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Updated: Jun 2, 2026

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water
Published on: August 2, 2012
Complex ion effects on polypeptide conformational stability: chloride and sulfate salts of guanidinium and
Christopher E Dempsey1, Philip E Mason, Pavel Jungwirth
1School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK. c.dempsey@bris.ac.uk
Abstract:
The effects of chloride and sulfate salts of tetrapropylammonium (TPA(+)) and guanidinium (Gdm(+)) on the conformational stabilities of tryptophan zipper (trpzip) and α-helical (alahel) peptides were measured by circular dichroism spectroscopy. Like Gdm(+), TPA(+) interacts with the planar tryptophan indole group, perturbing the conformational stability of trpzip peptides. TPA(+) effects are largely unaffected by sulfate, indicating an absence of the heteroion pairing that is observed in concentrated Gdm(2)SO(4) solutions. TPA(+) stabilizes helical conformations in alahel peptides, indicating exclusion from the peptide bond. The observations are broadly consistent with predictions of molecular dynamics simulations [Mason, P. E.; et al. J. Phys. Chem. B2009, 113, 3227-3234], indicating that the effects of complex ions on proteins are increasingly predictable in terms of ion hydration, complementary interactions with specific protein groups, and ion-pairing contributions.
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