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 language | English |
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Pages (from-to) | 9210-9218 |
Number of pages | 9 |
Journal | Langmuir |
Volume | 30 |
Issue number | 30 |
DOIs | |
Publication status | Published - 13 Jul 2014 |
Externally published | Yes |
Keywords
- SUPRAMOLECULAR ARCHITECTURES
- ORGANOGEL FORMATION
- WEIGHT GELATORS
- SPIN LABELS
- SOLVENT
- GELATION
- SOLUBILITY
- POLYMERIZATION
- PARAMETERS
- HYDROGELS
ASJC Scopus subject areas
- General Chemistry
- General Materials Science