Large scale chirality transduction with functional molecular materials
Definizione stile: BA_Title
Definizione stile: TA_Main_Text
Large scale chirality transduction with functional molecular materials
Serena Arnaboldi1,3‡, Bhavana Gupta1,5‡, Tiziana Benincori2, Giorgia Bonetti2, Xxxxxxx Cirilli4, Alexan- der Kuhn1*
1 Univ. Bordeaux, ISM CNRS UMR 5255, Bordeaux INP, ENSCBP, 00 xxxxxx Xxx Xxxxxxx, 00000 Xxxxxx, Xxxxxx,
2 Univ.degli Studi dell’Insubria, Dip. di Scienza e Alta Tecnologia, Xxx Xxxxxxxxx 00, 00000 Xxxx, Xxxxx
3 Univ. degli Studi di Milano, Dip. di Chimica, Xxx Xxxxx 00, 00000 Xxxxxx; Italy
4 Centro Nazionale per il Controllo e la Valutazione dei Farmaci, Istituto Superiore di Sanità, Xxxxx Xxxxxx Xxxxx 000, 00000 Xxxx, Xxxxx
5 National & Local Joint Engineering Research Center for Applied Technology of Hybrid Nanomaterials, Xxxxx Xxxxxxxxxx, Xxxxxxx 000000, Xxxxx.
KEYWORDS chiral recognition • bipolar electrochemistry • actuators • conducting polymers • enantioselectivity.
ABSTRACT: Transduction of chiral information can be achieved at different length scales. Among all possible approaches, we propose in this work a straightforward concept to transfer chiral features from the molecular level to the shape of macroscopic objects by combining the concepts of inherently chiral oligomers and bipolar electrochemistry. Hybrid freestanding lamellar films, composed of polypyrrole and the two oligomeric antipodes of a chiral monomer, are exposed in solution to a chiral target molecule (i.e. L- and D-DOPA) in the presence of an electric field. This leads to an electrochemically induced deformation of the film, which in fine results in one or the other of two macroscopic enantiomorphs, depending on which stereoisomer is present in the solution.
INTRODUCTION
Chirality can be defined at different length scales, ranging from the molecular to the supramolecular and macroscopic scale1. Local chirality refers to the molecular scale, and arises from variations in the configuration of a molecule. Global chi- rality is defined with respect to conformations at bigger length scales, such as in oligomers, polymers and supramolecular as- semblies. Macroscopic chirality refers to micrometer or larger scales, including crystals and biological structures.
The transmission mechanism of chirality from nano- to meso- and macroscopic length scales is rather complex and not yet well understood1. Since the first resolution experiments carried out by Xxxxxxx in 1848, many studies have addressed this fasci- nating topic of chirality transfer from the molecular scale to structures at the macroscopic level2-4. Various biological mate- rials, such as plant tendrils, flower petals and snail shells, ex- hibit chiral growth. In these natural materials, there are chiral elements that lead to the formation of various chiral morpholo- gies at the macroscopic scale with a specific handedness, either right or left. The investigation of the mechanisms related to chi- ral growth of biological materials is a fundamental issue, not only in biology, but also closely connected to materials science and technology fields. Scientists have explored chirality trans- mission mechanisms at different length scales with several con- cepts that in general try to mimic what happens in nature.
One of the way to transfer chirality could be through chiral recognition and/or enantioselective interactions between mole- cules; really important clue in biological, chemical and indus- trial applications5. In the chemical field, these processes are
usually studied by optical, spectroscopic and electrochemical methods. The transformation of the chiral signal into macro- scopic changes in the properties of a material is really attractive for the directly connection to other practical applications like chiral separation, catalysis and functional devices6-7.
Among the synthetic systems that mimic natural ones, chiral liquid crystals8, chiral metamaterials9, chiral catalysts10, chiral bio-sensors11, and chiral separation materials12 need to be cited.
In particular electronically conducting polymers are one of the most popular materials classes employed in advanced de- vices because of their good electron transfer and their easy func- tionalization to tune the material properties.13 They can be pre- pared trough many protocols, either by in situ electrodeposition from suitable monomers or by chemical synthesis followed by physical deposition processes. These materials can concurrently act as receptors and transducers, and be directly endowed with chirality, or a chiral monomer could be integrated during polymerization. In this way, the chiral signal is transferred from the guest chiral molecules, or the polymer itself, to the macro- scopic features of the material. On the other hand, these proper- ties can also be modified by external stimuli (solvent14-15, tem- perature16, pH16, electric field17) that directly influence the chi- ral conformation of the polymer chains at the macromolecular level.
Enantioselective interactions between chiral molecules and chiral conducting polymers could induce visible changes at the macroscopic scale; many polymers/oligomers have been so far developed mostly including chiral thiophene, pyrrole and ani- line derivatives. Some of these materials have been tested as
chiral electrodes in enantioselection discrimination processes in advanced sensing electrochemical devices.18 In most of these attempts the electrochemical enantioselectivity has been only partially achieved. Enantioselectivity manifestations are weak or labile and the kind of response (e.g., in terms of current or potential vs concentration) seems unsuitable for purposes of recognition and quantification by a single selector of either con- figurations of the probe enantiomer in mixture. A disadvantage could be that in most cases the stereogenic elements are either stereocenters localized in pendants external to the main back- bone responsible of the functionality of the material19 or a “sec- ondary” chiral structure easily lost as a function of operating conditions,20 or a chiral shape derived from external templating agents.21
In 2010 Xxxxxxxxx et al. designed a monomer22 with 3,3’- bibenzothiophene as a central scaffold, endowed with inherent chirality,23to be employed as racemic co-monomer in electro- synthesis. In other reports, tests were carried out using the indi- vidual enantiomers of this chiral molecule, separated by chiral HPLC.24 Their electrooligomerization resulted in chiral elec- trode surfaces, able to discriminate the enantiomers of chiral species by differences in peak potential recorded by cyclic volt- ammetry.25-26 This is a true advantage from an analytical point of view, because it is possible to achieve discrimination of ra- cemic mixtures of the analyte, in contrast to most of the ap- proaches discussed above for which the recognition is only based on differences in current intensity27-29.
In this context, a new concept of absolute chirality transfer from the molecular to the macroscopic level has been reported very recently30, based on the chirality dependent induction of motion of a hybrid polymer film. Analog to previous works31- 32, bipolar electrochemistry was used as a driving force to trig- ger the preferential oxidative conversion of an enantiomer at one extremity of the polymer film, whereas at the opposite ex- tremity the polymer undergoes a reduction, accompanied by site selective swelling and shrinking. The resulting deformation of the film can then be used as a readout of chiral information. In contrast to previous studies33-34, the combination of the robust concept of inherent chirality with the electromechanical propri- eties of polypyrrole (Ppy), allowed the development of a bipolar electroactuator with a true chirality-dependent on-off behav- ior30. The enantiopure inherently chiral oligomer was deposited on one side of a Ppy strip and used as bipolar electrode able to react differently, with a yes-no response, to the enantiomers of a redox active chiral analyte (L- or D-DOPA). The difference in terms of oxidation potentials between L- and D-DOPA is suf- ficient to observe the electromechanical actuation of Ppy only in the presence of the enantiomer that is easier to oxidize. Fur- thermore, the actuation is proportional to the concentration of the “good” enantiomer, and completely independent of the pres- ence of the other antipode30.
In the present work, we intend to make a further step towards the transfer of chiral information from the molecular to the mac- roscopic scale. In particular, the aim is to trigger by bipolar elec- trochemistry the deformation of a specifically designed hybrid material in such a way that it leads to the formation of two mac- roscopic objects, being not superimposable mirror images of each other.
RESULTS AND DISCUSSION
The electrooligomerization of enantiopure inherently chiral monomers on substrates like gold or glassy carbon in different
media (aqueous media and organic solvents) leads to enanti- opure surfaces with a well-pronounced enantioselection abil- ity18-21. In order to confirm in a first step that the oligomers show chiral recognition properties also when they are generated on a Ppy film, we carried out tests with Ppy films, modified with (R) or (S) enantiopure oligomer layers, analog to what has been re- ported earlier25. The inherently chiral monomer chosen for this purpose was 2,2’-bis[2-(5,2’-bithienyl)]-3,3’-bithianaphthene (BT2T4), already well-known and characterized by Xxxxxxx et al. 18-21. It is constituted of 3,3’-bibenzothiophene as an atro- pisomeric central scaffold, with a sufficiently high racemization barrier to yield stable enantiomers, and functionalized with two 2,2’-bithiophenic units featuring two α-homotopic positions of the terminal thiophene rings, granting a regioregular oligomer- ization. In preliminary tests, Ppy films were deposited by chronopotentiometry on gold coated glass slides and then cov- ered with oligo-(R) or oligo-(S)-BT2T4 according to a literature procedure30-31. The final hybrid films were peeled off from the gold-coated glass slide and used for a first, more classic enanti- orecognition tests, performed by differential pulse voltammetry (DPV) in the presence of aqueous solutions of 5 mM L- or D- DOPA and lithium perchlorate 0.1 M.
Figure 1. Top: Chemical structures of the enantiopure oligo- (S)- BT2T4 (A) and oligo-(R)-BT2T4 (B) molecules employed in the enantiorecognition tests. Bottom: Differential pulse voltam- metry signals of the enantioselective electrooxidation of 5 mM L- or D-DOPA in water and 0.1 M LiClO4 on a hybrid polymer layer composed of A) Ppy + oligo-(S)-BT2T4 and B) Ppy + ol- igo-(R)-BT2T4.
From Figure 1A, it is obvious that the (S)-hybrid surface is preferentially reacting with L-DOPA, with a peak-to-peak sep- aration between the two enantiomers of about 200 mV. The re- sults are also perfectly coherent when the opposite configura- tion of the BT2T4 oligomer is deposited. The (R)-hybrid allows a preferential oxidation of D-DOPA. Consequently, at ~0.45 V vs. AgCl/Ag it is possible to selectively electrooxidize only one of the two DOPA enantiomers, depending on which oligomer configuration is deposited on Ppy.
If this hybrid material is used as an electrode in a bipolar elec- trochemistry experiment, it should be possible to transform ex- clusively L- or D-DOPA on the positively polarized extremity of the film if the polarization potential difference is fine-tuned to a value that is just enough to oxidize the “good” enantiomer. At the other extremity of the bipolar object, a charge compen- sating reduction reaction has to occur simultaneously. Consid- ering that Ppy reduction occurs at about − 0.25 V vs. AgCl/Ag,
the theoretical threshold of the polarization potential difference between the two extremities of the bipolar electrode should be around 0.65 V in order to activate both reactions at the same time.
The schematic cell configuration employed in the bipolar ex- periments is represented in Scheme 1A. Two graphite rods are used as feeder electrodes and connected to a power supply. The bipolar electrode has a specific shape and composition in order to allow transmission of chiral information from the molecular to the macroscopic scale. Actually, the overall geometry has to be a scalene triangle with its two faces being constituted of (R)- and (S)-oligo-BT2T4, electrodeposited on Ppy, respectively. They are combined in a sandwich-type structure with an insula- tor in between in order to prevent electrons from passing from one face to the other (Scheme 1B and C). The final triangular object is placed directly at the bottom of the cell without using any kind of support. The solution contains L- or D-DOPA (5 mM) dissolved in water and 0.1 M LiClO4. When a suitable electric field is applied, only one of the two enantiopure faces is able to react as a function of which analyte enantiomer is pre- sent in the solution.
Scheme 1. A) Schematic illustration of the bipolar cell used for the experiments of chirality transmission through space. The distance between the feeder electrodes is 5 cm and the length of the bipolar electrode is 1.0 cm. The solution contains 5 mM L- or D-DOPA in water and 0.1 M LiClO4. B) and C) Magnifications of the sandwich like bipolar electrodes used for the experiments and the principle responsible for their operation. When L-DOPA is present in solu- tion, only the oligo-(S)-BT2T4 layer is able to react (B) and vice versa when D-DOPA is the analyte (C).
An electric field of proper amplitude leads to a δ+ and δ− po- larization at the extremities of the triangle. Under these condi- tions, one of the antipodes of DOPA gets selectively electroox- idized at the positively polarized end, while at the δ− side Ppy is reduced. The latter is accompanied by an uptake of solvated
Xxx cations that enter the polymer film in order to maintain elec- troneutrality35-37 (dodecylbenzene sulfonate anions, inside the polymer, are sufficient bulky to remain into the polymer). This process induces a face-selective swelling of the chiral object, depending on the stereochemistry of both the chiral analyte in solution and the chiral oligomer. Shrinking would occur only upon a reoxidation of the film, but in our specific case it is not possible considering that the extremity of the film which shows the deformation is negatively polarized, so only a reduction re- action is possible.
The result of this asymmetric electromechanical bending is that the hybrid polymer film starts curling in one direction or the other. As the initial geometry is a scalene triangle, meaning that no sides and no angles are equal, the final curved objects have no plane of symmetry and thus are macroscopic enantio- morphs as illustrated in the following.
Figure 2. Hybrid lamellar electrode strips exposed to an aqueous solution of 5 mM D-DOPA and 0.1 M LiCO4. A) (R)-oligo-BT2T4 is oriented towards the backside. B) (R)-oligo-BT2T4 is present at the front side. (a), (b) and (c) illustrate different stages during the bending process. A blue varnish dot is placed at the face modified with (R)-oligo-BT2T4 to guide the eye during the movement in- duced by the application of an electric field of 0.6 V cm-1.
The system was optimized considering that the initial film has not to be too thick to guarantee i) the electroactivity, ii) the diffusion of Li+ ions inside the PPy matrix upon reduction and iii) the flexibility that allows the object deformation by the elec- tric field. The thickness of 200 μm used in the current work (see Fig SI 1) is a good compromise in order to satisfy the dif- ferent requirements. The deposition procedure of Ppy together with the thickness were already optimized and widely discussed in previous works30-32. The insulating layer, which has a thick- ness of 100 μm, is as thin as technically possible in order to not introduce additional stiffness to the hybrid film. The capping enantiopure oligomer layer is extremely thin (less than 10 μm, Figure SI 2); it only serves as molecular recognition element, an almost monolayer-type modification would be still sufficient to ensure enantioselectivity.
Placing the hybrid object in the bipolar cell in the presence of L- or D-DOPA and applying an electric field of 0.6 V cm-1, the direction of curling is controlled by the chiral face involved in the electrooxidation, as illustrated in Figure 2 (see also Video S1 and S2). A blue spot of varnish has been added in order to better visualize the curling and it is positioned at the face mod- ified with (R)-oligo-BT2T4 to guide the eye. Both chiral hybrid films were exposed to a solution containing 5 mM D-DOPA and
0.1 M LiClO4. In Figure 2A, the (R)-oligo-BT2T4 is present at the back side (blue spot not visible in (a)), whereas in Figure 2B the same oligomer was deposited on the front side of the hybrid object. In both cases, electrooxidation of D-DOPA occurs on the face modified with the (R)-oligomer, causing a swelling of this part of the bilamellar strip. In fine this results in a controlled bending of the film, either towards the front (Figure 2A b-c, the blue spot which initially was not visible moves towards the front) or backwards (Figure 2B b-c, the initially visible blue spot moves towards the backside).
Both experiments can also be followed in real time by watch- ing the bending of the hybrid sheets from the side (Figure 3). In this case, the blue spot of varnish has always been added to the upper part of the lamellar object. In Figure 3A the (R)-BT2T4 oligomer is localized at the bottom face of the sheet in both cases ((a) and (b)). If these two identical objects are exposed to the molecular antipodes of DOPA, the bending occurs in oppo- site directions. In case (a), the bottom layer of oligomer reacts with the D-DOPA present in solution, because at the chosen po- larization potential only this one can react with D-DOPA (see CVs in Figure 1 and Supporting Video S3). This provides the electrons necessary for the reduction of Ppy. Consequently the bottom Ppy layer swells and thus starts bending upwards. For case (b), with L-DOPA in solution, it is the upper layer of the hybrid film, composed of (S)-oligo-BT2T4 and Ppy, which be- comes active. Therefore, the upper part starts swelling and the film is bending downwards. A perfectly complementary sce- nario of chiral selection is illustrated in Figure 3B. In this ex- ample the same enantiomer (D-DOPA) is present in both exper- iments (a) and (b), however the hybrid layer has a different ini- tial orientation. In (a) the (R)-BT2T4 oligomer is facing down, whereas in (b) it is (S)-oligo-BT2T4 which constitutes the bot- tom layer. The induced bending is analog to what has been ob- served in Figure 3A, but based on different diasteromeric cou- ples, as it is possible to change the chiral configuration of either the probe or of the selector to achieve the same result. In other words, the chiral information can be propagated to the macro- scopic scale in two different ways. In the first case (Figure 3A) the chiral recognition occurs between the two molecular an- tipodes of the probe (D-DOPA and L-DOPA) and one given configuration of the selector. In the second case (Figure 3B) two different selector configurations interact with one and the same enantiomer (D-DOPA). Both situations lead to opposite bend- ing due to the diasteromeric interactions between probe and se- lector.
Since the deformation of PPy is reversible and the composite object is constituted by two faces of (R)- and (S)-oligo-BT2T4, respectively, we can assume that the curling of the same object can be tuned in different directions by changing the configura- tion of the chiral probe dissolved in solution.
Figure 3. Side view of the triangular hybrid polymer objects, when an electric field of 0.6 V cm-1 is applied. A sequence of four time laps images, extracted from Supporting Video S3, are shown for each panel. A) The (R)-BT2T4 oligomer is orientated towards the bottom and the object is exposed to a 0.1 M LiClO4 solution con- taining either (a) D-DOPA or (b) L-DOPA. B) The (R)-BT2T4 oli- gomer is orientated towards either (a) the bottom or (b) the top and the object is exposed to a 0.1 M LiClO4 containing in both cases 5 mM D-DOPA.
The analyses of the bending angle and the curvature vs. time, in the presence or L- or D-DOPA in solution with (R)-BT2T4 oligomer orientated towards the bottom (Figures SI 3 and SI 4), have shown that there is an almost linear increase of both the figures of merit. The increment is less steep at lower range of time according to the object stiffness induced by the presence of the blue paint.
At the end of the bipolar experiments, when the curling is completed, the freestanding polymer films can be removed from the solution and dried. The resulting objects are shown in Figure 4. The polymer film illustrated in Figure 4a is the result of the curling experiment depicted in Figure 2A, whereas Figure 4b shows the final configuration of the object from Figure 2B. (R)-oligo-BT2T4 was located at the front side of the triangle, whereas in the other case it was at the backside (Figure 2A and 2B, respectively). Therefore, the bending occurs in opposite di- rections. The same type of experiments could be also carried out by depositing the (R)-oligo-BT2T4 on the same side of the two triangles, but with the objects being exposed to the two en- antiomers of DOPA, separately. Both type of experiments lead to identical results, based on diastereomeric interactions.
The final two objects are specular enantiomorphs, endowed with inherent chirality due to the particular geometry of the sca- lene triangles having three different angles and three edges of different length. This means that the molecular chirality has been successfully transferred to the macroscopic scale in a straightforward way.
Figure 4. Picture of the two (R)- and (S)-enantiomorphs recovered at the end of the bipolar experiments illustrated in Figure 2, illus- trating the transmission of molecular chirality to the macroscopic scale (scale bar 1 mm)
CONCLUSION
We have confirmed the robustness of the concept of inherent chirality that allows conferring intrinsic chiral features to the materials used as building blocks of hybrid bilayer objects. Fol- lowing this concept, it is possible to propagate chiral infor- mation along different length scales. After starting from the mo- lecular level with the inherently chiral monomers, the next step encompasses the supramolecular scale, via a transmission into helical macromolecular structures during electrooligomeriza- tion, and culminates in macroscopic chirality represented by the controlled generation of enantiomorphs through chirospecific curling, triggered by bipolar electrochemistry. Such an artificial version of macroscopic enantiogenesis, based on the synergy of well-chosen molecular ingredients and physico-chemical engi- neering, can be considered as a model system for the transmis- sion of chiral information through space in natural systems.
MATERIALS AND METHODS
Synthesis of the polypyrrole films. Pyrrole monomer (0.2 M) was dissolved in Milli Q water with dodecylbenzene sulfonate (0.25 M). After complete dissolution of both components, two gold coated glass slides were positioned parallel in a beaker. The beaker was filled with 12 cm3 of this solution and one gold coated glass slide was used as a working electrode while the other one as counter electrode and Ag/AgCl (3M KCl) was the reference electrode. A fixed current of 4 mA was applied for 1.5 h for the polymerization of pyrrole. After polymerization, the polymer coated substrate was washed with water, dried and used for further oligomerization of 2,2’-bis[2-(5,2’- bithienyl)]-3,3’-bithianaphthene chiral monomer.
Electrosynthesis of enantiopure oligo-(R)- or oligo-(S)-2,2’- bis[2-(5,2’-bithienyl)]-3,3’-bithianaphthene (oligo-(R)- or (S)- BT2T4). The electrosynthesis of enantiopure oligo-(S)-BT2T4 and ol- igo-(R)-BT2T4 was carried out by employing the polypyrrole coated substrate as working electrode in a small beaker containing 10 cm3 of
0.1 M solution of lithium perchlorate (LiClO4) in acetonitrile (MeCN) and the (R)- or (S)- enantiopure monomers at 5mM concentration. The counter electrode was a platinum grid together with an Ag/AgCl refer- ence electrode. Oligo-(S)-BT2T4 and oligo-(R)-BT2T4 were synthetized by chronopotentiometry at a fixed current value of 4 mA for 40 minutes onto the whole rough polypyrrole surface. After deposition of the oligo- (3,3’dibenzothiophene)-polypyrrole hybrid films, they were peeled off from the gold electrode and then properly cut in a triangular shape, with a 90° angle. In this way two bilayer systems were obtained: i) one sca- lene triangle with (R)-oligo-BT2T4 on top of the Ppy and ii) one scalene triangle with (S)-oligo-BT2T4 on top of the Ppy. The two triangles were
combined using expoxy glue with the smooth Ppy sides (the ones with- out the oligomers) facing each other. The resulting hybrid sandwich (see Scheme 1) was used as a bipolar electrode.
SEM analysis of the hybrid sandwich electrode. SEM experi- ments were carried out using a Hitachi TM-1000 tabletop microscope. A SEM micrograph of the cross section of the entire sandwich-like tri- angle is provided in the SI (Figure SI 1). Another SEM micrograph of the cross section of the Ppy + enantiopure oligomer composite film is depicted in Figure SI 2.
Differential pulse voltammetry (DPV) experiments. DPV experi- ments were carried out in a beaker, used as electrochemical cell, con- taining the enantiomers of L- or D-DOPA (5 mM) dissolved in water and 0.1 M LiClO4. The reference electrode was Ag/AgCl and a plati- num grid the counter electrode. The working electrodes were hybrid electrodes composed of an oligo-(S)-BT2T4 layer or an oligo-(R)-BT2T4 layer, deposited on a freestanding Ppy film. This film was carefully isolated on the backside with varnish and connected with copper tape to the potentiostat. The optimized DPV parameters used for recording the voltammetric signals of L- or D-DOPA were: step potential 10 mV, modulation amplitude 60 mV, modulation time 40 ms and interval time 200 ms.
Bipolar curling experiments. For bipolar curling experiments, en- antiopure (R)- or (S)-oligo-(3,3’-dibenzothiophene)-polypyrrole hybrid triangles were placed in the center of the bipolar cell without any sup- port. Two graphite feeder electrodes were positioned at the extremities of the cell (5 cm distance). 0.1 M LiClO4 was used as supporting elec- trolyte to provide a sufficient amount of ions for charge compensation in the conducting polymer during bipolar actuation in the presence of 5 mM L- or D-DOPA.
The chirality controlled deformation was recorded using a macro- scope (LEICA Z16 APO) in video mode.
Movie data treatment was carried out with the help of image J soft- ware.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website.
Video S1 Hybrid lamellar electrode strip exposed to an aqueous solution of 5mM D-DOPA and 0.1 M LiCO4, (R)- oligo-BT2T4 is deposited at the back (.avi)
Video S2 Hybrid lamellar electrode strip exposed to an aqueous solution of 5mM D-DOPA and 0.1 M LiCO4, (R)- oligo-BT2T4 is deposited at the front (.avi)
Video S3 Hybrid lamellar electrode strips with (R)-BT2T4 oligomer at the bottom exposed to an aqueous solution of either 5 mM D- DOPA or 5mM L-DOPA (.avi)
AUTHOR INFORMATION
Corresponding Author
* Xxxxxxxxx Xxxx- Univ. Bordeaux, CNRS UMR 5255, Bor- deaux INP, ENSCBP, 00 xxxxxx Xxx Xxxxxxx, 00000 Xxxxxx, Xxxxxx, e-mail: xxxx@xxxxxx.xx
Present Addresses
Xxxxxx Xxxxxxxxx- Univ. Bordeaux, CNRS UMR 5255, Bor- deaux INP, ENSCBP, 00 xxxxxx Xxx Xxxxxxx, 00000 Xxxxxx, Xxxxxx, Univ. degli Studi di Milano, Dip. di Chimica, Xxx Xxxxx 00, 00000 Xxxxxx; Italy
Xxxxxxx Xxxxx- Univ. Bordeaux, CNRS UMR 5255, Bor- deaux INP, ENSCBP, 00 xxxxxx Xxx Xxxxxxx, 00000 Xxxxxx, Xxxxxx
Xxxxxxx Xxxxxxxxx- Univ.degli Studi dell’Insubria, Dip. di Scienza e Alta Xxxxxxxxxx,Xxx Xxxxxxxxx 00, 00000 Xxxx, Xxxxx
Xxxxxxx Xxxxxxx- Univ.degli Studi dell’Insubria, Dip. di Scienza e Alta Xxxxxxxxxx,Xxx Xxxxxxxxx 00, 00000 Xxxx, Xxxxx
Xxxxxxx Xxxxxxx- Centro Nazionale per il Controllo e la Valu- tazione dei Farmaci, Istituto Superiore di Sanità, Xxxxx Xxxxxx Xxxxx 000, 00000 Xxxx, Xxxxx
Author Contributions
S.A. and B.G. designed and performed the experiments; wrote and edited the manuscript. A.K. proposed the research project, provided resources, designed experiments and edited the manuscript.
T.B. designed the inherently chiral monomers, G.B. synthetized the inherently chiral monomers, R.C separated the enantiomers of the inherently chiral monomers by chiral HPLC.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
The work has been funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and in- novation program (grant agreement n° 741251, ERC Advanced grant ELECTRA). This study has also received financial support from the French State in the framework of the ”Investments for the future” program, IdEx Bordeaux (reference ANR-10-IDEX-03- 02). S.A. gratefully acknowledges the financial support of Univer- sità degli Studi di Milano for a post-doc scholarship. The authors are very grateful for fruitful discussions with Xxxxxxxx Xxxxxxx and Xxxxx Xxxxx about this project and to Xxxxxxx Xxxxxxx for the SEM analysis.
ABBREVIATIONS
(R)- or (S)-2,2’-bis[2-(5,2’-bithienyl)]-3,3’-bithianaphthene ((R)- or (S)-BT2T4); differential pulse voltammetry (DPV); L- or D-3,4- dihydroxyphenylalanine (L- or D-DOPA); polypyrrole (Ppy); lith- ium perchlorate (LiClO4); potassium chloride (KCl), acetonitrile (MeCN)
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