Narrow Results

Modest fill factors (~0.2) and efficiencies for sensitized photocurrent generation are observed with porphyrins adsorbed to saturation on a nanocrystalline SnO₂ thin film employed as the working electrode in a photoelectrochemical cell. No dye aggregation is observed at the metal oxide/adsorbate interface, and no advantage in the photosensitization efficiency is seen with two porphyrins that exhibit a stable liquid crystalline phase over another porphyrin that does not.

The in vitro photodynamic effect of bis(tri-n-hexylsiloxy)silicon phthalocyanine has been evaluated against the melanotic M6 cell line. The results showed that at 10^-5 M dose, LD₅₀ is obtained for a 150 J cm^-2 light dose and LD₉₀ for 540 J cm^-2. Electron spin resonance spectroscopy was used with spin traps to study the type I and type II photochemical pathways involved and to detect active oxygen intermediates such as singlet oxygen, oxygen superoxide and hydroxyl radical. The two mechanisms occurred simultaneously and no change was observed when the phthalocyanine was entrapped in liposomes.

Pheophorbide a (Pheo) is a well-known hydrophobic photosensitizer used for photodynamic treatment of various diseases. The influence of the surroundings on the electronic properties of photosensitizers mainly accumulating in membrane structures is of relevance for their photoactivity. In this paper the current knowledge about the electronic properties of Pheo in different microheterogeneous environments is summarized and new findings about its incorparation in different model membranes are discussed.

Graft coronary artery disease (GCAD) limits long-term patient survival following heart transplantation. There are few treatment options. Exploration into less invasive diagnostic techniques and attenuation of allograft coronary disease is warranted. The selectivity of Antrin^® Injection (a motexafin lutetium sensitizer, Lu-Tex) and illumination with far-red light, approximately 732 nm, has been evaluated in several preclinical atherosclerosis models. Lu-Tex, using fluorescence microscopy, was found to partition into distinct punctate cytoplasmic compartments in cultured human bypass coronary smooth muscle cells (SMCs). Using specific organelle probes the chief subcellular localization sites were lysosomes and endoplasmic reticulum. The inhibitory effect of Lu-Tex-mediated photoactivation was demonstrated using SMCs; many cells died via an apoptotic pathway. Following illumination, fluorescence microscopy revealed sensitizer redistribution with fluorescence being observed in the mitochondria. The distribution of Lu-Tex was evaluated in a rat model of heterotopic cardiac allografts 60 days after transplantation. Lu-Tex was retained in the cardiac allograft, exhibiting a five-fold increase in retention between the allograft and native heart. These results encourage further exploration of Lu-Tex for diagnosis, and possible amelioration of chronic graft vascular disease using photodynamic therapy.

Lipophilic and axially substituted tri-n-hexylsiloxy aluminum phthalocyanine and cholesteryloxy diphenylsiloxy aluminum phthalocyanine were synthesized and assayed in PDT against M6 melanocytes. In the conditions used (λ > 480 nm, 10 mW cm^-2, egg-yolk lecithin or cremophor EL formulation) they both exhibited a higher photodynamic effect than chloroaluminum phthalocyanine. They displayed 2% to 3.5% cell viability at 10^-5M dose for 20 min irradiation. Hexadecafluoro zinc phthalocyanine was synthesized to increase the lipophilicity of zinc phthalocyanine, hexadecachloro zinc phthalocyanine was also included because it would theoretically enhance the phototoxicity. In all the delivery systems used, their photodynamic effect against M6 melanocytes was lower in comparison with zinc phthalocyanine and axially substituted aluminum phthalocyanines. A 2 h irradiation treatment with 3 × 10^-6M hexadecafluoro zinc phthalocyanine and 10^-5 M hexadecachloro zinc phthalocyanine led to 60% and 15% cell viability respectively. In all cases, the cell killing effect was light-and dose-dependent and was higher in cremophor EL micelles than in the egg-yolk lecithin formulation.

Photodynamic tumour therapy (PDT) on the basis of a sequential two-photon excitation of suitable sensitizers is expected 1) to prevent skin phototoxicity caused by day-light and 2) may occur via an oxygen-independent mechanism of photosensitization. Here we investigated cellular uptake, localization and phototoxicity of (t-butyl)₄-PcMg, a promising dye for a sequential two-step activation, in Jurkat cells (human T cell line) and murine hybridoma cells (B cells) in vitro. Pheophorbide a (pheo) was used as a classical Type II reference sensitizer. Excitation of higher singlet states was performed both by direct UV-excitation and by sequential two-step laser excitation in the Q-band with maximum photon flux densities of about 10²⁶ phot.cm⁻².s⁻¹. Irradiation of (t-butyl)₄-PcMg in cells in vitro is accompanied by a rapid destruction of the dye, as was proved by confocal fluorescence microscopy. Irradiated cells exhibit a less pronounced decrease of viability and a transient cell cycle arrest of about 24 h. Pheo incubated cells are characterized by a complete stop of proliferation. In contrast, no long-lasting phototoxicity was observed with (t-butyl)₄-PcMg. Low fluorescence levels and rapid photobleaching prevented the identification of intracellular dye-localization. Our data indicate the presence of a radical mechanism as origin of an irreversible dye destruction that accounts for the low phototoxicity of (t-butyl)₄-PcMg.

Tetracationic 5,10,15,20-tetrakis(4-N-pentylpyridyl)porphyrins, [(TPePyP)H₂]⁴⁺ and its zinc-porphyrin analogue [(TPePyP)Zn^II]⁴⁺ have been synthesized and characterized by ¹H NMR and UV-visible spectroscopic techniques. Photobleaching studies carried out in solutions of varying pH show that, in the presence of oxygen, [(TPePyP)H₂]⁴⁺ undergoes fast photodegradation in aqueous medium when the solution is irradiated with 560 nm light. The steady-state singlet oxygen quantum yields (Φ_Δ) for [(TPePyP)H₂]⁴⁺ is 0.80 and that for its Zn analogue is 0.85. These quantities were measured using 1,3-diphenylisobenzofuran (DPBF) as a singlet oxygen scavenger, in N,N-dimethyl-formamide solution. These Φ_Δ values are compared with those for other well known sensitizers such as protoporphyrindimethylester PPDME and hematoporphyrindihydrochloride HPDHC.

This paper provides a brief account of the prior studies of singlet-oxygen-sensitized delayed fluorescence (SOSDF) of phthalocyanines and related compounds caused by photosensitized singlet oxygen generation in dye solutions, and presents new results, which unambiguously demonstrate that SOSDF also appears in phthalocyanine solutions upon direct excitation of dissolved oxygen by 1270 nm laser radiation. In all cases, light emission was shown to appear owing to the unique property of phthalocyanine molecules to efficiently accumulate energy of two molecules of singlet oxygen. Dependences of the IR-excited SOSDF on the phthalocyanine concentration, laser power and addition of singlet oxygen quenchers have been studied and kinetic equations are proposed for analyses of these data.

Singlet molecular oxygen produced in the presence of 2,2,6,6-tetramethyl-4-piperidone (TMPD) in 1,4-dioxan, by boron subphthalocyanine chloride as the sensitizer, was monitored by Electron Paramagnetic Resonance (EPR) via the oxidation of TMPD to the corresponding aminoxyl radical. This radical product is formed in low yields along the singlet oxygen pathway. A kinetic analysis of the process allows one to understand the reasons behind this, while affording more accurate quantitative insights into the mechanistic details. A crucial aspect of this reaction system, which explains the low aminoxyl radical yields along the singlet oxygen pathway, is the disappearance of the sensitizer triplet state in a reaction with TMPD, which has a rate constant of 1 × 10⁹ M^-1.s^-1.

A series of ruthenium phthalocyanine centered dendrimers has been prepared with up to 32 ethyl ester end groups. The photophysical properties have been assessed in THF to reveal a correlation between the degree of dendritic environment and the ability to generate singlet oxygen. In the attempt to prepare the correponding highly water-soluble polyelectrolyte dendrimers upon saponification we observed the cleavage of the central esters moieties adjacent to the pyridine unit in all cases. However, despite the lack of shielding by a growing branched shell surrounding the photoactive center, the obtained tetracarboxylate-terminated ruthenium phthalocyanine derivative was still able to generate singlet oxygen in aqueous medium.

A series of tetraphenyl meso-substituted porphyrins with either p-amino or p-carboxy substituents has been studied as dyes for standard dye-sensitized solar cells (DSSCs). The porphyrins with greater numbers of amino groups generally show greater efficiency, primarily due to higher photocurrents; open-circuit voltage and fill factors are comparable. The most efficient sensitizer was the trans disubstituted zinc porphyrin, with an overall solar energy conversion efficiency of 5.66%, slightly higher than the triamino zinc porphyrin at 5.18%. The improved efficiency is attributed to the well known push–pull effect in porphyrinsensitized DSSCs with electrondonating groups opposite to the electronwithdrawing anchoring (carboxy) groups. It is suggested that porphyrin derivatives with cis diaminophenyl groups show somewhat diminished efficiency due to difficulties with regeneration of the dye from its oxidized form.

Singlet oxygen (¹O₂) is a highly reactive oxygen species involved in numerous chemical and photochemical reactions in different biological systems and in particular, in photodynamic therapy (PDT). However, the quantification of ¹O₂ generation during in vitro and in vivo photosensitization is still technically challenging. To address this problem, indirect and direct methods for ¹O₂ detection have been intensively studied. This review presents the available methods currently in use or under development for detecting and quantifying ¹O₂ generation during photosensitization. The advantages and limitations of each method will be presented. Moreover, the future trends in developing PDT-¹O₂ dosimetry will be briefly discussed.

A stable silver phosphate based plasmonic photocatalyst (Ag-Ag₃PO₄) was successfully fabricated, which can drive catalytic reaction under low-intensity visible light. The synthesized plasmonic photocatalyst shows high performance and stability on the photodegradation of RhB under visible-light irradiation, and represents obviously enhanced photocatalytic activity than the pure Ag₃PO₄ sample. The photosensitization process was carried out in the photodegradation of 2,4-DCP and RhB mixture, of which the photocatalyst shows the enhancement activity for 2,4-DCP while weaker for RhB. The investigation is likely to open up a new sight for the preparation of high efficient and stable plasmonic photocatalysts which utilizes visible light.

The following sections are included:

• Summary

• Introduction

• Antimicrobial efficiency of photosensitization

• Conclusions

• References