Sergei N. Magonov

Self-assembly of amphiphilic dendritic dipeptides into helical pores

Natural pore-forming proteins act as viral helical coats and transmembrane channels, exhibit antibacterial activity and are used in synthetic systems, such as for reversible encapsulation or stochastic sensing. These diverse functions are intimately linked to protein structure. The close link between protein structure and protein function makes the design of synthetic mimics a formidable challenge, given that structure formation needs to be carefully controlled on all hierarchy levels, in solution and in the bulk. In fact, with few exceptions, synthetic pore structures capable of assembling into periodically ordered assemblies that are stable in solution and in the solid state have not yet been realized. In the case of dendrimers, covalent and non-covalent coating and assembly of a range of different structures has only yielded closed columns. Here we describe a library of amphiphilic dendritic dipeptides that self-assemble in solution and in bulk through a complex recognition process into helical pores. We find that the molecular recognition and self-assembly process is sufficiently robust to tolerate a range of modifications to the amphiphile structure, while preliminary proton transport measurements establish that the pores are functional. We expect that this class of self-assembling dendrimers will allow the design of a variety of biologically inspired systems with functional properties arising from their porous structure.

Atomic Force Microscopy Studies of Semicrystalline Polymers at Variable Temperature

The capabilities of Atomic Force Microscopy, AFM, in studies of polymer phase transitions and, more generally, the semicrystalline polymer morphology are described. It is shown how variable temperature AFM can provide unique information on the organization of semicrystalline polymers at the nanometer scale and its evolution in the course of crystallization. The practical examples selected for this work illustrate applications of AFM to structural studies of homopolymers and polymer blends crystallized in the bulk, in thin films and in solutions. The investigated systems include solution grown single crystals of polyethylene, cold-crystallized poly(ether ether ketone), as well as melt-crystallized poly(ethylene terephthalate), poly(trimethylene terephthalate), syndiotactic polystyrene, poly(e-caprolactone), isotactic and syndiotactic polypropylene. The issues related to AFM image analysis and its quantitative comparison with the results of complementary techniques such as small-angle X-ray scattering (SAXS) are addressed. More specifically, it is shown how AFM can provide statistically meaningful parameters for the semicrystalline structure and an accurate choice of a structural model for the interpretation of SAXS data.