Photophysical Properties and Photoinduced Electron Transfer Within Host–Guest Complexes of 5,10,15,20-Tetrakis(4-N-methylpyridyl)porphyrin with Water-soluble Calixarenes and Cyclodextrins¶

Abstract

We report the formation of host-guest complexes between water-soluble calix[n]arene-p-tetrasulfonates (n = 4, 6, 8) or 2-hydroxypropyl-cyclodextrins (alpha-, beta-, gamma-) and the tetratosylate salt of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (TMPyP). The binding constants ranging between 10(2) and 10(5) M-1 were calculated from the absorption and fluorescence changes. Calix[4]arene-p-tetrasulfonate has a high binding affinity and forms with TMPyP a 1:1 complex, whereas other calixarenes bind two molecules of TMPyP. Electrostatic attraction is the dominating binding mode. Binding to calixarenes leads to a considerable decrease of the quantum yields of the triplet and excited singlet states and to shortening of the singlet and triplet lifetimes of TMPyP. The quenching mechanism is attributed to electron transfer between calixarene phenolates and excited TMPyP. Photoinduced electron transfer within a novel supramolecular complex calixarene/TMPyP (electron donor)/methyl viologen (electron acceptor) has been proven by absorption and fluorescence measurements. Electrostatic attraction between the cationic donor and cationic acceptor, on the one hand, and the anionic host, on the other, overcomes the electrostatic repulsion forces. In contrast, the interaction of cyclodextrin with TMPyP is hydrophobic in nature and only slightly influences the photophysical properties of TMPyP. The different behavior of TMPyP bound to either of the hosts has been assigned to the specific effects of the dominant binding modes, viz. the electrostatic attraction for calixarenes and the hydrophobic interactions for inclusion complexes with cyclodextrins.

Spectroscopic Studies of Water‐Soluble Porphyrins with Protein Encapsulated in Bis(2‐ethylhexyl)sulfosuccinate (AOT) Reverse Micelles: Aggregation versus Complexation

“…Figure 7B shows that the fluorescence spectrum of TMpyP in water changed from a nonstructured emission band ( λ max ∼720 nm) to two vibrational resolved emission bands ( λ max ∼660 and ∼720 nm) on increasing the βLG concentration in a similar manner to those obtained in nonprotic or apolar solvents 27. 28 These bands are consistent with π–π complex formation between βLG local residues and the porphyrin since complexation is expected to exclude water molecules from the solvation shell of the porphyrin, thus resulting in effective dielectric changes, similar to those reported for interaction with CT‐DNA and DNA nucleotides 29…”

Supramolecular Nanorods of (N-Methylpyridyl) Porphyrin With Captisol: Effective Photosensitizer for Anti-bacterial and Anti-tumor Activities

“…As claimed above, the strong complexation interaction at the N- methylpyridinium rings of TMPyP arrest the otherwise active intramolecular charge transfer pathways, thereby allowing extended lifetime for the excited singlet state, which may become advantageous for its photosensitizing and other photochemical features. Considering the availability of four such pyridinium moieties, TMPyP is expected to undergo multiple interactions with captisol, as observed with other hosts like calixarenes (Lang et al, 2001; Moschetto et al, 2002), cucurbiturils (Mohanty et al, 2008) and cyclodextrins (Moschetto et al, 2002; Cosma et al, 2006). In other words, the feasibility for such multiple binding would support for an extended/networked arrays of Captisol:TMPyP complex, realizing the formation of a new supramolecular assembly with altered photophysical properties of the TMPyP dye/drug.…”

“…Nevertheless, the non-covalent modification of porphyrins through macrocyclic hosts without affecting their chemical composition is another way to achieve the desired property of porphyrin for singlet oxygen generation and supramolecular photosensitizing behavior (Liu et al, 2013; Wang et al, 2016; Li et al, 2017, 2018; Rui et al, 2017; Semeraro et al, 2018; Gao et al, 2019). Among the huge collection of porphyrins, 5,10,15,20-tetrakis(4- N -methylpyridyl)porphyrin (TMPyP) has attracted a great deal of attention due to its efficient photosensitizing action in photodynamic therapy (Kaestner et al, 2003) and molecular assembly formation with macrocyclic receptors like cyclodextrins (Cosma et al, 2006), cucurbiturils (Mohanty et al, 2008), and calixarenes (Lang et al, 2001; Moschetto et al, 2002). In few recent studies, the enhanced antibacterial activity of TMPyP derivatives in the presence of cucurbit[7]uril against E. coli have been established (Liu et al, 2013; Chen et al, 2017).…”

Antibacterial effect of cationic porphyrazines and anionic phthalocyanine and their interaction with plasmid DNA

“…Since the decrease of the strength for the electronic interaction is expected as the cube of the distance between the chromophore and the DNA bases [17][18], the observed large hypochromism in the spectra of two porphyrazines strongly suggests a close proximity of the complexes to the plasmid bases. As shown in Fig.1, the hypochromism coincidences with a large bathochromic shift of the Q-band.…”