Inclusion complexes of Fe(III) tetrakis(4-sulfonatophenyl)porphyrin with cyclodextrins in aqueous solutions

In aqueous solutions, inclusion complexation of Fe(III) tetrakis(4-sulfonatophenyl)porphyrin (FeTSPP) with alpha -cydodextrin (alpha -CD), beta -CD, gamma -CD, and heptakis(2,3,6-tri-O-methyl)-beta -CD (TM-beta -CD) has been examined by means of absorption and induced circular dichroism spectroscopy. FeTSPP has been found to form inclusion complexes with beta -CD, gamma -CD, and TM-beta -CD in pH 3.2 buffers. At pH 10.1, where FeTSPP self-associates to form an ore-bridged dimer, FeTSPP also forms inclusion complexes with alpha -CD, beta -CD, gamma -CD, and TM-beta -CD. The stoichiometries of the CD-FeTSPP inclusion complexes are 1:1, except for TM-beta -CD in pH 10.1 buffers where its 1:1 inclusion complex associates with TM-beta -CD to form a 2:1 inclusion complex at high TM-B-CD concentrations. Equilibrium constants of FeTSPP for the formation of the 1:1 inclusion complexes have been evaluated for beta -CD, gamma -CD, and TM-beta -CD. Induced circular dichroism, spectra of FeTSPP in alpha -CD and P-CD solutions exhibit a signal pattern (a negative sign) that is different from those in acidic and basic solutions containing gamma -CD and that in basic solution containing TM-beta -CD, suggesting different inclusion modes towards FeTSPP. (C) 2001 Elsevier Science B.V. All rights reserved.