J- and H-Aggregates of 5,10,15,20-Tetrakis-(4-sulfonatophenyl)-porphyrin and Interconversion in PEG-b-P4VP Micelles

Abstract

Micellization of poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG114-b-P4VP61) induced by 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin (TPPS) in acidic solutions were studied by dynamic and static light scattering, atomic force microscope, and UV-vis spectroscopy. The resultant complex micelles had a core-shell structure with the electrostatically complex TPPS/P4VP as the core and the soluble PEG as the shell. The anionic TPPS in the micellar core formed J-aggregates at pH 1.5-2.5 and H-aggregates at pH 3.0-4.0, respectively. Interconversion between the J-aggregates and the H-aggregates was carried out by adjusting the pH value of the micelle solutions. It is worth noting that the micelles showed strong split Cotton effect in the circular dichroism spectra although TPPS and the copolymer were all achiral. The resulting chirality sign could be selected by the hydrodynamic forces of a stirring vortex. Positive or negative chiral signals appeared when stirring clockwise or anticlockwise.

Micellization of copolymers via noncovalent interaction with TPPS and aggregation of TPPS

“…The average D h of the initial prepared complex micelle at pH 4.0 was 73.5 nm, and the value increased to 111.2 nm accompanied by a broadening in the diameter distribution after adjusting the pH to 1.6. This result was similar to our earlier report [14]. J-aggregates of TPPS possessing side-by-side aggregation type and relative large aggregation number accounts for the larger diameter and broader distribution.…”

“…We have recently reported that PEG-b-P4VP, possessing aromatic units, resulted in the monomeric form and aggregates of TPPS, and the existence form was strongly depended on the pH and the 4VP/TPPS ratio [14,15]. As reported by Yuya Egawa and coworkers [16], cationic polymers which do not bear aromatic moieties were apt to induce H-aggregation of TPPS.…”

“…In the complex micellar core, TPPS existed as a combination of H-aggregates and deprotonated monomers, given by the overlap of the absorptions at 406 and 422 nm. The pyridyl rings of P4VP tended to - stacking interact with TPPS, resulting in the dispersed porphyrin monomers [15,29]. PDMAEMA blocks did not undergo aromaticaromatic interactions with the porphyrins due to non-aromatic moieties, but an electrostatic interaction with sulfonate residues of TPPS.…”

“…In Figures 2(A) and 2(B), With the decrease of pH value, the absorption at 406 nm which is attributed to H-aggregates first increases at the expense of the peak at 422 nm given by monomeric form, and then disappears accompanied by the appearance of a band at 490 nm due to J-aggregates. Actually, H-aggregates are formed by deprotonated TPPS and J-aggregation is induced by the protonation of TPPS as the pH decrease [15]. In the complex micelles, J-aggregation begins at pH below 3.2, indicating that the apparent pK a of the dye is largely decreased from 4.9 to about 3.2 in the presence of the copolymers.…”

Chiral Induction, Memory, and Amplification in Porphyrin Homoaggregates Based on Electrostatic Interactions

“…In the second stage, when PAA was added the free TPPS monomers in the solution totally self-aggregated to form J-aggregates (side-by-side arrangement) and fewer H-aggregates (face-to-face arrangement), which result from the association of p-conjugated porphyrin rings. [44] At the same time, PAA competed with Ala for binding to the sites (-SO 3 À ) of the formed chiral TPPS aggregates and replaced Ala quickly by the multiple-point electrostatic interaction between amino cations of PAA and peripheral sulfonato anions of the TPPS aggregates. The flexible PAA can easily combine with the chiral TPPS aggregates and twist along the helical direction in which peripheral sulfonato groups of TPPS aggregates arrange, forming the advanced stiff TPPS-PAA complexes.…”