Solutions, aqueous photochemistry

Wilhelm, P. and Stephan, D. (2007) Photodegradation of rhodamine B in aqueous solution via Si02 Ti02 nanospheres. Journal of Photochemistry and Photobiology A Chemistry, 185, 19-25. 

Molecular orbital calculations have been used to analyze the stabilities of dihydropterins <06H1705>. The photochemistry of 6-(hydromethyl)pterin in aqueous solution has been investigated <06HCA1090>. 

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 photochemistry of 4-nitrobenzaldehyde has been reinvestigated In aqueous solution, 4-nitrosobenzoic acid is formed. A ketene has been proposed as intermediate... 

Boule, P., Guyon, C., and Lemaire, J. Photochemistry and environment. IV. Photochemical behaviour of monochlorophenols in dilute aqueous solution, Chemosphere, 11(12) 1179-1188, 1982. 

Tanaka, F.S., Wien, R.G., and Mansager, E.R. Effect of nonionic snrfactants on the photochemistry of 3-(4-chlorophenyl)-l, 1-dimethylurea in aqueous solution, J. Agric. Food Chem., 27(4) 774-779, 1979. 

Orotic acid readily forms dimers even when irradiated in liquid medium [582, 583]. 5-Bromouracil (5-BrU) in DNA is dehalogenated, rather than forming cyclobutane-type dimers. Such DNA derivatives are more sensitive to ultraviolet irradiation than normal DNAs [584-594], Irradiation of 5-bromo-uracil and derivatives in aqueous medium produces 5,5 -diuracil [590, 591]. However, derivatives such as 3-sbutyl-5-bromo-6-methyluracil have been reported to yield cyclobutane dimers either by irradiation of frozen aqueous solutions, or by catalysis with free radical initiators, such as aluminium chloride, ferric chloride, peroxides or azonitriles [595]. 5-Hydroxymethyluracil is reported to dimerize very slowly in frozen water at 2537 A [596]. The fundamental research in the photochemistry of the nucleic acids, the monomeric bases, and their analogues has stimulated new experiments in certain micro-organisms and approaches in such diverse fields as template coding and genetic recombination [597-616]. 

Interest in the photochemistry of meso-ionic compounds is now developing, and an interesting result has been obtained by the photolysis of 5-amino-1,3-thiazolium salts (126, R = H). For example, irradiation of the salt 126, R = R = Ph, R = H, X = Cl, in aqueous solution yields the disulfide 130 (23%) and the keto amidine 131 (70%). It is proposed that this reaction involves a bicyclic intermediate (132). ... 

Latch D.E., J.L. Packer, W.A. Arnold, and K. McNeill (2003). Photochemical conversion of triclosan to 2,8-dichlorodibenzo-p-dioxin in aqueous solution. Journal of Photochemistry and Photobiology A 158 63-66. 

While many of the important reactions in radiation and photochemistry are fast, not all are diffusion-limited. The random flight simulation methodology has been extended to include systems where reaction is only partially diffusion-controlled or is spin-controlled [54,55]. The technique for calculating the positions of the particles following a reflecting encounter has been described in detail, but (thus far) this improvement has not been incorporated in realistic diffusion kinetic simulations. Random flight techniques have been successfully used to model the radiation chemistry of aqueous solutions [50] and to investigate ion kinetics in hydrocarbons [48,50,56-58]. 

Plane34-38 and Schlafer37,39 have argued that the photochemistry initiated by irradiation of the ligand field absorption bands of chro-mium(III) complexes in aqueous solutions near room temperature can... 

TABLE 8.9 Summary of Photochemistry of Some Species in Aqueous Solutions... 

Mixed-ligand Crm complexes have a particularly rich substitutional photochemistry in that two (or more) reaction modes are normally observed. Data for the well-studied class of acidoamine complexes are presented in Table 2. The dominant photochemical reaction for [CrX(NH3)5]2+ complexes in aqueous solution is NH3 aquation, with X- aquation occurring to a lesser extent (equation 31). In contrast, the latter pathway is the favored thermal reaction of these compounds. Such behavior again illustrates that the reactivity of ligand field excited states can differ sharply from that of the ground state. 

Solvated Electron Formation and Hydrogen Evolution in the Photochemistry of Aqueous Solutions... 

To assist with this, we have for some years now investigated in detail the spectroscopy and photochemistry of the ferrocyanide in aqueous solution. This work was carried out together with Mrs. M. Shirom (40). 

The ferrocyanide ion, stable at neutral pH, shows well understood optical transitions in the visible and near u.v. It carries four negative charges, which should facilitate solvated electron formation. A survey of its known photochemistry indicated that at neutral pH we may hope that solvated electron formation will be the only photochemical primary process. Indeed, after we commenced the work, Matheson, Mulac, and Rabani (31) found on flash photolysis the absorption spectrum of e aq in aqueous solutions of ferrocyanide. 

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