Study on the supramolecular system of meso-tetrakis (4-sulfonatophenyl) porphyrin and cyclodextrins by spectroscopy

The ability of beta -cyclodextrin (beta -CD), sulfurbutylether-beta -CD (SBE-beta -CD) and hydroxypropyl-beta -CD (HP-beta -CD) to break the aggregate of the meso-Tetrakis (4-sulfonatophenyl) porphyrin (TPPS4) and to form 2:1 inclusion complexes has been studied by adsorption and fluorescence spectroscopy. The formation constants are calculated, respectively by fluoremetry, from which the inclusion capacity of different CDs is compared and the inclusion mechanism of charged-beta -CD (SBE-beta -CD) is quite different from that of parent beta -CD. At lower pH, the complexation between HP-beta -CD and H2TPPS42+ (the form of the diprotonated TPPS4) hampers the continuous protonation of the pyrrole nitrogen of TPPS4 and the hydrophobic cavity may prefer to bind an apolar neutral porphyrin molecule. (HNMR)-H-1 data support the inclusion conformation of the porphyrin-cyclodextrin supramolecular system, indicating the interaction of meso-phenyl groups of TPPS4 With the cavity of CDs. For this host-guest inclusion model, cyclodextrin, being regarded as the protein component, which acts as a carrier enveloping the active site of heme prosthetic group within its hydrophobic environment, provides a protective sheath for porphyrin, creating artificial analogues of heme-containing proteins. However, the TPPS4, encapsulated within this saccharide-coated barrier, its physico-chemical, photophysical and photochemical properties changed strongly. (C) 2001 Elsevier Science B.V. All rights reserved.