Using EPR Spectroscopy as a Unique Probe of Molecular-Scale Reorganization and Solvation in Self-Assembled Gel-Phase Materials

Agneta Caragheorgheopol*, William Edwards, John G. Hardy, David K. Smith, Victor Chechik

*Corresponding author for this work

Research output: Contribution to journalArticle

4 Citations (Scopus)
248 Downloads (Pure)

Abstract

We describe the synthesis of spin-labeled bis-ureas which coassemble with bis-urea gelators and report on self-assembly as detected using electron paramagnetic resonance spectroscopy (EPR). Specifically, EPR detects the gel-sol transition and allows us to quantify how much spin-label is immobilized within the gel fibers and how much is present in mobile solvent pools-as controlled by temperature, gelator structure, and thermal history. EPR is also able to report on the initial self-assembly processes below the gelation threshold which are not macroscopically visible and appears to be more sensitive than NMR to intermediate-sized nongelating oligomeric species. By studying dilute solutions of gelator molecules and using either single or double spin-labels, EPR allows quantification of the initial steps of the hierarchical self-assembly process in terms of cooperativity and association constant. Finally, EPR enables us to estimate the degree of gel-fiber solvation by probing the distances between spin-labels. Comparison of experimental data against the predicted distances assuming the nanofibers are only composed of gelator molecules indicates a significant difference, which can be assigned to the presence of a quantifiable number of explicit solvent molecules. In summary, EPR provides unique data and yields powerful insight into how molecular-scale mobility and solvation impact on assembly of supramolecular gels.

Original languageEnglish
Pages (from-to)9210-9218
Number of pages9
JournalLangmuir
Volume30
Issue number30
DOIs
Publication statusPublished - 13 Jul 2014
Externally publishedYes

Keywords

  • SUPRAMOLECULAR ARCHITECTURES
  • ORGANOGEL FORMATION
  • WEIGHT GELATORS
  • SPIN LABELS
  • SOLVENT
  • GELATION
  • SOLUBILITY
  • POLYMERIZATION
  • PARAMETERS
  • HYDROGELS

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)

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