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Polymer 53 (2012) 6033e6038

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Polymer

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In situ Cu(II)-containing chiral polymer complex sensor for enantioselectiverecognition of phenylglycinol

Lu Wang, Fengyan Song, Jiali Hou, Junfeng Li, Yixiang Cheng*, Chengjian Zhu*

Key Lab of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China

a r t i c l e i n f o

Article history:Received 13 June 2012Received in revised form14 October 2012Accepted 24 October 2012Available online 1 November 2012

Keywords:Enantioselective recognitionPhenylglycinolCu(II)-containing polymer complex

* Corresponding authors.E-mail address: yxcheng@nju.edu.cn (Y. Cheng).

0032-3861/$ e see front matter � 2012 Elsevier Ltd.http://dx.doi.org/10.1016/j.polymer.2012.10.047

a b s t r a c t

A chiral polymer P1 was synthesized by the polymerization of 2,5-dibutoxy-1,4-di(benzaldehyde)-1,4-diethynylbenzene (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via Schiff’s base formation, and thechiral polymer P2 could be obtained by the reduction reaction of P1 with NaBH4. P2 can serve as a “turn-off” fluorescent sensor toward Cu2þ and Ni2þ. The in situ generated Cu(II)-containing polymer complex ofP2 (Cu(II)-P2) can exhibit remarkable “turn-on” fluorescence enhancement response and considerableenantioselectivity toward unmodified phenylglycinol via a ligand displacement mechanism. Moreimportantly, (R,R)-Cu(II)-P2 solution can turn on bright blue fluorescence color change again uponaddition of L-phenylglycinol under a commercially available UV lamp, which can be clearly observed bythe naked eyes for direct visual discrimination at low concentration. The simple, rapid and sensitivebenign process makes this protocol promising for recognition of phenylglycinol enantiomers.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

As chiral stereogenic carbon atoms are abundant in naturalproducts, such as amino acids, sugar, amine alcohols and a-hydroxyl carboxylic acids, chiral enantioselective recognitionplays an important role in many fields of science and technology[1e7]. Besides, studies on chiral recognition can contribute to theunderstanding of living systems on molecular level. Recently,more and more attentions have been paid on enantioselectiverecognition of chiral molecules using fluorescence sensors such aschiral macrocycles [8e11], dendrimers [12e15] and oligomers[16,17]. The progresses of these chiral enantiomers recognitionhave been generally achieved through intermolecular non-covalent interaction such as hydrogen bonding between thefluorescence sensors and the chiral molecules [18e25]. Aremaining drawback of this approach is the limited sensitivitydue to relatively low association constants between the sensorsand the chiral hydrogen bond donating substrates [26]. Therefore,the design and development of a novel approach for the highlyenantioselective recognition of chiral molecules and the rapiddetermination of their enantiomeric composition is highly desir-able. After coordination with metal ions, the fluorescence sensorsusually exhibit fluorescence changes and show distinguishing

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sensing properties, such as quenching or emission red/blue shift,which can be attributed to electron density variations [27].Moreover, while different chiral enantiomer guest were added tothe metal ion containing host, the mixture can usually appearobvious color change or form some complex precipitates due tothe competitive binding to metal ion between host and guest,which could be clearly observed by the naked eyes. This kinddirect visual detection can offer a very simple and rapid methodfor chiral enantiomer discrimination. Encouraged by the brilliantachievements of Anslyn’s [28,29], Wolf’s [26,30], Pu’s [31], andFeng’s previous works [32e34], recently, our group reported thein situ generated perazamacrocycle-Cu(II) complex as chiralflorescence sensor and successfully realized enantioselectiverecognition towards unmodified a-amino acids in protic solution[35]. To the best of our knowledge, most of the works on metalion containing complexes as chiral fluorescence sensors arefocused on chiral small molecules, however, almost no report onpolymer complex sensors. Compared to chiral small organicmolecules, polymer-based chiral sensors exhibit importantadvantages. They are highly sensitive to minor external structuralperturbations or to electron density changes within the polymerbackbone in the presence of analytes [36e41]. Moreover, thesechiral fluorescence-based polymers can also be systematicallymodified by the introduction of different functional groups withsteric and electronic properties, which can greatly improve boththe binding ability and recognition selectivity for specific analytes[42e44]. Inspired by these impressive progresses on metal ion

L. Wang et al. / Polymer 53 (2012) 6033e60386034

containing fluorescence sensors, we continued our interest inpolymer-based fluorescence sensor [45e51] and designed a novelchiral polymer P2, which can serve as a “turn-off” fluorescentsensor toward Cu2þ and Ni2þ. Interestingly, the in situgenerated Cu(II)-containing polymer complex of P2 (Cu(II)-P2)can exhibit remarkable “turn-on” fluorescence enhancementbehavior and considerable enantioselectivity toward unmodifiedphenylglycinol.

2. Experimental part

2.1. Instruments and materials

NMR spectra were obtained using a 300-Bruker spectrometer300 MHz for 1H NMR and 75 MHz for 13C NMR and reported asparts per million (ppm) from the internal standard TMS. FT-IRspectra were taken on a Nexus 870 FT-IR spectrometer. Fluores-cence spectra were obtained from an RF-5301PC spectrometer.Specific rotation was determined with a Ruololph ResearchAnalytical Autopol IV-T/V. Electrospray ionization mass spectra(ESI-MS) were measured on a Thermo Finnigan LCQ Fleet systemand time-of-flightmass spectrometry (TOF-MS)was determined ona Micromass GCT. C, H, N of elemental analyses were performed onan Elemental Vario MICRO analyzer. The gel permeation chroma-tography (GPC) analysis of the polymers was conducted on a Shi-madzu 10 Åwith THF as the eluent and polystyrene as the standard.The data were analyzed by using the software package provided byShimadzu Instruments. Thermogravimetric analyses (TGA) wereperformed on a PerkineElmer Pyris-1 instrument under N2 atmo-sphere. Circular dichroism (CD) spectra were carried out ona JACSCO J-810 Circular Dichroism Spectrophotometer. All solventsand reagents were commercially available A.R. grade. THF and Et3Nwere purified by distillation from sodium in the presence ofbenzophenone.

2.2. Synthesis of 4-ethynylbenzaldehyde 2

1,4-Diiodo-2,5-dibutoxybenzene 1 could be synthesized fromhydroquinone according to the reported procedures [52]. Tri-methylsilylacetylene (19.4 mL, 135.9 mmol) was added toa mixture of 4-bromobenzaldehyde (5.0 g, 27.18 mmol),Pd(PPh3)2Cl2 (950 mg, 1.36 mmol) and CuI (520 mg, 2.72 mmol)in Et3N (60 mL). The mixture was stirred overnight at 40 �C.After cooling to room temperature, the resulting ammonium saltwas filtered off, and the solvent was removed by rotary evapo-ration. The residue was purified by silica gel column chroma-tography with petroleum ether as eluent to afford 4-((trimethylsilyl)ethynyl)benzaldehyde as a yellow powder afterremoval of the solvent (4.0 g, 74%). 1H NMR (300 MHz, CDCl3)d 10.00 (s, 1H), 7.82 (d, J ¼ 8.5 Hz, 2H), 7.60 (d, J ¼ 8.2 Hz, 2H),0.27 (s, 9H).

4-((Trimethylsilyl)ethynyl)benzaldehyde (2.0 g, 10.0 mmol) andKOH (561 mg, 10.0 mmol) were dissolved in the mixed solvents ofCH2Cl2 (10 mL) and MeOH (5 mL). The mixture was stirred at roomtemperature for 6 h, and then the solvent was concentrated underreduced pressure. H2O (20 mL) and CH2Cl2 (20 mL) were added tothe obtained residue to afford a two-phase solution. The aqueouslayer was extracted with CH2Cl2 (2 � 20 mL), and the combinedorganic layers were washed with H2O, and then dried over MgSO4.The solution was filtered, and the solvent was removed by rotaryevaporation to give a light yellow powder identified as 4-ethynylbenzaldehyde 2 (1.17 g, 90%). 1H NMR (300 MHz, CDCl3)d 10.01 (s,1H), 7.86-7.81 (m, 2H), 7.63 (d, J¼ 8.2 Hz, 2H), 3.32 (s,1H).ESI-MS: m/z: 129.17 [M � H]�.

2.3. Synthesis of 4,40-((2,5-dibutoxy-1,4-phenylene)bis(ethyne-2,1-diyl))dibenzaldehyde (M-1)

The mixture of 1,4-dibutoxy-2,5-diiodobenzene 1 (474.1 mg,1.0 mmol), 4-ethynyl- benzaldehyde 2 (390.1 mg, 3.0 mmol),Pd(PPh3)2Cl2 (70.6 mg, 0.1 mmol), and CuI (37.5 mg, 0.2 mmol)was dissolved in the mixed solvents of THF (10 mL) and Et3N(30 mL). The reaction mixture was heated to 80 �C overnightunder N2 atmosphere. After cooling to room temperature, thesolvent was removed by a rotary evaporator. The residue waspurified by flash chromatography on silica gel (ethyl acetate/petroleum ether, 1:3, v/v). The solvent was removed to afford M-1as a bright yellow powder (242 mg, 51%). Mp: 150e152 �C. 1HNMR (300 MHz, CDCl3) d 10.03 (s, 2H), 7.88 (d, J ¼ 8.2 Hz, 4H), 7.68(d, J ¼ 8.1 Hz, 4H), 7.05 (s, 2H), 4.06 (t, J ¼ 6.4 Hz, 4H), 1.91e1.81(m, 4H), 1.59 (dd, J ¼ 15.0, 7.3 Hz, 4H), 1.02 (t, J ¼ 7.4 Hz, 6H).13C NMR (75 MHz, CDCl3) d191.42, 153.86, 135.42, 132.04, 129.62,116.82, 113.90, 94.26, 90.00, 77.22, 69.30, 31.31, 19.27, 13.90. TOF-MS: m/z: 478.1.

2.4. Synthesis of P1

A mixture of M-1 (100.0 mg, 0.19 mmol) and (R,R)-1,2-diaminocyclohexane (M-2, 21.0 mg, 0.19 mmol) was dissolvedin 2 mL of CHCl3. The solution was stirred at 40 �C for 4 h.20 mL of methanol was added to precipitate the yellow solid P1.The resulting P1 was filtrated and washed with methanolseveral times and dried in the yield of 85% (90.0 mg). GPCresults: Mw ¼ 21,170; Mn ¼ 7170; PDI ¼ 2.9. ½a�25D ¼ �435.0 (c0.20, THF). 1H NMR (300 Hz, CDCl3) d 8.17 (s, HC ¼ N), 7.62e7.57(m, ArH), 7.49e7.44 (m, ArH), 6.97 (s, ArH), 4.03e3.98 (t, CH2O),1.89e1.76 (m, CH2), 1.61e1.49(m, CH2), 1.03e0.96 (m, CH3). FT-IR(KBr, cm�1): 3416, 2928, 2858, 1697, 1636, 1502, 1382, 1273,1208, 830.

2.5. Synthesis of P2

0.1 g P1 was dissolved in the mixed solvents of 10 mL THFand 10 mL MeOH, and then NaBH4 (500 mg) was added inbatches to the above solution. The reaction mixture was stirredat room temperature until the yellow color turn light. Thesolution was stirred for another 30 min, and 10 mL water wasadded to stop the reduction reaction. The mixture was extractedwith CH2Cl2 (3 � 20 mL). The combined organic layers weredried with anhydrous Na2SO4 and evaporated under reducedpressure to afford polymer P2 as a yellow solid (0.08 g, 86%).GPC: Mw ¼ 21,400; Mn ¼ 7230; PDI ¼ 2.6. ½a�25D ¼ þ10.0 (c 0.20,THF). 1H NMR (300 Hz, CDCl3) d 7.52e7.49 (m, ArH), 7.33e7.31(m, ArH), 7.04e6.99 (m, ArH), 4.02e3.97 (m, NH), 3.75e3.67(m, CH2O), 2.42 (br, CH2N), 1.82e1.26 (m, CH2), 0.90e0.89 (m,CH3). FT-IR (KBr, cm�1): 3552, 3414, 2928, 2868, 1618, 1412, 1213,817, 617.

2.6. Fluorescence measurements

The concentrations of the stock solution of metal salts (nitrate)and the unmodified amino alcohols are 1.0� 10�2 mol/L in H2O and1.0 � 10�2 mol/L in THF, respectively. Initially each experiment wasstarted with a 3.0 mL polymer with a known concentration(1.0 � 10�5 mol/L corresponding to (R,R)-cyclohexane moiety inTHF). The adding amount of each experiment example of metal saltand unmodified amino alcohols is shown on the figureinterpretation.

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Fig. 1. TGA curves of the chiral polymers P1 and P2.

L. Wang et al. / Polymer 53 (2012) 6033e6038 6035

3. Results and discussion

3.1. Synthesis and structure feature of the polymers P1 and P2

Chiral small molecules 3 and 4 could be synthesized accordingto the reported procedures [53]. The synthetic routes of the twochiral polymers P1 and P2 are illustrated in Scheme 1. The mono-mer M-1, 4,40-((2,5-dibutoxy-1,4-phenylene)bis(ethyne-2,1-diyl))dibenzaldehyde, was prepared according to the reported proce-dures [47], and then reacted with 1,2-diaminocyclohexane (M-2) toafford the corresponding chiral polymer P1 as a yellow solid in85.0% yield. P2 could be obtained by the reduction reaction of P1with NaBH4 in 85.3% yield. As evident from 1H NMR spectra of thepolymers P1 and P2, P1 has one well-resolved peak at 8.17 ppmcorresponding to the imine group adjacent to the phenyl (eCH]Ne). But 8.17 ppm in 1H NMR spectra of the polymer P2completely disappears, which indicates the complete reduction ofimine group of P1 (Fig. S18). (R,R)-1,2-diaminocyclohexane moietyof P1 and P2 as a chiral site and ligand can orient a well-definedspatial arrangement in the regular polymer main chain backbone.GPC results of both P1 and P2 show moderate molecular weights.Both the chiral polymers P1 and P2 are air stable solids and havegood solubility in common organic solvents, such as toluene, THF,CHCl3 and CH2Cl2, which can be attributed to the nonplanarity ofthe twisted polymer backbone and the flexible n-butoxy groupsubstituents. In addition, the ethynyl linker can reduce sterichindrance between phenyl groups and also have a beneficialinfluence on the stability of the resulting chiral polymers. TGAresults of P1 and P2 suggest that the chiral polymers have highthermal stability without loss weight before 420 �C and 380 �C,respectively (Fig. 1). Therefore, the resulting chiral polymers P1 andP2 can provide a desirable thermal property for practical applica-tion as a fluorescence sensor.

3.2. The selective recognition of the polymer sensors of P2 on Cu2þ

The fluorescence spectra of P1 and P2 were carried out ina solution of THF. Both P1 and P2 can emit the strong fluorescence

Scheme 1. Synthesis procedure

with high fluorescence quantum yield of 0.77 and 0.54, respec-tively. The fluorescence response behavior of P1 and P2(1.0 � 10�5 mol/L corresponding to cyclohexane moiety in THF) onvarious metal ions have been investigated by fluorescence spectrawith the excitation at 381 nm and 371 nm, respectively. It wasfound that P1 has no obvious response to the addition of metalions (Fig. 2a). As is evident from Fig. 2b, almost no fluorescenceresponse can be observed upon the addition of Agþ, Al3þ, Ba2þ,Ca2þ, Cd2þ, Cr3þ, Fe3þ, Kþ, Mg2þ, Mn2þ, Naþ, Zn2þ, Zr4þ at 1:1 Mratio. But Cu2þ ions can lead to almost complete quenching of P2.Fig. 2c illustrates the fluorescence titration of chiral polymer P2towards Cu2þ. The quenching ratios (h) of P2 on Cu2þ can becalculated according to equation: h ¼ 1�I/I0. Herein, I0 is thefluorescent emission intensity in the absence of the quencher, andI is the fluorescent emission intensity in the presence of thequencher. As a result, the fluorescence quenching ratio of P2 is0.913 upon 1:1 M ratio addition of the Cu2þ salt solution. Thequenching efficiency of P2 is related to the Stern-volmer constant,KSV, and is determined by monitoring measurable changes in thefluorescence spectra via the Stern-volmer equation:

s of 3, 4, M-1, P1 and P2.

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Fig. 2. (a) Fluorescence responses of P1 (1.0 � 10�5 mol/L in THF, lex ¼ 381 nm); (b)P2 (1.0 � 10�5 mol/L in THF, lex ¼ 371 nm) to 1:1 M ratio of various metal ions; (c)Fluorescence spectra of P2 (1.0 � 10�5 mol/L in THF, lex ¼ 371 nm) in the presence ofincreasing amount of Cu2þ. The inset features the dependence of the intensity emissionat 422 nm on the concentration of Cu2þ (insert: the photo of the fluorescence color ofpolymer sensor P2 (1) and Cu(II)-P2 (2)).

L. Wang et al. / Polymer 53 (2012) 6033e60386036

I0/I ¼ 1 þ KSV[Q], herein, [Q] is the quencher concentration.Average lg KSV of the polymer P2 on Cu2þ is 6.245. The fluores-cence curve of P2 with Cu2þ reveals that the fluorescentquenching value I0/I exhibited a good linear response to the Cu2þ

concentration change from 0.1 to 1.0 � 10�5 mol/L, indicating thatthe polymer sensor can form a 1:1 Cu(II)-containing polymercomplex called Cu(II)-P2 (Fig. 2c). Moreover, the bright blue colorof the polymer sensor disappears under a commercially availableUV lamp after upon addition of Cu2þ. Meanwhile, it could be alsoobserved that Ni2þ ions can lead to obvious quenching of P2.

3.3. CD spectra of 3, 4, P1, P2 and Cu(II)-P2

The CD spectra of 3, 4, P1, P2 and Cu(II)-P2 are shown in Fig. 3(1.0 � 10�5 mol/L in THF). It can be observed that there is greatdifference between chiral small molecules and two chiral polymers.Both the chiral molecule 3 and the chiral polymer P1 exhibit strongCD signals with negative and positive Cotton effects at shortwavelengths in their CD spectra. It can also be found that P1 hasstrong negative Cotton effect at wavelengths of 331 nm, which canbe regarded as the extended conjugated structure in the repeatingunit and a high rigidity of polymer backbone [47,54e57]. P1appears the strongest Cotton effect in the longwavelength centeredat about 395 nm, which is attributed to significant chiral amplifi-cation arisen from the helical conformation backbone of chiralconjugated polymer chain [45,58,59,61]. In this paper the resultingchiral polymer P1 can adopt a stable helical configuration since the(R,R)-Schiff base moieties can orient a welledefined spatialarrangement in the regular and rigid polymer backbone, that is,each unit in the chiral polymer P1 acts independently with anorganized helical chain structure. A helix is highly regular structurein which all bonds that form the helix have the same configuration(either R or S) [55,60e62]. Takeishi pointed out that the mainchains composed of rigid segments are twisted to one-direction bythe chiral molecule linker and an ordered structure of the mainchain backbone can adopt the stable helical configuration [63].Yashima thought the generation of a helical structure should resultin significant chiral amplification [62]. On the contrary, chiral smallmolecule 4, chiral polymer P2 and the corresponding polymercomplex Cu(II)-P2 appear almost no Cotton effect in their CDspectra. It could be contributed to the reason that the chiral moiety(R,R)-1,2-diaminocyclohexane is no longer available for the conju-gated system [64]. It can be demonstrated by their specific rotationvalues (Table 1). ½a�25D of chiral small molecules 3 and 4 are �258.62(c 0.23, THF) and �86.15 (c 0.26, THF). And ½a�25D of the chiralpolymers P1 and P2 are �435.0 (c 0.20, THF) and þ10.0 (c 0.20,THF), respectively. Compared with 4 and P1, ½a�25D of P2 shows

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Fig. 3. CD spectra of 3, 4, P1, P2 and Cu(II)-P2 (1.0 � 10�5 mol/L in THF).

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Cu(II)-P2 + D-phenylglycinol

aTable 1½a�25D and CD data of 3, 4, P1 and P2.

3 4 P1 P2

½a�25D (THF) �258.62 (c 0.23) �86.15(c 0.26)

�435.0 (c 0.20) þ10.0 (c 0.20)

[q] � 105

(lmax in nm)þ12.91 (234.5)�16.18 (255.5)

e þ2.32 (248.5)þ2.32 (299.5)�4.20 (331.0)�6.98 (395.0)

þ2.71 (234.5)

L. Wang et al. / Polymer 53 (2012) 6033e6038 6037

opposite specific rotation signal, indicating the chiral repeating unitin the disordered state and the flexible chain backbone. ½a�25D of P1is much larger than its corresponding chiral small molecule 3,which can be attributed to the counteracting result of the repeatingchiral unit upon the formation of helical chiral polymer configu-ration [65e70].

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D-phenylglycinol

b

Fig. 4. (a) Fluorescence spectra of Cu(II)-P2 (1.0 � 10�5 mol/L in THF, lex ¼ 371 nm)with D- or L-phenylglycinol (2.0 � 10�3 mol/L in THF) and (b) plots of (I/I0) vs. phe-nylglycinol concentration during the titration of Cu(II)-P2 with D- or L-phenylglycinol(lex ¼ 371 nm, lem ¼ 422 nm). (insert: the photo of the fluorescence color changes ofCu(II)-P2 complex sensor (1), Cu(II)-P2 þ D-phenylglycinol (2) and Cu(II)-P2 þ L-phenylglycinol (3), [D- or L-phenylglycinol]: [Cu(II)-P2] ¼ 150: 1).

Scheme 2. Proposed mechanism of ligand displacement process.

3.4. Fluorescence recognition of the polymer complex Cu(II)-P2 onD- or L-phenylglycinol

In this paper we further investigated the fluorescence responsebehaviors of chiral polymer sensor towards phenylglycinol by usingP1 and P2. Almost no fluorescence response changes and enan-tioselectivities can be observed by adding phenylglycinol enantio-mers (Figs. S3 and S4). Interestingly, while using in situ generated1:1 Cu(II)-containing polymer complex Cu(II)-P2 as a fluorescencesenor, a remarkable difference in fluorescent enhancementresponse behaviors between these two enantiomers could bedetected as demonstrated in Fig. 4. The fluorescence spectra ofCu(II)-P2 (1.0 � 10�5 mol/L in THF) were carried out by addition ofL- or D-phenylglycinol (2.0 � 10�3 mol/L in THF). As is evident fromFig. 4a, L-phenylglycinol can lead to a large increase on the fluo-rescent intensity of Cu(II)-P2. D-isomer can also lead to the obviousfluorescence enhancement response of Cu(II)-P2, but its influenceshows lower than that of L-isomer. It can also be found that thefluorescent emission wavelengths do not show an obvious differ-ence between guest-free sensor and guest-sensor. More impor-tantly, Cu(II)-P2 solution can turn on bright blue fluorescence colorchange again upon addition of L-phenylglycinol under a commer-cially available UV lamp, which can be clearly observed by thenaked eyes for direct visual discrimination at low concentration(Fig. 4a). The obvious fluorescence enhancement of Cu(II)-P2 withphenylglycinol can be attributed to a ligand displacement mecha-nism [45e51]. As chelating ligands, amino alcohols are highlyassociable with many metal ions. Thus, they probably are able toassociate with Cu(II) and displace the fluorescence polymer P2from Cu(II)-P2, which may conduce to the fluorescence recovery ofP2 quenched by Cu(II) as shown on Scheme 2.

Herein, the interaction of Cu(II)-P2 with phenylglycinol wasstudied at a much broader concentration range. In regard to thefluorescence signal changes of this chiral polymer sensor onphenylglycinol, the fluorescence intensities appear gradualenhancement upon addition of L-phenylglycinol and D-phenyl-glycinol in the range from 1:10 to 1:700 M ratios (Fig. S5). Theenantiomeric fluorescence difference ratio ef [ef¼(IL�I0)/(ID�I0)] inthis case is 2.90 at 1:150 M ratio, which indicates that (R,R)-Cu(II)-P2 can exhibit considerable enantioselective response towards L-phenylglycinol. The reason may be attributed to an inherent chiralrecognition based on the steric repulsion of (R,R)-Cu(II)-P2precursor for L-phenylglycinol. The building block of in situgenerated 1:1 (R,R)-Cu(II)-P2 is controlled by the flexible CeNbond and can well fit for the insert of guest molecule L-phenyl-glycinol to coordinate with Cu(II) and displace the fluorescencepolymer P2.

In a set of comparable experiments, we also studied the inter-action of (R,R)-Cu(II)-P2 sensor with other amino alcoholsincluding phenylalaninol, alaninol and valinol (Scheme 3), almostno enantioselective recognition effect could be detected even theobvious fluorescence enhancement responses can be observed

.. .

Scheme 3. Chiral guests used in the enantioselective recognitions with Cu(II)-P2.

L. Wang et al. / Polymer 53 (2012) 6033e60386038

(Figs. S5eS11 and Table S1), suggesting that the increase of bulk ofthe group in the amino alcohols might be beneficial to theenhancement of enantioselectivity. To the best of our knowledge,this is the first report on Cu(II)-containing polymer Cu(II)-P2 asa fluorescence sensor for enantioselectivity recognition of chiralorganic molecule enantiomers.

4. Conclusions

We designed and synthesized a versatile chiral polymer P2 asa “turn-off” fluorescence sensor for Cu(II), and the in situ generated(R,R)-Cu(II)-P2 can exhibit remarkable “turn-on” fluorescentenhancement response and considerable enantioselectivitiestoward L-phenylglycinol via a ligand displace mechanism. Thiswork can be applied for direct detection of phenylglycinol enan-tiomers by a simple, rapid, visual, sensitive and selective method.

Acknowledgments

We gratefully acknowledge the National Natural Science Foun-dation of China (No. 21074054, 51173078, 21172106), National BasicResearch Program of China (2010CB923303) and Zhejiang Provin-cial Natural Science Foundation (No. Y4110141) for their financialsupport.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.polymer.2012.10.047.

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