title: Characterization of the self-assembly of meso-tetra(4-sulfonatophenyl)porphyrin (H(2)TPPS(4-)) in aqueous solutions.
abstract: The aggregation of meso-tetra(4-sulfonatophenyl)porphyrin (H(2)TPPS(4-)) in phosphate solutions was investigated as a function of pH, concentration, time, ionic strength, and solution preparation (either from dilution of a freshly prepared 2 mM stock or by direct preparation of μM solution concentrations) using a combination of complementary analytical techniques. UV-vis and fluorescence spectroscopy indicated the formation of staggered, side-by-side (J-type) assemblies. Their size and self-associative behavior were determined using analytical ultracentrifugation and small-angle X-ray scattering. Our results indicate that in neutral and basic solutions of H(2)TPPS(4-), porphyrin dimers and trimers are formed at micromolar concentrations and in the absence of NaCl to screen any ionic interactions. At these low concentrations and pH 4, the protonated H(4)TPPS(2-) species self-assembles, leading to the formation of particularly stable aggregates bearing 25 ± 3 macrocycles. At higher concentrations, these structures further organize or reorganize into tubular, rod-like shapes of various lengths, which were imaged by cryogenic and freeze-fracture transmission electron microscopy. Micron-scale fibrillar aggregates were obtained even at micromolar concentrations at pH 4 when prepared from dilution of a 2 mM stock solution, upon addition of NaCl, or both.
authors: Department of Chemistry and Macromolecular Studies Group, Louisiana State University, Baton Rouge, Louisiana 70803, United States.
authors: Javoris V
authors: JV
authors: Hollingsworth
authors: Allison J
authors: AJ
authors: Richard
authors: M Graça H
authors: MG
authors: Vicente
authors: Paul S
authors: PS
authors: Russo
mesh_terms: D020285:Cryoelectron Microscopy; D006863:Hydrogen-Ion Concentration; D046032:Microscopy, Energy-Filtering Transmission Electron; D015394:Molecular Structure; D011166:Porphyrins / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D014867:Water / Q000737:chemistry*
chemical_list: D011166:Porphyrins; C092400:meso-tetrakis(4-sulfonatophenyl)porphyrin; D014867:Water; D012965:Sodium Chloride