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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 17: Charged Soft Matter, Polyelectrolytes and Ionic Liquids I

CPP 17.2: Vortrag

Dienstag, 19. März 2024, 10:00–10:15, H 0107

Solvation Behavior of Elastin-like Polypeptides in Divalent Metal Salt Solutions — •Swaminath Bharadwaj^1,2, Yani Zhao¹, Ryan Myers³, Paul Cremer³, and Nico van der Vegt¹ — ¹Technical University of Darmstadt, 64287, Darmstadt, Germany — ²Shiv Nadar Institution of Eminence, Gautam Buddha Nagar, Uttar Pradesh 201314, India — ³Penn State University, University Park, PA 16802, USA

We studied the effects of CaCl₂ and MgCl₂ on the cloud point temperature of two different elastin-like polypeptides (ELPs) sequences. Cloud point measurements of these systems were performed along with molecular dynamics simulations and infrared spectroscopy measurements. Changes in the cloud point for the ELPs in aqueous divalent metal cation solutions were primarily governed by two competing interactions: the cation-amide oxygen electrostatic interaction and the hydration of the cation. In particular, Ca²⁺ cations can more readily shed their hydration shells and directly contact two amide oxygens by forming ion bridges. By contrast, Mg²⁺ cations were more strongly hydrated and preferred to partition towards the amide oxygens along with their hydration shells. Next, the partitioning of the cations was strongly influenced by the presence of triglycine motifs in the ELP sequence. In fact, although the more hydrophilic ELP V₅A₂G₃ was salted-out of solution by low concentrations of MgCl₂, it was salted-in at higher salt concentrations. By contrast, CaCl₂ salted the ELP sharply out of solution at higher salt concentrations because of the bridging effect.

Keywords: Specific-ion effects; Hofmeister series; thermoresponsive bio-polymers; polymer-cation bridging; ion hydration