Self-Assembly of DNA-Coupled Semiconducting Block Copolymers

May 21, 2014 - Xi-Jun Chen,. † and So-Jung Park*. ,†,‡. †. Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 191...
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Self-Assembly of DNA-Coupled Semiconducting Block Copolymers Amanda C. Kamps,† Ma. Helen M. Cativo,† Xi-Jun Chen,† and So-Jung Park*,†,‡ †

Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States Department of Chemistry and Nano Science, Global Top 5 Program, Ewha Womans University, 52 Ewhayeodae-gil, Seodaemun-gu, Seoul 120-750, Korea

‡

S Supporting Information *

ABSTRACT: We describe the synthesis and self-assembly of amphiphilic semiconducting polymers composed of a polythiophene derivative (i.e., poly[3-(2,5,8,11-tetraoxatridecanyl)thiophene] (PTOTT)) and an oligonucleotide, DNA-bPTOTT. These new bioconjugated polymers combine the excellent optoelectronic properties of semiconducting polymers and the programmable molecular recognition properties of DNA. Because of the unique combination of rigid polythiophene and highly negatively charged DNA, they self-assemble into size-controllable vesicles in water. DNA-modified one-dimensional polythiophene nanoribbons were formed by simultaneous assembly of DNA-b-PTOTT with PEG-b-PTOTT, demonstrating that various types of DNA-modified functional nanostructures can be formed by the mixed assembly. This approach offers a new pathway to couple various types of soft optoelectronic nanostructures with DNA’s molecular recognition properties.

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INTRODUCTION DNA block copolymers are a new emerging class of functional hybrid polymers that are composed of an oligonucleotide strand covalently attached to another polymer. Based on their amphiphilicity and molecular recognition properties,1,2 DNA block copolymers can be assembled into various types of nanostructures possessing useful characteristics for a number of applications ranging from DNA-templated syntheses3 to gene therapy4,5 and drug delivery.6 For example, Mirkin and coworkers showed that spherical micelles of DNA-blockpolystyrene (DNA-b-PS) can assemble into macroscopic polymer networks showing cooperative sharp melting transitions.7 We have utilized the simultaneous self-assembly of DNA-b-PS and magnetic nanoparticles to fabricate nanoparticle-loaded DNA block copolymer assemblies possessing dramatically enhanced DNA-binding properties.8 Researchers have also shown that DNA block copolymers can be assembled into various morphologies by utilizing the molecular recognition property of DNA. Gianneschi and co-workers have synthesized a DNA brush copolymer that undergoes a reversible sphere-to-cylinder morphology change by DNA cleavage and hybridization.9 Hermann et al. reported the formation of rodlike assemblies of DNA-block-poly(propylene oxide) (DNA-b-PPO) by using a long repetitive complementary DNA strand as a template.10 The rod-shaped aggregates showed a significantly higher cellular uptake than spheres,11 demonstrating that the ability to control the morphology of DNA-block copolymer assemblies is important for their biological and medical applications. An intriguing new possibility in this area comes from the chemical diversity and various chemical and physical properties of synthetic polymers. Owing to the tremendous advancement in polymer syntheses, a wide range of different end-function© 2014 American Chemical Society

alized polymers can be synthesized and possibly coupled to DNA in order to combine the recognition properties of DNA with various functionalities of synthetic polymers. However, in most previous work, the role of the organic polymer coupled to DNA was to grant the amphiphilicity for self-assembly, and therefore insulating coil-type polymers were typically used in the synthesis of DNA block copolymers.12 Among many different types of functional polymers, conjugated polymers are particularly interesting due to their unique optical and transport properties such as tunable absorption and photoluminescence in the visible region, high extinction coefficients, and high hole mobility, which have been extensively studied for a multitude of applications such as optoelectronic devices and biological sensing.13 Therefore, the coupling of DNA and conjugated polymers into a block copolymer structure can delve into a new realm of applications that combine the optoelectronic properties of the conjugated polymer with the programmable molecular recognition property of DNA. However, coupling DNA to a widely used conjugated polymer is a challenging task due to the poor water solubility of prototypical conjugated polymers. Therefore, earlier examples of DNA-coupled πconjugated systems utilized either conjugated oligomers14−16 or water-soluble conjugated polyelectrolytes.17,18 Here, we synthesized a novel π-conjugated block copolymer with a hydrophobic polythiophene derivative (Figure 1) and investigated their self-assembly behavior. Recently, Hermann et al. synthesized a DNA-coupled π-conjugated polymer, DNAblock-poly(9,9-di-n-octylfluorenyl-2,7-diyl) (DNA-b-PFO),19 and used them to disperse carbon nanotubes in water and Received: March 10, 2014 Revised: May 14, 2014 Published: May 21, 2014 3720

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are an unusual class of block copolymers that can act as a rod− coil or rod−rod block copolymer depending on the solution composition and DNA hybridization. Therefore, DNA-coupled π-conjugated polymers represent a new class of polymeric amphiphiles that allows us to extend our understanding of amphiphilic self-assembly and provide self-organizing hybrid materials with interesting combinations of properties from two disparate polymers. In our work, tetraethylene glycol was introduced as a side chain to increase the solubility of polythiophene in acetonitrile, a commonly used solvent for automated DNA syntheses, and therefore to improve the coupling yield of poly[3-(2,5,8,11tetraoxatridecanyl)thiophene] (PTOTT) and DNA. When brought into water, DNA-b-PTOTT self-assembled into an unusual vesicle structure with controllable sizes. The DNA-bPTOTT vesicles retained the recognition property of DNA and the optical properties of the PTOTT block. Their self-assembly behavior was investigated in various conditions and compared to relevant polymers, poly(ethylene glycol)-block-PTOTT (PEG-b-PTOTT) and DNA-b-PS. Furthermore, DNA-decorated one-dimensional nanoribbons of PTOTT were fabricated by the simultaneous self-assembly of PEG-b-PTOTT and DNA-b-PTOTT, demonstrating that various types of DNAmodified nanostructures of optoelectronic polymers can be fabricated by mixed self-assembly with DNA-coupled πconjugated polymers.

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RESULTS AND DISCUSSION Syntheses and Characterization of DNA-b-PTOTT. A DNA-coupled π-conjugated polymer, DNA-b-PTOTT, was synthesized by coupling PTOTT to the 5′ end of 25 base oligonucleotides (5′-A10ATCCTTATCAATATT-3′) synthesized on a solid support using standard phosphoramidite chemistry. The advantage of this synthetic approach on solid supports over solution chemistry is that relatively nonpolar polymers can be coupled to DNA before the deprotection step. Still, the type of polymer should be carefully chosen to ensure good solubility in a polar organic solvent such as acetonitrile in order to achieve a high yield;22 note that most widely used conjugated polymers such as poly(3-hexylthiophene) and PFO have low solubility in such polar organic solvents. Toward this end, a polythiophene derivative, PTOTT, was synthesized in

Figure 1. (A) Chemical structure of DNA-b-PTOTT and schematic depiction of the self-assembly of DNA-b-PTOTT into vesicles. (B) TEM images of DNA-b-PTOTT vesicles and (C) DNA-b-PTOTT vesicles stained with uranyl acetate.

subsequently to position them between two electrodes. However, thus far little is known about the self-assembly behavior of DNA-coupled π-conjugated polymers. It is wellknown that rod−coil type block copolymers show a richer structural diversity than common coil−coil type block copolymers due to the liquid crystal forming nature of rigidrod-type polymers.20,21 DNA-coupled π-conjugated polymers Scheme 1. Synthesis of DNA-b-PTOTT

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this study using a modified literature synthetic procedure.23,24 The tetraethylene glycol side chains impart enough polarity to the conjugated polymer and allow for sufficient solubility in typical polar solvents such as acetonitrile and DMF, thus allowing for efficient coupling. Allyl-terminated PTOTT (1) was synthesized by a modified Grignard metathesis (GRIM) method, and then the allyl endgroup was converted to the hydroxyl group by hydroboration and oxidation reactions (Scheme 1).25 The hydroxyl-terminated PTOTT homopolymer (2) was characterized by NMR, and the molecular weight of the polymer was determined to be 6875 g mol−1 by GPC (Supporting Information). The hydroxylterminated PTOTT was then reacted with chlorophosphoramidite to yield the corresponding PTOTT-phosphoramidite (3) (Scheme 1). The activated PTOTT-phosphoramidite was then coupled to the 5′ end of the DNA (4) (Scheme 1) which was synthesized on a solid support using a DNA synthesizer (see Supporting Information for details). After a series of washing steps to remove unreacted PTOTT homopolymers, DNA-b-PTOTT (5) was deprotected and cleaved from the solid support (Scheme S2). At this step, truncated DNA strands without PTOTT were washed away by quickly dissolving them into water followed by centrifugation (14 000 rpm, 25 min) to isolate DNA-b-PTOTT precipitates. The DNA-coupled πconjugated polymer, DNA-b-PTOTT, was successfully synthesized with a typical yield of 25%. The coupling of DNA and PTOTT was confirmed by gel electrophoresis (Figure S6). Self-Assembly of DNA-b-PTOTT. The DNA-b-PTOTT polymer was self-assembled by the slow addition of water to a DMF solution of the polymer followed by subsequent dialysis into water (Figure 1A). Transmission electron microscopy (TEM) images (Figure 1B,C, Figure S7) reveal that DNA-bPTOTT self-assembles into distinct vesicle structure with a diameter of 218 ± 80 nm. Amphiphilic block copolymers can assemble into various structures such as spherical micelles, rodlike micelles, vesicles, and bilayers in water depending on the relative block length.26 DNA block copolymers tend to form simple spherical micelles due to the highly negatively charged DNA backbone.1,7 The unusual vesicle formation observed here for DNA-b-PTOTT can be explained by the π−π interaction of the rigid PTOTT block. In the self-assembly of rod−coil block copolymers, the packing of the rigid-rod block plays an important role,27 and the assembly structure is determined by the trade-offs between interfacial energy, stretching of the coil block, and packing of the rod block. Organization of rod−coil block copolymers into simple micelles with a high curvature can create rod packing defects,20 and therefore vesicles with a lower surface curvature can be thermodynamically more favorable than simple micelles. The DNA-b-PTOTT in DMF absorbs at 450 nm and is brightly fluorescent as shown in the photoluminescence (PL) spectra presented in Figure 2. The absorption spectra of DNAb-PTOTT vesicles in water show a peak at 480 nm, which is slightly red-shifted from that of DNA-b-PTOTT in DMF (Figure 2A) presumably due to the planarization of the PTOTT backbone in polymer aggregates.28 The PL of PTOTT chains is completely quenched upon the addition of water to the DMF solution of DNA-b-PTOTT (Figure 2B), indicating that the PTOTT chains are closely packed as they self-assemble into vesicles.29,30 Size-Controlled Vesicle Formation. DNA-b-PTOTT assemblies were prepared at a series of different initial concentrations of the polymer in DMF to examine the

Figure 2. (A) Absorbance and (B) PL spectra of 3.5 μM DNA-bPTOTT dissolved in DMF (black) and self-assembled into vesicles in water (blue). PL spectra were collected using an excitation wavelength of 440 nm. Pictures of DNA-b-PTOTT solutions under ambient light (A, inset) and under UV light (B, inset) are given above the spectra.

concentration effect on the self-assembly structure. When DNA-b-PTOTT was assembled at a polymer concentration of 4 μM, well-defined vesicle structures were observed as shown in Figure 3. Interestingly, the vesicle size gradually increased with increasing the polymer concentration (Figure 3). The average diameter of vesicles as measured by TEM analysis increased from 218 ± 80 nm at 4 μM concentration to 468 ± 159 nm at 7 μM concentration and finally to 1312 ± 708 nm at 18 μM concentration of DNA-b-PTOTT. DLS data showed consistent

Figure 3. TEM images of DNA-b-PTOTT assemblies in water that were self-assembled from DMF at different concentrations of DNA-bPTOTT: (A) 4 μM, (B) 7 μM, and (C) 18 μM. (D) Size analysis of vesicle diameters measured from TEM images at different concentrations of DNA-b-PTOTT: 4 μM (red), 7 μM (blue), and 18 μM (green). 3722

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aggregates by the slow addition of water and dialysis from a good solvent. PTOTT homopolymers, however, assembled into irregular semispherical aggregates by the same procedure (Figure S10), and PTOTT aggregates did not undergo any morphology transition when salt solutions were added to the dispersion. These results confirm that the DNA block is responsible for the formation of well-defined size-controllable vesicles from DNA-b-PTOTT and that the salt-induced morphology transition is due to the highly charged DNA. DNA Recognition Properties. The molecular recognition property of DNA-b-PTOTT assemblies was first examined by introducing a complementary DNA strand to the DNA-bPTOTT assemblies in 0.1 M PBS (Figure 5). The sequence

size dependence (Figure S8). The formation of large vesicles is favored in terms of interfacial energy and rod packing, and small vesicles are favorable in terms of DNA charge repulsion and stretching. The size of vesicles is therefore determined by the interplay between these interactions. In general, increased polymer concentration results in an increase of aggregation number and generates larger sized assemblies. The increase of vesicle size with polymer concentration has been observed in other block copolymers as well,31 but the size range shown here is much larger than what was found in other systems. Note that commonly used vesicle fabrication methods such as film hydration rely on kinetic processes, and controlling the size of vesicles32 is not an easy task without a postprocess such as the size extrusion technique.33−35 Effect of Salt Addition. The DNA-b-PTOTT vesicles undergo a morphology transition to a sheet-type structure upon the addition of salt solution as shown in TEM images in Figure 4A,B. The salt-induced morphological change of DNA-b-

Figure 5. (A) Absorbance spectra of 2.5 μM ds-DNA-b-PTOTT in 0.1 M PBS at 25 °C (black), heated to 65 °C (red), and then cooled back down to 25 °C (green). (B) Melting curve of 2.5 μM ds DNA control (black) and 2.5 μM ds-DNA-b-PTOTT (red) in 0.1 M PBS.

Figure 4. TEM images of DNA-b-PTOTT assemblies (A) in water, (B) in 0.1 M PBS, and (C, D) dialyzed back into water after being in 0.1 M PBS.

specific hybridization event was monitored by measuring the absorbance at 260 nm.39 The melting curve of a ds-DNA of the same sequence was also measured and presented in Figure 5 for comparison. The melting temperature (Tm) of ds-DNA-bPTOTT was similar to that of ds-DNA with respective Tm of 56.4 and 56.9 °C. The hybridization properties of DNA-b-PTOTT were further studied by monitoring Förster resonance energy transfer (FRET) between dye-labeled DNA (FAM-DNA: 5′-AATATTGATAAGGATTTTTTTTTTT-FAM-3′) and DNA-bPTOTT. Because of the large extinction coefficient of PTOTT, the fluorescence of FAM-DNA was efficiently quenched by the FRET from FAM to PTOTT upon DNA hybridization as described in Figure 6A. Increasing the temperature above the melting temperature resulted in dehybridization and recovery of the FAM-DNA fluorescence (Figure 6B,C). The FRET efficiency was determined to be 0.32 and 0.38 at 0.1 M PBS and 0.3 M PBS salt concentrations, respectively, based on the changes in the fluorescence intensity of the donor (FAM-DNA) with and without the acceptor (DNA-b-PTOTT).40 This result clearly shows that DNA is indeed covalently attached to PTOTT, since energy transfer

PTOTT occurs due to the screening of negative charges on the phosphate backbone of DNA, which causes a transition to a lower curvature morphology where DNA strands are spaced more closely.36−38 The same membrane structure was obtained when the self-assembly was induced by the addition of 0.1 M PBS instead of water (Figure S9), indicating that the osmotic pressure is not responsible for the morphology change. The salt-induced morphology transition was found to be semireversible. When the membrane in 0.1 M PBS was dialyzed back into water for 24 h, the morphology returned to a mixture of vesicles and sheets as shown in Figure 4C,D. Although the vesicle structure found after dialysis looked more broken than the original structure, this indicates that the salt-induced morphology change is slow but reversible, and thus the morphology change is thermodynamically driven. Comparison of DNA-b-PTOTT with PTOTT Homopolymers. PTOTT is an amphiphilic polymer that is composed of a hydrophobic thiophene backbone and polar tetraethylene glycol side chains. Therefore, although PTOTT does not directly dissolve in water, it can be dispersed in water as small 3723

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Figure 7. (A) Schematic representation of mixed assemblies composed of PEG-b-PTOTT and DNA-b-PTOTT and their subsequent hybridization with complementary DNA-functionalized gold nanoparticles. (B) TEM image of mixed nanoribbons in water prepared from PEG-b-PTOTT:DNA-b-PTOTT ratio of 200:1 (initial solvent composition: 95% methanol:5% DMF). (C) TEM image of mixed nanoribbons hybridized to gold nanoparticles modified with complementary DNA.

Figure 6. (A) Schematic representation of the quenching of FAMlabeled complementary DNA (0.25 μM) due to hybridization with DNA-b-PTOTT nanostructures. (B) Change in FAM intensity over temperature for FAM-DNA in 0.1 M PBS (black), DNA-b-PTOTT/ FAM-DNA mixture in DI water (red), DNA-b-PTOTT/FAM-DNA mixture in 0.1 M PBS (green), and DNA-b-PTOTT/FAM-DNA mixture in 0.3 M PBS (blue). (C) Fluorescence spectra of DNA-bPTOTT/FAM-DNA mixture in 0.1 M PBS at 25 °C (black), heated to 67 °C (red), and then cooled back down to 25 °C (gray). PL spectra were collected using an excitation wavelength of 490 nm.

nanoribbons, DNA-modified gold nanoparticles (SH-3′-A10CTCCCTAATAACAAT-5′) and a complementary linker DNA (5′-GAGGGATTATTGTTAAATATTGATAAGGAT-3′) were added to the nanoribbon dispersion as described in Figure 7A. The TEM images in Figure 7C show gold nanoparticles bound to the nanoribbons through DNA hybridization. In a control experiment where PEG-b-PTOTT nanoribbons formed without DNA-b-PTOTT were subjected to the same condition, PEG-b-PTOTT nanoribbons did not show an association with the DNA-modified gold nanoparticles (Figure S11). This result demonstrates that the simultaneous self-assembly of conjugated amphiphilic polymers and DNA-modified conjugated polymers can be used to form mixed assemblies where the self-assembly structure is directed by the major species of PEG-b-PTOTT, and DNA can be used to build more complex architecture or to make connection with a device component.

can only occur when the donor (FAM) and acceptor (PTOTT) molecules are at close proximity. DNA-Functionalized PTOTT Nanoribbons by Mixed Self-Assembly. Mixed assembly of DNA-b-PTOTT and other π-conjugated block copolymers offers a way to add DNA’s molecular recognition properties to various types of selfassembly structures that can be made from conjugated block copolymers. To demonstrate a DNA modification of a technologically relevant nanostructure, DNA-b-PTOTT was simultaneously self-assembled with PEG-b-PTOTT, which we have previously shown to form well-defined one-dimensional nanoribbons.24 In typical experiments, PEG-b-PTOTT and DNA-b-PTOTT were mixed in a molar ratio of 200:1 in a methanol/DMF mixture. Mixed assemblies of PEG-b-PTOTT and DNA-b-PTOTT were formed by the slow addition of water to the solution containing two polymers followed by the subsequent dialysis into water (Figure 7A). Because a substantially larger amount of PEG-b-PTOTT was used, the self-assembly is driven by PEG-b-PTOTT, resulting in a welldefined nanoribbon structure (Figure 7A). The one-dimensional nanoribbon shape was maintained in salt solutions and did not show any salt-induced morphology change as the DNA density on the nanoribbon surface is low. To examine the accessibility of the DNA in the corona of the mixed

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CONCLUSIONS A new DNA block copolymer composed of a polythiophene derivative and an oligonucleotide strand, DNA-b-PTOTT, was successfully synthesized by standard phosphoramidite chemistry. Because of the rigid PTOTT block, DNA-b-PTOTT selfassembled into a distinct vesicle structure in water, while DNA block copolymers of typical coil-type polymers tend to form small micelles due to the electrostatic repulsion between DNA strands. The size of vesicles was controllable over a broad length scale from a couple of hundred nanometers to over a micrometer by varying the concentration of polymers. The 3724

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added to the block copolymer solution at a rate of 10 μL per 30 s while stirring. The mixture was kept under stirring for 12 h before adding an additional 1 mL of water at a rate of 50 μL per 30 s. Then, the samples were dialyzed against water for 24 h. Preparation of Mixed (PEG-b-PTOTT + DNA-b-PTOTT) Assemblies. In a typical experiment, 50 μL of a PEG108-bPTOTT40 solution (6.3 × 10−5 M) in chloroform was dried down under nitrogen and added to 50 μL of a DNA-b-PTOTT solution (3.2 × 10−7 M) in DMF and then redissolved in 1 mL of methanol (or 1 mL of DMF). 300 μL of water (18 MΩ-cm) was slowly added to the block copolymer solution at a rate of 10 μL per 30 s while stirring. The mixture was kept under stirring for 12 h before adding an additional 1 mL of water at a rate of 50 μL per 30 s. Then, the samples were dialyzed against water for 24 h.

DNA-b-PTOTT showed a salt-induced reversible morphology change from vesicles to bilayers due to the screening of negative charges on the phosphate backbone of DNA. Furthermore, a mixed assembly of PEG-b-PTOTT and DNA-b-PTOTT led to the formation of one-dimensional PTOTT nanoribbons modified with DNA. This approach offers a new pathway to combine organic semiconducting nanostructures of various shapes with the molecular recognition properties of DNA.

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EXPERIMENTAL SECTION

Materials. All reactions were carried out using standard Schlenk techniques under an inert atmosphere of prepurified nitrogen or argon, using oven-dried glassware. Tetrahydrofuran was freshly distilled from sodium/benzophenone to ensure anhydrous conditions. All nucleotide phosphoramidites and reagents used in solid-state DNA synthesis were purchased from Glen Research (Sterling, VA). Complementary DNA was purchased from Integrated DNA Technologies, Inc. (Coralville, IA). All other reagents were purchased from Aldrich or Fisher and were used without further purification. Instrumentation. Oligonucleotides were synthesized in a 10.0 μM scale on an automated DNA synthesizer (ABI, Applied Biosystems, Inc.). Electronic absorption spectra were acquired on an Agilent 8453 spectrophotometer. Thermal denaturation analysis was carried out using the same spectrophotometer equipped with a Peltier temperature controller. Photoluminescence spectra were acquired on a Spex Fluorolog 3 utilizing a R928 PMT detector. TEM was performed on a JEOL 1400 electron microscope operating at 120 kV accelerating voltage. Synthesis of Phosphoramidite-Terminated Poly[3-(2,5,8,11tetraoxatridecanyl)thiophene] (PTOTT-Phosphoramidite). The synthesis of PTOTT-phosphoramidite was based on a modified literature procedure.3,7 In a typical experiment, PTOTT-hydroxyl (150 mg, 0.015 mmol) was added to a 25 mL three-neck round-bottom flask. The reaction flask was vacuumed and purged with argon (×3). 10 mL of freshly distilled THF was added to the reaction flask followed by anhydrous diisopropylethylamine (0.1 mmol, 0.045 mL) and then 2-cyanoethyl N,N-diisopropylchlorophosphoramidite (0.1 mmol, 0.058 mL). The reaction proceeded for 2 h under argon. The product was then dried under vacuum on the Schlenk line and then redissolved into 10 mL of anhydrous DMF. The crude PTOTTphosphoramidite product (119 mg, 80% yield) was used in the DNAcoupling synthesis (within 2 h of being synthesized) without further purification. Synthesis of DNA-b-PTOTT. Block copolymers composed of an oligonucleotide block (DNA) and a PTOTT block were synthesized by coupling PTOTT-phosphoramidite to oligonucleotide grown on 1000 Å controlled pore glass (CPG) beads following modified literature procedures.3,7 PTOTT-phosphoramidite was activated with a 0.5 M tetrazole activator solution and was then immediately added via the cannula transfer technique under argon flow to a 50 mL three-neck round-bottom flask containing CPG-DNA in 2 mL of anhydrous acetonitrile. The coupling reaction proceeded under argon for 10 h. The CPG beads were then washed with anhydrous DMF to remove the uncoupled PTOTT. Oxidizing solution (0.001 M iodine in pyridine/THF/H2O) was added to the CPG beads for 30 s in a roundbottom flask. The supernatant was discarded, and the CPG beads were washed with acetonitrile three times. The DNA-b-PTOTT product and truncated DNA strands were then deprotected and cleaved from the CPG beads via incubation in concentrated ammonium hydroxide at 55 °C for 8 h. Excess DMF was then added to the filtered ammonium hydroxide solution followed by an extraction with chloroform and water to isolate the DNA-b-PTOTT product in the organic phase. Truncated DNA strands are extracted to the aqueous phase. The organic phase was dried over anhydrous MgSO4, filtered, and then dried under argon flow to yield the DNA-b-PTOTT product as an orange solid (25% yield). Preparation of DNA-b-PTOTT Vesicles. In a typical experiment, 150 μL of a DNA-b-PTOTT solution (1.5 × 10−5 M) in DMF was added to 600 μL of DMF. 300 μL of water (18 MΩ·cm) was slowly

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ASSOCIATED CONTENT

S Supporting Information *

Detailed synthetic procedure and additional characterization data of PTOTT and its monomers; additional DNA hybridization and characterization data (PAGE gel, DLS, FRET studies, etc.) of DNA-b-PTOTT and its vesicles; additional DNA hybridization studies and characterization data of nanoribbons formed from the self-assembly of DNA-bPTOTT and PEG-b-PTOTT; additional TEM images. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected] (S.-J.P.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the NSF Career Award (DMR 0847646), ARO Young Investigator Award (W911NF-09-10146), the Camille Dreyfus Teacher Scholar Award, and the Nano/Bio Interface Center through the National Science Foundation IGERT DGE02-21664.

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REFERENCES

(1) Fuks, F.; Talom, R. M.; Gauffre, F. Chem. Soc. Rev. 2011, 40, 2475−2493. (2) Alemdaroglu, F. E.; Herrmann, A. Org. Biomol. Chem. 2007, 5, 1311−1320. (3) Alemdaroglu, F. E.; Ding, K.; Berger, R.; Herrmann, A. Angew. Chem., Int. Ed. 2006, 45, 4206−4210. (4) Liu, H. P.; Zhu, Z.; Kang, H. Z.; Wu, Y. R.; Sefan, K.; Tan, W. H. Chem.Eur. J. 2010, 16, 3791−3797. (5) Kwak, M.; Musser, A. J.; Lee, J.; Herrmann, A. Chem. Commun. 2010, 46, 4935−4937. (6) Alemdaroglu, F. E.; Alemdaroglu, N. C.; Langguth, P.; Herrmann, A. Adv. Mater. 2008, 20, 899−902. (7) Li, Z.; Zhang, Y.; Fullhart, P.; Mirkin, C. A. Nano Lett. 2004, 4, 1055−1058. (8) Chen, X.-J.; Sanchez-Gaytan, B. L.; Hayik, S. E. N.; Fryd, M.; Wayland, B. B.; Park, S.-J. Small 2010, 6, 2256−2260. (9) Chien, M.-P.; Rush, A. M.; Thompson, M. P.; Gianneschi, N. C. Angew. Chem., Int. Ed. 2010, 49, 5076−5080. (10) Ding, K.; Alemdaroglu, F. E.; Boersch, M.; Berger, R.; Herrmann, A. Angew. Chem., Int. Ed. 2007, 46, 1172−1175. (11) Alemdaroglu, F. E.; Alemdaroglu, N. C.; Langguth, P.; Herrmann, A. Macromol. Rapid Commun. 2008, 29, 326−329. (12) Schnitzler, T.; Herrmann, A. Acc. Chem. Res. 2012, 45, 1419− 1430. 3725

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(13) Tran, H. D.; Li, D.; Kaner, R. B. Adv. Mater. 2009, 21, 1487− 1499. (14) Hoeben, F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J. Chem. Rev. 2005, 105, 1491−1546. (15) Jatsch, A.; Schillinger, E. K.; Schmid, S.; Bauerle, P. J. Mater. Chem. 2010, 20, 3563−3578. (16) Ruiz-Carretero, A.; Janssen, P. G. A.; Kaeser, A.; Schenning, A. P. H. J. Chem. Commun. 2011, 47, 4340−4347. (17) Yang, C. J.; Pinto, M.; Schanze, K.; Tan, W. Angew. Chem., Int. Ed. 2005, 44, 2572−2576. (18) Lee, K.; Povlich, L. K.; Kim, J. Adv. Funct. Mater. 2007, 17, 2580−2587. (19) Kwak, M.; Gao, J.; Prusty, D. K.; Musser, A. J.; Markov, V. A.; Tombros, N.; Stuart, M. C. A.; Browne, W. R.; Boekema, E. J.; ten Brinke, G.; Jonkman, H. T.; van Wees, B. J.; Loi, M. A.; Herrmann, A. Angew. Chem., Int. Ed. 2011, 50, 3206−3210. (20) Olsen, B. D.; Segalman, R. A. Mater. Sci. Eng., R 2008, 62, 37− 66. (21) Klok, H. A.; Lecommandoux, S. Adv. Mater. 2001, 13, 1217− 1229. (22) Lutz, J. F.; Borner, H. G. Prog. Polym. Sci. 2008, 33, 1−39. (23) Sheina, E. E.; Khersonsky, S. M.; Jones, E. G.; McCullough, R. D. Chem. Mater. 2005, 17, 3317−3319. (24) Kamps, A. C.; Cativo, M. H. M.; Fryd, M.; Park, S.-J. Macromolecules 2014, 47, 161−164. (25) Iovu, M. C.; Jeffries-El, M.; Sheina, E. E.; Cooper, J. R.; McCullough, R. D. Polymer 2005, 46, 8582−8586. (26) Choucair, A.; Eisenberg, A. Eur. Phys. J. E 2003, 10, 37−44. (27) Kamps, A. C.; Fryd, M.; Park, S.-J. ACS Nano 2012, 6, 2844− 2852. (28) Meier, H.; Stalmach, U.; Kolshorn, H. Acta Polym. 1997, 48, 379−384. (29) Tu, G. L.; Li, H. B.; Forster, M.; Heiderhoff, R.; Balk, L. J.; Sigel, R.; Scherf, U. Small 2007, 3, 1001−1006. (30) Tung, Y.-C.; Wu, W.-C.; Chen, W.-C. Macromol. Rapid Commun. 2006, 27, 1838−1844. (31) Choucair, A. A.; Kycia, A. H.; Eisenberg, A. Langmuir 2003, 19, 1001−1008. (32) Hickey, R. J.; Koski, J.; Meng, X.; Riggleman, R. A.; Zhang, P.; Park, S.-J. ACS Nano 2013, 8, 495−502. (33) Nardin, C.; Hirt, T.; Leukel, J.; Meier, W. Langmuir 2000, 16, 1035−1041. (34) Lee, J. C. M.; Bermudez, H.; Discher, B. M.; Sheehan, M. A.; Won, Y.-Y.; Bates, F. S.; Discher, D. E. Biotechnol. Bioeng. 2001, 73, 135−145. (35) Kita-Tokarczyk, K.; Grumelard, J.; Haefele, T.; Meier, W. Polymer 2005, 46, 3540−3563. (36) Discher, D. E.; Ahmed, F. Annu. Rev. Biomed. Eng. 2006, 8, 323− 341. (37) Zhang, L.; Eisenberg, A. Macromolecules 1996, 29, 8805−8815. (38) Geng, Y.; Ahmed, F.; Bhasin, N.; Discher, D. E. J. Phys. Chem. B 2005, 109, 3772−3779. (39) Tataurov, A. V.; You, Y.; Owczarzy, R. Biophys. Chem. 2008, 133, 66−70. (40) Lytton-Jean, A. K. R.; Mirkin, C. A. J. Am. Chem. Soc. 2005, 127, 12754−12755.

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dx.doi.org/10.1021/ma500509u | Macromolecules 2014, 47, 3720−3726