Properties of surface-cross-linked micelles probed by fluorescence spectroscopy and their catalysis of phosphate ester hydrolysis

Cross-linking of a tripropargylated ammonium surfactant by a diazide cross-linker in the presence of Cu(I) catalysts yielded surface-cross-linked micelles (SCMs) as water-soluble nanoparticles. Cross-linking had a profound impact on the properties of the micelles. The binding of 1-anilinonaphthalene-8-sulfonic acid (ANS) indicated that the SCMs contained two types of binding sites, favoring the polar and nonpolar excited states of the probe, respectively. The SCMs also shielded the excited states of ANS from solvent exposure better than the micelles of cetyltrimethylammonium bromide (CTAB). The SCMs inhibited the excited state proton transfer (ESPT) of a polyanionic probe, pyranine, more strongly than CTAB micelles. The ESPT of a more hydrophobic probe, 2-naphthol, was found to be influenced by the stronger surface basicity of the SCMs, as well as their better shielding of the probe from the aqueous phase than the CTAB micelles. The stronger surface basicity of the SCMs also enabled them to catalyze the hydrolysis of an activated phosphate ester at neutral pH better than CTAB micelles.

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► Cross-linked micelles were obtained by click chemistry.
► Fluorescence showed important differences between normal and cross-linked micelles.
► Cross-linking enhanced the surface basicity of the micelles.
► The surface basicity enabled the micelles to hydrolyze phosphate ester at pH = 7.