Porphyrin and metalloporphyrin derivatives are at the forefront of the photosensitizers currently investigated for the photodynamic therapy (PDT) of cancer. Earlier examples included various porphyrins and chlorins, some of them already approved for clinical work, but lately emphasis has been given to the development of stable bacteriochlorin derivatives. The spectroscopy, photochemistry, and electrochemistry of porphyrins and bacteriochlorins, and some of their representative metal complexes, are reviewed and related to the design of photosensitizers capable of producing reactive oxygen species with high quantum yields. Efficacy in vitro is evaluated in terms of a phototherapeutic index, and efficacy in vitro is assessed using tumor growth delays. Guidelines are proposed for the design of more efficient PDT photosensitizers.

Design of porphyrin-based photosensitizers for photodynamic therapy

Femtosecond degenerate four-wave mixing (DFWM) was used to study third-order nonlinear optical properties of electropolymerized Fe(III) tetrakis(p-hydroxyphenyl)porphyrin films. Third-order nonlinear susceptibility χ1111(3)(−ω;ω,ω,−ω) was determined at 760−1350 nm. Susceptibility χ(3) values for a 500 nm thick porphyrin film ranged between (2−15)×10-20 m2V-2 ((1.4−10.7)×10-12 esu). The time response of electronic nonlinearities was faster than 120 fs. The sum-over-states model was applied to determine real and imaginary components for χ(3) and molecular second hyperpolarizability, γ. At wavelengths <800 nm, porphyrin film χ(3) is enhanced due to the 700 nm one-photon charge-transfer (CT) band. Nonlinear properties at longer wavelengths are determined by a two-photon resonance with a 17 400 cm-1 state. This state was not observed for other porphyrins and is attributed to a two-photon CT transition. Due to the resonance with the two-photon state, porphyrin Im χ(3) and two-photon absorption cross-section δ i...

Charge-transfer states determine iron porphyrin film third-order nonlinear optical properties in the near-IR spectral region

2 – Catalysis and Surface Science

X-ray diffraction, hydrogen and carbon monoxide chemisorption, transmission electron microscopy combined with energy-dispersive analysis of X-ray (TEM-EDAX) and Mossbauer effect spectroscopy (MS) were used to study the genesis and the final chemical states of bimetallic Fe-M (MCo, Ni, Ru, Rh, Pd, Ir or Pt) clusters supported over an activated carbon. While iron reducibility was inhibited in Fe-M (MCo, Ni) bimetallics, noble metals facilitate the reduction of iron atoms. However, a residual fraction of Fe3+ remains in all samples, even when reduced in hydrogen at 723 K for 12 h. Formation of alloy was detected in all catalysts after treatment in hydrogen at 673 K. The iron reducibility and/or the nature of the second alloying metal, as well as the reduction temperature affect the sizes of the resulting metal aggregates. The reactivity with oxygen followed by MS, and the EDAX of various catalyst regions (zone and single particle analysis) seem to indicate that small metal crystallites are constituted by alloys while higher metal aggregates are segregation phases containing only one metal.

Carbon supported bimetallic catalysts containing iron: I. Preparation and characterization

The transient evolution of protoporphyrin IX (PPIX) and hemin following the Soret band excitation was measured in the 410–600 nm spectral region with sub-picosecond time resolution. In PPIX the relaxation pathway was characterized in the femto- and picosecond time scale by two processes with time constants of 350 fs and ∼6 ps, describing the evolution of the system through internal Qy → Qx conversion and vibrational relaxation and cooling in the Qx state. The lifetime of the Qx state was found to be 10.4 ns by time resolved fluorescence measurements. In hemin, the ground state is completely recovered in tens of picoseconds through pathways involving CT and (d,d) states. The experimentally observed vibrational dynamics is mainly due to “hot” ground state transitions.

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Excited-state absorption and ultrafast relaxation dynamics of protoporphyrin IX and hemin.

Mossbauer spectral studies were made of samples of α-Fe2O3 highly dispersed on silica gel before and after activation, which consisted of evacuated heating at 475°C. The spectra gave Ividence that Fe2+ ions were produced from α-Fe2O3 during the activation process. Reduction was impossible after the activation and oxidation had been repeated three times. However, the inactivated sample came to be again reduced by activation after having been exposed to water vapor at room temperature. In order to explain these facts, a working hypothesis was advanced that the hydroxyl groups near the surface of the particles play a principal role in reacting with organic contamination from the vacuum system, as a result bringing about the partial reduction of α-Fe2O3.

Mössbauer Spectral Observation of α-Fe2O3 Supported on Silica Gel during Activation

The visible absorption spectra of the high-spin iron(III) complexes of the tetra-para-substituted derivatives of 5,10,15,20-tetraphenylporphyrin, Fe(p-Rtpp)X (R = OMe, H, F or Cl; X = Cl, Br or I), have been compared with each other in order to clarify the electronic effects of the phenyl substituents and axial ligands. Two charge-transfer bands shift to higher energy as the electron-withdrawing ability of the substituents increases. This is attributed to a stabilization of the porphyrin a1u(π) and a2u(π) orbitals involved in the electronic transition. These bands shift to lower energy in the order X = Cl < Br < I; the energies of these bands for I are the lowest of the three. By considering the predominantly ionic character of the bond between Fe and X, it has been proved that the iron dyz and dzx levels are lowered in this order, thereby causing a red shift. The Qv porphyrin transition shifts to lower energy in the order X = Cl < Br < I, and the Q0 transition exhibits the same trend to a less extent. Th...

Comparative Study of the Visible Spectra of the Iron(III) Complexes of para-Substituted Tetraphenylporphyrins. Electronic Effects of Substituents and Axial Ligands.

Toshie Ohya

Papers

Mössbauer Spectral Observation of α-Fe2O3 Supported on Silica Gel during Activation

Comparative Study of the Visible Spectra of the Iron(III) Complexes of para-Substituted Tetraphenylporphyrins. Electronic Effects of Substituents and Axial Ligands.