Photosensitization photoactivation

If the radiation is absorbed by a photosensitizer which decomposes into radicals on photoactivation, or which brings about initiation in some other manner, then Iahs = cCsIo for sufficiently small concentrations Cs of the sensitizer. The rate expression resembles Eq. (12) Rp is proportional to and to... 

In general, photosensitive protecting groups are removed by photosolvolysis, making use of the different reactivities of the excited and ground states, or by intramolecular, photoactivation reactions. 

Photochemical preparation of stable dyes by irradiation of aminotriarylacetonitriles Photosensitive leucocyanide compositions Photoactivation of leucocyanides Solid photosensitive compositions Purification of triarylrnethane leucocyanides Fuchsine cyanide... 

For solution phase photopolymerization, photosensitive solutions must be prepared immediately before use. In film-based compositions, stability and sensitivity are lost in 2-5 days (compare Tables 6, 10). The lack of stability is directly related to the nature of the activator, although not in a way that necessarily parallels photosensitivity. The photoactivated reaction, dye-activator redox chemistry, is a go/no-go process and does not contribute to the dark reaction. Rather, dark reactions are in general a consequence of the basicity of most common activators, for example, amines, sulfinates, or enolates. Deprotonation of active methylene groups on some dyes (e.g.,... 

A ferric NHase from Rhodococcus sp. N-771 [54], which is probably the same as that from Rhodococcus sp. N-774 because of the coincidence in amino acid sequences, shows a photosensitive phenomenon both in vivo and in vitro [55,56], Its NHase activity is increased by exposure to near ultraviolet light. Absorption and fluorescence spectra indicated that the chromophore involved in the photoactivation is the iron complex. Crystallographic parameters of the Rhodococcus sp. N-771 NHase have been determined by precision X-ray diffraction studies [57]. 

DPL Two-step photoactivation of electron transfer at simultaneous excitation of both photosensitizers in the membrane 64,65... 

Photodynamic therapy is a powerful medical procedure that exploits the combined action of light and a photosensitizing agent for the destruction of abnormal tissues. Ideally, the photosensitizer should accumulate in the tumor cells, and the photoactivation should be carried out by irradiation with innocuous red or near-infrared (NIR) light (photodynamic window = 650-1000 nm) in order to promote the photodynamic effects only at the injured areas. Because of their suitable photochemical and photophysical properties, porphyrins and mthe-nium-polypyridine complexes are potentially useful photosensitizers for application in photodynamic therapy (217-222). 

The power of these two terms comes from their ability to represent the effectiveness of incident radiation to change the test sample. They effectively provide the user with a map identifying which wavelengths produce the greatest photochemical change. Once this information has been obtained, the user can then determine which wavelengths might be most effective for a photoactivation or in need of suppression for a photosensitive sample. 

A phenomenon closely related to photosensitization is that of photoactivated adsorption, in which non-stoicheiometric soUds show enhanced adsorption of molecules from solution during illumination. The... 

In cases 1.1 to 1.4 the role of the photon is played outside the catalytic cycle, which explains why the quantum yield of P is usually greater than 1. In stoichiometric photogenerated catalysis [9] (Scheme 1.5), also labeled photoassisted [8, 14], photoenhanced [15], or photoactivated [16], the role of the photon is inside the catalytic cycle therefore every S —> P transformation consumes a photon and the overall quantum yield for the production of P is smaller than 1. Scheme 1, case 1.5 should not be confused with sensitization because in the step S + C —> P + pC both the substrate and the catalyst are in their ground state, which is not the case for photosensitization. 

Phototoxicity is photosensitivity that is independent of immunological responses. Phototoxic responses are dose dependent and will affect almost anyone when sufficient dosage is applied or when taken concurrent with UV exposure. In phototoxic reactions, photoactivated chemicals cause direct cellular damage. UV absorption produces either excited state chemicals or metabolites of these chemicals. These, in turn, can be converted into either free radicals or singlet oxygen, either of which results in biomo-lecular oxidation)10 ... 

Rather than attempt to incorporate complex terminology that would be precisely descriptive of each mechanism, I will use the very general terms photoactivated toxicity or phototoxicity throughout this chapter. Only where particular mechanisms have been identified, or are of importance to the discussion, will the more specific terms just discussed be applied, generally where photodynamic photosensitization or photomodified toxicity has been demonstrated. 

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