Photosensitized reduction experiments

Photosensitized reduction experiments have evidenced that for both the A-type and B-type families of dendrimers a fraction of the monoreduced viologen units undergoes dimerization and that such a process prevails for the dendrimers in which the bulky tetraaryhnethane terminal groups have been removed. 

Later, an improved system for C02 photofixation was reported by the same authors.164 The new system consisted of 6.5 x 1(T5 M tris(2,2 -bipyridine)ruthenium(II), Ru(bpy)3, as the photosensitive electron donor, methyl viologen (MV2+, 20 mM) as the electron acceptor, and triethanolamine (TEOA, 0.6 M) as a sacrificial electron donor in a C02-saturated aqueous solution (Fig. 18). Under irradiation with a 300-W high-pressure Hg lamp with a CuS04 chemical filter (A > 320 nm), formic acid, which was detected by isotachophoresis, was produced in quantum yields of ca. 0.01%. Recently, however, Kase et al.165 have repeated this experiment using a 13C02 tracer and have claimed that the formic acid obtained was produced not by C02 reduction but rather by oxidative cleavage of TEOA. 

No photosensitizer yields only one type of reactive species. The reactive pathways that the excited molecule follows depend on the nature of the sensitizer and its environment. This emphasizes the need for using more than one experimental model in the evaluation of drug photoreactivity and to take into account pharmacokinetic parameters and method specificity in the discussion of the normalized results. Observation of drug photoreactivity in vitro does not necessarily mean that the same combination of reactions will take place in vivo. A certain in vitro-in vivo correlation should be obtained, however, if the in vitro photoassay is carefully designed. The assay will then result in a reduction in the number of animal experiments required in development of new drug substances and drug formulations. 

WUlner and co-workers reported interesting applications of enzymes to the reductive fixation of CO2 into organic substrates. In these experiments, 16 was employed as the photosensitizer, thiols (RSH) as an electron donors, methylviolo-gen (MV ) as an electron carrier, an NADP/enzyme combination as le /2e relay,... 

In a second step, the in-situ synthesis of Ag NPs within the microfibrous scaffold is implemented by photoreduction reaction in the presence of both a silver precursor and a photosensitizer. SEM and TEM experiments confirm the formation and dispersion of Ag NPs on the surface of the modified fibers (Fig. 6.11). PHBHV microfibrous scaffolds including silver nanoparticles led to a tremendous inhibition of the adhesion of E. Coli and a reduction by 98% of the adherence of S. aureus. 

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