Light model systems

Willner, I and Willner, B. Artifical Photosynthetic Model Systems Using Light-Induced Electron Transfer Reactions in Catalytic and Biocatalytic Assemblies. 159, 153-218... 

Considerable studies have been done on the effects of the most important chemical and physical factors involved in the degradation of anthocyanins (temperature, light, pH, SO2, metal, sugar, and oxygen) in model systems and food extracts. In addition, anthocyanin concentrations, its chemical structures, and media compositions are fundamental factors influencing stability. 

Dyrby, M., Westergaard, N., and Stapelfeldt, H., Light and heat sensitivity of red cabbage extract in soft drink model systems. Food Chem., 72, 431, 2001. 

In the recent past much ejperimental and theoretical effort has been undertaken to understand the microsoopic steps of heterogeneous surface reactions. Ihe main problem oonsists of evaluating the total energy of the reacting coponents (including tiie surface atoms ) as a function of all nuclear coordinates at any reaction time. The solution of this problem is extremely difficult. Detailed studies with model systems, however, can shed same light ipon the various steps of the interaction pattern. 

These experiments proved that a light-excited, reduced flavin is indeed able to photoreduce cyclobutane pyrimidine dimers and that these dimers undergo a spontaneous cycloreversion. The quantum yield of about 0=5% clarified that the overall dimer splitting process is highly efficient, even in these simple model systems ((]) photolyase 70%). 

Petersen, M., L. Wiking, and H. Stapelfeldt. 1999. Light sensitivity of two colorants for Cheddar cheese. Quantum yields for photodegradation in an aqueous model system in relation to light stability of cheese in illuminated display. J. Dairy Res. 66 599-607. 

Warwel, S., Sojka, M., and Riisch, M. Synthesis of Dicarboxylic Acids by Transition-Metal Catalyzed Oxidative Cleavage of Terminal-Unsaturated Fatty Acids. 164, 79-98 (1993). Willner, I., and Willner, B. Artificial Photosynthetic Model Systems Using Light-Induced Electron Transfer Reactions in Catalytic and Biocatalytic Assemblies. 159, 153-218 (1991). 

An important basis for the choice of Phycomyces as a model system is its wide range of sensitivity to light which covers about nine decades and which is therefore similar to vertebrate vision. This makes the organism especially suitable for the study of range adjustment, i.e., the phenomenon of adaptation. The potential of Phycomyces as a model system for investigation of differentiation and photo-differentiation has not yet been fully exploited. 

The molecule [ReI(MQ+)(CO)3(dmb)]2+ has been a model system for studying intramolecular electron transfer over the last two decades. Here, MQ+ is the monodentate ligand Af-methyl-4,4/-bipyridinium, dmb is the bidentate ligand 4,4r-dimethyl-2,2r-bipyridine, and the three CO ligands are facially coordinated. Irradiation of this complex at room temperature in solution with near-UV light leads to a sequence of intramolecular electron-transfer events as shown in Fig. 7. 

In a very special system, the photoelectrochemical regeneration of NAD(P)+ has been performed and applied to the oxidation of the model system cyclohexanol using the enzymes HLADH and TBADH. In this case, tris(2,2 -bipyridyl)ruthenium(II) is photochemically excited by visible light [43]. The excited Ru(II) complex acts as electron donor for AT,AT -dimethyl-4,4 -bipyridinium sulfate (MV2+) forming tris(2,2 -bipyridyl)ruthenium(III) and the MV-cation radical. The Ru(III) complex oxidizes NAD(P)H effectively thus... 

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