Unusual light-tunable thermoresponsive behavior of OEGylated homopolypeptide with azobenzene and thioether spacers

Abstract OEGylated homopolypeptide (i.e., P(Azo-S-OEG 7 )) bearing azobenzene, thioether spacers, and oligo(ethylene glycol) OEG tails were prepared via a copper-mediated 1,3-dipolar cycloaddition. P(Azo-S-OEG 7 ) showed an upper critical solution temperature (UCST)-type thermo-, light-, and oxidation-responsive in ethanol/water solvent mixtures. The UCST-type cloud point temperature ( T cp ) decreased after UV irradiation and it increased after visible light irradiation due to the trans - cis isomerization of azobenzene moieties. P(Azo-S-OEG 7 ) can be readily oxidized in the presence of H 2 O 2 , yielding P(Azo-S OX -OEG 7 ) with sulfone or sulfoxide spacers. P(Azo-S OX -OEG 7 ) showed an increase of UCST-type T cp after UV irradiation and the T cp decreased after visible light irradiation, which is an opposite trend to the UCST-type phase behavior of P(Azo-S-OEG 7 ) as well as previous report. P(Azo-S-OEG 7 ) showed poor water-solubility, yet it underwent H 2 O 2 induced solution phase transition yielding P(Azo-S OX -OEG 7 ) with lower critical solution temperature (LCST)-type phase behavior in water. The P(Azo-S OX -OEG 7 ) aqueous solutions showed a decrease of LCST-type T cp after UV irradiation and consequently T cp decreased after visible light irradiation.