Monomerization of Phthalocyanines in Water via Their Supramolecular Interactions with Cucurbiturils

Aggregation of phthalocyanines (Pcs) represents a problematic
feature
that decreases the potential of these macrocycles in a number of applications.
In this work, we present a supramolecular approach based on the interaction
of aminoadamantyl-substituted Pcs with bulky and hydrophilic cucurbit[7]­uril
(CB[7]) to increase the levels of Pc monomers in water. A series of
zinc­(II) Pcs substituted at positions α or β by an aminoadamantyl
substituent (with a different level of alkylation of nitrogen) were
prepared from the corresponding phthalonitriles. A 1H nuclear
magnetic resonance study of the interaction of phthalonitriles with
CB[7] in water confirmed the formation of an inclusion complex with
an aminoadamantyl moiety with Ka values
of ∼1012 M–1. The interaction
of CB[7] with Pcs in water substantially weakened H-type aggregation
and improved both fluorescence and singlet oxygen production, confirming
that this approach is efficient for the monomerization of Pcs. In vitro evaluation of the photodynamic activity of prepared
Pcs led to EC50 values in the submicromolar range on HeLa
and SK-MEL-28 cells. However, the activity decreased for at least
an order of magnitude after host–guest interaction with CB[7]
despite better photophysical properties. This was attributed to a
much lower uptake by cells due to the very bulky and hydrophilic character
of the Pc-CB[7] assembly.