Thermoresponsive materials with a lower critical solution temperature (LCST) are receiving growing attention, of which examples of nonpolymeric small molecules are limited. Monodisperse oligoethylene glycol amphiphiles that contain aromatic units with a LCST in water have been developed and applied to peptide extraction. Concentration-dependent hysteretic transmittance changes were observed in response to temperature elevation and reduction. Dynamic light scattering measurements and phase contrast microscopy revealed the formation of micrometer-sized aggregates upon heating at a concentration above 5.0 mm; these aggregates self-assembled to form larger aggregates upon cooling before dissolution. The "interaggregate" interactions are likely to cause the hysteretic behavior. As an application of this thermodriven phase separation, selective extraction of peptide fragments containing high percentages of hydrophobic and aromatic amino acid residues was successfully demonstrated.
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