Complexation of Polyelectrolytes Studied by Cryogenic-Temperature Electron Microcopy

Complexation of polyelectrolytes with charged small molecules or with other polyelectrolytes is a phenomenon of great basic scientific and practical importance. Such complexation processes produce a variety of nanostructural-aggregates thar have profound influence on the macroscopic properties of the system. That nanostructure of the aggregates is studied by a variety of experimental techniques, but the analysis is incomplete without direct imaging of the system. The resolution needed and the nature of the liquid systems studied call for the application of cryogenic-temperature electron microscopy (cryo-EM), namely, electron microscopy of ultrafast-cooled (vitrified) specimen, observed at cryogenic temperatures.  Cryo-EM allows direct-imaging of a liquid systems with its nanostructure preserved at its original concentration and temperature. Cryo-EM can be performed either in transmission electron microscopy (cryo-TEM) or in scanning electron microscopy (cryo-SEM), the latter is more useful for highly concentrated liquids, or when fine nanostructure is to be imaged in microscopic or larger aggregates. In all our studies we compare our cryo-EM data to data from other, non-imaging, methodologies, such as x-ray and neutron scattering, and rheological measurements.

In my lecture I will briefly describe the basics of cryo-EM, followed by cryo-TEM nanostructural analysis of several aqueous systems. I will demonstrate the effect on the polyelectrolyte complexes of charge ratio of the complexed species and the solution pH, and their interaction with proteins and lipids.