Electrostatic Control of Polymorphism in Charged Amphiphile Assemblies

Changrui Gao, Honghao Li, Yue Li, Sumit Kewalramani, Liam C. Palmer, Vinayak P. Dravid, Samuel I. Stupp, Monica Olvera De La Cruz*, Michael J. Bedzyk

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


Stimuli-induced structural transformations of molecular assemblies in aqueous solutions are integral to nanotechnological applications and biological processes. In particular, pH responsive amphiphiles as well as proteins with various degrees of ionization can reconfigure in response to pH variations. Here, we use in situ small and wide-angle X-ray scattering (SAXS/WAXS), transmission electron microscopy (TEM), and Monte Carlo simulations to show how charge regulation via pH induces morphological changes in the assembly of a positively charged peptide amphiphile (PA). Monte Carlo simulations and pH titration measurements reveal that ionic correlations in the PA assemblies shift the ionizable amine pK ∼ 8 from pK ∼ 10 in the lysine headgroup. SAXS and TEM show that with increasing pH, the assembly undergoes spherical micelle to cylindrical nanofiber to planar bilayer transitions. SAXS/WAXS reveal that the bilayer leaflets are interdigitated with the tilted PA lipid tails crystallized on a rectangular lattice. The details of the molecular packing in the membrane result from interplay between steric and van der Waals interactions. We speculate that this packing motif is a general feature of bilayers comprised of amphiphilic lipids with large ionic headgroups. Overall, our studies correlate the molecular charge and the morphology for a pH-responsive PA system and provide insights into the Å-scale molecular packing in such assemblies.

Original languageEnglish (US)
Pages (from-to)1623-1628
Number of pages6
JournalJournal of Physical Chemistry B
Issue number7
StatePublished - Feb 23 2017

ASJC Scopus subject areas

  • Materials Chemistry
  • Surfaces, Coatings and Films
  • Physical and Theoretical Chemistry


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