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See detailProbing recognition processes, forces and motions within single molecules
Willet, Nicolas ULg; Duwez, Anne-Sophie ULg

Scientific conference (2012, May 09)

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See detailInvestigation of mechanochemical processes by single-molecule AFM
Willet, Nicolas ULg

Scientific conference (2012, March 23)

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See detailMolecular manipulation with atomic force microscopy
Duwez, Anne-Sophie ULg; Willet, Nicolas ULg

Book published by Taylor & Francis group – CRC Press (2012)

With the invention of scanning probe techniques in the early 1980s, scientists can now play with single atoms, single molecules, and even single bonds. Force, dynamics, and function can now be probed at ... [more ▼]

With the invention of scanning probe techniques in the early 1980s, scientists can now play with single atoms, single molecules, and even single bonds. Force, dynamics, and function can now be probed at the single-molecule level. Molecular Manipulation with Atomic Force Microscopy (AFM) presents a series of topics that discuss concepts and methodologies used to manipulate and study single (bio)molecules with AFM. The first part is dedicated to the pulling of single molecules with force spectroscopy to investigate molecular interactions, mechanics, and mechanochemical processes, and the second part to the manipulation, repositioning, and targeted delivery of single molecules on substrates. Single molecule manipulation is an exciting area of research which made important breakthroughs in nanoscience and which could find potential applications in a diverse range of disciplines, including chemistry, biology, physics, material and polymer science, and engineering. New and experienced AFM researchers looking for applications beyond imaging will find a wealth of information in this informative volume. [less ▲]

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See detailNew functional poly(N-vinylpyrrolidone) based (co)polymers via photoinitiated cobalt-mediated radical polymerization
Debuigne, Antoine ULg; Schoumacher, Matthieu ULg; Willet, Nicolas ULg et al

in Chemical Communications (2011), 47(47), 12703-12705

The photoinitiated cobalt-mediated radical polymerization enables the synthesis of novel alpha-functional and alpha,omega-telechelic polymers. In combination with ring-opening polymerization, it also ... [more ▼]

The photoinitiated cobalt-mediated radical polymerization enables the synthesis of novel alpha-functional and alpha,omega-telechelic polymers. In combination with ring-opening polymerization, it also produces new amphiphilic copolymers which self-assemble into flower-like vesicles in water. [less ▲]

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See detailMechanochemistry of a single polypeptide molecule: Study of force-induced conformational transitions
Willet, Nicolas ULg; Hinterdorfer, Peter; Lecommandoux, Sébastien et al

Conference (2011, August)

The aim of this study is to investigate the mechanochemical behavior of homopolypeptides able to change their conformation is a stimuli-responsive way. The peptidic secondary structures were studied in ... [more ▼]

The aim of this study is to investigate the mechanochemical behavior of homopolypeptides able to change their conformation is a stimuli-responsive way. The peptidic secondary structures were studied in detail by atomic force microscopy (AFM) at the single-molecule level. Synthetic copolymers containing a polypeptide block were prepared by N-carboxyanhydride amino acid ring-opening polymerization. The polymer chains were grafted as a dilute brush onto gold surfaces via disulfide end-groups. Their mechanochemical behavior was then studied by AFM single-molecule force spectroscopy (SMFS). The investigated polypeptide blocks were based on poly(L-glutamic acid), which undergoes a transition from alpha-helix to random coil. This can be induced by external stimuli (pH, ionic strength, temperature) or simply by applying a force. We were able to study the mechanically driven unfolding of the peptide by stretching-release cycles of the biomacromolecule. Stretching the helical peptide resulted in original features in the force-distance traces. Plateaus that are specific for the helical conformation were detected, quantified and discussed. Pulling-relaxing SMFS experiments eventually led to a better understanding of the force induced unfolding of a alpha-helix and the reversibility of the phenomenon. [less ▲]

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See detailProbing recognition processes, forces and motions within single molecules
Willet, Nicolas ULg

Scientific conference (2011, June)

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See detailMechanochemical Study of a Single Polypeptide Molecule: Force-Induced Conformational Transition
Willet, Nicolas ULg; Hinterdorfer, Peter; Lecommandoux, Sébastien et al

Conference (2011, June)

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See detailMolecular recognition force spectroscopy
Willet, Nicolas ULg; Lamprecht, Constanze; Rankl, Christian et al

in Duwez, Anne-Sophie; Willet, Nicolas (Eds.) Molecular manipulation with atomic force microscopy (2011)

This chapter describes the state of the art in molecular recognition force spectroscopy performed by AFM. The different aspects of the topic are discussed, as the appropriate techniques for the ... [more ▼]

This chapter describes the state of the art in molecular recognition force spectroscopy performed by AFM. The different aspects of the topic are discussed, as the appropriate techniques for the functionalization of cantilever tips and for the preparation of (biological) samples. The principles of single-molecule force spectroscopy are then explained, together with exciting and recent examples on synthetic and biological samples. Finally, the main techniques to map molecular recognition interactions are reviewed and discussed in terms of performances. Novel and interesting applications illustrate the use of these imaging methods. [less ▲]

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See detailThe pulling force of a synthetic molecular machine
Lussis, Perrine ULg; Svaldo-Lanero, Tiziana; Willet, Nicolas ULg et al

Conference (2010, September 07)

The widespread utilization of sub-molecular motion in key biological processes is inspiring chemists who synthesize molecular machines able to imitate the machinery of biological world. It has been proved ... [more ▼]

The widespread utilization of sub-molecular motion in key biological processes is inspiring chemists who synthesize molecular machines able to imitate the machinery of biological world. It has been proved possible to design synthetic molecular systems in which positional displacements of sub-molecular components occur upon the application of external stimuli.1-3 The architecture of synthetic systems is crucial to translate molecular level effects into a useful response exploitable in the macroscopic world. Pioneering works1-2 have shown that rotaxanes (molecules consisting of a ring threaded onto an axle capped with bulky end-stoppers) are a particularly promising kind of synthetic 'molecular shuttles'. Although nanodevices based on molecular machines have been conceived, there is a huge gap between those exploratory studies and truly functional systems, able to use an external source of energy to induce a directional motion and perform useful tasks.4 One of the major challenges is the interfacing between the molecular machines and the outside world. Here we to demonstrate the feasibility of transducing sub-molecular movements into mechanical work by combining the controlled translational motion of the ring in a rotaxane coupled to a polymer chain, and the ability of AFM-based single molecule force spectroscopy to be used as a mechanical device.5 For that purpose, a rotaxane with a long thread and two stations onto which the ring can bind through H-bonds was synthesized. We have attached a polymer chain to the ring and the resulting system was grafted onto substrates. We then fished the polymer chain with an AFM tip and realized single molecule pulling-relaxing cycles. The ring was moved away from the most stable station along the thread and was found to shuttle back to this station against the external force, thus delivering mechanical work against the AFM cantilever. We have estimated the work done by the ring and show that the value is in good agreement with predicted theoretical values.2 1 J.F. Stoddart et al., Special Issue on Molecular Machines, Acc. Chem. Res. 2001, 34, 409-522. 2 E R Kay, D A Leigh and F Zerbetto, Angew. Chem. Int. Ed. 2007, 46, 72. 3 D. A. Leigh et al., Nature 2000, 406, 608; Science 2001, 291, 2124; Nature 2003, 424, 174; Science 2004, 306, 153; Nature 2006, 440, 286; Nature 2007, 445, 523; Nature 2009, 458, 314. 4 W. R. Browne, B. L. Feringa, Nature Nanotech. 2006, 1, 25. 5 H. E. Gaub et al., Science 2002, 296, 1103. [less ▲]

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See detailBiomimetic coatings with robust antibacterial properties
Jérôme, Christine ULg; Cécius, Michaël; Faure, Emilie ULg et al

Conference (2010, July 01)

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See detailSingle molecule interactions of bio-adhesive-inspired polymers with inorganic and organic surfaces
Willet, Nicolas ULg; Giamblanco, Nicoletta ULg; Faure, Emilie ULg et al

Conference (2010, July)

Numerous living creatures have developed adhesion strategies to stick to inorganic or organic surfaces in wet environments. A classic example of permanent bioadhesion is exemplified by mussels, which ... [more ▼]

Numerous living creatures have developed adhesion strategies to stick to inorganic or organic surfaces in wet environments. A classic example of permanent bioadhesion is exemplified by mussels, which secrete adhesive proteins containing a high concentration of 3,4-dihydroxyphenylalanine (DOPA) 1, 2. The catechol species of DOPA are thought to be responsible for the strong adhesion to inorganic surfaces, whereas the oxidized o-quinone species trigger the cross-linking of the glue, ensuring cohesion. The unoxidized form of DOPA is known to adhere to a large variety of inorganic surfaces, although the adhesion mechanism is not yet fully understood.3, 4 A clear understanding is however essential for the design of synthetic adhesive polymers required in many surface science applications. Here we investigate at the single-molecule level the interaction forces between AFM tips coated with bio-inspired polymers and a variety of inorganic and organic surfaces. We prepared polymers bearing several amounts of DOPA units and covalently attached them to AFM tips following our previously published strategy.5, 6 They were homo-or co-polymers and were cross-linked or not. These original bio-inspired tips were used to perform single-molecule force spectroscopy on a range of model, as well as industrial such as stainless and galvanized steel, substrates. The specific interaction forces measured in water were compared with the ones exerted by the same polymers without DOPA. It was found that, depending on the nature of the substrate, the presence of DOPA strongly, or only slightly, increases the interaction forces with the surface. We also investigated the influence of the oxidation state of the catechol species on the intensity of the interaction forces. Again, this influence is strongly related to the nature of the substrate. Finally, we studied the effect of polymer cross-linking on the adhesive interactions. 1. Waite, J. H.; Tanzer, M. L. Science 1981, 212, 1038. 2. Waite, J. H.; Housley, T. J.; Tanzer, M. L. Biochemistry 1985, 24, 5010. 3. Lee, H.; Scherer, N. F.; Messersmith, P. B. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 12999. 4. Wang, J.; Nawaz Tahir, M.; Kappl, M.; Tremel, W.; Metz, N.; Barz, M.; Theato, P.; Butt, H.-J. Adv. Mater. 2008, 20, 3872. 5. Gabriel, S.; Jérôme, C; Jérôme, R.; Fustin, C.-A.; Pallandre, A.; Plain, J.; Jonas, A. M.; Duwez, A.-S. J. Am. Chem. Soc. 2007, 129, 8410. 6. Cecchet, F.; Lussis, P.; Jérôme, C.; Gabriel, S.; Silva-Goncalves, E.; Jérôme, R.; Duwez, A.-S. Small 2008, 4, 1101. [less ▲]

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See detailA green and refillable antibacterial coating for stainless steel
Faure, Emilie ULg; Charlot, Aurélia; Sciannaméa, Valérie et al

Poster (2010, June 29)

Because of its resistance to corrosion and chemicals, relevant mechanical and esthetical properties, stainless steel (SS) is widely used in the daily life (food industry, household appliances, surgery … ... [more ▼]

Because of its resistance to corrosion and chemicals, relevant mechanical and esthetical properties, stainless steel (SS) is widely used in the daily life (food industry, household appliances, surgery …). However, SS is unable to prevent bacteria from adhering, proliferating and forming a resistant biofilm when ageing. Therefore, surface modification is needed for providing durable antibacterial properties. We report here on an all-in-one approach to prepare refillable antimicrobial films using the layer-by-layer deposition of polyelectrolytes. Specifically designed biocidal multilayered polyelectrolyte films that bear 3,4-dihydroxyphenylalanine (DOPA), known as a promoter of adhesion to inorganic surfaces, were deposited onto SS. DOPA was incorporated in the polycationic chains by radical copolymerisation of N-methacrylated DOPA with the quaternary ammonium salt of 2-(dimethylamino)ethyl methacrylate (DMAEMA+). In order to boost the antibacterial activity of the polycationic layer, AgNO3 was added to the aqueous solution of P(DOPA)-co-P(DMAEMA+), which resulted in the in-situ formation of silver based nanoparticles, sources of biocial Ag+. The layer-by-layer deposition of aqueous P(DOPA)-co-P(DMAEMA+)/AgCl/Ag0 suspension and aqueous solution of poly(styrene sulfonate) provides high antibacterial activity against Gram-negative E. Coli bacteria. Moreover, after silver depletion, films retain some antimicrobial activity, thanks to ammonium groups of the copolymer. We also show that the antibacterial activity of the films can then be easily re-boosted. [less ▲]

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See detailA robust antibacterial coating for stainless steel
Faure, Emilie ULg; Charlot, Aurélia; Sciannaméa, Valérie et al

Conference (2010, March 23)

Because of corrosion, chemical resistance, relevant mechanical and esthetical properties, stainless steel is widely used in the daily life, not only in the building industry but also in the food industry ... [more ▼]

Because of corrosion, chemical resistance, relevant mechanical and esthetical properties, stainless steel is widely used in the daily life, not only in the building industry but also in the food industry, the appliances or in the medical field, including implants in orthopedic surgery. However, stainless steel is unable to prevent bacteria from adhering, proliferating and forming a resistant biofilm. Therefore, surface modification is needed for providing the metal surface with antibacterial properties. The scientific literature is very rich in describing various methods for imparting antibacterial properties to different inorganic supports. However, the activity of the coating is generally time limited by the diffusion of the biocide in the environment. Novel robust and stable antibacterial coatings on stainless steel are thus highly desirable for the durability of the functionality. In this communication, we report on an all-in-one approach to prepare robust antimicrobial films on stainless steel using the layer-by-layer deposition of polyelectrolytes. Novel biocidal multilayered polyelectrolyte films in which the polycationic layer is silver loaded and bears 3,4-dihydroxyphenylalanine (DOPA), known as a promoter of adhesion to inorganic surfaces, were deposited onto stainless steel. DOPA was incorporated in the polycationic chains by radical copolymerisation of N-methacrylated DOPA with the commercially available quaternary ammonium salt of 2-(dimethylamino)ethyl methacrylate (DMAEMA+). Polystyrene sulfonate (PSS) was the polyanionic constituent of the films. In order to boost the antibacterial activity of the polycationic layer, AgNO3 was added to the aqueous solution of P(DOPA)-co-P(DMAEMA+), which resulted in the in-situ formation of silver based nanoparticles (Ag° and AgCl) that are sources of biocial Ag+. The layer-by-layer deposition of aqueous P(DOPA)-co-P(DMAEMA+)/AgCl/Ag0 suspension and aqueous solution of PSS provides stainless steel with high antibacterial activity against Gram-negative E. Coli bacteria. Moreover, after silver depletion, films retain some antimicrobial activity, thanks to the ammonium groups of the copolymer. We will also show how the antibacterial activity of the films can then be easily re-boosted. The multi-functionality of the P(DOPA)-co-P(DMAEMA+) is a key issue in this process (i) the DOPA co-units are anchored to stainless steel, (ii) these co-units reduce partly AgNO3 into Ag0 nanoparticles and stabilize them by chelation, (iii) the chloride counter-anions react with AgNO3 by ionic exchange, leading to the in situ formation of AgCl particles, and (iv) the ammonium groups are responsible for permanent antibacterial activity. Besides the advantage of the all-in-one process, another major advantage of the approach proposed here is the implementation of the whole process of film formation, including the synthesis of P(DOPA)-co-P(DMAEMA+), in aqueous media under very mild conditions. It makes the strategy very attractive for industrial scaling-up and sustainability applications. [less ▲]

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See detailBioadhesive-inspired AFM Tips and their Interaction with Inorganic Surfaces
Giamblanco, N.; Willet, Nicolas ULg; Detrembleur, Christophe ULg et al

Conference (2010, February 05)

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See detailPoly(acrylic acid) with disulfide bond for the elaboration of pH-responsive brush surfaces
Van Camp, Wim; Du Prez, Filip E; Alem, Halima et al

in European Polymer Journal (2010), 46(2), 195-201

We report on a new route for the facile prepn. of pH-responsive tethered brushes on metallic surfaces, starting from poly(acrylic acid) (PAA) contg. a disulfide (S-S) bond (PAA-S-S-PAA). First, atom ... [more ▼]

We report on a new route for the facile prepn. of pH-responsive tethered brushes on metallic surfaces, starting from poly(acrylic acid) (PAA) contg. a disulfide (S-S) bond (PAA-S-S-PAA). First, atom transfer radical polymn. (ATRP) of 1-ethoxyethyl acrylate (EEA) with a disulfide-contg. initiator was performed to obtain the poly(EEA) precursor polymer (PEEA-S-S-PEEA). Deprotection of PEEA by a heating step resulted in the desired PAA chains without any further purifn. The brushes, obtained by the grafting to' of PAA-S-S-PAA onto gold, were then characterized by at. force microscopy in water at various pH values. The results evidence a large collapsing/swelling capacity. [less ▲]

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See detailAll-in-one strategy for the fabrication of antimicrobial biomimetic films on stainless steel
Charlot, Aurélia; Sciannamea, Valérie; Lenoir, Sandrine et al

in Journal of Materials Chemistry (2009), 19

Here we report on an all-in-one approach to prepare robust antimicrobial films on stainless steel. The strategy is based on the layer-by-layer deposition of polyelectrolytes. A polycationic copolymer ... [more ▼]

Here we report on an all-in-one approach to prepare robust antimicrobial films on stainless steel. The strategy is based on the layer-by-layer deposition of polyelectrolytes. A polycationic copolymer bearing 3,4-dihydroxyphenylalanine units (DOPA, a major component of natural adhesives) was synthesized and co-deposited with precursors of silver nanoparticles as the first layer. The presence of DOPA units ensures a strong anchoring on the stainless steel substrate, and the silver nanoparticles are sources of biocidal Ag+, providing stainless steel with antimicrobial activity. We show that multilayered films, obtained by alternating this nanoparticle-loaded polycationic copolymer with polystyrene sulfonate, a commercial polyanion, results in stainless steel with high antibacterial activity against Gram-negative E. coli bacteria. The polycationic layers are a reservoir of Ag+ that can be reactivated after depletion. The whole process of film formation, including the synthesis of the copolymer, is conducted in aqueous media under very mild conditions, which makes it very attractive for industrial scale-up and sustainable applications. [less ▲]

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See detailGold-loaded carbon nanoparticles from poly(vinyl alcohol)-b-poly(acrylonitrile) non-shell-cross-linked micelles
Bryaskova, Rayna; Willet, Nicolas ULg; Duwez, Anne-Sophie ULg et al

in Chemistry : An Asian Journal (2009), 4(8), 1338-1345

Herein we show that a new amphiphilic poly(vinyl alcohol)-b-poly(acrylonitrile) block copolymer dispersed in water can be easily loaded with gold nanoparticles by addition of chlorauric acid followed by ... [more ▼]

Herein we show that a new amphiphilic poly(vinyl alcohol)-b-poly(acrylonitrile) block copolymer dispersed in water can be easily loaded with gold nanoparticles by addition of chlorauric acid followed by reduction by sodium borohydride. After deposition of the so-loaded micelles onto a silicon wafer, followed by an appropriate thermal treatment, the poly(acrylonitrile) core of the micelles is carbonized, while the poly(vinyl alcohol) shell is completely decomposed and volatilized, leading to gold encapsulated in carbon nanoparticles. The morphology of the micelles is maintained during thermal treatment without requiring shell-cross-linking of the micelles prior to pyrolysis. [less ▲]

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See detailFeeling the force of a synthetic molecular shuttle
Lussis, Perrine ULg; Willet, Nicolas ULg; Bertocco, Andrea et al

Conference (2009, May 14)

The widespread utilization of sub-molecular motion in key biological processes is inspiring chemists that have been trying to synthesize molecular machines able to imitate the machinery of biological ... [more ▼]

The widespread utilization of sub-molecular motion in key biological processes is inspiring chemists that have been trying to synthesize molecular machines able to imitate the machinery of biological world. In recent years, it has been proved possible to design synthetic molecular systems in which positional displacements of sub-molecular components occur upon the application of external stimuli.[1-4] The architecture of synthetic systems is crucial to translate molecular level effect into a useful response exploitable in the macroscopic world. The pioneering work of Stoddart, Sauvage and others[1-3] has shown that molecular machines with mechanically interlocked architecture are particularly suited for these sorts of applications, because they permit the controlled, large amplitude, movement and positioning of one mechanically interlocked component with respect to another. Among these architectures, rotaxanes -i.e. molecules consisting of a ring threaded on a linear molecule capped with bulky end stoppers- are a particularly promising kind of synthetic 'molecular shuttles'. Truly functional systems based on synthetic molecular machines have not yet been proposed because some key questions remain unanswered: What are the structural features necessary for molecules to convert this controlled motion into useful function? At what level (single molecule, nanoscopic, microscopic, macroscopic) can this be done? Can we address and utilize the induced-motion in a single molecular machine? To answer those questions we are advocating the use of molecular shuttles coupled to a polymeric scaffold and interfaced with AFM. We are convinced that this is an efficient route to translate the sub-molecular motion into a useful response that can be exploited to perform physical tasks Our objective is to demonstrate the feasibility of transducing sub-molecular movements into mechanical work by combining the controlled translational motion of the ring in a rotaxane coupled to a polymer chain, and the ability of AFM-based single molecule force spectroscopy to be used as a mechanical device.[5] For that purpose, a bistable hydrogen-bonded rotaxane with one fumaramide and one succinic amide ester station was synthesized. The equilibrium distribution of the ring between the two stations is in favour of the fumaramide station (>95%).[6] If an external force forces the ring to leave the preferred binding site, it will move back to this preferred binding site through biased Brownian motion. We have attached a poly-ethylene oxide (PEO) chain to the ring and the resulting rotaxane-polymer compound was grafted onto gold substrates. We then fished the PEO chain with an AFM tip. The applied force exerted on the ring when pulling on the polymer chain causes the H bonds linking the ring to the fumaramide station to break. When trying to move away the ring, it shuttles back to its station in the opposite direction of the pulling force, doing work against the AFM cantilever. We have estimated the work done by the ring and show that the value is in good agreement with the theoretical value predicted by Altieri et. al.[6] [1] Special Issue on Molecular Machines, Acc. Chem. Res. 2001, 34, p. 409-522. [2] V. Balzani, A. Credi, M. Venturi, Molecular Devices and Machines – A Journey into the Nano World, Wiley-VCH, Weinheim, Germany, 2003. [3] E R Kay, D A Leigh and F Zerbetto, Angew. Chem. Int. Ed. 2007, 46, 72. [4] a) V Bermudez, N Capron, T Gase, F G Gatti, F Kajzar, D A Leigh, F Zerbetto and S Zhang, Nature, 2000, 406, 608. b) A M Brouwer, C Frochot, F G Gatti, D A Leigh, L Mottier, F Paolucci, S Roffia, G W H Wurpel, Science , 2001, 291, 2124. c) D A Leigh, J K Y Wong, F Dehez and F Zerbetto, Nature, 2003, 424, 174. d) J V Hernandez, E R Kay and D A Leigh, Science, 2004, 306, 153. e) E R Kay and D A Leigh, Nature, 2006, 440, 286. f) V Serreli, C-F Lee, E R Kay and D A Leigh, Nature, 2007, 445, 523. [5] T. Hugel, N. B. Holland, A. Cattani, L. Moroder, M. Seitz, H. E. Gaub, Science 2002, 296, 1103. [6] A. Altieri, G. Bottari, F. Dehez, D A Leigh, J.K.Y Wong, F Zerbetto, Angew. Chem. Int. Ed. 2003, 42, 2296. [less ▲]

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