Photochemistry reductions

Oxidation-Reduction Photochemistry of Polynuclear Complexes in Solution... 

One problem we have had to overcome in developing metal-cluster oxidation-reduction photochemistry is the tendency of excited clusters to dissociate into radical fragments (for... 

H. B. Gray We must remember that we are still in the initial stages of systematic study of inorganic oxidation-reduction photochemistry. Nature has indeed some slick ways to optimize photochemical energy conversion. I am confident that inorganic chemists will do as well or better, perhaps even before the turn of the century ... 

Chromium, hexacyano-, 3, 703, 777 hexaamminecobaltate coordination isomerism, 1, 183 ligand field photochemistry, 1, 398 photochemistry excited states, 1, 398 production, 3, 704 Chromium, hexafluoro-, 3, 927 Chromium, hexabalo-, 3, 889 Chromium, hexaiodo-, 3, 766 Chromium, hexakis(dimethyl sulfoxide)-photoanation, 1, 399 Chromium, u-oxalatodi-reduction... 

The second direction in which redox properties of sulfones and sulfoxides could manifest themselves in photochemistry is redox photosensitization108,110-114. In such a photosensitization the photosensitizer is transformed by light into a short-lived oxidant or reductant able to react with the substrate to be activated. Tazuke and Kitamura115 have discussed the parameters to play with when one... 

Aqueous plutonium photochemistry is briefly reviewed. Photochemical reactions of plutonium in several acid media have been indicated, and detailed information for such reactions has been reported for perchlorate systems. Photochemical reductions of Pu(VI) to Pu(V) and Pu(IV) to Pu(III) are discussed and are compared to the U(VI)/(V) and Ce(IV)/(III) systems respectively. The reversible photoshift in the Pu(IV) disproportionation reaction is highlighted, and the unique features of this reaction are stressed. The results for photoenhancement of Pu(IV) polymer degradation are presented and an explanation of the post-irradiation effect is offered. 

Studies of actinide photochemistry are always dominated by the reactions that photochemically reduce the uranyl, U(VI), species. Almost any UV-visible light will excite the uranyl species such that the long-lived, 10-lt seconds, excited-state species will react with most reductants, and the quantum yield for this reduction of UQ22+ to U02+ is very near unity (8). Because of the continued high level of interest in uranyl photochemistry and the similarities in the actinyl species, one wonders why aqueous plutonium photochemistry was not investigated earlier. 

The high concentration of oxygen in the atmosphere plays a central role in the photochemistry and chemical reactivity of the atmosphere. Atmospheric oxygen also defines the oxidation reduction potential of surface waters saturated with oxygen. The presence of oxygen defines the speciation of many other aquatic species in surface waters. 

Kohno, Y., Hayashi, H., Takenaka, S., Tanaka, T., Funabiki, T. and Yoshida, S. Photo-enhanced reduction of carbon dioxide with hydrogen over Rh/Ti02. Journal of Photochemistry and Photobiology. 1999. A 126,117-123. 

Hirano, K., Inoue, K., and Yatsu, T. (1992) Photocatalysed reduction of C02 in aqueous Ti02 suspension mixed with copper powder. Journal of Photochemistry and Photobiology A Chemistry, 64 (2), 255-258. Adachi, K., Ohta, K., and Mizuno, T. (1994) Photocatalytic reduction of carbon dioxide to hydrocarbon using copper-loaded titanium dioxide. Solar Energy,... 

Brezova, V., Blazkova, A., Surina, I., and Havlmova, B. (1997) Solvent effect on the photocatalytic reduction of 4-nitrophenol in titanium dioxide suspensions. Journal of Photochemistry and Photobiology A Chemistry, 107 (1-3), 233-237. 

It is possible that colloidal photochemistry will provide a new approach to prebiotic syntheses. The work described previously on redox reactions at colloidal ZnS semiconductor particles has been carried on successfully by S. T. Martin and co-workers, who studied reduction of CO2 to formate under UV irradiation in the aqueous phase. ZnS acts as a photocatalyst in the presence of a sulphur hole scavenger oxidation of formate to CO2 occurs in the absence of a hole scavenger. The quantum efficiency for the formate synthesis is 10% at pH 6.3 acetate and propionate were also formed. The authors assume that the primeval ocean contained semiconducting particles, at the surface of which photochemical syntheses could take place (Zhang et al 2007). 

There is always interest in the photochemistry of the pyrimidine nucleic acid bases and related simple pyrimidinones, due to its importance in genetic mutation. In addition to damaging DNA, photo-induced reactions may also repair the damage, as in the reduction, by FADH, of the thymine glycol 64 back to thymine <06JACS10934>. Another report related to repair of DNA involved a model study, by means of the linked dimer 65, of the involvement of tryptophan in the electron-transfer leading to reversion of thymine oxetane adducts <06OBC291>. 

An interesting alternative mechanism of activation is the photochemical reduction of Pt(IV) to Pt(II) (Fig. 3). In addition to photoreduction, photosubstitution and photoisomerization can also occur, making the photochemistry of Pt complexes difficult to predict and a careful analysis of the photoproducts imperative (21). We have been involved particularly in the development of photochemotherapeutic agents based on Pt(IV) and the study of their photodecomposition and (subsequent) interactions with... 

Photochemical reactions, like any chemical reaction, can be classified into various groups, depending on the reactants and products, for example, elimination, isomerization, dimerization, reduction, oxidation, or chain reaction. One important practical field of photochemistry is organic photochemistry. In solution photochemical reactions, the nature of the solvent can markedly influence the reaction. The absorbtion of the solvent and of the reaction products is an important parameter for the choice of the reaction conditions. It is useful to have a solvent with a relatively low absorption in the desired wavelength. Sometimes photosensitizers are used these are substances that absorb light to further activate another substance, which decomposes. 

The substituent effects on the photochemistry between benzene and secondary aliphatic amines53 were studied. Irradiation of toluene or chlorobenzene with diethylamine results in the formation of mixtures of addition and substitution products (equations 34 and 35). Irradiation of anisole or benzonitrile with diethylamine gives the substitution product 7V,7V-diethylaniline (equations 36 and 37). Irradiation of benzylfluoride with diethylamine results in a side-chain substitution (equation 38). The photoreaction of p-fluorotoluene with diethylamine gives both substitution and reduction products (equation 39). 

The amide functionality plays an important role in the physical and chemical properties of proteins and peptides, especially in their ability to be involved in the photoinduced electron transfer process. Polyamides and proteins are known to take part in the biological electron transport mechanism for oxidation-reduction and photosynthesis processes. Therefore studies of the photochemistry of proteins or peptides are very important. Irradiation (at 254 nm) of the simplest dipeptide, glycylglycine, in aqueous solution affords carbon dioxide, ammonia and acetamide in relatively high yields and quantum yield (0.44)202 (equation 147). The reaction mechanism is thought to involve an electron transfer process. The isolation of intermediates such as IV-hydroxymethylacetamide and 7V-glycylglycyl-methyl acetamide confirmed the electron-transfer initiated free radical processes203 (equation 148). 

The present volume contains 13 chapters written by experts from 11 countries, and treats topics that were not covered, or that are complementary to topics covered in Volume 1. They include chapters on mass spectra and NMR, two chapters on photochemistry complementing an earlier chapter on synthetic application of the photochemistry of dienes and polyenes. Two chapters deal with intermolecular cyclization and with cycloadditions, and complement a chapter in Volume 1 on intramolecular cyclization, while the chapter on reactions of dienes in water and hydrogen-bonding environments deals partially with cycloaddition in unusual media and complements the earlier chapter on reactions under pressure. The chapters on nucleophiliic and electrophilic additions complements the earlier chapter on radical addition. The chapter on reduction complements the earlier ones on oxidation. Chapters on organometallic complexes, synthetic applications and rearrangement of dienes and polyenes are additional topics discussed. 

Ihmels H, Otto D (2005) Intercalation of Organic Dye Molecules into Double-Stranded DNA - General Principles and Recent Developments. 258 161-204 lida H, Krische MJ (2007) Catalytic Reductive Coupling of Alkenes and Alkynes to Carbonyl Compounds and Imines Mediated by Hydrogen. 279 77-104 Imai H (2007) Self-Organized Formation of Hierarchical Structures. 270 43-72 Indelli MT, Chiorboli C, Scandola F (2007) Photochemistry and Photophysics of Coordination Compounds Rhodium. 280 215-255 Indelli MT, see Chiorboli C (2005) 257 63-102 Inoue Y, see Borovkov VV (2006) 265 89-146 Ishii A, Nakayama J (2005) Carbodithioic Acid Esters. 251 181-225... 

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