Primary photosensitization

Other coumarin-related compounds include furans, found in moldy sweet potatoes, and the furan coumarin complexes (furanocoumarins) found in parsnip leaves (psoralens). They are photoreactive compounds (primary photosensitizers) that exacerbate sunburn to psoralen exposed skin. 

Hypericin from St. John s wort is another phenolic compound with multiple rings and multiple double bonds. This compound readily absorbs UV light and is a primary photosensitizing agent that will result in severe sunburn in species that either ingest the plant or come in contact with plant dust or leaf extracts. 

The last syndrome reported sporadically in sheep is a primary photosensitization. The toxin responsible has not been identified. 

The results of a study of the photolysis of the uranyl-malonic acid-bimalonate system suggest that the primary photosensitive species is a (1 1) uranyl bimalonate complex, which forms as a precipitate. Kinetic and other evidence supports the mechanism shown in equations (10)—(13), where Mai = malonate. 

Epstein S (1939) Photoallergy and primary photosensitivity to sulfanilamide. J Invest Dermatol 2 43... 

Hexachlorophene, widely used and described in more detail under antiseptics (Sect. M), is rarely, if at all, documented as a primary photosensitizer (O Quinn et al. 1967 Freeman and Knox 1968). 

Another class of carbonyl compounds that has received much attention is the cyclohexadienones. The primary photolysis product of 4,4-diphenylcyclohexadienone, for example, is 5. Quenching and photosensitization experiments have indicated that the... 

Direct irradiation of substituted 1,4-dihydro-1,4-epoxy naphthalenes gives small quantities of 3-benzoxepins 16 amongst other products.144 146,256 The primary product of this reaction is probably a 3-oxaquadricyclane derivative which can react to give the benzoxepin under thermal conditions. The formation of benzoylindene compounds as the main products from the photochemical rearrangement of l,4-diphenyl-l,4-dihydro-l,4-epoxynaphthalenes has been shown to proceed via the corresponding 3-benzoxepins.146 The irradiation of naphthalene 1,4-oxides in the presence of a photosensitizer did not lead to benzoxepin derivatives.144... 

The photosensitized results are from I.B.C. Matheson and J. Lee 118h It is seen that the quantum yields in photosensitized oxidation depend on the concentrations of luminol and base, and on temperature. At higher temperature (50°) and low luminol concentrations, the quantum yields reached those of hemin-catalyzed hydrogen peroxide oxidation of luminol in aqueous-alkaline solution. Primary products of the photosensitized oxidation are singlet oxygen (1Ag02) or a photoperoxide derived from methylene blue, but neither of these is directly responsible for the luminol chemiluminescence. 

Sulfur dissolves in liquid ammonia to give intensely coloured solutions. The colour is concentration-dependent and the solutions are photosensitive. Several S-N anions are present in such solutions.76,77 The primary reduction products are polysulfides Sx2, which dissociate to polysulfur radical anions, notably the deep blue S3 ion. In a 1M solution, the major S-N anion is cyc/0-[S7N] with smaller amounts of 21 and a trace of 20.76... 

In this example, the Hg atom is the primary absorber of light. If the primary absorber is regenerated, it can participate in subsequent cycles, and is called a photosensitizer. In other cases, the photoactive species yields the active species directly. Thus, chlorine molecules can absorb light and dissociate into chlorine atomic radicals ... 

One of the primary reasons ultraviolet radiation is of interest in the context of autoimmune diseases is because of induction of photosensitive cutaneous lesions (cutaneous lupus erythematosus)82 and dermatomyositis.83 A recent global evaluation of the frequency of dermatomyositis and associated autoantibodies in referral centers around the world showed a positive correlation with the intensity of ultraviolet irradiation at those locations.84... 

The N-diazeniumdiolates are quite photosensitive. Studies of various 02-substi-tuted compounds, both alkyl and aryl, revealed a primary photochemical reaction involving cleavage of the N=N bond to yield a nitrosoamine and an O-substituted nitrene which rearranges to a C-nitroso compound (Scheme 3.31), the latter is often isolated as the oxime [224]. 

In an attempt to understand further the carcinogenicity of azathioprine, recent work in the authors laboratory has concentrated on the photodegradation of two compounds associated with the drug. l-Methyl-4-nitro-5-thioimid-azole is a metabolite and 5-hydroxy- l-methyl-4-nitroimidazole a hydrolysis product. Both gave, on irradiation at wavelengths greater than 300 nm, 1-methylparabanic acid (248) [152], The primary metabolites of azathioprine had previously been shown to be more potent than the parent drug as photosensitizers. Both 6-mercaptopurine and these imidazoles may play roles in its neoplastic action [151]. 

The quantum yield, Oco = 1.8, reported94 for the photosensitized reaction indicates that the primary process... 

The mercury-photosensitized decomposition of N20 was studied first by Manning and Noyes160 and later in greater detail and more quantitatively by Cveta-novic161,162. The primary reaction step is... 

Monoisotopic mercury photosensitization shows163 that HgO is not formed in the primary quenching reaction. 

The photosensitized electron transfer by 9,10-dicyanoanthracene (DCA) has been shown to initiate the addition of the a-silyl amine 44 to 4,4-dimethylcyclohexenone47 (equation 14). Intramolecular addition of a-silyl amine 45 was also shown to be feasible45,46 (equation 15). The primary step is electron transfer to give the aminium... 

Photosensitized animation of several aromatic compounds including phenanthrene, anthracene, naphthalene with ammonia or primary amines has also been investigated106 (equations 47-49). 

Wasserman and Keehn ") have also carried out the photosensitized auto-oxidation of anti-[2.2](l,4)naphthalenophane (34A). Irradiation of anti-34 in methanol and simultaneous reaction with singlet oxygen affords the oxidation product 127 in 20% yield. The primary step in the reaction is assumed to be formation of a peroxide (128) whose geometry permits an intra-annular Diels—Alder reaction as second step methanol-ysis then leads to 127 which was isolated. 

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