- Email: [email protected]
A achiral AIEE-active polymer-Cu(II) complex sensor for highly selective and enantioselective recognition of histidine
Journal Pre-proofs A achiral AIEE-active polymer-Cu(II) complex sensor for highly selective and enantioselective recognition of histidine Guo Wei, Yuliang Jiang, Fang Wang PII: DOI: Reference:
S0040-4039(20)30145-3 https://doi.org/10.1016/j.tetlet.2020.151722 TETL 151722
To appear in:
Tetrahedron Letters
Received Date: Revised Date: Accepted Date:
16 December 2019 4 February 2020 6 February 2020
Please cite this article as: Wei, G., Jiang, Y., Wang, F., A achiral AIEE-active polymer-Cu(II) complex sensor for highly selective and enantioselective recognition of histidine, Tetrahedron Letters (2020), doi: https://doi.org/ 10.1016/j.tetlet.2020.151722
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A achiral AIEE-active polymer-Cu(II) complex sensor for highly selective and enantioselective recognition of histidine
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Guo Wei*, Yuliang Jiang, Fang Wang School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China 12 10
I/I0
8
OC8H17-n
P1-Cu2++His P1-Cu2++other amino acids
6
N NN
4 2 0
OC8H17-n 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
P1
O H3N
N N N Cu2+
N
m
O N
NH
*
L/D-Histidine
1
Tetrahedron Letters journal homepage: www.elsevier.com
A achiral AIEE-active polymer-Cu(II) complex sensor for highly selective and enantioselective recognition of histidine Guo Wei*, Yuliang Jiang, Fang Wang School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China
———
*ACorresponding R T I C L Eauthors. I N Fe-mail: O [email protected]
ABSTRACT
Article history: Received Received in revised form Accepted Available online
A new achiral aggregation-induced emission enhancement (AIEE)-active conjugated polymer P1 incorporating tetraphenylethene (TPE) and metal binding part structure was designed and synthesized. The polymer emits bright green fluorescence in the mixture of tetrahydrofuran (THF) and water. The coordination between Cu2+ and P1 causes fluorescence quenching from green to almost no emission, and the resulting polymer-Cu2+ complex responds to histidine selectively over other competing amino acids with obvious fluorescence recovery. In addition, the distinct circular dichroism (CD) response proved the success of the enantioselective recognition of P1-Cu2+ complex towards the enantiomers of histidine.
Keywords: AIEE polymer histidine enantioselective recognition
1. Introduction The naturally occurring amino acids are well known as key building blocks of proteins in nature, and play key roles in biological system and processes. They can serve as cheap and easily available chiral resources for asymmetric catalysis[1] and biologically active compounds[2] in chemical and pharmaceutical technology. Among them, histidine is a typical kind of amino acid, which has been proved a neurotransmitter and regulator of metal transmission[3]. The abnormal level of histidine in human body could result in various diseases, such as chronic kidney, asthma and liver cirrhosis[4]. Therefore, specific attention has been paid to histidine detection[5]. However, the free amino acids can only be dissolved in water or aqueous solution, in which most fluorescent sensor will be quenched. Moreover, the enantioselective recognition of amino acids are not too much reported[6]. The concept of aggregation-induced emission (AIE) was firstly raised in 2001 by Tang’s group[7a]. After that, Park’s group found aggregation-induced emission enhance (AIEE) character in a new kind of fluorescent organic nanoparticles[7b]. Since then, a large number of AIE or AIEE-active molecules have been applied in the fields like chiral fluorescent sensors[8] and optical devices[9]. These results provide us a feasible solution to develop fluorescent sensors in aqueous phase with strong emission staying on. Meanwhile, with the help of circular dichroism (CD) spectra, enantioselective recognition becomes convenient, in which the structure of the fluorescent sensors are not required to be chiral any more, and thus the scope of sensors is enlarged tremendously[10].
2009 Elsevier Ltd. All rights reserved.
Based on the previous work[11], herein we report an achiral polymer-based fluorescent sensor with AIEE feature for histidine detection and enantioselective recognition in aqueous phase. The fluorescent polymer sensor P1 was synthesized by the Pdcatalyzed Sonogashira reaction. In pure tetrahydrofuran (THF) solution, the polymer sensor P1 can show weak fluorescence due to its conjugated polymer main chain backbone. Upon the addition of water, the fluorescence intensity of the solution gradually increases and emits the brightest green fluorescence when the fraction of water (fw) is 90%. After the metal ion Cu2+ was added, the fluorescence was almost completely quenched, which can be reversibly recovered followed by the addition of histidine. The mirror CD spectra of P1-Cu2+ complex toward the enantiomers of histidine allow the assignment of enantioselective recognition. 2. Results and Discussion The structure of P1 is outlined in Fig. 1, it was synthesized by the Pd-catalyzed Sonogashira reaction between two monomers (blue and red part in Fig. 1), which are designed to act as AIE group and binding site, respectively. In order to improve the solubility of P1 in organic solvents, two n-octyl substituents were introduced on TPE group. The product of P1 was obtained in 70% yield as yellow solid, which can be dissolved in various common organic solvents (CH2Cl2, THF, and toluene), indicating P1 can be practically applied as a fluorescent sensor.
Tetrahedron Letters
2 OC8H17-n
N
N N N
m
Binding site
AIE group OC8H17-n
N N N
P1
Fig. 1. Structure of the polymer sensor P1.
The AIEE experiments of P1 were conducted in mixed solvents of THF (good solvent) and water (poor solvent), and the concentration was fixed at 1 × 10-5 mol·L-1 (corresponding to the etraphenylethene moiety). As shown in Fig. 2a, in pure THF solution, P1 has weak fluorescence due to its conjugated polymer main chain backbone. Upon the addition of water, the fluorescent intensity of the P1 solution gradually increases and reaches the maximum when the fraction of water (fw) is 90%, emitting the brightest green fluorescence, with the relative emission intensity up to 4.23-fold at 520 nm (Fig. 2b). In addition, the fluorescence color changes of the AIEE phenomena can be visually observed under commercially available 365 nm UV lamp (Fig. 2b, inset).
Fig. 2. (a) Fluorescence spectral changes of P1 in THF/H2O mixtures with different water fraction. Solution concentration: 1.0 × 10-5 mol·L-1 (λex = 360 nm). (b) Plot of (I/I0) values at 520 nm versus the compositions of the aqueous mixtures. I0 = fluorescent intensity of P1 in pure THF solution. Inset: Photographs of P1 in THF/H2O mixtures (left: fw = 0%; right: fw = 90%) taken under 365 nm UV illumination.
The fluorescent response of P1 towards Cu2+ was conducted in THF and water mixtures (1.0 × 10-5 mol·L-1, λex = 360 nm, fw = 90%). As can be seen from Fig. 3a, the addition of Cu2+ into P1 solution could sharply weaken the fluorescence, which may be attributed to the ligand to metal charge transfer (LMCT)-based heavy metal ion effect[12] induced by the coordination between P1 and Cu2+. The fluorescence can be quenched as much as 95% when the concentration of Cu2+ is more than 30 equivalents, with the solution fluorescent color changed from bright green to almost no emission (Fig. 3b). It’s worth noting that, a certain amount (more than 30 equivalents) of Cu2+ are needed to almost completely quench the fluorescence of P1 solution. Meanwhile, the value of quenching efficiencies (I/I0) are not linear relation versus the concentration of Cu2+. Herein we propose some possible reasons. Firstly, the solvent of solution is a mixture of 10% THF and 90% water, due to the hydration effect, the Cu2+ are surrounded by vast water molecules, making it difficult for the coordination between P1 and Cu2+. Secondly, the state of P1 in solution is aggregates, instead of unfolded status in pure THF, thus Cu2+ can only coordinates with the surfaces of the polymer aggregates. Finally, the polymer sensor P1 is in fact a mixture of various polymer chains with different polymerization degrees, so the coordination between Cu2+ and polymer chains are not uniformly distributed.
Fig. 3. (a) Fluorescence spectral changes of P1 (1.0 × 10-5 mol·L-1 in THF/H2O mixtures, fw = 90%, λex = 360 nm) upon the addition of increasing amounts of Cu2+. (b) Plot of fluorescent quenching efficiencies (I/I0) versus the concentration of Cu2+ at 520 nm. I0 = fluorescent intensity of P1 in the absence of Cu2+. Inset: visible fluorescence of the P1 solution before (left) and after (right) the addition of 30 equivalents of Cu2+ under 365 nm UV lamp.
As is shown in Fig. 4a and 4b, the polymer sensor P1 exhibits two absorption peaks at 228 nm and 310 nm, which could be assigned to the cross-shaped conjugation structure formed by the TPE moiety (blue part of Fig. 1) and designed metal binding part structure (red part of Fig. 1). As to the weak broad peak around 360 nm, it could be attributed to the successfully formed D-π-A type structure between electrodonating TPE moiety and the electron-accepting metal binding part group. After the addition of Cu2+, the peaks at 230 nm, 310 nm and 360 nm increase gradually until at least 30 equivalents of Cu2+ were added in, indicating a strong and deep interaction between P1 and Cu2+. The UV-vis spectral change of P1 towards Cu2+ could be regarded as the result of reduction of the πconjugated main chain backbone induced by the coordination between the binding part structure and Cu2+.
Fig. 4. (a) UV-vis spectral changes of P1 (1.0 × 10-5 mol·L-1 in THF and water mixtures, fw = 90%) upon the addition of increasing amounts of Cu2+. (b) Plot of absorbance (blue line at 230 nm, red line at 310 nm) versus the concentration of Cu2+.
Based on the above results, we further investigated the in situ generated P1-Cu2+ complex for the recognition of histidine. As illustrated in Fig. 5a, the addition of histidine can gradually enhance the fluorescence, reaching the maximum of 11.5 times of the original value when the concentration of histidine is about 200 equivalents (Fig. 5b), with the fluorescent color back to bright green (Fig. 5b, inset). Compared with the fluorescent intensity of P1 without Cu2+ at 520 nm, the addition of histidine can recover the fluorescence by 60 percentage.
Fig. 5. (a) Fluorescence spectral changes of P1 with 30 equivalents Cu2+ (1.0 × 10-5 mol·L-1 in THF/H2O mixtures, fw = 90%, λex = 360 nm) upon the addition of increasing amounts of histidine. (b) Plot of
3 fluorescent enhancement (I/I0) versus the concentration of histidine at 520 nm. I0 = fluorescence intensity of P1 with 30 equivalents Cu2+ in the absence of histidine. Inset: visible fluorescence of the P1 solution with 30 equivalents Cu2+ before (left) and after (right) the addition of 200 equivalents of histidine under 365 nm UV lamp.
In a set of comparable experiments, we continued to study the selectivity of the polymer-Cu2+ complex over other amino acids. The results are shown in Fig. 6. Only histidine can cause obvious fluorescent recovery by 60 percentage, and the other amino acids have slight fluorescent enhancement. Among them, cysteine (Cys), tryptophan (Trp) and methionine (Met) have major influences (I/I0 > 3), which could be attributed the strong coordination ability of the indole group and sulphur atom. The results demonstrate that the P1-Cu2+ complex can act as a highly selective fluorescent sensor for histidine.
Fig. 7. The CD spectra of P1-Cu2+ complex in the presence of 200 equivalents of L- or D- histidine. (1.0 × 10-5 mol·L-1 in THF/H2O mixtures, fw = 90%)
3. Conclusion In summary, a new achiral AIEE-active polymer P1 was designed and synthesized. After coordinated with Cu2+ in aqueous solution, the P1-Cu2+ complex can not only show highly fluorescent selectivity towards histidine among various amino acids, but also can act as an effective chiral recognition sensor through the CD results due to the successful chiral transfer and amplification from chiral histidine to the polymer main chain backbone. Fig. 6. The bar graphs of the relative fluorescent intensity(I/I0) of the P1-Cu2+ complex (1.0 × 10-5 mol·L-1 in THF/H2O mixtures, fw = 90%, λex = 360 nm) towards various kinds of amino acids (200 equivalents), I0 = fluorescence intensity of P1 with 30 equivalents of Cu2+. (1) Cys, (2) Trp, (3) Met, (4) Asn, (5) Tyr, (6) Leu, (7) Phe, (8) Arg, (9) Ser, (10) Lle, (11) Glu, (12) Lys, (13) Asp, (14) Asn, (15) Thr, (16) Ala, (17) Gly, (18) Pro, (19) Gln, (20) His.
On the basis of the results above, we tried the enantioselective recognition of P1-Cu2+ complex towards histidine using CD spectrometer. The CD results are shown in Fig. 7, mirror Cotton effects at 273 nm, 330 nm are observed, which can be regarded as the results of the successful chirality transfer and amplification from L/D-histidine to P1-Cu2+ complex. The orientation of small chiral histidine molecules are randomly distributed in solution, after coordinated to the P1-Cu2+ complex with its main chain backbone at a welldefined level, a higher dissymmetric architecture of P1-Cu2+histidine complex can be obtained, making the chiral recognition with CD spectra possible. The gabs values at 273 nm 330 nm are calculated as 1.29 × 10-4 and 0.89 × 10-4, respectively. In addition, the CD results also reveal the process of the fluorescent recovery by histidine is that histidine coordinates to P1-Cu2+ complex to form a ternary P1-Cu2+-histidine complex, instead of that histidine displaces Cu2+ off to release free P1 and restore its fluorescence, otherwise the CD signals at 273 nm and 330 nm will not appear.
Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 21604041). Supplementary Material Supplementary data related to this article can be found in the online version, at
References and notes 1.
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A achiral AIEE-active polymer-Cu(II) complex sensor for highly selective and enantioselective recognition of histidine Guo Wei*, Yuliang Jiang, Fang Wang School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China Email: [email protected]
Highlights: 13. 14.
A new achiral AIEE-active polymer sensor P1 was designed and synthesized. The P1-Cu2+ complex can exhibit selectively “turnon” response towards histidine. The P1-Cu2+ complex can enantioselectively recognize histidine through CD spectra.
S0040-4039(20)30145-3 https://doi.org/10.1016/j.tetlet.2020.151722 TETL 151722
To appear in:
Tetrahedron Letters
Received Date: Revised Date: Accepted Date:
16 December 2019 4 February 2020 6 February 2020
Please cite this article as: Wei, G., Jiang, Y., Wang, F., A achiral AIEE-active polymer-Cu(II) complex sensor for highly selective and enantioselective recognition of histidine, Tetrahedron Letters (2020), doi: https://doi.org/ 10.1016/j.tetlet.2020.151722
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier Ltd.
Graphical Abstract
To create your abstract, type over the instructions in the template box below. Fonts or abstract dimensions should not be changed or altered.
A achiral AIEE-active polymer-Cu(II) complex sensor for highly selective and enantioselective recognition of histidine
Leave this area blank for abstract info.
Guo Wei*, Yuliang Jiang, Fang Wang School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China 12 10
I/I0
8
OC8H17-n
P1-Cu2++His P1-Cu2++other amino acids
6
N NN
4 2 0
OC8H17-n 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
P1
O H3N
N N N Cu2+
N
m
O N
NH
*
L/D-Histidine
1
Tetrahedron Letters journal homepage: www.elsevier.com
A achiral AIEE-active polymer-Cu(II) complex sensor for highly selective and enantioselective recognition of histidine Guo Wei*, Yuliang Jiang, Fang Wang School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China
———
*ACorresponding R T I C L Eauthors. I N Fe-mail: O [email protected]
ABSTRACT
Article history: Received Received in revised form Accepted Available online
A new achiral aggregation-induced emission enhancement (AIEE)-active conjugated polymer P1 incorporating tetraphenylethene (TPE) and metal binding part structure was designed and synthesized. The polymer emits bright green fluorescence in the mixture of tetrahydrofuran (THF) and water. The coordination between Cu2+ and P1 causes fluorescence quenching from green to almost no emission, and the resulting polymer-Cu2+ complex responds to histidine selectively over other competing amino acids with obvious fluorescence recovery. In addition, the distinct circular dichroism (CD) response proved the success of the enantioselective recognition of P1-Cu2+ complex towards the enantiomers of histidine.
Keywords: AIEE polymer histidine enantioselective recognition
1. Introduction The naturally occurring amino acids are well known as key building blocks of proteins in nature, and play key roles in biological system and processes. They can serve as cheap and easily available chiral resources for asymmetric catalysis[1] and biologically active compounds[2] in chemical and pharmaceutical technology. Among them, histidine is a typical kind of amino acid, which has been proved a neurotransmitter and regulator of metal transmission[3]. The abnormal level of histidine in human body could result in various diseases, such as chronic kidney, asthma and liver cirrhosis[4]. Therefore, specific attention has been paid to histidine detection[5]. However, the free amino acids can only be dissolved in water or aqueous solution, in which most fluorescent sensor will be quenched. Moreover, the enantioselective recognition of amino acids are not too much reported[6]. The concept of aggregation-induced emission (AIE) was firstly raised in 2001 by Tang’s group[7a]. After that, Park’s group found aggregation-induced emission enhance (AIEE) character in a new kind of fluorescent organic nanoparticles[7b]. Since then, a large number of AIE or AIEE-active molecules have been applied in the fields like chiral fluorescent sensors[8] and optical devices[9]. These results provide us a feasible solution to develop fluorescent sensors in aqueous phase with strong emission staying on. Meanwhile, with the help of circular dichroism (CD) spectra, enantioselective recognition becomes convenient, in which the structure of the fluorescent sensors are not required to be chiral any more, and thus the scope of sensors is enlarged tremendously[10].
2009 Elsevier Ltd. All rights reserved.
Based on the previous work[11], herein we report an achiral polymer-based fluorescent sensor with AIEE feature for histidine detection and enantioselective recognition in aqueous phase. The fluorescent polymer sensor P1 was synthesized by the Pdcatalyzed Sonogashira reaction. In pure tetrahydrofuran (THF) solution, the polymer sensor P1 can show weak fluorescence due to its conjugated polymer main chain backbone. Upon the addition of water, the fluorescence intensity of the solution gradually increases and emits the brightest green fluorescence when the fraction of water (fw) is 90%. After the metal ion Cu2+ was added, the fluorescence was almost completely quenched, which can be reversibly recovered followed by the addition of histidine. The mirror CD spectra of P1-Cu2+ complex toward the enantiomers of histidine allow the assignment of enantioselective recognition. 2. Results and Discussion The structure of P1 is outlined in Fig. 1, it was synthesized by the Pd-catalyzed Sonogashira reaction between two monomers (blue and red part in Fig. 1), which are designed to act as AIE group and binding site, respectively. In order to improve the solubility of P1 in organic solvents, two n-octyl substituents were introduced on TPE group. The product of P1 was obtained in 70% yield as yellow solid, which can be dissolved in various common organic solvents (CH2Cl2, THF, and toluene), indicating P1 can be practically applied as a fluorescent sensor.
Tetrahedron Letters
2 OC8H17-n
N
N N N
m
Binding site
AIE group OC8H17-n
N N N
P1
Fig. 1. Structure of the polymer sensor P1.
The AIEE experiments of P1 were conducted in mixed solvents of THF (good solvent) and water (poor solvent), and the concentration was fixed at 1 × 10-5 mol·L-1 (corresponding to the etraphenylethene moiety). As shown in Fig. 2a, in pure THF solution, P1 has weak fluorescence due to its conjugated polymer main chain backbone. Upon the addition of water, the fluorescent intensity of the P1 solution gradually increases and reaches the maximum when the fraction of water (fw) is 90%, emitting the brightest green fluorescence, with the relative emission intensity up to 4.23-fold at 520 nm (Fig. 2b). In addition, the fluorescence color changes of the AIEE phenomena can be visually observed under commercially available 365 nm UV lamp (Fig. 2b, inset).
Fig. 2. (a) Fluorescence spectral changes of P1 in THF/H2O mixtures with different water fraction. Solution concentration: 1.0 × 10-5 mol·L-1 (λex = 360 nm). (b) Plot of (I/I0) values at 520 nm versus the compositions of the aqueous mixtures. I0 = fluorescent intensity of P1 in pure THF solution. Inset: Photographs of P1 in THF/H2O mixtures (left: fw = 0%; right: fw = 90%) taken under 365 nm UV illumination.
The fluorescent response of P1 towards Cu2+ was conducted in THF and water mixtures (1.0 × 10-5 mol·L-1, λex = 360 nm, fw = 90%). As can be seen from Fig. 3a, the addition of Cu2+ into P1 solution could sharply weaken the fluorescence, which may be attributed to the ligand to metal charge transfer (LMCT)-based heavy metal ion effect[12] induced by the coordination between P1 and Cu2+. The fluorescence can be quenched as much as 95% when the concentration of Cu2+ is more than 30 equivalents, with the solution fluorescent color changed from bright green to almost no emission (Fig. 3b). It’s worth noting that, a certain amount (more than 30 equivalents) of Cu2+ are needed to almost completely quench the fluorescence of P1 solution. Meanwhile, the value of quenching efficiencies (I/I0) are not linear relation versus the concentration of Cu2+. Herein we propose some possible reasons. Firstly, the solvent of solution is a mixture of 10% THF and 90% water, due to the hydration effect, the Cu2+ are surrounded by vast water molecules, making it difficult for the coordination between P1 and Cu2+. Secondly, the state of P1 in solution is aggregates, instead of unfolded status in pure THF, thus Cu2+ can only coordinates with the surfaces of the polymer aggregates. Finally, the polymer sensor P1 is in fact a mixture of various polymer chains with different polymerization degrees, so the coordination between Cu2+ and polymer chains are not uniformly distributed.
Fig. 3. (a) Fluorescence spectral changes of P1 (1.0 × 10-5 mol·L-1 in THF/H2O mixtures, fw = 90%, λex = 360 nm) upon the addition of increasing amounts of Cu2+. (b) Plot of fluorescent quenching efficiencies (I/I0) versus the concentration of Cu2+ at 520 nm. I0 = fluorescent intensity of P1 in the absence of Cu2+. Inset: visible fluorescence of the P1 solution before (left) and after (right) the addition of 30 equivalents of Cu2+ under 365 nm UV lamp.
As is shown in Fig. 4a and 4b, the polymer sensor P1 exhibits two absorption peaks at 228 nm and 310 nm, which could be assigned to the cross-shaped conjugation structure formed by the TPE moiety (blue part of Fig. 1) and designed metal binding part structure (red part of Fig. 1). As to the weak broad peak around 360 nm, it could be attributed to the successfully formed D-π-A type structure between electrodonating TPE moiety and the electron-accepting metal binding part group. After the addition of Cu2+, the peaks at 230 nm, 310 nm and 360 nm increase gradually until at least 30 equivalents of Cu2+ were added in, indicating a strong and deep interaction between P1 and Cu2+. The UV-vis spectral change of P1 towards Cu2+ could be regarded as the result of reduction of the πconjugated main chain backbone induced by the coordination between the binding part structure and Cu2+.
Fig. 4. (a) UV-vis spectral changes of P1 (1.0 × 10-5 mol·L-1 in THF and water mixtures, fw = 90%) upon the addition of increasing amounts of Cu2+. (b) Plot of absorbance (blue line at 230 nm, red line at 310 nm) versus the concentration of Cu2+.
Based on the above results, we further investigated the in situ generated P1-Cu2+ complex for the recognition of histidine. As illustrated in Fig. 5a, the addition of histidine can gradually enhance the fluorescence, reaching the maximum of 11.5 times of the original value when the concentration of histidine is about 200 equivalents (Fig. 5b), with the fluorescent color back to bright green (Fig. 5b, inset). Compared with the fluorescent intensity of P1 without Cu2+ at 520 nm, the addition of histidine can recover the fluorescence by 60 percentage.
Fig. 5. (a) Fluorescence spectral changes of P1 with 30 equivalents Cu2+ (1.0 × 10-5 mol·L-1 in THF/H2O mixtures, fw = 90%, λex = 360 nm) upon the addition of increasing amounts of histidine. (b) Plot of
3 fluorescent enhancement (I/I0) versus the concentration of histidine at 520 nm. I0 = fluorescence intensity of P1 with 30 equivalents Cu2+ in the absence of histidine. Inset: visible fluorescence of the P1 solution with 30 equivalents Cu2+ before (left) and after (right) the addition of 200 equivalents of histidine under 365 nm UV lamp.
In a set of comparable experiments, we continued to study the selectivity of the polymer-Cu2+ complex over other amino acids. The results are shown in Fig. 6. Only histidine can cause obvious fluorescent recovery by 60 percentage, and the other amino acids have slight fluorescent enhancement. Among them, cysteine (Cys), tryptophan (Trp) and methionine (Met) have major influences (I/I0 > 3), which could be attributed the strong coordination ability of the indole group and sulphur atom. The results demonstrate that the P1-Cu2+ complex can act as a highly selective fluorescent sensor for histidine.
Fig. 7. The CD spectra of P1-Cu2+ complex in the presence of 200 equivalents of L- or D- histidine. (1.0 × 10-5 mol·L-1 in THF/H2O mixtures, fw = 90%)
3. Conclusion In summary, a new achiral AIEE-active polymer P1 was designed and synthesized. After coordinated with Cu2+ in aqueous solution, the P1-Cu2+ complex can not only show highly fluorescent selectivity towards histidine among various amino acids, but also can act as an effective chiral recognition sensor through the CD results due to the successful chiral transfer and amplification from chiral histidine to the polymer main chain backbone. Fig. 6. The bar graphs of the relative fluorescent intensity(I/I0) of the P1-Cu2+ complex (1.0 × 10-5 mol·L-1 in THF/H2O mixtures, fw = 90%, λex = 360 nm) towards various kinds of amino acids (200 equivalents), I0 = fluorescence intensity of P1 with 30 equivalents of Cu2+. (1) Cys, (2) Trp, (3) Met, (4) Asn, (5) Tyr, (6) Leu, (7) Phe, (8) Arg, (9) Ser, (10) Lle, (11) Glu, (12) Lys, (13) Asp, (14) Asn, (15) Thr, (16) Ala, (17) Gly, (18) Pro, (19) Gln, (20) His.
On the basis of the results above, we tried the enantioselective recognition of P1-Cu2+ complex towards histidine using CD spectrometer. The CD results are shown in Fig. 7, mirror Cotton effects at 273 nm, 330 nm are observed, which can be regarded as the results of the successful chirality transfer and amplification from L/D-histidine to P1-Cu2+ complex. The orientation of small chiral histidine molecules are randomly distributed in solution, after coordinated to the P1-Cu2+ complex with its main chain backbone at a welldefined level, a higher dissymmetric architecture of P1-Cu2+histidine complex can be obtained, making the chiral recognition with CD spectra possible. The gabs values at 273 nm 330 nm are calculated as 1.29 × 10-4 and 0.89 × 10-4, respectively. In addition, the CD results also reveal the process of the fluorescent recovery by histidine is that histidine coordinates to P1-Cu2+ complex to form a ternary P1-Cu2+-histidine complex, instead of that histidine displaces Cu2+ off to release free P1 and restore its fluorescence, otherwise the CD signals at 273 nm and 330 nm will not appear.
Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 21604041). Supplementary Material Supplementary data related to this article can be found in the online version, at
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A achiral AIEE-active polymer-Cu(II) complex sensor for highly selective and enantioselective recognition of histidine Guo Wei*, Yuliang Jiang, Fang Wang School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China Email: [email protected]
Highlights: 13. 14.
A new achiral AIEE-active polymer sensor P1 was designed and synthesized. The P1-Cu2+ complex can exhibit selectively “turnon” response towards histidine. The P1-Cu2+ complex can enantioselectively recognize histidine through CD spectra.