The hematoporphyrin derivative, Hpd, has been successfully introduced in the phototherapy of tumors. We here report the separation of Hpd into four main components and their characterization with respect to absorption spectra, fluorescence spectra, fluorescence quantum yield and singlet oxygen quantum yield. Furthermore, the influence of human serum on these parameters were investigated. The affinity for serum proteins and the tendency to dimerize in aqueous solutions increased with decreasing polarity of the components. Dimers as well as monomers of the porphyrins were found to bind to serum proteins, with monomerization for some of the Hpd components. Binding of monomers to serum proteins resulted in a 20% decrease in the quantum yields of fluorescence and singlet oxygen. The corresponding quantum yields of the least water-soluble Hpd components increased upon binding to serum proteins. This was found to be related to monomerization.
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Moan et al. (1981) studied this question.
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