Micelles as containers for self-assembled nanodevices: a fluorescent sensor for lipophilicity

Potentiometric titrations, fluorescence versus pH titrations, dynamic
light scattering and fluorescence polarization anisotropy
studies demonstrate that inside the nanodimensioned Triton
X-100 micelles, 1-pyrenecarboxylic acid, PCOO, forms an apical
complex with the Zn2+ cation encircled by a lipophilic cyclen
ligand and hugely increasing its fluorescence. The ability of the
Zn2+-cyclen-PCOO complex plus its micellar container to act as
a fluorescent sensor to evaluate the lipophilicity of molecular species
is demonstrated on the fatty acid series CH3ACHTUNGTRENUNG(CH2)xCOOH
ACHTUNGTRENUNG(x=0–16). At pH 7.4 a decrease in fluorescence is observed on the
addition of fatty acids that is directly related to their chain
length, that is, to their tendency to enter the micellar containers,
where they dislocate PCOO from the Zn2+ centre. The independent
determination of fatty acid pKa values in the presence of
Triton X-100 micelles confirms that our fluorescent micellar
device is capable of sensing their lipophilicity