Dramatic specific ion effect in supramolecular hydrogels

Sangita Roy, Nadeem Javid, Pim Frederix, Dimitrios Lamprou, Andrew Urquhart, Neil Hunt, Peter Halling, Rein Ulijn

Research output: Contribution to journalArticle

60 Citations (Scopus)

Abstract

We report on a pronounced specific-ion effect on the intermolecular and chiral organization, supramolecular structure formation, and resulting materials properties for a series of low molecular weight peptide-based hydrogelators, observed in the presence of simple inorganic salts. This effect was demonstrated using aromatic short peptide amphiphiles, based on fluorenylmethoxycarbonyl (Fmoc). Gel-phase materials were formed due to molecular self-assembly, driven by a combination of hydrogen bonding and pi-stacking interactions. Pronounced morphological changes were observed by atomic force microscopy (AFM) for Fmoc-YL peptide, ranging from dense fibrous networks to spherical aggregates, depending on the type of anions present. The gels formed had variable mechanical properties, with G' values between 0.8 kPa and 2.4 kPa as determined by rheometry. Spectroscopic analysis provided insights into the differential mode of self-assembly, which was found to be dictated by the hydrophobic interactions of the fluorenyl component, with comparable H-bonding patterns observed in each case. The efficiency of the anions in promoting the hydrophobic interactions and thereby self-assembly was found to be consistent with the Hofmeister anion sequence. Similar effects were observed with other hydrophobic peptides, Fmoc-VL and Fmoc-LL. The effect was found to be less pronounced for a less hydrophobic peptide, Fmoc-AA. To get more insights into the molecular mechanism, the effect of anions on sol-gel equilibrium was investigated, which indicates the observed changes result from the specific-ion effects on gels structure, rather than on the sol-gel equilibrium. Thus, we demonstrate that, by simply changing the ionic environment, structurally diverse materials can be accessed providing an important design consideration in nanofabrication via molecular self-assembly.
Original languageEnglish
Pages (from-to)11723-11731
Number of pages9
JournalChemistry - A European Journal
Volume18
Issue number37
Early online date6 Aug 2012
DOIs
Publication statusPublished - 10 Sep 2012

Keywords

  • supramolecular hydrogels
  • ions
  • hydrogels
  • specific ion-effect
  • intermolecular
  • chiral organization
  • supramolecular structure formation
  • materials properties
  • low molecular weight
  • peptide-based hydrogelators

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