Small angle X-ray scattering study of meso-tetrakis (4-sulfonatophenyl) porphyrin in aqueous solution: a self-aggregation model.

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.

Interaction of Fe(III)- and Zn(II)-tetra(4-sulfonatophenyl) porphyrins with ionic and nonionic surfactants: aggregation and binding.

Interactions of the water soluble Fe(III)- and Zn(II)-tetra(4-sulfonatophenyl) porphyrins, FeTPPS(4) and ZnTPPS(4), with ionic and nonionic 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 both Fe(III)- and Zn(II)TPPS(4) in cationic cetyltrimethylammonium chloride (CTAC) solution has been unequivocally demonstrated: free metalloporphyrin monomers or dimers (pH 9), metalloporphyrin monomers or aggregates (possibly micro-oxo dimers) bound to the micelles, and nonmicellar metalloporphyrin/surfactant aggregates. The surfactant:metalloporphyrin ratio for the maximum nonmicellar aggregate formation is around 5-8 for Fe(III)TPPS(4) both at pH 4.0 and 9.0; for Zn(II)TPPS(4) this ratio is 8, and the spectral changes are practically independent of pH. In the case of zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and non-ionic polyoxyethylene lauryl ether (Brij-35) and t-octylphenoxypolyethoxyetanol (Triton X-100), the nonmicellar aggregates were not observed in the pH range from 2.0 to 12.0. Binding constants were calculated from optical absorption data and are of the order of 10(4) M(-1) for both CTAC and HPS, values which are similar to those previously obtained for the porphyrin in the free base form. For Brij-35 and Triton X-100 the binding constant for ZnTPPS(4) at pH 4.0 is a factor of 3-5 lower than those for CTAC and HPS, while in the case of FeTPPS(4) they are two orders of magnitude lower. Our data show that solubilization of ZnTPPS(4) within nonpolar regions of micelles is determined, in general, by nonspecific hydrophobic interactions, yet it is modulated by electrostatic factors. In the case of FeTPPS(4), the electrostatic factor seems to be more relevant. NMR data indicated that Fe(III)TPPS(4) is bound to the micelles predominantly as a monomer at pH 4.0, and at pH 9.0 the bound aggregated form (possibly micro-oxo dimers) remains. The metalloporphyrins were incorporated into the micelles near the terminal part of their hydrocarbon chains, as evidenced by a strong upfield shift of the corresponding peaks of the surfactants.

Binding of the Mn(III) complex of meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin to DNA. Effect of ionic strength.

Interactions of the water-soluble Mn(III) complex of meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin (Mn(III)TMPyP) with DNA in aqueous solutions at low (0.01 M) and high (0.2 M) ionic strengths have been studied by optical absorption, resonance light scattering (RLS) and 1H NMR spectroscopies. Optical absorption and RLS measurements have demonstrated that in DNA solutions at low ionic strength the Mn(III)TMPyP form aggregates, which are decomposed at DNA excess. At high ionic strength the aggregation was not observed. We explain this effect by assuming that upon increase in ionic strength, Mn(III) TMPyP dislocates from the DNA sites, which produces better conditions for the porphyrin aggregation, to sites where the aggregation is hindered. The 1H NMR data demonstrated that the aggregation observed at low ionic strength reduces the paramagnetism of Mn(III)TMPyP. This phenomenon was not observed at the high ionic strength in the absence of aggregation.

Photophysical studies of excited-state characteristics of meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin bound to DNA.

The interaction of meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin (TMPyP) with DNA has been investigated at ionic strength (IS) values of 0.01 and 0.20 M (pH 6.8) using the flash-photolysis technique along with optical absorption and fluorescence data. It is found that the aggregation of TMPyP observed at the porphyrin excess reduces its total fluorescence intensity (JT) and the T-T absorption. At low IS the JT and the T-T absorption for the TMPyP monomers bound to the GC DNA sites are lower than those for the free ones, whereas binding to the AT sites (high IS) increases JT. At low IS the triplet decay of TMPyP is mono-exponential, the lifetime increasing with the [DNA] increase, while at high IS the addition of DNA transforms this profile to a bi-exponential form with lifetimes of the components independent of [DNA]. Binding to DNA reduces the quenching constants of the porphyrin triplet states by molecular oxygen (kq), the effect depending on the site and mode of binding. So, at low IS the kq value for the TMPyP externally bound to the GC sites (3.0 x 10(8) M-1 s-1) is five times lower than that for the free porphyrin and twice as high as that for the intercalated one. At high IS the TMPyP binding reduces the kq three-fold for the AT sites in the minor groove and 16-fold in the major groove as compared with the free one (approximately or equal to 1.6 x 10(9) M-1 s-1).