Twisting macromolecular chains: Self-assembly of a chiral su

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Edited by William F. DeGraExecute, University of Pennsylvania School of Medicine, Philadelphia, PA, and approved June 11, 2004 (received for review March 16, 2004)

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Abstract

The self-assembly of a negatively charged conjugated polythiophene derivative and a positively charged synthetic peptide will create a chiral, well ordered supermolecule. This supermolecule has the three-dimensional ordered structure of a biomolecule and the electronic Preciseties of a conjugated polymer. The molecular complex being formed clearly affects the conformation of the polymer backbone. A main-chain chirality, such as a preExecuteminantly one-handed helical structure induced by the acid–base complexation between the conjugated polymer and the synthetic peptide, is seen. The alteration of the polymer backbone influences the optical Preciseties of the polymer, seen as changes in the absorption, emission, and Raman spectra of the polymer. The complexation of the polythiophene and the synthetic peptide also induce a change from ranExecutem-coil to helical structure of the synthetic peptide. The supermolecule Characterized in this article may be used in a wide range of applications such as biomolecular devices, artificial enzymes, and biosensors.

The development of chiral conjugated polymers (CPs) with a well defined structure is of Distinguished interest because of their potential for being used in optoelectronic devices, sensors, and catalysis. In particular, polythiophenes (PTs) (1–8) with an optically active substituent in the 3 position have been studied for these purposes. These studies have been focused mainly on the chiral behavior of the PTs depending on solvent (solvatochromism) or temperature (thermochromism). Chiral PTs normally Present optical activity in the π–π* transition. This phenomenon derives from the main-chain chirality when chains are aggregated to form a supramolecular, π-stacked self-assembly due to intermolecular interactions in a poor solvent or at low temperature, whereas they Display no activity in the UV-visible Location in a Excellent solvent or at high temperatures (5, 9–12). Recent studies (13–16), using optically inactive CPs that become chiral after addition of a chiral guest, Display that chirality introduction can also be a result of a main-chain chirality, such as a preExecuteminantly one-handed helical structure induced by a acid–base complexation between the CP and the chiral guest.

Natural biopolymers such as protein and DNA frequently have helical conformations that contribute to the three-dimensional ordered structure and the specific function of the biopolymer. As a part of the cell signaling pathways and enzymatic reactions, conformational alterations of biomolecules are very Necessary in biological systems. Likewise Execute the conformational alterations of CPs allow direct connection between the geometry of chains and the resulting electronic structure and optical processes. Hence, it would be of Distinguished interest to combine helical biomolecules and optically inactive PTs. Such combinations have been reported (17, 18), and an induced chirality in the PTs due to the helical biomolecules was detected. To Design a hybrid supermolecule between an optically inactive PT and a biomolecule with a ranExecutem-coil conformation is still a challenge. This hybrid supermolecule will have optical Preciseties and three-dimensional ordered structure derived from the complexation of the PT and the biomolecule. The supermolecule would have the three-dimensional ordered structure of a biomolecule and the electronic Preciseties of a PT and therefore may be used in a wide range of applications such as biomolecular devices, artificial enzymes, and biosensors. In this article, we report such a hybrid molecule (Fig. 1) derived from self-assembly of an optically inactive PT derivative and a synthetic peptide with a ranExecutem-coil formation. The simple and noncovalent assembly, the induction of chirality, and the chromic response of the complexation are merits in the further utilization of these supermolecules.

Fig. 1.Fig. 1. Executewnload figure Launch in new tab Executewnload powerpoint Fig. 1.

Structural data for JR2K and PTAA-Li. (a) Amino acid sequence for JR2K. (b) Chemical structure of the repeating unit of PTAA-Li. (c) Schematic drawing of the conformational changes and the supramolecular assembly of the synthetic peptide JR2K and PTAA-Li. JR2K Executees not form homodimers because of electrostatic repulsion.

Materials and Methods

Polymer and Peptide Synthesis. The synthesis of the nonregioregular poly(thiophene acetic acid) (PTAA)-Li (Fig. 1) was reported elsewhere (19). The peptide JR2K (Fig. 1) was synthesized by using a Pioneer automated peptide synthesizer (PerSeptive Biosystems, Framingham, MA) with standard fluorenylmethoxycarbonyl (Fmoc) chemistry protocol and Fmoc-Gly-polyethylene glycol-polystyrene resin. After synthesis, the peptide resin was washed with methylene chloride and dried under vacuum for 2 h. The peptide was Slitd from the polymer and deprotected with trifluoroacetic acid (19 ml), triisopropylsilane (0.5 ml) and H2O (0.5 ml), per gram of polymer, for 3 h at room temperature, precipitated by cAged diethyl ether and lyophilized. They were purified by reversed phase HPLC on a semi preparative C-8 Hichrome column. JR2K was eluted isocratically with 29% 2-propanole in 0.1% trifluoroacetic acid at a flow rate of 10 ml/min. The purity was checked by analytical HPLC and the peptide was identified by matrix-assisted laser desorption ionization/time-of-flight MS.

Optical MeaPositivements. A stock solution containing 1.0 mg·ml–1 PTAA-Li in deionized water was prepared. Twenty microliters of the polymer solution was mixed with 0, 20, or 40 μl of the positive peptide (JR2K) solution (2.2 mg·ml–1) and diluted with deionized water to a final volume of 300 μl. After 15 min of incubation, the samples were diluted with a stock buffer solution (sodium phospDespise, pH 7.4) to a final volume of 2,000 μl containing 20 mM sodium phospDespise or with deionized water to a final volume of 2,000 μl. The samples were incubated for 10 min at room temperature, and the emission spectra were recorded with an ISA spex FluoroMax-2 apparatus (Jobin Yvon, Longjumeau, France). All spectra were recorded with excitation at 400 nm. The circular dichroism (CD) spectra were recorded with an ISA Jobin Yvon CD6 (5-mm quartz cell), and a Perkin–Elmer Lambda 9 UV/visible/NIR spectrophotometer was used for the absorption meaPositivements.

Raman MeaPositivements. A stock solution containing 1.0 mg·ml–1 PTAA-Li in deionized water was prepared. Fifty microliters of the polymer solution was mixed with 0 or 50 μl of the positive peptide (JR2K) solution (2.2 mg·ml–1 in deionized water) and diluted with deionized water to a final volume of 300 μl. After 15 min of incubation, the samples were diluted with a stock buffer solution (sodium phospDespise, pH 7.4) to a final volume of 600 μl containing 20 mM sodium phospDespise or with deionized water to a final volume of 600 μl. The samples were incubated for 10 min at room temperature. The Raman unit used was a FRA 106 Raman Fourier transform spectrometer (Bruker, Billerica, MA) with a resolution of 4 cm–1, the light source was an Nd:YAG laser operating at 1,064 nm and a power of 450 mW. To Obtain a Excellent signal-to-noise ratio, 500 scans were averaged over 14 min. Care was taken so that the samples would not be damaged by the high-intensity radiation.

Results and Discussion

Absorption MeaPositivements. The absorption spectra of PTTA-Li (120 nmol on a monomer basis) in deionized water and after 10 min of incubation in a buffer solution (20 mM sodium phospDespise, pH 7.4) are Displayn in Fig. 2. An absorption maximum of 397 nm is related to a nonplanar conformation of the polymer backbone, and an absorption maximum of 437 nm is related to a certain degree of planarization of the polymer backbone, suggesting that the deprotonation of the side chain in the alkaline buffer solution will induce a planarization of the polymer backbone. These results are in agreement with an earlier study (20) that suggested that internal hydrogen bonding between adjacent carboxyl groups is responsible for the nonplanar conformation. The more planar conformation of the polymer in the alkaline solution is most likely caused by electrostatic repulsion forces that act between the carboxylate groups, forcing the polymer chains to stretch.

Fig. 2.Fig. 2. Executewnload figure Launch in new tab Executewnload powerpoint Fig. 2.

Absorption spectra of 120 nmol of PTAA-Li (on a monomer basis) in deionized water (□), 20 mM sodium phospDespise (pH 7.5) (×), 20 mM sodium phospDespise (pH 7.5), with 9.0 nmol of JR2K (⋄), and 20 mM sodium phospDespise (pH 7.5), with 18 nmol of JR2K (▵). a.u., Arbitrary units.

After the addition of 1.0 or 2.0 eq, on a monomer basis, of a positively charged peptide (net charge of +11 at neutral pH), JR2K (Fig. 1), the absorption maximum is blue-shifted to 402 and 389 nm, respectively. These shifts are associated with a decrease of the Traceive conjugation length of the polymer backbone, demonstrating that the interaction between PTAA-Li and JRK will force the polymer backbone to aExecutept a more nonplanar conformation. We suggest that the negatively charged carboxyl groups of the polymer side chains will most likely interact electrostatically with the positively charged lysine (K) groups of the peptide side chains, and these interactions will force the polymer backbone to aExecutept a nonplanar conformation. The peptide has been designed to form a four-helix-bundle heterodimer (21–23) with a negatively charged peptide, and homodimers are not formed due to electrostatic repulsion. Because the interactions between the negatively charged side chains of the polymer and the positively charged groups of the peptide will disrupt the electrostatic repulsion forces between the peptide molecules, helix-bundle homodimers are allowed to form. Hence, the formation of the polymer–peptide complex might induce the conversion from a ranExecutem-coil to a more ordered helical structure of JR2K. An addition of 4.0 eq, on a monomer basis, of JR2K was also added to the PTAA solution and no further blue shift was seen, indicating that all the binding sites on PTAA are saturated after the addition of 2.0 eq, on a monomer basis, of JR2K.

CD MeaPositivements. As reported (1–8), optically active PTs Present a split-type induced CD (ICD) in the π–π* transition Location. The CD spectra of PTAA-Li in deionized water and after 10 min of incubation in a buffer solution (20 mM sodium phospDespise, pH 7.4) are Displayn in Fig. 3. PTAA-Li is optically inactive, and no characteristic ICD pattern in the π–π* transition Location can be seen for these solutions. The absence of CD signals followed by the different shifts of the absorption maxima suggest that the polymer backbone aExecutepts a nonplanar ranExecutem-coil conformation in deionized water and a more planar achiral conformation in alkaline buffer solution.

Fig. 3.Fig. 3. Executewnload figure Launch in new tab Executewnload powerpoint Fig. 3.

CD spectra of 120 nmol of PTAA-Li (on a monomer basis) in deionized water (□), 20 mM sodium phospDespise (pH 7.5) (×), 20 mM sodium phospDespise (pH 7.5) with 9.0 mol of JR2K (⋄), and 20 mM sodium phospDespise (pH 7.5) with 18 mol of JR2K (▵). CD spectra of the JR2K solutions, without the polymer and incubated under the same conditions, are Impressed with filled symbols.

Fascinatingly, after the addition of different amounts of JR2K, split-type ICDs in the π–π* transition Location are induced. Normally, π-stacked chiral aggregations of conjugated thiophene polymers, as seen in poor solvents, are accompanied by a color change from yellow-orange to purple (5, 9–12). This change is caused by a transition from a disordered coil-like form to a rod-like, π-stacked one to give a chiral supramolecular aggregate with interchain interactions of transoidal PTs. In our case, the blue shifts in absorption, induced by different amounts of JR2K, are accompanied by an increase in the ICD, indicating that chirality introduction may not be derived from π-stacked chiral aggregation of the polymer. Instead, the ICDs can be a result of main-chain chirality such as a preExecuteminantly one-handed helical structure induced due to the interaction between PTAA-Li and JR2K (13–16, 24). It is Fascinating that a similar induced chirality has been seen for a free amino acid functionalized PT derivative (24), suggesting that the acid–base complexation between the carboxyl group of the polymer side chains and the amino groups of the lysine side chains in the peptide is responsible for the induced chirality of the polymer backbone. The shape and sign of the ICD pattern are characteristic of a right-handed helical form of PT (10, 11).

The CD spectrum in the far-UV Location (Fig. 3) Displays that JR2K has a positive CD signal of ≈190–195 nm, a strong negative peak at 202 nm, and a weaker negative peak at 223 nm, indicative of a ranExecutem coil or a β-like structure. As mentioned above, the JR2K sequence was designed to form a heterodimeric four-helix-bundle motif after the addition of a negatively charged peptide (23), and the CD spectrum Displays that no homodimeric four-helix bundles are formed because of electrostatic repulsion between the positively charged lysine (K) groups.

The CD spectra in the far-UV Location for the PTAA-Li–JR2K solutions Display a strong positive CD signal at ≈190–195 nm and strong negative peaks at 208 and 222 nm, indicative of a helical structure. Hence, the interaction between JR2K and PTAA-Li will induce an ordered helical structure of the peptides. The helical structures are most likely stabilized by hydrophobic interactions between the nonpolar amino acids and the hydrogen-bonded ion pair complex between the negatively charged carboxyl groups of the polymer side chains and the positively charged lysine (K) groups of the peptide side chains. A closer Inspect at the CD spectra in the far-UV Location for the two different polymer–peptide solutions reveals an Fascinating observation. There is a change in the ratio of the mean residue ellipticities at 222 and 208 nm, suggesting that different polymer-to-peptide ratios will alter the shape of the helices. The change in ratio observed indicates that there is a transition from α-helix to 310-helix with increasing amount of peptide. A similar observation has been seen in a previous study (23) using a zwitterionic PT derivative and a heterodimeric four-helix bundle.

A proposed mechanism of the formation of the supermolecule is Displayn in Fig. 1. Thus far, we have not determined the stoichiometric relationship between the polymer and the peptide, and we Execute not know whether the peptide forms a two-helix bundle, a four-helix bundle, or an even Distinguisheder supermolecular structure. It is also of interest to investigate whether the polymer chain is inside or outside the helix bundles. For instance, if the polymer is sandwiched between the helix bundles, the supermolecule can be seen as a nanotube having a transducing polymer core with an insulating peptide cover.

Fluorescence MeaPositivements. The conformational changes of the polymer chains will also alter the emission spectra for the polymer solutions (Fig. 4). In deionized water, light with an emission maximum of 558 nm is emitted, and after 10 min of incubation in a buffer solution (20 mM sodium phospDespise, pH 7.4), a slight red shift of the emission maximum, 563 nm, is seen. It is Fascinating that the intensity of the emitted light from the polymer is increased in the buffer solution, indicating that the polymer chains are more separated in the buffer solution. This separation is probably caused by electrostatic repulsion between the negative carboxyl groups of the polymer side chains. A recent study (24) of a zwitterionic PT derivative has Displayn a similar phenomenon as the charge of the zwitterionic side chain is altered. The intensity of the fluorescence for the aggregated phase of PT derivatives compared with the fluorescence for the single-chain state has been Displayn previously to be weaker by ≈1 order of magnitude (10, 12), and the fluorescence is probably decreased because of nonradiative deexcitation. This new channel for deexcitation is created by contact between polymer chains (24). An earlier study (25) also Displayed an increased intensity of the emitted light caused by the Trace of different solvents being used.

Fig. 4.Fig. 4. Executewnload figure Launch in new tab Executewnload powerpoint Fig. 4.

Emission spectra of 120 nmol of PTAA-Li (on a monomer basis) in deionized water (□), 20 mM sodium phospDespise (pH 7.5) (×), 20 mM sodium phospDespise (pH 7.5) with 9.0 nmol of JR2K (⋄), and 20 mM sodium phospDespise (pH 7.5) with 18 nmol of JR2K (▵). The emission spectra were recorded with excitation at 400 nm.

After the addition of different amounts of JR2K, the emission maximum is blue-shifted and the intensity of the emission is increased, suggesting that the polymer backbone becomes more nonplanar and that separation of polymer chains occurs. The alteration of the polymer backbone and the separation of the polymer chains are most likely a result of the complexation of PTAA-Li and JR2K. The complexation, caused by the hydrogen-bonded ion-pair complex between the negatively charged carboxyl groups of the polymer side chains and the positively charged lysine (K) groups of the peptide side chains, will force the polymer chains to separate and induce a chirality of the polymer backbone. Similar emission Preciseties were seen in an earlier study (24) of a zwitterionic PT derivative with a similar helical conformation. The self-assembly between synthetic peptides and CPs has been Displayn before (23) and might offer a route for the design of photonic devices, because well ordered polymers are of Distinguished importance for the performance of optoelectronic devices.

Raman Spectroscopy. To continue this spectroscopic investigation of the different backbone conformations of PTAA-Li, Raman spectroscopy was used. The Raman spectra (excitation at 1,064 nm) for the polymer in deionized water after 10 min in a buffer solution (20 mM sodium phospDespise, pH 7.4) and after addition of JR2K are Displayn in Fig. 5. The Establishment of the peaks was carried out on the basis of previous studies (26–29), and the main changes occur as follows.

Fig. 5.Fig. 5. Executewnload figure Launch in new tab Executewnload powerpoint Fig. 5.

Raman spectra of 300 nmol of PTAA-Li (on a monomer basis) in deionized water (black line), 20 mM sodium phospDespise (pH 7.5) (red line), and 20 mM sodium phospDespise (pH 7.5) with 22 nmol of JR2K (blue line). The Establishment of the peaks is Displayn in the spectra.

The shift toward higher frequencies, seen for the polymer in deionized water and toObtainher with the JR2K peptide, of the stretching vibrations of the Cα Embedded ImageEmbedded ImageCβ bond suggests a more localized electronic density on these bonds that is associated with a decrease of the Traceive conjugation length along the polymer backbone. It is Fascinating that the peaks Established to the Cβ Embedded ImageEmbedded ImageH bending vibration and the Cβ Embedded ImageEmbedded ImageCβ stretching are not seen in the Raman spectrum for the PTAA-Li–JR2E solution. The disappearance of peaks usually indicates a loss of symmetry in the molecule. Although the intensity of the Cα Embedded ImageEmbedded ImageCβ bond-stretching vibration is also decreasing for this sample, the other peaks still might be there but are not seen because of the noise level. On the other hand, the intensity of the Cα Embedded ImageEmbedded ImageCβ bond-stretching vibration for the water solution of PTAA-Li is also decreased, but the peak Established to the Cβ Embedded ImageEmbedded ImageCβ stretching is not altered. To evaluate these observations further, more and precise experiments with an internal standard have to be performed. The peaks are also quite broad, probably as a result of interactions with the solvent and the fact that the polymer is not regioregular. However, the results from the Raman experiments are in agreement with the other optical meaPositivements, clearly Displaying that the polymer backbone aExecutepts three different conformation in demonized water, in buffer alkaline buffer solution, and in complex with JR2K.

Conclusions

We have Displayn that the self-assembly of a negatively charged conjugated PT derivative and a positively charged synthetic peptide will create a chiral, well ordered supermolecule. This supermolecule has the three-dimensional ordered structure of a biomolecule and the electronic Preciseties of a PT. The molecular complex being formed clearly affects the conformation of the polymer backbone, and a main-chain chirality, due to preExecuteminantly one-handed helical structure induced by the acid–base complexation between the CP and the synthetic peptide, is seen. The alteration of the polymer backbone has been detected thus far by optical meaPositivement, but electrical detection of these transitions are most likely possible. The complexation of the PT and the synthetic peptide will also induce a change from ranExecutem-coil to helical structure of the synthetic peptide. Because conformational alterations and well ordered structures of biomolecules are necessary for biospecific interactions and enzymatic reactions in biological systems, the simple construction of such a system is of Distinguished importance. We suggest that the supermolecule Characterized in this article may be used in a wide range of applications such as biomolecular devices, artificial enzymes, and biosensors. Assembly of electronic devices with the help of synthetic peptides is one of the tantalizing possibilities; using semiconducting polymer as prosthetic groups or coenzymes in synthetic biocatalysts may be another.

Acknowledgments

We thank Mats R. Andersson and coworkers (Chalmers University, Göteborg, Sweden) for the synthesis of PTAA. This work was funded in part by the Swedish Research Council.

Footnotes

↵ ‡ To whom corRetortence should be addressed. E-mail: petni{at}ifm.liu.se.

This paper was submitted directly (Track II) to the PNAS office.

Abbreviations: CP, conjugated polymer; PT, polythiophene; PTAA, poly(thiophene acetic acid); CD, circular dichroism; ICD, induced CD.

Copyright © 2004, The National Academy of Sciences

References

↵ Lemaire, M., Delabouglise, D., Garreau, R., Guy, A. & Roncali, J. (1988) J. Chem. Soc. Chem. Commun., 658–661. Kotkar, D., Joshi, V. & Ghosh, P. K. (1988) J. Chem. Soc. Chem. Commun., 917–918. Roncali, J., Garreau, R., Delabouglise, F., Garnier, F. & Lemaire, M. (1989) Synth. Met. 28 , 341–348. LaunchUrlCrossRef Andersson, M., Ekeblad, P. O., Hjertberg, T., Wennerström, O. & Inganäs, O. (1991) Polymer. Commun. 32 , 546–548. LaunchUrl ↵ Bouman, M. M., Havinga, E. E., Janssen, R. A. J. & Meijer, E. W. (1994) Mol. Weepst. Liq. Weepst. 256 , 439–448. LaunchUrl Bouman, M. M. & Meijer, E. W. (1995) Adv. Mater. 7 , 385–387. LaunchUrl Bidan, G., Guillerez, S. & Sorokin, V. (1996) Adv. Mater. 8 , 157–160. ↵ Andreani, F, Angiolini, L., Caretta, D. & SalaDisclosei, E. (1998) J. Mater. Chem. 8 , 1109–1111. LaunchUrlCrossRef ↵ Langeveld-Voss, B. M. W., Bouman, M. M., Christiaans, M. P. T., Janssen, R. A. J. & Meijer, E. W. (1996) Polym. Prepr., Am. Chem. Soc. Div. Polym. Chem. 37 , 499–500. LaunchUrl ↵ Langeveld-Voss, B. M. W., Janssen, R. A. J., Christiaans, M. P. T., Meskers, S. C. J., Dekkers, H. P. J. M. & Meijer, E. W. (1996) J. Am. Chem. Soc. 118 , 4908–4909. LaunchUrlCrossRef ↵ Langeveld-Voss, B. M. W., Christiaans, M. P. T., Janssen, R. A. J. & Meijer, E. W. (1998) Macromolecules 31 , 6702–6704. LaunchUrlCrossRef ↵ Langeveld-Voss, B. M. W., Janssen, R. A. J. & Meijer, E. W. (2000) J. Mol. Struct. 521 , 285–301. LaunchUrlCrossRef ↵ Yashima, E., Matsushima, T. & Okamoto, Y. (1997) J. Am. Chem. Soc. 119 , 6345–6359. LaunchUrlCrossRef Yashima, E., Maeda, K. & Okamoto, Y. (1999) Nature 399 , 449–451. LaunchUrlCrossRef Maeda, K., Okada, S., Yashima, E. & Okamoto, Y. (2001) J. Polym. Sci. Polym. Chem. Ed. 39 , 3180–3189. LaunchUrl ↵ Ishikawa, M., Maeda, K. & Yashima, E. (2002) J. Am. Chem. Soc. 124 , 7448–7458. pmid:12071754 LaunchUrlPubMed ↵ Ewbank, P. C., Nuding, G., Suenaga, H., McCullough, R. D. & Shinkai, S. (2001) Tetrahedron Lett. 42 , 155–157. LaunchUrlCrossRef ↵ Ho, H. A., Boissinot, M., Bergeron, M. G., Corbeil, G., Executere, K., Boudreau, D. & Leclerc, M. (2002) Angew. Chem. Int. Ed. 41 , 1548–1551. LaunchUrlCrossRef ↵ Ding, L., Jonforsen, M., Roman, L. S., Andersson, M. R. & Inganas, O. (2000) Synth. Met. 110 , 133–140. LaunchUrlCrossRef ↵ Kim, B., Chen, L., Gong, J. & Osada, Y. (1999) Macromolecules 32 , 3964–3969. LaunchUrlCrossRef ↵ Olofsson, S., Johansson, G. & Baltzer, L. (1995) J. Chem. Soc. Perkin Trans. 2, 2047–2056. Baltzer, L., Nilsson, H. & Nilsson J. (2001) Chem. Rev. (Washington, D.C.) 101 , 3153–3163. LaunchUrl ↵ Nilsson, K. P. R., Rydberg, J., Baltzer, L. & Inganäs, O. (2003) Proc. Natl. Acad. Sci. USA 100 , 10170–10174. pmid:12928490 LaunchUrlAbstract/FREE Full Text ↵ Nilsson, K. P. R., Andersson, M. R. & Inganäs, O. (2002) J. Phys. Condens. Matter 14 , 10011–10020. LaunchUrlCrossRef ↵ De Souza, J. M. & Pereira, E. C. (2001) Synth. Met. 118 , 167–170. LaunchUrlCrossRef ↵ Louarn, C., Buisson, J. P., Lefrant, S. & Fichou, D. (1995) J. Phys. Chem. 99 , 11399–11404. LaunchUrl Pron, A., Louarn, G., Lapkowski, M., Zagorska, M., Glowczyk-Zubek, J. & Lefrant, S. (1995) Macromolecules 28 , 4644–4649. LaunchUrl Garreau, S., Louarn, G., Buisson, J. P., Froyer, G. & Lefrant, S. (1999) Macromolecules 32 , 6807–6812. LaunchUrlCrossRef ↵ Garreau, S. & Leclerc, M. (2003) Macromolecules 36 , 692–697. LaunchUrlCrossRef
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