Cyclodextrin carriers of positively charged porphyrin sensitizers

Abstract

The cationic sensitizer 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) forms supramolecular complexes with native, per-methylated, sulfonated and dimethyl-sulfonated cyclodextrins (CDs). Binding interactions were proved by NMR, mass spectra, capillary zone electrophoresis, UV-Vis and fluorescence spectroscopy. The 2D-NMR experiments on native CDs indicate that the interaction of TMPyP with the external CD surface is the dominant binding mode. The high binding affinity of TMPyP towards sulfonated CDs is due to electrostatic interactions. Binding is accompanied by an increase of the TMPyP basicity. Whereas βCD does not affect the lifetime of the TMPyP triplet states, binding with sulfonated CDs causes the protonation of the TMPyP triplet states even in neutral solution. The diprotonated anionic sensitizer 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPSH₂²⁺) forms host–guest complexes with native βCD and γCD, similarly as in its non-protonated state. The positive charge of pyrrole nitrogen atoms does not significantly influence the mode of the interaction. In contrast to TMPyP, the lifetimes of the triplet states of bound TPPSH₂²⁺ to native CDs increase.