Talk on

GLOBULAR PROTEIN GELS: MULTI-SCALE STRUCTURAL APPROACH and PARTICLE DIFFUSION

Abstract

Many globular proteins have a tendency to self assemble after denaturation. Some of them may be considered as good model systems to investigate the competition between processes of aggregation, gelation and phase separation which play a major role in the self assembly of complex systems. In fact, according to the experimental conditions of pH and ionic strength, a large variety of different textures can be obtained.

The transition between the finely stranded and coarse gels induced by a reduction of the electrostatic repulsion has been studied in details using a combination of techniques (Confocal Laser Scanning Microscopy, Light and X-ray Scattering) allowing to cover a wide range of length scales (1nm-100µm). By this way, we were able to characterize on a very large scale gel structures varying from transparent to highly opaque in terms of the amplitude and the correlation length of the concentration fluctuations. We have shown that the transition is caused by a phase separation process that is frozen-in by gelation. Phase separation leads to the formation of dense protein domains with a radius of a few microns that stick together to form a system spanning network. The control of the competition between aggregation and phase separation allowed us to build a large variety of protein gels with various controlled correlation lengths, i.e. various pore sizes.

The displacement of fluorescent spheres with different sizes was followed using CLSM. If the pore size of the gel is significantly larger than particles, their displacement is diffusional and the self diffusion coefficient was related to the gel structure. Below a critical value of the correlation length, the mean square displacement is no longer diffusional, but is described by a power law. These results are compared with computer simulations of tracer diffusion in gels. This extensive study of globular protein gels allows one to get a better understanding of the texturing and the transport properties in complex systems formed by the self assembly of particles.

Talk on

Supramolecular Drugs and Polymers: From Design to Reality

Abstract

Supramolecular drugs and polymers have been recently in the focus as an interesting class of new materials and found to be suitable for many applications [1-4]. The use of different types such as nanotubes and nanoparticles allows designing and developing new concepts for sophisticated drug delivery and other systems. Several model systems with carbon and inorganic nanotubes have been studied and examples of their interaction products and composites are given in regard of their interactions with biological cells in the cellular interphases [4]. The novel nanomaterials are expected to have an application potential in many areas.

Acknowledgement. This work was supported by the World Class University (WCU) program through a grant provided by the Ministry of Education, Science and Technology (MEST) of Korea (Project No. R31-10026) and the Department of Medical System Engineering.

References
[1] K. E. Geckeler (Ed.), Advanced Macromolecular and Supramolecular Materials and Processes, Kluwer Academic/Plenum Publishers, New York, 2003.
[2] K. E. Geckeler and E. Rosenberg (Eds.), Functional Nanomaterials, American Scientific Publishers, Valencia, USA, 2006.
[3] K.E. Geckeler and H. Nishide (Eds.), Advanced Nanomaterials, Wiley-VCH Publishers, Weinheim, Germany, 2009.
[4] Y. Lee and K. E. Geckeler, Advanced Materials, 22, 4076 (2010).