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pH‐Dependent modification of lipophilicity of porphyrin‐type photosensitizers
Author(s) -
Čunderliková Beata,
Kaalhus Olav,
Čunderlik Róbert,
Mateášik Anton,
Moan Johan,
Kongshaug Magne
Publication year - 2004
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2004.tb00391.x
Subject(s) - lipophilicity , protonation , chemistry , porphyrin , titration , partition coefficient , ionic bonding , octanol , tetra , ionic strength , photochemistry , inorganic chemistry , stereochemistry , medicinal chemistry , organic chemistry , ion , aqueous solution
Structural modifications of photosensitizers (changes in protonation, ionic state and aggregation state) under different environmental conditions should be precisely determined to understand the interaction of the photosensitizers with biological systems. In the present study partition coefficients of hematoporphyrin IX (HpIX), disulfonated meso ‐tetraphenylporphine, meso ‐tetra(3‐hydroxyphenyl) porphine (mTHPP) and meso ‐tetra (3–hydroxyphenyl)chlorin in the 1‐octanol‐phosphate buffer system were determined in the pH region 4.0‐8.0. Only the partition coefficients of HpIX and mTHPP were found to be pH dependent. Computer processing of fluorimetric titration data was applied to estimate p K a values of the imino nitrogens of mTHPP. Monoprotonated species of mTHPP seem to be unstable or nonexistent. The possibility that both imino nitrogens of this dye are protonated according to a common p K a is proposed. The p K a value of the imino nitrogens of mTHPP was found to be 2.99 ± 0.04 after the application of a model taking aggregation of the drug into account. The contributions of various qqueous ionic species of mTHPP as functions of pH were calculated and compared with partition coefficients.