Unusual Stepwise Protonation and J‐Aggregation of meso‐Tetrakis(N‐methylpyridinium‐4‐yl)porphine on Binding Poly(sodium vinylsulfonate)

Abstract

The binding of a tetracationic porphyrin to a highly charged polymer like poly(sodium vinylsulfonate) has been investigated over a wide pH range and under various experimental conditions. We present evidence that, depending on the pH, the high electrostatic field exerted by the polymer stabilizes the diprotonated form of the free base porphyrin at unusual pH values or otherwise causes the formation of H-type aggregates. In particular, at a low polymer concentration, lowering the pH at first allows the formation of the diacid species then it determines its reorganization in close-packed J-type aggregates. The employment of various metallo-derivatives of the title porphyrin enables a better insight into the nature of all the detected species.

Cationic porphyrins with large side arm substituents as resonance light scattering ratiometric probes for specific recognition of nucleic acid G-quadruplexes

“…Taking TMPipEOPP and OMHEPzEOPP as examples, Job plot analysis based on the RLS signal intensity ratio gave a 1:1 binding stoichiometry for both of them to KRAS (Supplementary Figure S29), thus suggesting they might interact with KRAS by an end-stacking mode. Since high density of negative charges of G-quadruplex can promote the gathering of H + ions around DNA surface, such a binding mode can then lead to the N-protonation of TMPipEOPP (43,50), thus giving the emergence of absorption peak at 695 nm in UV-vis spectrum and RLS peak at 702 nm in RLS spectrum. Collectively, the RLS signal changes in the low wavelength range are caused by DNA-assisted porphyrin aggregation, but the signal changes in the high wavelength range that we used for specific G-quadruplex-probing are related to the porphyrin protonation promoted by end-stacking of porphyrin on G-quadruplexes.…”

Planar and Nonplanar Free‐Base Tetraarylporphyrins: β‐Pyrrole Substituents and Geometric Effects on Electrochemistry, Spectroelectrochemistry, and Protonation/Deprotonation Reactions in Nonaqueous Media

“…A number of articles have reported the chemical, structural, and optical properties of planar and nonplanar free‐base porphyrins in their neutral and diprotic forms 4–20. A nonplanar conformation of the porphyrin macrocycle will result from repulsive interactions among the peripheral substituents that also induces dramatic redshifts of the electronic absorption spectral bands 10.…”

Electrochemical and Spectroelectrochemical Properties of Free‐Base Pyridyl‐ and N‐Alkyl‐4‐Pyridylporphyrins in Nonaqueous Media

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More than three dozen different metal ions have been incorporated into the macrocyclic core of water-soluble tetra-N-methylpyridylporphyrins, and many of these complexes have been studied with respect to their physicochemical [1][2][3][4][5][6][7][8][9] and electrochemical [10][11][12][13][14][15][16][17][18][19][20][21][22] properties in both aqueous and nonaqueous media. These compounds are easily reducible in both water and nonaqueous solvents, and an umber of the complexes have been used in nuclear medicine, [21,[23][24][25][26] examples being given by tetra-N-methylpyridylporphyrins having the formula [M(TMPyP)] n + (X À ) n where TMPyP represents the porphyrin macrocycle with four meso-substituted N-methylpyridyl groups, n = 4o r5 ,X À = an anion and M = In II ,Mn III ,Fe III ,o rG d III .

The electrochemistry of [M(TMPyP)] n + (X À ) n in nonaqueous media has been characterizeda lmoste xclusively with respect to the reductionst hat can occur at the conjugated p-ring system of the macrocycle, the electroactive N-methylpyridyl substituents, and, in some cases, at the central metal ions.

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