Project Summary Ions are ubiquitous in nature and all charged biomolecules subsequently develop an ion atmosphere. Unfortunately, our understanding of ion atmospheres at the atomic level is rather limited, and this severely impacts our ability to determine and rationalize protein-protein and protein-DNA interactions, for example. Here, we propose to use the Kirkwood-Buff theory of solutions, coupled with local electroneutrality constraints, to generate an improved view of the ion atmosphere around a variety of biomolecules. The results generate exact relationships between the distribution of anions and cations around charged biomolecules and provide a way to separate the ion contributions to electroneutrality from those related to the preferential interaction of a salt for a biomolecule. A series of theoretical and computer simulation studies are proposed to achieve the two major aims of the project. Aim 1: To Develop an Improved Description of Ion Atmospheres in Biological Systems. Aim 2: To Determine the Consequences of Local Electroneutrality Requirements. The results from these studies will provide a new view of the structure and extent of ion atmospheres around any biomolecular ion and will improve our interpretation of the results from several biophysical techniques, such as osmotic pressure and ion counting studies. Subsequently, this will impact our understanding of a wide range of systems of importance for the study of many health-related diseases.

Project Narrative The presence of ion atmospheres around charged biomolecules is known to affect their properties and interactions. Here we develop a new view of ion atmospheres using an innovative combination of solution theory and local electroneutrality constraints. This new view has consequences for our understanding of several biophysical approaches used to characterize biomolecules and their properties, and has subsequent implications for a wide range of systems governing a variety of health-related problems.