No abstract

No abstract

Interactions of the water-soluble tetra(4-sulfonatophenyl)porphyrin (TPPS4) with ionic micelles in aqueous solutions have been studied by optical absorption, fluorescence, resonance light-scattering (RLS), and 1H NMR spectroscopies. The presence of three different species of TPPS4 in cationic cetyltrimethylammonium chloride (CTAC) solution has been unequivocally demonstrated:  free porphyrin monomers, monomers bound to micelles, and nonmicellar porphyrin/surfactant aggregates. This result is similar to our previous findings for TPPS4 interactions with biomacromolecules (serum albumin and DNA). The surfactant:porphyrin ratio for maximum aggregate formation is around 4:1−5:1 and 14:1 at pH 3.0 and pH 7.5, respectively. In the case of zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) the aggregates were not observed. Binding constants estimated from these data were of the order of 104 M-1 for CTAC and HPS. Our data show that solubilization of porphyrins within nonpolar regions of micelles is determined, in general, by nonspecific hydrophobic interactions, yet it is significantly modulated by electrostatic factors. NMR chemical shift, T 1, and nuclear Overhauser effect data indicate that TPPS4 is located mainly in the hydrophobic core in CTAC and HPS micelles, while in lysophosphatidylcholine its involvement in the polar area is more significant.

The aggregate morphology of meso-tetrakis(4-sulfonatophenyl) porphyrin (TPPS(4)) in aqueous solution is investigated by using small angle x-ray scattering (SAXS) technique. Measurements were performed at pH 4.0 and 9.0 to monitor the pH influence on the structural parameters of the aggregates. Radii of gyration were obtained from distance distribution functions p(r) analysis. The experimental data of TPPS(4) at pH 4.0 showed well-defined oscillations characteristic of large aggregates in contrast to the SAXS curve of 5 mM TPPS(4) at pH 9.0, where both a significant decrease in the intensity and the disappearance of the oscillation peaks suggest the dissociation of the aggregate. A 340-A long "hollow" cylinder with shell thickness of 20 A, compatible to the porphyrin molecule dimension, represents well the scattering curve of the aggregates at pH 4.0. According to the fitting parameters, 26 porphyrin molecules self-associate into a ringlike configuration in the plane of the cylinder cross-section. The total number of porphyrin molecules in the whole aggregate was also estimated as approximately 3000. The model compatible to SAXS data of a hollow cylinder with J-aggregation in the cross-section and H-aggregation (columnar stacking) between the cylinder layers is consistent with optical absorption spectroscopic data both in the literature and obtained in this work.

We used the spin label electron spin resonance technique to monitor the hydration effect on the molecular dynamics of lipids at C-5, C-12, and C-16 positions of the alkyl chain. Increase in water content of neonatal rat SC leads to an increase in membrane fluidity, especially in the region near the membrane-water interface. The effect is less pronounced deeper inside the hydrophobic core. The reorientational correlation time at the C-16 position of hydrocarbon chains showed a higher change up to approximately 18% (w/w) of water content. This behavior was accompanied by an exponential decay both in elastic modulus and electrical resistance with water content. On the contrary, the segmental motion at C-5 and C-12 positions of the chain and the permeability constant increased in the range of around 18% w/w) up to the fully hydrated condition (58 +/- 7%). Our results give a better characterization of the fluidity of SC and show that it is the principal parameter involved in the mechanism of the permeability of different compounds through skin.

No abstract

No abstract

No abstract