Induction of circular dichroism of symmetrical porphyrins bound to random coil polypeptides in aqueous solutions

Spectroscopic studies of the interaction of cationic water-soluble iron(III) meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (FeTMPyP) with ionic and nonionic micelles

Interactions of cationic FeTMPyP with ionic and nonionic micelles have been studied by optical absorption, resonance light scattering (RLS) and 1 H NMR spectroscopies. The equilibrium behavior of FeTMPyP as a function of pH is described by several species in aqueous solution. The presence of phosphate anions leads to the existence of additional species in the acid p H region, probably due to the coordination of phosphates to the iron. FeTMPyP solution as a function of pH in the presence of anionic SDS showed a simplified equilibrium in acidic pH region, favoring the transition to the dimeric species. Titration of FeTMPyP as a function of SDS surfactant concentration showed the presence of three different porphyrin species: free metalloporphyrin monomers (or dimers depending on pH), metalloporphyrin monomers (or dimers) bound to the micelles, and nonmicellar metalloporphyrin/surfactant aggregates. In the case of zwitterionic LPC and HPS, and nonionic TRITON X-100 the nonmicellar metalloporphyrin/surfactant aggregates were not observed. Binding constants were calculated from optical absorption data and have values of 2 × 103 M −1 for SDS being much smaller for HPS (58 M −1), LPC and TRITON X-100. Comparison with our previous data for anionic FeTPPS 4 shows that both the electrostatic factor and hydrophobic forces are relevant in the porphyrin-surfactant interaction: for FeTPPS 4 binding constants to cationic CTAC and zwitterionic HPS are of the same order of magnitude, 1-3 × 104 M −1; for FeTMPyP the delocalization of the positive charges from the periphery substituents into the macrocycle ring leads to reduction of both electrostatic attraction to the micelle as well as hydrophobic character of the porphyrin ring, leading to a 10-fold reduction of binding to the micelles of opposite charge to the porphyrin. NMR data indicated that FeTMPyP is bound to the micelles as an equilibrium of two forms of monomer at pH 2.0, and at pH 9.0 the bound aggregated form (possibly dimers) is observed predominantly with some amount of a monomeric form.

Supramolecular chirality and chiral inversion of tetraphenylsulfonato porphyrin assemblies on optically active polylysine

The self-assembly and induced supramolecular chirality of a dianionic meso-tetraphenylsulfonato porphyrin (TPPS) on the optically active polylysine has been investigated. Our research has confirmed that in the presence of poly(l-lysine) (PLL) or poly(d-lysine) (PDL), TPPS could form both H and J aggregates and the exciton type Cotton effect was induced in the corresponding absorption bands of H and J-aggregates. We have further revealed that the induced chirality of the H-band always followed the chirality of PLL or PDL, while the sign of the exciton couplet in the J-band could be the same as or opposite to that of the H-band depending on the mixing sequence and the ratio of PLL or PDL to TPPS (P/T ratio). At a P/T ratio less than 4, both the J and H aggregates showed the same symbolic CD signal. At a P/T ratio larger than 4, the opposite sign of the exciton couplet was observed for H and J-bands when TPPS was added into PLL, while the same sign was obtained when PLL was added into TPPS. Interestingly, the J-band with the same sign as that of the H-band can be inverted into the opposite sign under heating. A mechanism relating to the dynamic and thermodynamic formation of the chiral aggregates in the presence of PLL or PDL was proposed.

Circular dichroism spectroscopic study of non-covalent interactions of poly-L-glutamic acid with a porphyrin derivative in aqueous solutions

The interactions of poly-L-glutamic acid and a cationic porphyrin derivative in aqueous solutions were studied by the combination of vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectroscopies. It was found that non-covalent interactions between both agents influence the structure of the polymeric matrix and the guest porphyrins and vice versa, but the physico-chemical properties of the solutions, especially the pH and the relative permittivity of the solvent, play a key role in the structure of the polypeptide part of the formed complexes. It was shown that the interaction with porphyrins prevents the precipitation of poly-L-glutamic acid in aqueous solution at acidic pH. In special conditions, the porphyrins attached to the polypeptide probably possess face-to-face interaction as demonstrated by the enhancement of the characteristic ECD signal and the appearance of sidebands on its short and long wavelength sides.

Dimerization of tetracationic porphyrins: ionic strength dependence

Cationic porphyrins are under study in a number of contexts including their interaction with biological targets, as possible therapeutic agents and as building blocks for molecular devices such as molecular photodiodes and solar cells. Many cationic porphyrins dimerize readily in aqueous solution. Dimerization in turn can control the properties of the porphyrin as well as its binding to its target. The propensity of a porphyrin to dimerize in aqueous solution can be estimated by recording the optical spectrum of the solution as a function of the concentration of added salt. Analysis of the data in terms of the Debye-Hückel formalism gives an estimate of the extent of dimerization as a function of ionic strength. Data for TMPyP4 [meso-tetrakis(4-N-methylpyridinium)porphyrin] and its butyl and octyl homologs; TMAP [meso-tetrakis(4-N,N,N-trimethylanilinium)porphyrin]; T theta PP [meso-tetrakis[4-N-[(3-(trimethyl-ammonio)propyl)oxy]phenyl]porphyrin] and the ferrocenyl porphyrin P3Fc are discussed. Dimerization may affect binding of the cationic porphyrins to their targets, e.g., DNA.