Mechanistic understanding and the
control of molecular self-assembly
at all hierarchical levels remain grand challenges in supramolecular
chemistry. Functional realization of dynamic supramolecular materials
especially requires programmed assembly at higher levels of molecular
organization. Herein, we report an unprecedented molecular control
on the fibrous network topology of supramolecular hydrogels and their
resulting macroscopic properties by biasing assembly pathways of higher-order
structures. The surface-catalyzed secondary nucleation process, a
well-known mechanism in amyloid fibrilization and chiral crystallization
of small molecules, is introduced as a non-covalent strategy to induce
physical cross-links and bundling of supramolecular fibers, which
influences the microstructure of gel networks and subsequent mechanical
properties of hydrogels. In addition, seed-induced instantaneous gelation
is realized in the kinetically controlled self-assembled system under
this study, and more importantly, the extent of secondary nucleation
events and network topology is manipulated by the concentration of
seeds.
The intrinsic luminescence of Tb III in ac holate (Ch) hydrogel has been found to be much higher than that in water or SDS micellar media. We have examined the role of the gel medium in enhancing the emission of Tb III in detail, and we also report ar emarkably simple methodf or detecting two important drugs,n aproxen andp ropranolol, by using the luminescence of Tb III in aT bCh hydrogel. The gel medium played ac rucial role in the sensing of these drugs, because little sensitization of Tb III took place in solution.T he drug detection could be performed down to sub-ppb levels, both for commercially availablet ablets and for (spiked) samples of blood serum without any pre-processing. This technique could also be used to differentiate between pairs of closely related drugs, for example, naproxen/ibuprofen and propranolol/atenolol. This rapid (< 2min) ands ensitived etectiont echnique may make such gels suitable as ag eneral platform for the sensing of appropriate analytes.
A detailed understanding of gelation mechanism can enable the properties of gels to be tuned for various applications, and may possibly help in understanding the aggregation of different biomolecules. We report a detailed study of the morphological and physio‐chemical changes, dynamics (of a probe), and kinetics during the gelation of europium and calcium cholate hydrogels, leading to the development of a growth model. AFM images showed the transition of aggregated particles (100–150 nm) in the sol phase growing to a fibrous network in the gel through the entanglement of fibres, and not by dendritic growth (height analysis). The dynamic changes during this phase transformation were studied using a fluorescence probe (change in intensity and lifetime). We have been able to delineate the growth mechanism by using a combination of Eu(III) luminescence and a polarity sensitive fluorescence probe. The growth was found to follow the nucleation–elongation model, and these two phases responded in distinctly different fashions in rheological and luminescence measurements.
Silver(I) forms a hydrogel in the presence of cholate with unusual properties, which are not observed with other cations. Polarity-sensitive probes have shown that the spherical aggregates observed in the gel have 'pockets' with hydrophobicity comparable to that of degassed cyclohexane. The gel exhibited thermo- and mechanoresponsive properties. Color tunability from blue to cyan and green was observed with prodan. The two sol phases of the gel formed by applying stress and temperature showed very different properties.
Eu3+ was found to form gel with cholate in methanol and comparative study was done with the hydrogel. Water is a well known quencher of Eu3+ luminescence, and its quenching rate constant is higher than that of MeOH. In a Eu3+ derived luminescent material, therefore, the replacement of water by methanol should lead to enhanced Eu3+ luminescence. However, significant pyrene‐mediated sensitizatized luminescence of Eu3+ was observed in a Eu3+ cholate hydrogel, but not in the methanolic gel. We provide experimental data that rationalize this apparent paradox.
Fluorescence Resonance Energy Transfer (FRET) in pairs of chromophores has mostly been achieved using covalently bound chromophores. In this work, we have demonstrated energy transfer in FRET pairs by taking...
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