (2013CB834504), the National Natural Science This journal is © The Royal Society of Chemistry [year]
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I. Vayá, V. Lhiaubet-Vallet, M. C. Jiménez and M. A. Miranda, Chem. Soc. Rev., 2014, 43, 4102-4122. C. J. Hastings, M. D. Pluth, S. M. Biros, R. G. Bergman, K. N. Raymond, Tetrahedron, 2008, 64, 8362–8367. J. L. Brumaghim, M. Michels, and K. N. Raymond, Eur. J. Org. Chem. 2004, 4552-4559. M. Wanderley, C. Wang, C. Wu and W. Lin, J. Am. Chem. Soc., 2012, 134, 9050-9053. J. Rebek,Jr. Acc. Chem. Res. 2009, 42, 1660-1668. W. Xuan, M. Zhang, Y. Liu, Z., Chen, Y. Cui, J. Am. Chem. Soc., 2012, 134,6904-6907. W. Huang, P. Y. Zavalij and L. Isaacs, Angew. Chem., Int. Ed., 2007, 46, 7425-7427. K. Kodama, Y. Kobayashi, and K. Saigo, Chem. Eur. J. 2007, 13, 2144-2152. T. Liu, Y. Liu, W. Xuan and Y. Cui, Angew. Chem., Int. Ed., 2010, 49, 4121-4124. L. Pu, Acc. Chem. Res., 2012, 45, 150-163. Y. Zhou and J. Yoon, Chem. Soc. Rev., 2012, 41, 52-67. F. Song, N. Fei, F. Li, S. Zhang, Y. Cheng and C. Zhu, Chem. Commun., 2013, 49, 2891-2893. T. Tu, W. Fang, X. Bao, X. Li and K. H. Doetz, Angew. Chem., Int. Ed., 2011, 50, 6601-6605. Q. Jin, L. Zhang, X. Zhu, P. Duan and M. Liu, Chem. Eur. J., 2012, 18, 4916-4922. H. Jintoku, M. Takafuji, R. Oda and H. Ihara, Chem. Commun., 2012, 48, 4881-4883. X. Chen, Z. Huang, S. Chen, K. Li, X. Yu and L. Pu, J. Am. Chem. Soc., 2010, 132, 7297-7299. W. Edwards, D. K. Smith, J. Am. Chem. Soc., 2014, 136, 1116-1124. H. Cao, X. Zhu and M. Liu, Angew. Chem. Int. Ed. 2013, 52, 41224126. W. Miao, L. Zhang, X. Wang, L. Qin, and M. Liu, Langmuir, 2013, 29, 5435−5442. N. Liu, S. Song, D. Li and Y. Zheng, Chem. Commun., 2012, 48, 4908–4910. T. Tu, W. Fang and Z. Sun, Adv. Mater., 2013, 25, 5304-5313. Q. Jin, L. Zhang and M. Liu, Chem. Eur. J., 2013, 19, 9234-9241. H. Nagatani, T. Sakamoto, T. Torikai and T. Sagara, Langmuir, 2010, 26, 17686-17694. R. Corradini, A. Dossena, G. Galaverna, R. Marchelli, A. Panagia, G. Sartor, J. Org. Chem. 1997, 62, 6283-6289. M. Vasilescu, A. Caragheorgheopol, H. Caldararu, R. Bandula, H. Lemmetyinen, H. Joela,. J. Phys. Chem. B 1998, 102, 7740-7751. M. Masuda, T. Shimizu, Langmuir, 2004, 20, 5969-5977. J. Y. Lee, P. C. Painter, M. M. Coleman, Macromolecules 1988, 21, 954-960. J. Gao, Y. N. He, F. Liu, X. Zhang, Z. Q. Wang, X. G. Wang, Chem. Mater. 2007, 19, 3877-3881.
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with PPLG assemblies. The dispersion of PPLG assemblies with L-DNSP 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 L-DNSP solution, indicating that the PPLG nanostructures have no obvious interaction with L-DNSP. While the D-DNSP interacted with various nanostructures, blue-green emission was all observed with a slight change. For example, the nanofiber structure of PPLG made the emission band showing at 501nm, the nanotwist 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 indicated that the chiral recognition occurred between the PPLG nanostructures and enantiomer DNSP.
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Self-assembled chiral nanostructures formed by a pyridylpyrazole-conjugated L-glutamide showed an enantioselectivity for a fluorescence labeled chiral amino acid.
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ChemComm Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: L. Zhang, Q. Jin, K. Lv, L. Qin and M. Liu, Chem. Commun., 2015, DOI: 10.1039/C5CC00261C.
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
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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* 5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x Self-assembled chiral nanostructures such as nanofibers, nanotubes formed by a pyridylpyrazole-conjugated Lglutamide showed an enantioselective recognition to a fluorescence labeled chiral amino acid.
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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 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.1-3 Thus the chiral self-assembled supramolecular host formed by various non-covalent interactions 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 block.4-9 Therefore, instead of the chiral recognition between molecules10-12, the interaction between the chiral architecture and the chiral molecules becoming an important issue.13-21 It is expected how supramolecular assembling can be used to show enhanced enantioselective recognition. Here, we report a new chiral recognition system using the chiral nanostructure as the host, which showed enantioselective recognition to the chiral amino acids. The chiral nanostructures were fabricated through an organogelation from a pyridylpyrazole-linked glutamide 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 to the environment and exhibits different fluorescence in a hydrophobic or hydrophilic environment.23-25 We have found that the chiral nanostructures of PPLG showed a clearly different fluorescence toward D- and L-amino acids. While the L-amino acid attached a dansyl group (L-DNSP) remains a yellow fluorescence with the emission band at 550 nm when meet with PPLG nanofibers, it shows a dramatically blue shift to 490nm when D-DNSP solution is used. The results provided a simple way to recognize chiral species through the visualized emission difference. This journal is © The Royal Society of Chemistry [year]
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.
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Figure 1. (A) The molecular structure of PPLG, PPLGOEt and DNSP; the fluorescence of (B) enantiomer of DNSP solution in water-ethanol (9:1); (C) dispersion of DNSP enantiomer with PPLG assemblies in water-ethanol (9:1). The concentration of DNSP is 1×10-4M, the PPLG is 4mg/mL.
In the experiment, various nanostructures of PPLG were obtained through gelation with different organic solvents. Then PPLG was fabricated into xerogels, the nanostructure of which is verified from the SEM observation. 22 Figure 1B shows the emission spectrum of enantiomeric DNSP (10mM) measured in 90:10 H2O-ethanol solutions. Both L-DNSP and D-DNSP show an emission peak at 550 nm and a yellow luminance is observed 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 L-DNSP remains the yellow fluorescence with the emission band at 550 nm when PPLG nanofiber is added, which is the same as that of the L-DNSP in water-ethanol. However, it is interesting to note that the λmax blue shifts dramatically to 490nm when the PPLG xerogels is dispersed into D-DNSP solution. This emission band shows a large blue shift compared with the band of D-DNSP solution or the dispersion of L-DNSP with PPLG. It is well known that the DNS exhibits faint yellow emission in water and shows blue shifts when the solvent polarity decreases.23,25 Herein, [journal], [year], [vol], 00–00 | 1
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the blue shift of λmax of D-isomer 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. In order to make it clear the differences of the PPLG assemblies with the L/D-DNSP, the UV spectra, CD spectra and SEM pictures were investigated. The SEM images of PPLG in the absence and the presence of enantiomeric DNSP are shown in Figure 2. The nanofiber structures with the width of 100-200nm and the length of several micrometers were found for the PPLG xerogels obtained from ethanol. After dispersing in the L-DNSP solution, most of the nanofiber structures were kept. However, when dispersed in D-DNSP solution, the long nanofiber structures were cut into short nanorod structures, indicating that PPLG nanostructure was strongly reacted with D-DNSP.
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Figure 2. The SEM image of PPLG assemblies (A) PPLG xerogel obtained from ethanol; (B) PPLG xerogels was dispersed into L-DNSP solution; (C) dispersed into D-DNSP solution.
It is suggested that such chiral recognition could be due to the different interaction between the PPLG assemblies and the enantiomeric DNSP. The D-DNSP was interacted with PPLG and entered into the hydrophobic microenvironment of PPLG assemblies. Thus, the D-DNSP interacted with PPLG might be more effective than that of L-DNSP. In order to confirm this,, the 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 D-and LDNSP solution, whereas, an obvious difference was found when PPLG was interacted with the enantiomer of DNSP. As for LDNSP, the intensity of absorption band kept constant, and the adsorption intensity of D-DNSP/PPLG dropped remarkably. More evidence came from CD spectra measurements. The CD spectra of D-DNSP and L-DNSP solutions showed as mirror image. However, when PPLG nanostructures were introduced, the CD intensity of D-DNSP system exhibited much lower intensity than that of L-DNSP system. All these results indicated that the PPLG assemblies interacted more efficient with D-DNSP than with L-DNSP. Hence, more D-DNSP was adsorbed in the assembly of PPLG than that of L-isomer. Thus, after remove PPLG and D-DNSP bound on PPLG, the intensity of adsorption band and CD band of D-DNSP decreased obviously.
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Figure 3. The UV-vis spectra (A) and CD spectra (B) of DNSP solution and after removing DNSP binding on PPLG assemblies by filtering. a) D-DNSP solution; b) L-DNSP solution; c) and d) represents the filter liquor of D-DNSP and L-DNSP system after interacting with PPLG assemblies. The concentration of DNSP is 1×10-4M, the PPLG is 4mg/mL.
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 cm-1, respectively, indicated that the amide groups formed strong hydrogen bonds.26 Bands at 1725 and 1590 cm-1 for DNSP sample suggested the existence of carboxylic group and carboxylate. The FTIR spectrum of the PPLG/D-DNSP mixture (1:4) displayed two new broad vibration bands at around 2360 and 2105 cm-1, which are typical of carboxylic acid – pyridine hydrogen-bond interactions.27,28 In the case of L-DNSP/PPLG, there was no these two peaks, indicating that the PPLG assemblies prefer to interact with D-enantiomer. It should be noted that the analog of PPLG, PPLGOEt without long hydrophobic chain, could not show such chiral recognition. The PPLGOEt cannot self-assemble 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 in PPLGOEt dispersion was the same as that of in the water/ethanol solution. The D- and L- 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 the DNSP water-ethanol solution without forming the nanostructures, there is also no differences in the fluorescence for L-DNSP and D-DNSP. 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. 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 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 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 LDNSP and D-DNSP exhibited different emission after interacting This journal is © The Royal Society of Chemistry [year]
ChemComm Accepted Manuscript
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Given the structure of the DNSP and PPLG molecule, the hydrogen bonding between the pyridine and phenylalanine resulted in the DNSP closing to PPLG assembly and being captured in the hydrophobic cavity. The PPLG are more favorable D-DNSP closing than L-DNSP owing to the steric hindrance, as shown in Scheme 1. The more favorable interaction will be greatly amplified in the chiral supramolecular assembly, leading to the fluorescent enantioselective response.
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Foundation of China (Nos. 21473219, 21321063, 91427302) and the Fund of the Chinese Academy of Sciences (No. XDB12020200)..
Notes and references 50
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a
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: [email protected] b Henan Provincial Key Laboratory of Surface & Interface Science, 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 part and FT-IR spectra]. See DOI: 10.1039/b000000x/ 1. 2.
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Scheme 1. The enantiomer of DNSP can be selectively trapped into the chiral assemblies and showing different emission.
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Conclusions
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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 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 supermolecules used as chiral separation system is ongoing.
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Acknowledgements This work was supported by the Basic Research Development Program (2013CB834504), the National Natural Science This journal is © The Royal Society of Chemistry [year]
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with PPLG assemblies. The dispersion of PPLG assemblies with L-DNSP 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 L-DNSP solution, indicating that the PPLG nanostructures have no obvious interaction with L-DNSP. While the D-DNSP interacted with various nanostructures, blue-green emission was all observed with a slight change. For example, the nanofiber structure of PPLG made the emission band showing at 501nm, the nanotwist 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 indicated that the chiral recognition occurred between the PPLG nanostructures and enantiomer DNSP.
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Self-assembled chiral nanostructures formed by a pyridylpyrazole-conjugated L-glutamide showed an enantioselectivity for a fluorescence labeled chiral amino acid.
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