Interaction of Porphyrins with a Dendrimer Template:  Self-Aggregation Controlled by pH

Abstract

The interaction between self-aggregated porphyrins such as 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and 5,10,15,20-tetrakis(4-phosphonatophenyl)porphyrin (TPPP), and a generation 5 (G5) PAMAM dendrimer template is governed by minute differences of porphyrin acido-basic properties. While at neutral pH both monomeric TPPS and TPPP form complexes with G5, decreasing pH did not lead to porphyrin ring protonation (pK(a) approximately 5) but rather to the preferential formation of H-aggregates (probably H-dimers), most likely due to protonation of the G5. Upon further acidification of the solution, this face-to-face orientation of the porphyrin units is being converted to edge-to-edge aligned J-aggregates with a tightly defined structure. This process starts by protonation of the porphyrin ring at pH below 2.3 and 2.8 for TPPS and TPPP, respectively. The AFM imaging of porphyrin/G5 nanostructures obtained at pH 0.7 shows the formation of long nanorods of TPPS with partially aggregated G5 and small aggregates of TPPP connected to individual G5 molecules.

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

“…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. The results are similar to the literature reported earlier [12]. The largest amount of monomeric form was achieved at pH 5.0, which is close to the pK a of P4VP.…”

“…Many efforts have been made to investigate the well-known phenomenon. 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin (TPPS) has been the focus of extensive studies, because of its ability to self-aggregate to form H-aggregates (face-to-face) or J-aggregates (side-byside) at a high concentration and low pH value [6], in the presence of ions [7,8], surfactant [9,10], biological substan ces [11], and po lymer temp lates [12,13].…”

Chiral Polymeric Micelles From Electrostatic Assembly Between Achiral Porphyrins and Block Copolymers

“…[13] The micellar solution ( Figure 2b) shows a sharp red shift of the Soret band to 420 nm, which indicates that the monomeric units of TPPS are binding to the positively charged P(4VPH þ ) and forming H-aggregates. [14] In addition, a relative weak Soret band at 490 and Q-band at 709 nm are ascribed to J-aggregates of TPPS. [13] The disappearance of the Soret band of the TPPS monomer and the emergence of a new Soret band indicates that the TPPS has aggregated into both the H-and J-aggregates during micellization.…”

“…The different aggregates are possibly formed as following: When the TPPS is added into the solution of PEG 114 -b-P(4VPH þ ) 38 , the four -SO À 3 anions on the periphery of the TPPS are immediately bonded onto the chains of copolymers, as a result of electrostatic interactions, and forms H-aggregates, which is indicated by the appearance of the peak at 420 nm; With the increase of TPPS, the J-aggregates predominate in the solution, because they are much more stable than the H-aggregates. [14] With the micellization, the TPPSs successfully form H-and J-aggregates in the micellar core. In fact, the aggregates of TPPS play the role of crosslinker of the P(4VPH þ ) blocks to form the micellar core.…”

Protonation of Tetrakis(4-sulfonatophenyl)porphyrin in Aqueous Solutions of Acetonitrile and Dioxane

“…The diprotonated (H 4 tpps 2− ) species are able to form two types of J-aggregates and H-aggregates in which monomers are arranged in an edge-to-edge and face-to-face structure, respectively. J-aggregates are characterized by strong red shifted absorption compared to the absorption band of the monomer, whereas H-aggregates show blue shifted absorption [14,15]. The aggregate formation of TPPS varies depending on various conditions such as porphyrin concentration, acidity and ionic strength in the medium [16].…”