Zwitterions modulate interfacial interactions across electrolyte solutions Kieran Agg and Susan Perkin University of Oxford, UK Cellular functionality relies on the ability to maintain structure and function of biological macromolecules such as proteins, key to which is the surrounding chemical environment: the cytosol. Cytosol composition not only dictates the osmotic balance of cells with their surroundings, but also determines the range and nature of inter-protein interactions within the cell 1 . While the role of ionic solutes in destabilising proteins is well known, as illustrated by the Hofmeister series, the role that zwitterionic “osmolytes” play in these interactions is less clear. Here we will present a study of surface force measurements across model cytosol solutions, some of which have been recently reported 2 . These aqueous solutions containing pure zwitterion and salt-zwitterion mixtures reveal that common osmolytes such as trimethyl glycine and proline act to influence the interaction potential between charged mica sheets, including by enhancing the strength and range of electrostatic repulsion, disrupting water structure and forming molecular layers at charged interfaces. This multifaceted nature of zwitterionic osmolytes may be significant in how these molecules impart stability and balance in the cellular environment. References 1. Wennerström, H., Vallina Estrada, E., Danielsson, J.& Oliveberg, M. (2020). Colloidal stability of the living cell. Proc. Natl. Acad. Sci. , 117 (19), 10113–10121. 2. Hallett, J. E., Agg, K. J.& Perkin, S. (2023). Zwitterions fine-tune interactions in electrolyte solutions. Proc. Natl. Acad. Sci. , 120 (8),
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