Overview of this Thesis
2.5 Individual Contributions to Joint Publications
The results presented in this thesis were obtained in collaboration with others, and have been published or are submitted to publication as indicated below. In the following, the contributions of all the coauthors to the different publications are specified. The asterisk denotes the corresponding author.
Chapter 3
This work is published in Macromol. Biosci., 2011, 11, 199-210 under the title:
“Glycopolymer-Grafted Polystyrene Nanospheres”
by André Pfaff, Vaishali S. Shinde, Yan Lu, Alexander Wittemann, Matthias Ballauff and Axel H. E. Müller*
I conducted all experiments and wrote the publication.
Exceptions are stated in the following:
Vaishali S. Shinde performed the experiments regarding the photopolymerization towards glycopolymer-grafted nanospheres and was involved in the discussion.
Yan Lu prepared the ungrafted polystyrene particles and was involved in the discussion.
Alexander Wittemann was involved in the discussion.
Matthias Ballauff and Axel H. E. Müller were involved in the discussion and corrections of this manuscript.
Chapter 4
This work is published in Eur. Polym. J., 2011, 47, 805-815 under the title:
“Surface Modification of Polymeric Microspheres using Glycopolymers for Biorecognition”
by André Pfaff, Leonie Barner, Axel H. E. Müller* and Anthony M. Granville*
I conducted all experiments and wrote the publication.
Exceptions are stated in the following:
Leonie Barner was involved in the discussion.
36
Axel H. E. Müller and Anthony M. Granville were involved in discussion and corrections of this manuscript.
Chapter 5
This work is published in Macromolecules, 2011, 44, 1266-1272 under the title:
“Hyperbranched Glycopolymer-Grafted Microspheres”
by André Pfaff and Axel H. E. Müller*
I conducted all experiments and wrote the publication.
Exceptions are stated in the following:
Axel H. E. Müller was involved in discussion and corrections of this manuscript.
Chapter 6
This work is submitted to Biomacromolecules under the title:
“Magnetic, Fluorescent Glycopolymer Hybrid Nanoparticles for Intranuclear Optical Imaging”
by André Pfaff, Anja Schallon, Thomas M. Ruhland, Alexander P. Majewski, Holger Schmalz, Ruth Freitag and Axel H. E. Müller*
I conducted all experiments and wrote the publication.
Exceptions are stated in the following:
Anja Schallon performed epifluorescence microscope measurements and was involved in the discussion.
Thomas M. Ruhland was involved in the discussion.
Alexander P. Majewski prepared the iron oxide particles and was involved in the discussion.
Holger Schmalz was involved in the discussion.
Ruth Freitag and Axel H. E. Müller were involved in the discussion and corrections of this manuscript.
37
38
Chapter 3
Glycopolymer-Grafted Polystyrene Nanospheres
André Pfaff,
1Vaishali S. Shinde,
1,2Yan Lu,
3,4Alexander Wittemann,
4Matthias Ballauff
3,4and Axel H. E. Müller
1*1 Makromolekulare Chemie II and 4 Physikalische Chemie I, Universität Bayreuth, 95440 Bayreuth, axel.mueller@uni-bayreuth.de
2 Department of Chemistry, University of Pune, Pune 411007, Maharashtra, India
3 Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 14109 Berlin
39
40
Abstract
The synthesis and characterization of spherical sugar-containing polymer brushes consisting of PS cores onto which chains of sugar-containing polymers have been grafted via two different techniques are described. Photopolymerization in aqueous dispersion using the functional monomer MAGlc and crosslinked or non-crosslinked PS particles covered with a thin layer of photo-initiator yielded homogeneous glycopolymer brushes attached to spherical PS cores. As an alternative, ATRP was used to graft poly(N-acetylglucosamine) arms from crosslinked PS cores. Deprotection of the grafted brushes led to water-soluble particles that act as carriers for catalytically active gold nanoparticles. These glycopolymer chains show a high affinity to adsorb WGA whereas no binding to BSA or PNA could be detected.
Keywords: Atom Transfer Radical Polymerization (ATRP); glycopolymer; gold nanoparticles; lectin recognition; spherical brush
3.1 Introduction
Glycopolymers, synthetic sugar-containing macromolecules, which display complex functionalities similar to those found in natural glycoconjugates are attracting ever-increasing interest from the chemistry community due to their role as biomimetic analogues and their potential for commercial applications.1-5 They are used as surfactants,6 texture-enhancing food additives,7 drug release systems,8, 9 and biologically active polymers.10, 11 It is now clear that structural control of glycopolymers has a significant impact on their recognition functions, which has prompted researchers to develop new synthetic routes to a variety of sugar-displaying polymers with controlled architectures and functionalities.12-14 Various types of synthetic polymers bearing sugar residues have been described, such as linear polymers,15 comb polymers,16 dendrimers,17 and crosslinked hydrogels.18
In particular, carbohydrate-modified vinyl polymers have been extensively investigated because of their relatively simple synthesis via radical polymerization. In this case, controlled/”living” radical polymerizations have been reported as a very facile approach for well-defined and controlled synthesis of glycopolymers.19-23
In this paper, we describe the synthesis of sugar-containing colloidal spherical polymer brushes by two different polymerization approaches. Photopolymerization of the
41 functional monomer 3-O-methacryloyl-D-glucose (MAGlc) was used to attach glycopolymer chains to colloidal polystyrene (PS) spheres by a “grafting from” technique.24, 25 As shown in Scheme 1, the synthesis of these particles can be carried out in three steps: In the first step, PS core particles are prepared by a conventional emulsion polymerization.26 In the second step of emulsion polymerization, these core particles are covered by a thin layer of the photo-initiator 2-[p-(2-hydroxy-2-methylpropiophenone)]-ethyleneglycol methacrylate (HMEM). In the third step, polymerization of MAGlc is started by UV irradiation of the suspension of these latex particles. By this grafting-from strategy sugar-displaying polymer brushes are generated on the surface of the core particles.
Scheme 1. Synthesis of the sugar-displaying polymer brush via photo-induced free radical polymerization.
The use of an unprotected functional monomer for the preparation of polymer brushes by means of photopolymerization avoided potentially damaging deprotection steps.
Moreover, crosslinked PS core particles covered with a thin layer of photo-initiator were used for the first time for photopolymerization. Until now, all spherical polymer brush systems reported by Ballauff and coworkers are limited to water-soluble monomers in aqueous condition.27-29 The use of crosslinked PS core particles makes the photopolymerization also possible for water insoluble monomers in organic solvents.
The increase with time of PS-MAGlc particle size under UV-irradiation was studied by means of dynamic light scattering (DLS), whereas cryogenic transmission electron microscopy (cryo-TEM) was the method of choice to study the morphology of the brushes in situ. All data discussed herein, demonstrate the successful preparation of glucose-displaying polymer brushes by photopolymerization.
Furthermore, we investigated the use of a protected glycomonomer, tetraacetylglucosamine (tetAcGlc), and a controlled radical polymerization technique,
42
namely atom transfer radical polymerization (ATRP), to create spherical polymer brushes with well-defined poly-(N-acetylglucosamine) arms. Using the “grafting from” approach, chains were grown from a crosslinked polystyrene core covered with a thin layer of ATRP initiator (Scheme 2). The subsequent deprotection of the sugar units led to water soluble spherical brushes consisting of poly-(N-acetyl-D-glucosamine) chains.
Scheme 2. Synthesis of the glucosamine-containing polymer brushes via emulsion polymerization and subsequent ATRP. After deprotection of the sugar moieties, hydrophilic sugar particles were obtained.
One motivation for the preparation of these sugar-containing polymer brushes was to investigate whether these brushes could act as carriers for catalytically active gold nanoparticles. In general, gold nanoparticles are of special interest because of their potential applications in electronic, optical and biomedical materials.30-35
Apart from this, glycopolymers are of great interest because of binding interactions between carbohydrates and lectins. Interactions between saccharides and proteins are usually weak but can be markedly increased by displaying multiple saccharides in close proximity to each other, yielding multivalent binding sites, commonly known as the “glyco-cluster effect”.36 Therefore, we were interested in developing polymerization methodology capable of producing poly-(N-acetylglucosamine) chains as glycomimetics, and subsequently in investigating their binding behavior to wheat germ agglutinin (WGA) using turbidity measurements and surface plasmon resonance (SPR) spectroscopy.
43