Fluorescent cyclodextrin carriers for a water soluble ZnII pyrazinoporphyrazine octacation with photosensitizer potential

A nitro-benzofurazan-triazolyl carboxymethylated beta-cyclodextrin (NBFT-CM beta CyD) and an oligomer of carboxymethyl beta-cyclodextrin (sodium salt), crosslinked with epichlorohydrin and labeled with rhodaminyl groups (p beta CyD-Rh), exhibit very high affinity in aqueous solution for octacationic photosensitizer [(CH3)(8)LZn](8+) neutralized by I- ions (L = tetrakis-2,3-[5,6-di(2-(pyridiniumyl) pyrazino] porphyrazinato dianion). The photosensitizer (PS) forms complexes with 1 : 2 and 2 : 2 CyD: PS stoichiometry, which were characterized as binding constants and UV-Vis absorption and fluorescence properties. The self-association tendency of [(CH3)(8)LZn](8+), leading to a monomer-dimer equilibrium shift towards the dimer even at very low concentrations (approximate to 10 (6) M), is not contrasted by either NBFT-CM beta CyD or the p beta CyD-Rh oligomer, both of which completely convert the [(CH3)(8)LZn](8+) monomer fraction to the dimer form in the bound state. Quenching of fluorescence observed in [(CH3)(8)LZn](8+) upon binding with either hosts is consistent with the conversion of the monomer to the negligibly fluorescent dimer. The complexes formed with the CM beta CyD units of the p beta CyD-Rh oligomer have average association constants, which are larger by 6-7 orders of magnitude than those with the CM beta CyD monomer in the NBFT-labeled derivative.