Colloquium

Monday 31 October 2022

Speaker

Alexandros Chremos

Affiliation

Section on Quantitative Imaging and Tissue Sciences, Eunice Kennedy Shriver National, Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA

Title

Solvation of ionic species in aqueous solutions, a Tale of Genji

Location

online.

Time

17:00

Language

English

Abstract

The tendency of highly charged polymer chains (e.g., DNA and proteins) and particles having the same charge to form dynamic clusters in solution has attracted significant interest because many biological functions and processes rely on this phenomenon. However, an accepted theoretical framework that can account for this ubiquitous phenomenon has been slow to develop. The theoretical difficulties are especially great for flexible polyelectrolytes due to the additional complex coupling between the polyelectrolyte chain configurations and the spatial distribution of the ionic species in the solution. As a result, a diffuse `polarizable’ cloud of counter-ions forms around these polymers for highly charged polyelectrolytes. An effect has significant implications for the function of proteins and other naturally occurring polyelectrolytes, as emphasized long ago by Kirkwood and co-workers. To better understand the origins of the self-association of highly charged species, we utilize molecular dynamics simulations that include both salt and an explicit solvent. We find that an increase in the counter-ion and polyelectrolyte solvation and the suppression of the ion mobility results in the ionization of the polyelectrolyte backbone and the enrichment of the counter-ion cloud surrounding the polymers that make these polymers highly polarizable giving rise to effective long-range attractions. Our findings provide insights into a number of unexplained experimental observations of (poly)electrolyte solutions, such as the upturn in scattering profiles at large distances and the disappearance of polyelectrolyte peak, as well as the importance of solvation in the Hofmeister series of electrolyte solutions.

References

1. Communication: Counter-ion solvation and anomalous low-angle scattering in salt-free polyelectrolyte solutions, A. Chremos and J. F. Douglas, J. Chem. Phys. 147, 241103 (2017).
2. Coarse-Grained Model of the Dynamics of Electrolyte Solutions, M. Andreev, A. Chremos, J. de Pablo, and J. F. Douglas, J. Phys. Chem. B 121, 8195 (2017).
3. Influence of Ion Solvation on the Properties of Electrolyte Solutions, M. Andreev, J. de Pablo, A. Chremos, and J. F. Douglas, J. Phys. Chem. B 122, 4029 (2018).
4. Polyelectrolyte association and solvation, A. Chremos, and J. F. Douglas, J. Chem. Phys. 149, 163305 (2018).
5. Influence of solvation on the structure of highly charged nanoparticles in salt-free solutions, A. Chremos and J. F. Douglas, Polymer Journal 170, 107 (2019).
6. Disappearance of the polyelectrolyte peak in salt-free solutions, A. Chremos, F. Horkay, Phys. Rev. E 102, 012611 (2020).
7. Bottlebrush polymers in the melt and polyelectrolytes in solution share common structural features, J. M. Sarapas, T. B. Martin, A. Chremos, J. F. Douglas, B. L. Kathryn, Proceedings of National Academy of Science 117, 5168-5175 (2020).