INTERACTION OF PORPHYRINS WITH PROTEINS IN AOT REVERSE MICELLES: AGGREGATION
VS. COMPLEXATION
Suzana M. Andrade, and Sílvia M.B. Costa
Centro de Química Estrutural, Complexo 1, Instituto Superior Técnico 1049001 Lisboa, Portugal Email: [email protected]
Porphyrins and related compounds have been used as therapeutic drugs in important areas such ascancer detection and/or photosensitizers in photodynamic therapy. In this process, porphyrins areusually introduced in the blood in relatively concentrated solutions which may diminish its actiondue to spontaneous aggregation processes. The investigation of water soluble porphyrins isinteresting because their selfaggregation can lead to defined ordered structures that can beclassified as being of Jtype and Htype aggregates which makes them potential candidates forapplications in nonlinear optics. In particular, the anionic porphyrin tetrakis(4sulfonatophenyl)porphyrin (TSPP) was reported to selfaggregate under certain conditions of concentration, pHand ionic strength or promoted by the presence of template agents like surfactants and proteins.Reverse micelles (RM) as nanoreactors could be a means to control the size of nanoparticles. Inthis context, we have studied the role of space confinement and size of the AOT RM on theaggregation pattern of TSPP and on TSPPProtein interaction at different pH conditions. Thecomplex spectroscopic dependence found upon changing the water amount 0=[H2O]/[AOT], isdiscussed in terms of different types of aggregates (J and Htype), see scheme 1, andcomplemented with timeresolved fluorescence data. Data is further compared with that obtainedwith the positively charged mesotetrakis(Nmethylpyridinium4yl)porphyrin (TMpyP) andsome nonionic porphyrins covalently linked to hydrophobic amino acids – methionine andphenylalanine. By contrast to TSPP, no aggregation of the positively charged porphyrin isdetected by either the protein or encapsulation in AOT RM. However, the amino acid derivatizedporphyrins present a complex aggregation pattern dependent both on water and micelleconcentration.
ω0M
HJ
M
Scheme 1 – Effect of the water amount present in AOT RM on the aggregation pattern of TSPP at pHext=2and 7. At low 0( 0=[water]/[AOT]), monomeric species (M) in an interfacial region coexist with Htypeaggregates (H) of TSPP at both pH, while at high water contents the latter reverts to Jaggregates (J) and themonomer goes deeper into waterpools.
Acknowledgements: This work was supported by CQE4/FCT and project POCTI/35398/QUI/2000 and 3º QuadroComunitário de Apoio (FEDER). S.M. Andrade thanks FCT for the award of PostDoc grant BPD/9439/2002.