Photophysical properties of porphyrinoid sensitizers non-covalently bound to host molecules; models for photodynamic therapy

A series of derivatives of 5,10,15,20-tetrakis-(4-N-methylpyridyl)-porphine, where one N-methyl group was replaced by a hydrocarbon chain ranging from C6 to C22, were characterized for their photophysical and photosensitizing properties. The absorption and fluorescence features of the various compounds in neutral aqueous solutions were typical of largely monomeric porphyrins, with the exception of the C22 derivative, which appeared to be extensively aggregated. This was confirmed by the very low triplet quantum yield and lifetime of the C22 derivative as compared with 0.2–0.7 quantum yields and 88–167 μs lifetimes for the other porphyrins. The photophysical properties and photosensitizing activity toward N-acetyl-l-tryptophanamide of the C22 porphyrin became comparable to those typical of the other derivatives in 2% aqueous sodium dodecyl sulfate, where the C22 compound is fully monomerized. All the porphyrin derivatives exhibited at micromolar concentrations photoinactivation activity against bo...

Photophysical Properties and Antibacterial Activity of Meso-substituted Cationic Porphyrins¶

The fluorescent properties of the cationic free base tetrakis(4-N-methylpyridy1)porphyrin (H2TMPyP(4)) in aqueous solution have been the subject of considerable discussion. Conclusions by various authors on the presence of homo-aggregation of H2TMPyP in these solutions are contradictory. The present work reports spectroscopic data for three isomers of H2TMPyP(n) (n = 2,3, or 4) at varying concentrations, solvent polarity, and temperature. 'H NMR spectra of H2TMPyP(4) show no ground-state monomers below M in water. Fluorescence spectra of the three isomers in aqueous solutions indicate the absence of aggregates both in the ground and excited state. Fluorescence lifetimes of the three isomers both in solution as well as adsorbed on solid surfaces can be explained by taking into account their dependence on the steric hindrance for rotation of the pyridinium groups of the three isomers with respect to the porphyrin macrocycle. Molecular mechanics confirms a higher degree of steric hindrance of H2TMPyP(2) as compared to the two other isomers. From the experimental results it is concluded that the first excited singlet state SI of the porphyrin mixes with a nearby CT state slightly above this SI state. In this CT state an electron is transferred from the porphyrin macrocycle to the pyridinium group. The amount of SI-CT mixing, responsible for the spectroscopic differences, is determined by the degree of coplanarity and resonance interaction of the porphyrin and the pyridinium n-systems, and by the solvent polarity which determines the energy difference between the two states.

Intramolecular Interactions in the Ground and Excited State of

Interactions of porphyrin derivatives 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphyrin (TMPyP4) and 5,10,15,20-tetrakis(N-propylpyridinium-4-yl)-21H,23H-porphyrin (TPrPyP4) with human telomeric AG3(T2AG3)3G-quadruplex DNAs in 150 mM K+-containing buffer in the presence or absence of 40% molecular crowding agent poly(ethylene glycol) (PEG 200) were studied by absorption titration fitting and time-resolved fluorescence spectroscopy. The results show that two TMPyP4 (or TPrPyP4) molecules bind to antiparallel/parallel hybrid structure of AG3(T2AG3)3G-quadruplex by end-stacking and outside groove binding modes in the absence of PEG. Interestingly, in the presence of PEG one porphyrin molecule is stacked between two parallel AG3(T2AG3)3 G- quadruplexes to form a sandwich structure, another porphyrin molecule is bound to the groove of the G-quadruplex. The interactions of TMPyP4 with different structures of AG3(T2AG3)3G-quadruplex are non cooperative, the binding constants of two independent binding sites are 1.07 × 106 and 4.42 × 108 M−1 for an antiparallel/parallel hybrid structure of AG3(T2AG3)3, 8.67 × 105 and 2.26 × 108 M−1 for parallel-stranded AG3(T2AG3)3G-quadruplex. Conversely, the two binding sites are cooperative for TPrPyP4, the apparent association constants are 5.58 × 106 and 1.24 × 107 M−1 for parallel-stranded and antiparallel/parallel hybrid structures of AG3(T2AG3)3G-quadruplex, respectively.

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Evidence for the binding mode of porphyrins to G-quadruplex DNA

Molecular relaxation processes following Soret band excitation of tetrakis(N-methyl-4-pyridyl)porphyrin (H2TMPyP(4)) and tetrakis(N-methyl-4-pyridyl)porphyrin-Zn(II)
(ZnTMPyP(4)) have been investigated by femtosecond transient absorption measurements in the spectral range 420–600 nm. The analysis has been carried out by comparison to zinc (II) tetraphenylporphyrin (ZnTPP). For all compounds the transient absorption kinetics has been found to be multiexponential and the resulting amplitudes have been assigned to molecular processes by considering both their spectral shapes and their related time constants. A very distinct stimulated emission band decaying in about 2 ps has been detected in the case of ZnTPP. Its transient spectra also showed a very fast component of about 150 fs which has been assigned to energy redistribution within S2 state. In the case of H2TMPyP(4) and ZnTMPyP(4) no band has been found to be attributable to the stimulated emission from the S2 state. Hence, it has been concluded that the S2 state lifetime is much shorter than 100 fs and the detected transient absorption component of 150 fs has been assigned to vibrational relaxation within the S1 state. For both H2TMPyP(4) and ZnTMPyP(4) this fast component was found to be followed by a slower one of 3 ps which has been attributed to either an excited state conformational change or a molecule cooling process by dissipation of excess energy within the solvent.

Femtosecond relaxation processes from upper excited states of tetrakis(N-methyl-4-pyridyl)porphyrins studied by transient absorption spectroscopy

The photophysical parameters (fluorescence quantum yield and lifetime, triplet state formation and lifetime) of a cationic prophyrin, i.e. 5,10,15,20-tetrakis(4-N-methylpyridyl) porphyrin (H2(TMpy-P4)), were determined directly in phosphate buffer solution in the native state and in complexes with calf thymus DNA, [poly(dA-dT)]2 and [poly(dG-dC)]2. In [poly(dG-dC)]2-porphyrin complexes (mostly intercalative), interaction induced an efficient fluorescence quenching and decrease in the triplet state quantum yield. No such effects were observed in [poly(dA-dT)]2-pophyrin complexes (mostly non-intercalative). The case of DNA was intermediate between the other two. On the basis of the redox properties of the various nucleic bases, it was shown that these observations can be interpreted in terms of fast reversible intermolecular electron transfer from the guanine moiety to the porphyrin in the excited state, when the porphyrin is intercalated with an appropriate geometry within the DNA duplex. These observations and interpretations support a type I (electron transfer) mechanism as the primary event leading to the photodynamic activity of cationic free base porphyrins used as photosensitizers in the process of photoinduced DNA strand breaks.

Photophysics of cationic 5,10,15,20-tetrakis-(4-N-methylpyridyl) porphyrin bound to DNA, [poly(dA-dT)]2 and [poly(dG-dC)]2: on a possible charge transfer process between guanine and porphyrin in its excited singlet state

Nicolai N. Kruk

Papers

Photophysics of cationic 5,10,15,20-tetrakis-(4-N-methylpyridyl) porphyrin bound to DNA, [poly(dA-dT)]2 and [poly(dG-dC)]2: on a possible charge transfer process between guanine and porphyrin in its excited singlet state

Coordination and Spectral Properties of Oxa-Substituted Tetraphenylporphyrin Derivatives