Study on spectroscopic characterization of meso-tetrakis (4-hydroxyphenyl) porphyrin (THPP) in β-cyclodextrin and its derivatives

Meso-Tetrakis (4-hydroxylphenyl) porphyrin (THPP) is a photosensitize offering an alternate approach to the treatment of cancer in the form of photodynamic therapy (PDT). The supramolecular system of THPP and β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and carboxymethyl-β-cyclodextrin (CM-β-CD), in aqueous solution has been studied by fluorescence and UV-vis spectroscopy. The formation of inclusion complexes has been observed on the base of change of spectroscopy properties. It is noted that the addition of HP-β-CD leads to remarkably strong enhancement of fluorescence intensity (nearly 300 times) of THPP. THPP forms 1:1 inclusion complex with β-CD and 1:2 inclusion complexes with the two other derivatives. Comparative to β-CD and CM-β-CD, the strongest inclusion ability of HP-β-CD can be explained that the hydrogen bond plays significant role in the inclusion process. In addition, the UV-vis experimental showed that the cavity of HP-β-CD causes the transform of the state of THPP, which is in agreement with the effect of polarity of solvent. Comparative to the pure buffer solution, the distinct equilibrium, H4THPP2+⇌H2THPP, has been observed in the solution of HP-β-CD. It is certain that the enhancement factor of nearly 300 of fluorescence presents a potential application in the detection of THPP in pharmacokinetics and biodistribution studies.