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See detailSynthesis of poly(vinyl acetate)-b-poly(vinyl chloride) block copolymers by cobalt-mediated radical polymerization (CMRP)
Piette, Yasmine; Debuigne, Antoine ULg; Bodart, Vinent et al

in Polymer Chemistry (2013), 4(5), 1685-1693

The synthesis of poly(vinyl acetate)-b-poly(vinyl chloride) (PVAc-b-PVC) block copolymers by Cobalt-Mediated Radical Polymerization (CMRP) is investigated for the first time in this paper. A PVAc–Co(acac ... [more ▼]

The synthesis of poly(vinyl acetate)-b-poly(vinyl chloride) (PVAc-b-PVC) block copolymers by Cobalt-Mediated Radical Polymerization (CMRP) is investigated for the first time in this paper. A PVAc–Co(acac)2 macroinitiator is prepared by CMRP using the V-70/Co(acac)2 binary system or a preformed alkylcobalt(III) compound. Then, the block copolymerization occurs in the bulk at 40 °C by the addition of VC. The addition of water to the polymerization medium or the slow generation of alkyl radicals during the whole polymerization is beneficial to the process by consuming part of the excess of deactivator (Co(acac)2) that blocks the polymer chains into the dormant form. Dynamic light scattering (DLS) measurements and AFM analyses evidence that the PVAc-b-PVC forms core–shell micelles in a selective solvent of the PVAc block, i.e. methanol, evidencing the blocky structure of the copolymer. PVAc-b-P(VC-co-VAc) copolymers are also successfully prepared by initiating the radical copolymerization of VC and VAc at 40 °C from a PVAc–Co(acac)2 macroinitiator. [less ▲]

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See detailSINGLE-MOLECULE AFM STUDY OF ADHESIVE POLYMERS PREPARED BY COBALT-MEDIATED RADICAL POLYMERIZATION AND NITRONE-MEDIATED RADICAL COUPLING
Willet, Nicolas ULg; Sluysmans, Damien ULg; Delvaux, Cédric ULg et al

Scientific conference (2012, September 10)

Well-defined poly(vinyl acetate) (PVAc) chains prepared by CMRP (cobalt-mediated radical polymerization) were coupled using an alkyne-functional nitrone via NMRC (nitrone-mediated radical coupling).1 In ... [more ▼]

Well-defined poly(vinyl acetate) (PVAc) chains prepared by CMRP (cobalt-mediated radical polymerization) were coupled using an alkyne-functional nitrone via NMRC (nitrone-mediated radical coupling).1 In all the cases, the coupling efficiencies were close to 90% or higher. The polymers mid-chain functionalized with an alkyne group were then reacted with azide-functionalized atomic force microscopy (AFM) tips via copper-catalyzed azide-alkyne cycloaddition (CuAAC). As a result, polymers having a double-branch architecture were linked to AFM tips via a short linker. The structure and the molecular parameters of the polymers were determined by NMR and GPC, whereas the ‘click’ step onto AFM tips was assessed by performing the same CuAAC reaction onto macroscopic surfaces and characterizing them by ATR FT-IR. The adhesive properties of these double-branched polymers were studied by AFM single-molecule force spectroscopy. By performing approach-retraction cycles in solution upon a glass surface, the interaction between single PVAc chains and the surface was investigated. The effect of the double-branch architecture on the adhesion forces was under focus. Setting a residence time of the tip on the surface before retraction was found to have a beneficial influence on the adhesion forces. Signs of multiple interactions acting in parallel were detected in the experimental force-distance traces. [less ▲]

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See detailUNFOLDING SYNTHETIC PEPTIDES BY AFM AT THE SINGLE-MOLECULE LEVEL
Willet, Nicolas ULg; Hinterdorfer, Peter; lecommandoux, Sébastien et al

Conference (2012, September)

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 and 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 will eventually lead to a better understanding of the force-induced unfolding of an alpha-helix and the reversibility of the phenomenon. [less ▲]

Detailed reference viewed: 23 (1 ULg)
See detailUNFOLDING SYNTHETIC PEPTIDES BY AFM AT THE SINGLE-MOLECULE LEVEL
Willet, Nicolas ULg; Hinterdorfer, Peter; Lecommandoux, Sébastien et al

Poster (2012, September)

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 and 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 will eventually lead to a better understanding of the force-induced unfolding of an alpha-helix and the reversibility of the phenomenon. [less ▲]

Detailed reference viewed: 27 (1 ULg)
Peer Reviewed
See detailMechanochemical Study of Conformational Transitions in a Single Synthetic Peptide Chain
Willet, Nicolas ULg; Hinterdorfer, Peter; Lecommandoux, Sébastien et al

Poster (2012, June 05)

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 an alpha-helix and the reversibility of the phenomenon. [less ▲]

Detailed reference viewed: 46 (0 ULg)
See detailNanobodies as structural probes to investigate the mechanism of fibril formation by the amyloidogenic variants of human lysozyme
Dumont, Janice ULg; pardon, Els; Aumont-Nicaise, Magali et al

Poster (2012, June)

Six variants of human lysozyme (single-point mutatants I56T, F57I, W64R, D67H and double mutants F57I/T70N, W112R/T70N) are associated with a hereditary non-neuropathic systemic amyloidosis. These ... [more ▼]

Six variants of human lysozyme (single-point mutatants I56T, F57I, W64R, D67H and double mutants F57I/T70N, W112R/T70N) are associated with a hereditary non-neuropathic systemic amyloidosis. These proteins form extracellular amyloid fibrils that deposit in a wide range of tissues and organs such as liver, spleen and kidneys where they cause damages [1]. It was shown that the D67H and I56T mutations cause a loss in stability and more particularly a loss of global cooperativity of protein [1]. Consequently, under physiologically relevant conditions, these variants can transiently populate a partially unfolded state in which the beta-domain and the C-helix are cooperatively unfolded while the rest of the protein remains native like [1]. The formation of intermolecular interactions between the regions that are unfolded in this intermediate state is likely to be a fundamental trigger of the aggregation process that ultimately leads to the formation and deposition of fibrils in tissues. We have also shown that the binding of three variable domain of camelid antibodies (VHHs) - raised against the wild type human lysozyme inhibit in vitro the formation of amyloid fibrils by the lysozyme variants. These three VHHs bind on different regions of lysozyme and act as amyloid fibril inhibitor through different mechanisms [2, 3, and unpublished results]. In the present work, sixteen new VHHs specific of human lysozyme have been generated. Competition experiments have shown that they bind to five non-overlapping epitopes. We have demonstrated that five of these VHHs are able to bind lysozyme in conditions used for amyloid fibril formation, and interestingly two of them recognize two epitopes that are different from those of the three VHHs previously characterized [2, 3, and unpublished results]. The effects of these new VHHs on the properties of lysozyme variants such as stability, cooperativity and aggregation will be discussed. [1] Dumoulin, M., J.R. Kumita, and C.M. Dobson, Normal and aberrant biological self-assembly: Insights from studies of human lysozyme and its amyloidogenic variants. Acc Chem Res, 2006, 39(9), 603-610. [2] Dumoulin, M., et al., A camelid antibody fragment inhibits the formation of amyloid fibrils by human lysozyme. Nature, 2003, 424, 783-788. [3] Chan, P.H., et al., Engineering a camelid antibody fragment that binds to the active site of human lysozyme and inhibits its conversion into amyloid fibrils. Biochemistry, 2008, 47, 11041-11054. [less ▲]

Detailed reference viewed: 58 (7 ULg)
See detailSynthesis of novel poly(N-vinyl amide)s containing copolymers by cobalt-mediated radical polymerization
Kermagoret, Anthony ULg; Hurtgen, Marie ULg; Liu, Ji ULg et al

Poster (2012, May 10)

Poly(N-vinyl amide)s are found in many applications due to their valued properties including water solubility, biocompatibility, metal-coordination ability, etc. Although N-vinyl amides are easily ... [more ▼]

Poly(N-vinyl amide)s are found in many applications due to their valued properties including water solubility, biocompatibility, metal-coordination ability, etc. Although N-vinyl amides are easily polymerized via radical pathways, their growing radicals are quite reactive due to the lack of stabilizing group, rendering the synthesis of well-defined poly(N-vinyl amide)s challenging. Thus, we explored the organometallic-mediated radical polymerization (OMRP) of a series of N-vinyl amides using bis(acetylacetonato)cobalt(II) as controlling agent in order to develop a platform for the precision synthesis of poly(N-vinyl amide)s. [less ▲]

Detailed reference viewed: 41 (7 ULg)
See detailProbing recognition processes, forces and motions within single molecules
Willet, Nicolas ULg; Duwez, Anne-Sophie ULg

Scientific conference (2012, May 09)

Detailed reference viewed: 6 (0 ULg)
See detailInvestigation of mechanochemical processes by single-molecule AFM
Willet, Nicolas ULg

Scientific conference (2012, March 23)

Detailed reference viewed: 23 (0 ULg)
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 ▲]

Detailed reference viewed: 59 (32 ULg)
Full Text
Peer Reviewed
See detailNew functional poly(N-vinylpyrrolidone) based (co)polymers via photoinitiated cobalt-mediated radical polymerization
Debuigne, Antoine ULg; Schoumacher, Matthieu; 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 ▲]

Detailed reference viewed: 42 (10 ULg)
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 ▲]

Detailed reference viewed: 52 (2 ULg)
See detailProbing recognition processes, forces and motions within single molecules
Willet, Nicolas ULg

Scientific conference (2011, June)

Detailed reference viewed: 8 (1 ULg)
Full Text
See detailMechanochemical Study of a Single Polypeptide Molecule: Force-Induced Conformational Transition
Willet, Nicolas ULg; Hinterdorfer, Peter; Lecommandoux, Sébastien et al

Conference (2011, June)

Detailed reference viewed: 11 (0 ULg)
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 ▲]

Detailed reference viewed: 20 (3 ULg)
See detailBiomimetic coatings with robust antibacterial properties
Jérôme, Christine ULg; Cécius, Michaël; Faure, Emilie ULg et al

Conference (2010, July 01)

Detailed reference viewed: 21 (4 ULg)
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 ▲]

Detailed reference viewed: 104 (4 ULg)