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Spectroscopic Studies of Water‐Soluble Porphyrins with Protein Encapsulated in Bis(2‐ethylhexyl)sulfosuccinate (AOT) Reverse Micelles: Aggregation versus Complexation
Author(s) -
Andrade Suzana M.,
Costa Sílvia M. B.
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500047
Subject(s) - chemistry , porphyrin , micelle , monomer , aqueous solution , human serum albumin , protein aggregation , quenching (fluorescence) , aggregation number , fluorescence , hydrophobic effect , photochemistry , chromatography , critical micelle concentration , organic chemistry , biochemistry , polymer , physics , quantum mechanics
We have investigated the interaction of two water‐soluble free‐base porphyrins (negatively charged meso ‐tetrakis( p ‐sulfonatophenyl)porphyrin sodium salt (TSPP) and positively charged meso ‐tetrakis( N ‐methylpyridinium‐4‐yl)porphyrin (TMpyP)) with two drug‐carrier proteins (human serum albumin (HSA) and β‐lactoglobulin (βLG)) in bis(2‐ethylhexyl)sulfosuccinate (AOT)/isooctane/water reverse micelles (RM) by using steady‐state and transient‐state fluorescence spectroscopy. TSPP exhibited a complex pattern of aggregation on varying the RM size and pH in the absence of the protein: at low ω 0 (the ratio of water concentration to AOT concentration, the emission of H‐aggregates prevails under acidic or neutral “pH ext ” conditions. Upon formation of the water‐pool, J‐aggregates and monomeric diacid species dominate at low “pH ext ” but only monomer is detected at neutral “pH ext ”. The aggregation number increases with ω 0 and the presence of the protein does not seem to contribute to further growth of the aggregate. The presence of protein leads to H‐deaggregation but promotes J‐aggregation up to a certain protein/porphyrin ratio above which, complexation with the monomer bound to a hydrophobic site of the protein prevails. The effective complex binding constants are smaller than in free aqueous solution; this indicates a weaker binding in these RM probably due to some conformational changes imposed by encapsulation. Only a weak quenching of TMpyP fluorescence is detected due to the presence of protein in contrast to the negative porphyrin.