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Nanotechnology with Single Macromolecules

Final Activity Report Summary - NASIMA (Nanotechnology with Single Macromolecules)

Each of the major steps in nature involves mechanical movement at the single molecule level. Moreover, the macroscopic properties of polymeric materials are closely related to primary chemical composition, structure, conformation and interactions at single molecule level. Nanomechanical studies of single polymer chains contribute to the understanding of fundamental aspects of the structural, mechanical and binding properties of macromolecules. Understanding the elastic behaviour, or deformation, of individual macromolecules is an essential issue in biopolymer science and materials science, and this is described in the first of the publications that are listed in the end of this report.

Single molecule tools contribute to the discovery, identification and description of temporally and spatially distinct states of a molecular species. They make it possible to follow, in real time and at individual molecule level, the movements, forces and strains developed during a reaction or a conformational change.

We focussed on the manipulation and physical studies of single-polymer chains. Atomic force microscopy based-single molecule force spectroscopy (AFM-SMFS), described in the second publication of the list, was used as an 'enabling' tool. We aimed at the investigation of the translation of external stimuli into forces at the single polymer-chain level. This was an extension of previous work in our group on AFM-SMFS, presented in the third publication, to externally addressable single molecular units and actuators. When single macromolecules were subjected to external fields, such as electric or thermal, changes in the chain torsional potential energy landscape could be induced. This manifested itself in controlled variations in the macromolecular characteristic ratio, causing dimensional changes of addressable polymers under stress. In our case, this occurred when the corresponding units were reduced and electrochemically oxidised, as in organometallic polymers, or when the polymer reacted to changes in, for example, temperature, such as in thermal-responsive polymers.

For this purpose, surface-immobilised redox-active organometallic poly(ferrocenylsilanes) (PFS) polymers, presented in detail in publication (4) were investigated using AFM-based single molecule force spectroscopy. Our group investigated PFS as model systems for the realisation of molecular motors powered by a redox process. For further details refer in publication five. In this work, a closed thermodynamic cycle applying external electrochemical potential and force in a periodic way was performed in the development of the project, allowing us to study single-molecule thermodynamic 'motors'. Based on the novel information that was obtained, we anticipated novel and highly efficient applications in sensors, nanofluidics and microfluidics, e.g. valves, as well as in the area of responsive coatings, such as anti-fouling or switchable biocompatibility.

Moreover, a study was performed on the conformational rearrangements of a single polysaccharide molecule, Hyaluronic acid (HA), which was thermally or mechanically induced. HA was a glycosaminoglycan present in the intercellular matrix of most vertebrate connective tissues and in some bacterial capsules (refer to publication six). The understanding of its elastic and conformational behaviour might contribute to the comprehension of the mechanisms and roles of this biomacromolecule in its natural environment at the single chain level.

This report was based on information from the following publications:

1. Fleer et al. Polymers at Interfaces, Chapman and Hall, 1993, 'Scanning probe microscopies beyond imaging: Manipulation of molecules and nanostructures', ed. P. Samorì, Wiley-VCH, 2006
2. Binnig et al. Physical Review Letters, 1986, 56, 930; Carrion-Vazquez et al. Proceedings of the National Academy of Science, United States of America, 1999, 96, 3694; Viani et al. Review of Scientific Instruments, 1999, 70, 4300
3. Schönherr et al. Journal of the American Chemical Society 2000, 122, 4963; Zapotoczny et al. Langmuir 2002, 18, 6988; Auletta, et al. Journal of the American Chemical Society 2004, 126, 1577; Schönherr et al. Journal of the American Chemical Society 2000, 122, 3679
4. Foucher et al. Journal of the American Chemical Society 1992, 114, 6246; Rasburn et al. Chemistry of Materials 1995, 7, 871
5. Zou et al. Macromolecular Rapid Communications 2006, 27, 103; Zou et al. Polymer 2006, 47, 2483
6. Hascall, Biol. Carbohydr. 1981, 1, 1; Hardingham, Biochemical Society Transactions 1981, 9, 489