On Conducting Polymer Coated Electrodes: a Versatile Platform for the Modiﬁcation of Electrode Surfacesa

Full Paper http://www.paper.edu.cn

‘‘Click’’ on Conducting Polymer Coated Electrodes: A Versatile Platform for the Modiﬁcation of Electrode Surfacesa

Yan Li, Weixia Zhang, Jing Chang, Jinchun Chen, Guangtao Li,* Yong Ju*

Two types of N-substituted pyrroles with azide and terminal alkyne groups have been synthesized and electropolymerized. ‘‘Click’’ chemistry, specifically Huisgen 1,3-dipolar cycloaddition, was used as a general method for functionalization of the polypyrrole films. Several model compounds, including redox active (quinone), bioactive (cholic acid) and recognition elements (carbohydrate and thymidine) could easily be attached onto the electrode surfaces without loss of functionality or the electroactivity of the underlying conducting polymers. The results suggest that the polypyrrole films are clickable and provide a novel biocompatible and versatile platform for efficient modifications on electrode surfaces.

Introduction catalysis.[1,2] A key factor in such investigations and applications is the achievement of an efficient interface The immobilization of functional units, such as electro- between the functional groups and the conductive active, bioactive and biological recognition elements, onto surface.[3,4] conductive surfaces is of enormous interest, both in Compared to various protocols developed for confining studies of functional groups themselves and in numerous functional units onto solid surfaces, electrodeposition of applications ranging from disease diagnosis to electro- conducting polymers offers a simple and attractive approach for such a purpose.[5] Besides their excellent surface confinement capability, such polymers hold promise for Y. Li, W. Zhang, G. Li inducing electrical, electrochemical or optical signals Key Laboratory of Organic Optoelectronics and Molecular accrued from the interaction of functional groups with Engineering, Tsinghua University, Beijing 100084, China their environments, and are particularly suitable for the Fax: þ86 10 6279 2905; E-mail: [email protected] development of high performance bio- or chemosensory Y. Li, Y. Ju systems.[6,7] Key Laboratory of Bioorganic Phosphorus Chemistry and Synthesis of the functionalized monomers followed by Chemical Biology, Tsinghua University, Beijing 100084, China E-mail:[email protected] electropolymerization represents the most straightfor- ward method of creating the above-mentioned function- [7] J. Chang, J. Chen alized electrode systems. Although this strategy is useful Department of Pharmaceutical Engineering, Beijing University of and many functional groups were attached onto con- Chemical Technology, Beijing 100029, China ductive surfaces, the successful implementation of this a : Supporting information for this article is available at the bottom strategy depends to a great extent on the compatibility of of the article’s abstract page, which can be accessed from the the functional units introduced with the electropolymer- journal’s homepage at http://www.mcp-journal.de, or from the ization reaction. In some extreme cases, the polymeriza- author. tion process is completely blocked when substitutes have

Macromol. Chem. Phys. 2008, 209, 322–329 322 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/macp.200700436 转载中国科技论文在线 http://www.paper.edu.cn ‘‘Click’’ on Conducting Polymer Coated Electrodes: A Versatile Platform ...

bulky molecular size[8] or possess a lower oxidation Experimental Part potential than that of the corresponding monomers.[9] Moreover, due to harsh polymerization conditions, this Chemicals approach is critical or problematic for the immobilization Tetrabutylammonium hexafluorophosphate (TBAPF6), cholic acid, [6] of sensitive, valuable biomolecules. 1,10-dibromodecane, 30-azido-30-deoxythymidine (AZT) and pro- A useful alternative to the approach described above is pargyl amine were purchased from Sigma Company. Pyrrole, to establish a reactive conducting polymer, and then to glucose and the solvents were purchased from Beijing Chemicals attach the desired functional groups to polymer surfaces Company. All reagents and solvents were used without further by chemical grafting.[6] Several polymer systems contain- purification, unless otherwise noted. The synthetic protocols for [17] [18] ing reactive amino, carboxyl or active ester groups have N-(10-bromodecyl)pyrrole and glycosyl azide pentaacetate were adapted from published reports. been developed and widely employed for the functionalization of electrodes.[10] Nevertheless, the coupling reactions used rely on traditional nucleophilic-electrophilic reactions that are susceptible to side reactions.[11] For Instruments instance, the popular N-hydroxysuccinimide ester is prone to hydrolysis before and during the coupling reaction, Infrared spectra were obtained on ITO glass using a Perkin-Elmer which can both reduce coupling yields and make the yields spectrum GX FT-IR system in reflection mode. NMR spectra were 1 irreproducible.[12] Therefore, it is highly desirable and recorded at 300 MHz on a JOEL JNM ECA300 spectrometer. H NMR useful to develop novel polymer systems containing more chemical shifts are given in ppm relative to TMS. The ESI-MS was efficient reactive groups, which allow post-function- measured on a Bruker Esquire-LC ion trap mass spectrometer operated in positive mode. The fluorescence measurements were alization on the electrode not only easily and selectively carried out using a Fluorescene Spectrometer (Perkin-Elmer, LS55). under mild reaction conditions, but also in high yields without by-products. As a result of our continuous interest in the design and functionalization of conducting polymer coated sur- Synthesis faces,[9,10b] we were attracted by the recent development of click chemistry, especially the copper (I) catalyzed N-(10-Azidodecyl)pyrrole (1) Huisgen reaction between azide and terminal alkyne. This 1,3- dipolar cycloaddition reaction is recognized as the best N-(10-Bromodecyl)pyrrole (412 mg, 2 mmol) was heated in dry example of click chemistry and can be performed to give a DMF (35 mL) with sodium azide (650 mg, 10 mmol) for 20 h quantitative yield, in multiple solvents (including water) at 90 8C. The mixture was then cooled to room temperature and and in the presence of various functional groups, as well as added to a separating funnel containing 60 mL of a saturated aqueous solution of NaCl. The mixture was extracted with under mild reaction conditions.[13] Over the past few years, Et O(3 40 mL). The solvent was then evaporated and the product due to its efficiency and simplicity, this spring-loaded 2 purified by chromatography on a silica gel column with 4% ethyl reaction has been proved to be a promising candidate for acetate in petroleum as an eluent, yielding compound 1 (410 mg, [14] preparing biointerface designs and functional poly- 83% yield) as a light yellow oil. [15] mers. The azide, alkyne and the resulting triazole groups IR (KBr): 2 926.8, 2 954.0, 2 095.0, 1 500.1, 1 281.7, 1 043.6, are thermally stable and inert during electrooxidative 721.2 cm1. [16] 1 processes. It is conceivable that, if the electrodeposition H NMR (CDCl3): d ¼ 6.66 (2H, t, H-b), 6.13 (2H, t, H-a), 3.86 (3H, t, of conjugated polymers and the power of click chemistry NCH2), 3.25 (3H, t, CH2N3), 1.75 (2H, m, NCH2CH2), 1.60 (2H, are combined, a useful method would be developed for m, N3CH2CH2), 1.26–1.34 (14H, m, aliphatic H). þ creating an efficient interface between the functional ESI-MS (þ): m/z ¼ 249 [M þ H] . groups and the conductive surface. N-[10-(Propargyl ether)decyl]pyrrole (2) Based on the above, two types of N-substituted pyrrole monomers bearing azide and terminal alkyne groups To a CH3CN solution (25 mL) of propargyl alcohol (112 mg, 2 mmol) respectively were synthesized. The pyrrole subunit KOH (140 mg, 2.5 mmol) was added. The mixture was stirred for about 10 min and then N-(10-bromodecyl)pyrrole (412 mg, was used for the formation of the conducting polymer 2 mmol) was added. The resulting solution was stirred for 10 h at films anchored to an electrode. The azide and alkyne room temperature and evaporated under vacuum. The residue groups served as reactive sites for the covalent binding of was extracted with Et2O and washed with deionized water, dried functional units. Herein we report the preparation of two over MgSO4, concentrated in a vacuum, and purified by column types of clickable polypyrrole-based conducting polymer chromatography with 2% ethyl acetate in petroleum to give the films and demonstrate their potential application as a compound 2 as a colorless oil in 75% yield. biocompatible and versatile platform for efficient mod- IR (KBr): 2 926.8, 2 954.0, 2 095.0, 1 500.1, 1 281.7, 1 043.6, ification of electrode surfaces. 721.2 cm1.

Macromol. Chem. Phys. 2008, 209, 322–329 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mcp-journal.de 323 中国科技论文在线 http://www.paper.edu.cn Y. Li, W. Zhang, J. Chang, J. Chen, G. Li, Y. Ju

1 3 H NMR (CDCl3): d ¼ 6.66 (2H, t, H-b), 6.13 (2H, t, H-a), 3.86 (3H, t, monomers was increased to 20 10 M and the system

NCH2), 3.25 (3H, t, CH2N3), 1.75 (2H, m, NCH2CH2), 1.60 (2H, electropolymerized by successive scanning in a potential range.

m, N3CH2CH2), 1.26–1.34 (14H, m, aliphatic H). After the polymerization, the polymer was rinsed with fresh ESI-MS (þ): m/z ¼ 262 [M þ H]þ. acetonitrile and characterized by electrochemical and spectral methods. Synthesis of Cholic Acid Derived Propargyl Amide (5)

Cholic acid (0.816 g, 2 mmol), DCC (0.794 g, 2.2 mmol) and HOBt (0.297 g, 2.2 mmol) were dissolved in 6 mL of dry DMF. After General Procedure for the Modiﬁcation of the 10 min of stirring at 0 8C, propargyl amine (0.110 g, 2.0 mmol) was Polypyrrole Coated Electrode added and the mixture was kept at ambient temperature for 20 h. Afterwards, the solution was separated from precipitate and Cycloaddition reactions were carried out by immersing the azide poured into 30 mL of ethyl acetate. The ﬁltrate was washed with functionalized polypyrrole coated Pt electrode in 0.1 M appropriate

brine and dried over MgSO4. The crude product was puriﬁed on alkynes (solvent H2O/t-BuOH ¼ 1:2). 6 mol-% of CuCl2 was added, silica gel, using CH2Cl2/CH3OH (20:1–10:1) as the eluent. followed by 15 mol-% of sodium ascorbate. The reaction was left Concentration of the product-containing fractions gave a white for 24 h at room temperature. Then the electrodes were carefully solid (579.1 mg, 65% yield). rinsed with a small amount of ethanol and distilled water to 1 H NMR (CDCl3): d ¼ 6.60 (1H, br, s, NH), 4.02 (2H, m, CH2C CH), ensure that any physically absorbed alkyne moieties and copper 3.95 (1H, br, s, 12 a-H), 3.82 (1H, br, s, 7 a-H), 3.42 (1H, m, 3 a-H), residue were washed off. Finally, the electrodes were dried in a 2.23 (1H, t, C CH), 1.03–2.24 (28H, m, aliphatic H), 0.98 (3H, d, vacuum for IR and electrochemistry characterization. Cycloaddi- 19-CH3), 0.92 (3H, s, 18-CH3), 0.66 (3H, s, 21-CH3). tion reactions between the alkyne-functionalized polypyrrole and þ ESI-MS (þ): m/z ¼ 468 [M þ Na] . azide moieties were carried out in a similar manner. Synthesis of N-propargyl Iminodiacetic (7)

Propargyl amine (550 mg, 10 mmol) was dissolved in 25 mL of Results and Discussion

dry CH3CN. To this solution, K2CO3 (1.656 g, 12 mmol) and t-butyl 2-bromoacetate (3.88 g, 20 mmol) were added. The mixture was As a key intermediate for the synthesis of N-functionalized heated at 90 8C for 10 h. After the mixture was cooled to room pyrrole derivatives, N-(10-bromodecyl)pyrrole was synthe- temperature, the solvent was evaporated. The residue was sized by an alkaline-mediated coupling reaction between dissolved in CH2Cl2 and extracted with brine. The organic layer pyrrole and 1,10-dibromodecane. Subsequently, the result- was dried over MgSO4, filtered and concentrated. The chromato- ing bromide was transformed into the target molecules graphy afforded a t-butyl ester protected derivative 6 as a light with azide or alkyne groups in good yield following the yellow oil (1.783 g, 62% yield). 1 standard organic synthetic methods (Scheme 1). These H NMR (CDCl3): d ¼ 3.66 (2H, d, CH2C CH), 3.44 (4H, s, molecules are characterized by the following features: (1) a 2 NCH2CO), 2.41 (1H, t, C CH), 1.47 (18H, s, 6 CH3). 13C NMR: d ¼ 81.25, 78.81, 43.47, 55.00, 43.07, 28.19. polymerizable subunit (pyrrole) that can electrochemically ESI-MS (þ): m/z 284 [M þ H]þ. form uniform conductive films on a variety of solid The obtained ester (1.416 g, 5 mmol) and KOH (0.5 g, 8.7 mmol) surfaces; (2) a terminal reactive site that can enable a were dissolved in 30 mL of a mixture of water and ethanol (1:2). general method for covalently attaching a functional The reaction mixture was refluxed at 90 8C and monitored by TLC moiety through ‘‘click’’ chemistry; (3) a long spacer that and ESI-MS. After the reaction was complete, the mixture was can decouple the influence between the two terminal units acidified with HCl (5%) to pH 6–7 and concentrated under and facilitate reactions on the polymer surface. reduced pressure. The resulting residue was used for Cu(I) Cyclic voltammograms (CV) of both monomer 1 and 2 in catalyzed 1,3-dipolar cycloaddition directly without further acetonitrile solution using TBAPF as a supporting electro- purification. 6 lyte showed an irreversible oxidation peak at 1.1 V, comparable to that of other N-alkyl pyrroles.[19] Upon repeated cycling of the potential, an increase in anodic and General Procedure for the Electrosynthesis of Polypyrrole Films

The electropolymerization was carried out with a HEKA PG310 potentiostat (Dr. Schulz GmbH, Germany) by cyclic voltammetry in a three electrode single compartment cell. Platinum, vitreous carbon and ITO glass can be used as working electrodes. The counter electrode was a platinum wire and a saturated Ag/AgCl electrode was chosen as the reference electrode. The oxidation potentials of the monomers were determined in a highly dilute 3 acetonitrile solution (2 10 M) containing 0.1 M TBAPF6 as the Scheme 1. Synthesis of N-substituted pyrrole monomers bearing supporting electrolyte. Then the concentration of corresponding azide and terminal alkyne groups.

Macromol. Chem. Phys. 2008, 209, 322–329 324 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/macp.200700436 中国科技论文在线 http://www.paper.edu.cn ‘‘Click’’ on Conducting Polymer Coated Electrodes: A Versatile Platform ...

3 Figure 1. CV recorded from a reaction medium involving 20 10 M monomer and 0.1 M TBAPF6 in MeCN solution using a bare Pt electrode at a scan rate of v ¼ 100 mV s1: (A) monomer 1; (B) monomer 2. Characterization of the resulting polymer films P1 (C) and P2 (D) in a monomer-free electrolyte medium at different scan rates. cathodic currents was observed in both cases [Figure 1(A) Conductive polymers terminated with primary amine and 1(B)], indicating that the electropolymerization of both groups could not be obtained directly by electropolymer- monomers led to the formation of thin films of the ization of amine functionalized monomers because of the corresponding electroactive polymer P1 and P2 on the low oxidation potential of amines.[9] To obtain the amine electrodes (Pt, ITO, etc.). Once the polymer film was formed, functionalized conjugate polymers, tedious protect and the coated electrode was then removed from solution and deprotect procedures were required.[8,9] Postfunctionaliza- examined by CV in a fresh, monomer-free electrolyte tion of conducting polymers using ‘‘click’’ chemistry opens solution. The resulting N-substituted polypyrroles showed up a new opportunity to circumvent this problem. typical reversible redox behaviors and exhibited relatively After exposure of the P1-coated electrode to a coupling good stability under redox cycling. The magnitude of solution of propargyl amine and Cu(I) catalyst at room the anodic peak current for these processes indicated a temperature, the strong IR absorbance at 2 094 cm1 due to linear dependence on potential scan rate, confirming that the azide antisymmetric stretch completely disappeared the redox reaction was confined to the electrode surface [Figure 3(A)], indicating that the coupling reaction [Figure 1(C) and 1(D)]. Moreover, FT-IR measurements proceeded in almost a quantitative yield. In this case, confirmed that the reactive groups (azide or alkyne) the primary amine introduced was further derivatized remained unchanged after the polymerization (Figure S1 by reacting with 2,3-dichloronaphthoquinone under [10] and S2, see Supporting Information). the presence of Et3N, and the quinone functionalized To assess whether the reactive coatings P1 and P2 can be electrode P1b was formed. Besides the IR measure- used for heterogeneous click reactions, different types of ment which showed absorption of a carbonyl group model compounds, including redox active (quinone), at 1 675 cm1 [Figure 3(A)], the electrochemistry of bioactive (cholic acid), biological ligands (IDA) and recog- the freshly modified polymer clearly demonstrated the nition elements (carbohydrate and thymidine) were successful immobilization of quinone groups [Figure 3(B)]. studied for the immobilization process (Scheme 2). The Two electroactive subunits (the quinone group in the resulting post-functionalized polypyrrole films were char- negative potential range and the polypyrrole backbone in acterized well by FT-IR and electrochemical methods. the positive potential range) appeared in the CV, which

Macromol. Chem. Phys. 2008, 209, 322–329 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mcp-journal.de 325 中国科技论文在线 http://www.paper.edu.cn Y. Li, W. Zhang, J. Chang, J. Chen, G. Li, Y. Ju

the reaction molecule to access every reactive site on the surface. However, a nearly quantitative yield (>90%) was obtained after the temperature was elevated to 50 8C. The fact that cholic acid can be attached onto the surface is testimony that many other bulky biomolecules can be covalently attached to the polypyrrole coated film through Cu (I)-catalyzed 1,3- dipolar cycloaddition. The immobilization of large sensitive biomolecules on electrogenerated conducting polymeric films in a con- trolled manner that fully preserves their biological activity is the subject [6] Scheme 2. Schematic illustration of the immobilization of functional units on azide- of much research effort. Compared containing polymer P1 using Huisgen 1, 3-dipolar cycloaddition. with physical adsorption and covalent attachment, a method based on affinity ligands is more effective and useful.[25] It is well recognized that clearly indicated the presence of the redox group. In proteins with a string of terminal histidine residues addition, this experiment also suggests that the electro- (his-tag) can form a complex with a Cu (II) and an nitrogen- activity of polypyrrole was retained after the click reaction. oxygen-donor ligand.[26] In our work, such a biological Unfortunately, the modified polymer was not stable ligand, iminodiacetic acid (IDA), was also attached onto the and the profile of the CV graph of the quinone group, polymer P1 surface using click chemistry (Figure S3, see which is similar to the polymer made by the conventional Supporting Information), giving a conductive polymer approach,[20] was not as well defined as the quinone itself coated electrode with a pendant IDA residue. in electrolyte solution. We also found that the electrical Generally, the resulting IDA modified electrode needs to signal of the quinone group could only be observed in the first be complexed with Cu2þ and then used as a ligand for case of the thin film formed on a small Pt electrode immobilization of the enzyme.[26,27] In the Cu (I) catalyzed (2 mm2), whereas electroactivity was completely lost on Huisgen 1,3-dipolar cycloaddition, however, we found that larger Pt electrodes and ITO glass. The same phenomenon the Cu (II)-IDA complex can be formed in one pot during has also been encountered and reported in other literature the click reaction of N-propargyl iminodiacetic with articles.[21,22] The reason for this phenomenon is most polymer P1 and without the need to immerse the electrode likely that, due to the electrical insulation in the reduced into the Cu2þ solution deliberately. This is due to the fact form, the electric charge transport in these unpolar that the instable Cu (I) ions generated by sodium ascorbate polymers may be hampered. (reductant) are partly transformed into Cu2þ during the Cholic acid is a natural occurring compound and plays a process of the click reaction, as evidenced by the color prominent role in biological systems.[23] Besides its bio- change from yellowish green to greenish blue. As a conse- logical importance, it is now well recognized that this quence, the Cu2þ ions formed are expected to complex molecule is an attractive building block in various fields, with the attached IDA groups in situ. In order to confirm such as biomimetic, asymmetric synthesis and supramo- our hypothesis, the following experiment was carried out. lecular chemistry.[24] In our work, cholic acid derived Initially, we destroyed the electroactivity of the azide propargyl amide reacted with the pendant azide group of functionalized polypyrrole P1 by electrochemical over- polymer P1 and was attached to the surface of the poly- oxidation. Then, a click reaction was performed between pyrrole coated electrode. Compared with the results using the alkyne modified IDA and the azide group at the surface smaller model compounds, it was found that this reaction of the electrode. Finally, the resulting polymer was did not proceed to give high yields under normal condi- carefully washed with a small amount of distilled water 1 tions. According to the peak areas of vas(N3) at 2 094 cm and characterized by CV. As shown in Figure 4, the cyclic in the IR spectra [Figure 2(A)], the reaction gave only about voltammogram recorded in phosphate buffer (pH ¼ 7.2) a 65% yield in the ambient environment. The most exhibited a well-defined oxidation peak at 0.06 V and a probable reason for this is that, due to the large and rigid broad reduction peak at 0.39 V, which is the typical redox skeleton of cholic acid, steric crowding makes it difficult for behavior of chelate Cu2þ.[26,27] After immersing the same

Macromol. Chem. Phys. 2008, 209, 322–329 326 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/macp.200700436 中国科技论文在线 http://www.paper.edu.cn ‘‘Click’’ on Conducting Polymer Coated Electrodes: A Versatile Platform ...

Figure 3. FT-IR spectra of P1 (lower spectrum), the cholic acid modiﬁed P1 (performed at room temperature, middle spectrum) and the cholic acid modiﬁed P1 (performed at 50 8C, upper spectrum).

electrode in a high concentration of imidazole (0.2 M) led to a dramatic decrease of the fluorescence, suggesting the protein was desorbed from the film into the imidazole solution [Figure 5(B)]. As a control experiment, the immobilization of the same protein on the IDA-modified polymer surface P1f was performed. As expected, only very weak and sparse fluorescence was observed after washing Figure 2. (A) FT-IR spectra of (a) P1, (b) P1a (after treatment with with water, indicating solely non-specific physical absorp- propargyl amine on P1) and (c) P1b (after treatment with 2, tion [Figure 5(C)].[27,28] All of these results imply that the P1a P1b 3-dichloronaphthoquinone on ). (B) CV of modified Pt efficient immobilization of the enzyme originated from electrode (diameter ¼ 2 mm) in 0.1 M TBAPF6/CH3CN solution at a scan rate of v ¼ 80 mV s1. The dashed line represents the CV of the Cu-IDA ligand attached to the electrode surface. naphthoquinone derivative 5 itself using a bare Pt electrode in the same electrolyte solution.

electrode in EDTA solution, both the peaks completely disappeared, indicating that Cu2þ ions were removed via the coordination with EDTA. To demonstrate the potential use of the Cu (II)-IDA ligand modified electrode for the immobilization of biomolecules, fluorescence-tagged insulin equipped with six terminal histidine residues, which was shown to fluoresce at 495 nm, was used to form a complex with the attached ligand on the polymer surface. An incident light fluorescence microscope was employed to probe the His-tagged insulin on the electrode, as shown in Figure 5 (for color picture, see Figure S6 Supporting Information). Once exposed to protein solution, a strong fluorescence was detected on the polymer film P1d even after washing Figure 4. CV of Cu-IDA modified Pt electrode P1d in phosphate several times with distilled water, which reflects the stable buffer (pH ¼ 7.2) at a scan rate of v ¼ 80 mV s1. The dashed line immobilization of the protein on the electrode surface represents the CV of the same electrode treated with EDTA [Figure 5(A)]. Moreover, incubation of the enzyme solution.

Macromol. Chem. Phys. 2008, 209, 322–329 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mcp-journal.de 327 中国科技论文在线 http://www.paper.edu.cn Y. Li, W. Zhang, J. Chang, J. Chen, G. Li, Y. Ju

Figure 5. (a) Fluorescence images of the surface of P1d coated electrode pre-treated for 5 min with 0.5 mg mL1 of ﬂuorescence-His-tagged insulin in phosphate buffer (pH ¼ 7.2) and carefully washed with distilled water. (b) As in (a), but incubating the enzyme electrode in a solution of imidazole (0.2 M) for 3 h. (c) As in (a), but ﬁrstly immersing in EDTA solution (0.1 M) for 5 h. The scale bar is 50 mm.

To further extend the concept for click chemistry-based immobilization of a wide variety of biomolecules on conductive surfaces, a polypyrrole derivative with a terminal alkyne group was also synthesized. The electrode coated with this type of conductive polymer can react with various azide moieties in a similar manner to polymer P1, as described above. In this case, the immobilization of two important biological recognition elements (carbohydrate and thymidine) was examined (Scheme 3). As shown in Figure 6(A), carbohydrate derivatives can be easily introduced onto the polypyrrole ﬁlm in nearly quantative yields, as evidenced by the disappearance of the band for the carbon-carbon triple bond at 3 285 cm1 and the presence of a strong absorption of the carbonyl group at about 1 720 cm1. The reaction quality was comparable to

Figure 6. (A) (a) FT-IR spectra of the polymer P2 and (b) the same polymer after treatment with glycosyl azide pentaacetate P2a. (B)

CV of P2 coated Pt electrode in 0.1 M TBAFP6/CH3CN solution at a Scheme 3. Schematic illustration of the immobilization of func- scan rate of 100 mV s1 (dashed line) and CV of the same polymer tional units on alkyne-containing polymer P2 using Huisgen 1, coated electrode treated with glycosyl azide pentaacetate P2a 3-dipolar cycloaddition. (solid line) under the same conditions.

Macromol. Chem. Phys. 2008, 209, 322–329 328 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/macp.200700436 中国科技论文在线 http://www.paper.edu.cn ‘‘Click’’ on Conducting Polymer Coated Electrodes: A Versatile Platform ...

that of the azide fuctionalized polypyrrole. After the post- Keywords: click coupling reaction; conducting polymer; electro- functionalization, the electroactivity of the polymer was chemistry; functionalization of polymers kept, except for a small incease of the oxidation potential and reduce of the maximum current [Figure 6(B)]. The results also indicate that, although model compounds were just attached to the surface of a conducting polymer, the influence of the pendant group with the backbone [1] R. D. Rocklin, R. W. Murray, J. Phys. Chem. 1981, 85, 2104. could still lead to the observed changes in the electro- [2] L. A. Thompson, J. Kowalik, M. Josowicz, J. Janata, J. Am. Chem. chemical properties of the polymers. A similar phenom- Soc. 2003, 125, 324. enon was also observed for the immobilization of [3] H. Korri-Youssoufi, F. Garnier, P. Srivastava, P. A. Yassar, J. Am. 30-azido-30-deoxythymidine (AZT), a bioactive nucleic acid Chem. Soc. 1997, 119, 7388. derivative (Figure S4 and S5, see Supporting Information). [4] J. Wang, Chem. Eur. J. 1999, 5, 1681. [5] G. Bidan, Sens. Actuators B 1992, 6, 45. Since polypyrrole is biocompatible, the resulting con- [6] S. Cosnoer, Anal. Bioanal. Chem. 2003, 377, 507. ductive polymer film with biogenetic compounds may [7] J. Roncali, Chem. Rev. 1997, 97, 173. increase the biocompatibility of the polypyrrole films and [8] L. Zhai, R. L. Pilston, K. L. Zaiger, K. K. Stokes, R. D. McCullough, may find applications as new biosensor materials. Macromolecules 2003, 36, 61. [9] G. T. Li, G. Koßmehl, W. Kautek, W. Plieth, H. Zhu, H. S. O. Chan, S. Choon-Ng, Macromol. Chem. Phys. 2000, 201, 21. Conclusion [10] [10a] S. Bernier, S. Garreau, M. Bera-Aberem, C. Gravel, M. Leclerc, J. Am. Chem. Soc. 2002, 124, 12463; [10b] G. T. Li, S. Bhosale, S. Y. Tao, S. Bhosale, J. Fuhrhop, J. Polym. Sci., Part Two types of polypyrrole films bearing azide and terminal A: Polym. Chem. 2005, 43, 4547. alkyne groups were successfully prepared by electrochem- [11] N. K. Devaraji, G. P. Miller, W. Ebina, B. Kakaradov, ical polymerization and various species of interest were J. P. Collman, E. T. Kool, C. E. D. Chidsey, J. Am. Chem. Soc. 2005, 127, 8600. easily attached using a click coupling reaction. The fabri- [12] P. Gong, D. W. Grainger, Surf. Sci. 2004, 570, 67. cation and characterization of these clickable conducting [13] H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. Int. Ed. polymers offers a novel biocompatible and versatile plat- 2001, 40, 2004. form for efficient modification of electrode surface. [14] H. Nandivada, H. Chen, L. Bondarenko, J. Lahann, Angew. Compared with other surface modification methods like Chem. Int. Ed. 2006, 45, 3360. [15] W. H. Binder, R. Sachsenhofer, Macromol. Rapid Commun. self-assembled monolayers (SAM) and chemical vapor 2007, 28, 15. deposition (CVD), electrodeposition of the conducting [16] T. Lummerstorfer, H. Hoffmann, J. Phys. Chem. B 2004, 108, polymers can not only be easily performed over a wide 3963. range of substrates, but can also form polymer coatings [17] R. R. Guo, G. T. Li, W. X. Zhang, G. Q. Shen, D. Z. Shen, Chem. that exhibit distinct optical, electrical and electrochemical Phys. Chem. 2005, 6, 2025. [18] S. Chittaboina, F. Xie, Q. Wang, Tetrahedron Lett. 2005, 46, properties. The combination of these features of the 2331. electrogenerated polymer layers with the power of click [19] Y. Chen, C. T. Imrie, K. S. Ryder, J. Mater. Chem. 2001, 11, 990. chemistry further extends the concept of click chemis- [20] J. Grimshaw, S. D. Perara, J. Electroanal. Chem. 1990, 281, 125. try-based immobilization, which could find great potential [21] J. Davis, D. H. Vaughan, M. F. Cardosi, J. Electroanal. Chem. applications in tailoring surface functionalities, as well as 1996, 403, 213. [22] G. T. Li, G. H. Koßmehl, W. G. Engelmann, W. Hunnius, the development of bio/chemosensors and biomedical W. Plieth, H. Zhu, Macromol. Chem. Phys. 1998, 199, 2255. devices. [23] J. Sjo¨vall, Lipids 2004, 39, 703. [24] E. Virtanen, E. Kolehmainen, Eur. J. Org. Chem. 2004, 3385. [25] S. Cosnoer, Electroanalysis 2005, 19, 1701. Acknowledgements: We gratefully acknowledge financial sup- [26] B. Ronald, L. Benoit, S. Bernd, S. Jean-Laurent, Y. Dounia, port from the National Science Foundation of China (20473044, Langmuir 2005, 21, 3362. 20533050, 20772071) and the 973 Program (2006CB806200). [27] N. Haddour, S. Cosnier, C. Gondran, J. Am. Chem. Soc. 2005, 127, 5752. Received: August 9, 2007; Revised: September 16, 2007; Accepted: [28] J. S. Kim, C. A. Valencia, R. Liu, W. Lin, Bioconjugate Chem. September 18, 2007; DOI: 10.1002/macp.200700436 2007, 18, 333.

Macromol. Chem. Phys. 2008, 209, 322–329 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mcp-journal.de 329