Photochemical cycle

M. C. Nuss, W. Zinth, W. Kaiser, E. Kolling, and D. Oesterhelt. Femtosecond spectroscopy of the first events of the photochemical cycle in bacteriorhodopsin. Chem. Phys. Lett, 117(l) l-7, 1985. 

Barbeau K, Rue EL, Bruland KW, Butler A (2001) Photochemical Cycling of Iron in the Surface Ocean Mediated by Microbial Iron(III)-Binding Ligands. Nature 413 409... 

A number of cobalt(III) encapsulated cage complexes have been used as electron-transfer agents their advantage over viologens is their long-term stability in photochemical cycles. The most effective complex is [CoL] where L is l-chloro-3,6,10,13,16,19-hexaazabicyclo[6.6.6]eico-sane at a concentration of 4 x 10 mol dm , this cage exhibits a similar ability to methylviolo-gen to produce Laser flash photolysis in sodium dodecyl sulfate and sodium laurate... 

Mitchell, North Carolina, Air Waste, 43, 1074-1083 (1993). Arakaki, T., C. Anastasio, P. G. Shu, and B. C. Faust, Aqueous-Phase Photoproduction of Hydrogen Peroxide in Authentic Cloud Waters Wavelength Dependence, and the Effects of Filtration and Freeze-Thaw Cycles, Atmos. Environ., 29, 1697-1703 (1995). Arakaki, T., and B. C. Faust, Sources, Sinks, and Mechanisms of Hydroxyl Radical ( OH) Photoproduction and Consumption in Authentic Acidic Continental Cloud Waters from Whiteface Mountain, New York The Role of the Fe(r) (r = II, III) Photochemical Cycle, . /. Geophys. Res., 103, 3487-3504 (1998). Atkinson, R., D. L. Baulch, R. A. Cox, R. F. Hampson, Jr., J. A. Kerr, M. J. Rossi, and J. Troe, Evaluated Kinetic and Photochemical... 

Society is facing several crucial issues involving atmospheric chemistry, Species containing nitrogen are major players in each. In the troposphere, nitrogen species are catalysts in the photochemical cycles that form ozone, a major urban and rural pollutant, as well as other oxidants (references 1 and 2, and references cited therein), and they are involved in acid precipitation, both as one of the two major acids (nitric acid) and as a base (ammonia) (3, 4). In the stratosphere, where ozone acts as a shield for the... 

I and II. At very low temperatures a transient form photorhodopsin with a wavelength maximum at 580 nm may precede bathorhodopsin.461b,501-502a Furthermore, nanosecond photolysis of rhodopsin has revealed a blue-shifted intermediate that follows bathorhodopsin within 40 ns and decays into lumirhodopsin.500,503,504 The overall result is the light-induced isomerization of the bound 11-czs-retinal to all-fraus-retinal (Eq. 23-38) and free opsin. Tire free opsin can then combine with a new molecule of 11-czs-retinal to complete the photochemical cycle. 

Y— X relaxation on the lower surface is small or absent, the entire photochemical cycle is reversible. 

Barbeau K., Rue E. L., Bruland K. W., and Butler A. (2001) Photochemical cycling of iron in the surface ocean mediated by microbial iron(III)-binding ligands. Nature 413, 409-413. 

Effects of pH on the photochemical cycle of bacteriorhodopsin have special... 

NOjc and the Production of Ozone NO and NO2 are important air pollutants originating mainly in combustion processes. Most of the NO. formed in combustion is NO but some NO can become oxidized in the combustion process to NO2. Even small amounts of NO2 are sufficient to cause a complex series of reactions involving organics that lead to photochemical smog. The following is a simplified interpretation of the photochemical cycle of NO2, NO, and O3. (For details see Seinfeld, 1986, and Finlayson-Pitts and Pitts, 1986.)... 

As shown in the scheme at the beginning of this section, the reduction ofQa to QbH2 in a photochemical cycle involves two charge-separation reactions which result in the transfer of two electrons and two protons, as well as the oxidation of two cytochrome molecules to restore the (twice) oxidized primary donor P870 to its original reduced state. In Fig. 6 we present the details ofthe quinone-reduction cycle, as currently perceived, to aid our discussion ofthe individual reactions that are to be monitored. 

Fig. 6. Photochemical cycles showing coupling of electron transfer to proton transfer, cytochrome oxidation and quinone exchange in (A) native reaction centers where two Cyt c are oxidized in the cycie, (B) reaction centers where uptake of the first proton is inhibited, and (C) reaction centers where uptake ofthe second proton is inhibited (shading indicates the quinone pool). Figure source (A) Paddock, Rongey, McPherson, Juth, Feher and Okamura (1994) Pathway of proton transfer in bacterial reaction centers role of aspartate-L21Z in proton transfers associated with reduction of quinone to dihydroquinone. Biochemistry 33 734 (B) Okamura and Feher (1992) Proton transfer in reaction centers from photosynthetic bacteria. Annu Rev Biochemistry. 61 868 (C) Feher, Paddock, Rongey and Okamura (1992) Proton transfer pathways in photosynthetic reaction centers studied by site-directed mutagenesis. In A Pullman, J Jortner and B Pullman (eds) Membrane Proteins Structures, Interactions and Models, p 485. Kluwer.

Figure 10. Schematic summary of siderophore-mediated photochemical cycling of iron in seawater [206]. Fe(iii)L represents a photoreactive iron(iii)-siderophore complex, L-F is the oxidized ligand photoproduct, and Lj is another chelating ligand. The Fe(ii) and its initial oxidation product, Fe(iii) are readily assimilated by marine organisms but Fe(iii) also can be readily hydrolyzed to Fe hydroxides which can then slowly polymerize to form unreactive, non-bioavailable iron(hydroxy)oxides. [Adapted from Barbeau et al. [206], Figure 4, p. 411, Copyright 2001, Nature. ]...

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