Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Using EPR spectroscopy as a unique probe of molecular-scale reorganization and solvation in self-assembled gel-phase materials
AU - Caragheorgheopol, Agneta
AU - Edwards, William
AU - Hardy, John G.
AU - Smith, David K.
AU - Chechik, Victor
PY - 2014/7/13
Y1 - 2014/7/13
N2 - 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.
AB - 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.
KW - SUPRAMOLECULAR ARCHITECTURES
KW - ORGANOGEL FORMATION
KW - WEIGHT GELATORS
KW - SPIN LABELS
KW - SOLVENT
KW - GELATION
KW - SOLUBILITY
KW - POLYMERIZATION
KW - PARAMETERS
KW - HYDROGELS
KW - Chemistry(all)
KW - Materials Science(all)
U2 - 10.1021/la501641q
DO - 10.1021/la501641q
M3 - Journal article
VL - 30
SP - 9210
EP - 9218
JO - Langmuir
JF - Langmuir
SN - 0743-7463
IS - 30
ER -