chlorophyll-a and phthalocyanine

Many aspects in the regulation of photosynthetic light-harvesting of plants are still quite poorly understood. For example, it is still a matter of debate which physical mechanism(s) results in the regulation and dissipation of excess energy in high light. Many researchers agree that electronic interactions between chlorophylls (Chl) and certain states of carotenoids are involved in these mechanisms. However, in particular, the role of the first excited state of carotenoids (Car S1) is not easily revealed, because of its optical forbidden character. The use of two-photon excitation is an elegant approach to address directly this state and to investigate the energy transfer in the direction Car S1 → Chl. Meanwhile, it has been applied to a large variety of systems starting from simple carotenoid-tetrapyrrole model compounds up to entire plants. Here, we present a systematic summary of the observations obtained by two-photon excitation about Car S1 → Chl energy transfer in systems with increasing complexity and the correlation to fluorescence quenching. We compare these observations directly with the energy transfer in the opposite direction, Chl → Car S1, for the same systems as obtained in pump-probe studies. We discuss what surprising aspects of this comparison led us to the suggestion that quenching excitonic Car-Chl interactions could contribute to the regulation of light harvesting, and how this suggestion can be connected to other models proposed.

Topics: Carotenoids; Chlorophyll; Energy Metabolism; Indoles; Isoindoles; Light; Light-Harvesting Protein Complexes; Models, Biological; Plant Physiological Phenomena

The literature on the synthesis and the biological properties of boron-containing chlorins and phthalocyanines is reviewed. A series of homologous derivatives of pyropheophorbide A is described. The compounds contain the B(12)H(11)SH(2-) cluster attached to the single carboxyl group and vary in the length of the alkyl chain (methyl, propyl, pentyl, heptyl and nonyl) attached via an ether linkage to the former vinyl group. Cellular uptake was found for all derivatives except the nonyl sidechain. The compounds were moderately cell-toxic. Localization in lysosomes could be excluded; the compounds localized probably in the mitochondria.

Topics: Animals; Antineoplastic Agents; Boron Compounds; Boron Neutron Capture Therapy; Chlorophyll; Indoles; Isoindoles; Porphyrins; Pyrazines

Photodynamic therapy is a useful new antitumoral treatment, since it is relatively selective and noniatrogenic. The photosensitizers become preferentially localized in the tumoral tissue, where their excitation by light causes the production of free cytotoxic radicals. If haematoporphyrin derivatives are the most widely used photosensitizers, numerous molecules are being tested. Now used as a palliative photodynamic therapy could logically be used as adjuvant treatment in curative surgical excision. The practical utility of peroperative photodynamic therapy in gastroenterological surgery is being evaluated experimentally and clinically.

Topics: Chlorophyll; Digestive System Neoplasms; Free Radicals; Hematoporphyrins; Humans; Indoles; Intraoperative Care; Isoindoles; Lasers; Photochemotherapy

Singlet oxygen plays a crucial role in photo-dermatology and photodynamic therapy (PDT) of cancer. Its direct observation by measuring the phosphorescence at 1270 nm, however, is still challenging due to the very low emission probability. It is especially challenging for the time-resolved detection of singlet oxygen kinetics in vivo which is of special interest for biomedical applications. Photosensitized generation of singlet oxygen, in pig ear skin as model for human skin, is investigated here. Two photosensitizers (PS) were topically applied to the pig ear skin and examined in a comparative study, which include the amphiphilic pheophorbide-a and the highly hydrophobic perfluoroalkylated zinc phthalocyanine (F64PcZn). Fluorescence microscopy indicates the exclusive accumulation of pheophorbide-a in the stratum corneum, while F64PcZn can also accumulate in deeper layers of the epidermis of the pig ear skin. The kinetics obtained with phosphorescence measurements show the singlet oxygen interaction with the PS microenvironment. Different generation sites of singlet oxygen correlate with the luminescence kinetics. The results show that singlet oxygen luminescence detection can be used as a diagnostic tool, not only for research, but also during treatment. The detection methodology is suitable for the monitoring of chemical quenchers’ oxidation as well as saturation at singlet oxygen concentration levels relevant to PDT treatment protocols.

Topics: Animals; Chlorophyll; Humans; Indoles; Isoindoles; Luminescent Measurements; Microscopy, Fluorescence, Multiphoton; Photochemotherapy; Photolysis; Photosensitizing Agents; Singlet Oxygen; Skin; Swine

Topics: Adsorption; Chemical Phenomena; Chemistry; Chlorophyll; Hematoporphyrins; Indoles; Isoindoles; Light; Pigments, Biological; Porphyrins; Research

Topics: Chlorophyll; Electrodes; Indoles; Isoindoles; Porphyrins