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| Home > Publications database > Simulations and Potentiometric Titrations Enable Reliable Determination of Effective p K a Values of Various Polyzwitterions |
| Journal Article | FZJ-2022-03676 |
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2022
Soc.
Washington, DC
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Please use a persistent id in citations: http://hdl.handle.net/2128/32325 doi:10.1021/acs.macromol.2c01121
Abstract: We synthesized three different polyzwitterions─poly(N,N-diallyl glutamate) (PDAGA), poly(dehydroalanine) (PDha), and poly(2-(imidazol-1-yl)acrylic acid) (PImAA)─and investigated how their ionization states respond to changes in solution pH. We used molecular simulations to determine how the net charge per monomer and the ionization states of individual acidic and basic groups differ from the ideal (Henderson–Hasselbalch) behavior. To complement the theoretical predictions, we performed potentiometric titrations and zeta-potential measurements of all studied polyzwitterions. By comparing these experiments with theoretical predictions, we could show that molecular simulations can predict and explain the origin of the differences between the effective and bare pKa values of individual titratable groups. Furthermore, we have shown that it is not possible to obtain these effective pKa values directly from the equivalence point recognition criterion (ERC), commonly used in potentiometric titrations. However, the effective pKa values can be reliably obtained by calculating the net charge per monomer from the potentiometric titration curves and validating these results against theoretical predictions. The approach we propose works reliably for polyzwitterions in which the ionization response is dominated by electrostatic interactions, such as PDAGA or PDha; however, it fails if other specific interactions contribute significantly, such as in the case of PImAA.
Keyword(s): Polymers, Soft Nano Particles and Proteins (1st) ; Soft Condensed Matter (2nd)
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