87261-83-4Relevant articles and documents
Photocatalytic reduction of artificial and natural nucleotide co-factors with a chlorophyll-like tin-dihydroporphyrin sensitizer
Oppelt, Kerstin T.,W??, Eva,Stiftinger, Martin,Sch?fberger, Wolfgang,Buchberger, Wolfgang,Kn?r, Günther
, p. 11910 - 11922 (2013/11/19)
An efficient photocatalytic two-electron reduction and protonation of nicotine amide adenine dinucleotide (NAD+), as well as the synthetic nucleotide co-factor analogue N-benzyl-3-carbamoyl-pyridinium (BNAD +), powered by photons in the long-wavelength region of visible light (λirr > 610 nm), is demonstrated for the first time. This functional artificial photosynthetic counterpart of the complete energy-trapping and solar-to-fuel conversion primary processes occurring in natural photosystem I (PS I) is achieved with a robust water-soluble tin(IV) complex of meso-tetrakis(N-methylpyridinium)-chlorin acting as the light-harvesting sensitizer (threshold wavelength of λthr = 660 nm). In buffered aqueous solution, this chlorophyll-like compound photocatalytically recycles a rhodium hydride complex of the type [Cp*Rh(bpy)H]+, which is able to mediate regioselective hydride transfer processes. Different one- and two-electron donors are tested for the reductive quenching of the irradiated tin complex to initiate the secondary dark reactions leading to nucleotide co-factor reduction. Very promising conversion efficiencies, quantum yields, and excellent photosensitizer stabilities are observed. As an example of a catalytic dark reaction utilizing the reduction equivalents of accumulated NADH, an enzymatic process for the selective transformation of aldehydes with alcohol dehydrogenase (ADH) coupled to the primary photoreactions of the system is also demonstrated. A tentative reaction mechanism for the transfer of two electrons and one proton from the reductively quenched tin chlorin sensitizer to the rhodium co-catalyst, acting as a reversible hydride carrier, is proposed.
Redox Chemistry of Metalloporphyrins in Aqueous Solution
Harriman, A.,Richoux, M. C.
, p. 4957 - 4965 (2007/10/02)
A series of water-soluble metalloporphyrins has been prepared and the redox chemistry investigated by electrochemical and pulse radiolytic techniques.All of the metalloporphyrins exhibit reasonably intense absorption transitions (ε = ca. 2 X 104 dm3 mol-1 cm-1) in the visible region and a strong absorption (ε = (2-7) X 105 dm3 mol-1 cm-1) around 430 nm.Cyclic voltammetry showed that the compounds undrgo well-defined reduction and oxidation steps, although the oxidation processes were not readily reversible.For diamagnetic metalloporphyrins, the difference in E1/2 between addition and removal of an electron for a particular compound was 2.05 +/- 0.20 V while the difference in E1/2 between addition of one and two electrons was 0.28 +/- 0.12 V.Similarly, E1/2 for the removal of a second electron from the porphyrin ? system was some 0.25 +/- 0.10 V higher than that for removal of the first electron.These findings are consistent with the central metal ion exerting only an inductive effect upon the porphyrin ? levels.The absorption spectra of the one-electron reduction and oxidation products were recorded by pulse radiolysis methods.Both products exhibit broad absorption transitions stretching across the entire visible and near-IR regions.The reduction products were identified as ?-radical anions and, in many cases these were unstable with respect to disproportionation.The oxidation products were identified as ?-radical cations and these were also unstable in aqueous solution but the decay route remains obscure.