Interaction of cationic water-soluble meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) with ionic and nonionic micelles: aggregation and binding
Contribuinte(s) |
UNIVERSIDADE DE SÃO PAULO |
---|---|
Data(s) |
20/10/2012
20/10/2012
2008
|
Resumo |
The equilibrium of meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) in aqueous solution in the presence of surfactants was studied by optical spectroscopic techniques and SAXS (small angle X-ray scattering). Anionic SDS (sodium dodecyl sulfate), zwitterionic HPS (N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate) and nonionic TRITON X-100 (t-octyl-phenoxypolyethoxyethanol), surfactants were used. TMPyP is characterized by a protonation equilibrium with a pK(a) around 1.0, associated with the diacid-free base transition, and a second pK(a) around 12.0 related with the transition between the free base and the monoanion form. Three independent species were observed for TMPyP at pH 6.0 as a function of SDS concentration: free TMPyP, TMPyP-SDS aggregates and porphyrin monomer bound to micelles. For HPS and TRITON X-100, the equilibrium of TMPyP as a function of pH is quite similar to that obtained in pure aqueous solution: no aggregation was observed, suggesting that electrostatic contribution is the major factor in the interaction between TMPyP and surfactants. SAXS data analysis demonstrated a prolate ellipsoidal shape for SDS micelles; no significant changes in shape and size were observed for SDS-TMPyP co-micelles. Moreover, the ionization coefficient, alpha, decreases with the increase of the porphyrin concentration, suggesting the ""screening"" of the anionic charge of SDS by the cationic porphyrin. These results are consistent with optical absorption, fluorescence and RLS (resonance light scattering) spectroscopies data, allowing to conclude that neutral surfactants present a smaller interaction with the cationic porphyrin as compared with an ionic surfactant. Therefore, the interaction of TMPyP with the ionic and nonionic surfactants is predominantly due to the electrostatic contribution. Copyright (c) 2008 Society of Porphyrins & Phthalocyanines. |
Identificador |
JOURNAL OF PORPHYRINS AND PHTHALOCYANINES, v.12, n.8, p.942-952, 2008 1088-4246 |
Idioma(s) |
eng |
Publicador |
WORLD SCI PUBL CO INC |
Relação |
Journal of Porphyrins and Phthalocyanines |
Direitos |
closedAccess Copyright WORLD SCI PUBL CO INC |
Palavras-Chave | #cationic porphyrin #TMPyP #surfactants #ionic and nonionic micelles #optical absorption spectroscopy #small angle X-ray scattering #resonance light scattering #ELECTRONIC ABSORPTION-SPECTROSCOPY #X-RAY-SCATTERING #PORPHYRINS #SURFACTANTS #H-1-NMR #MESO-TETRAKIS(4-SULFONATOPHENYL)PORPHYRIN #NUCLEOTIDES #PARTITION #LOCATION #DNA #Chemistry, Multidisciplinary |
Tipo |
article proceedings paper publishedVersion |