- Photocatalytic reduction of artificial and natural nucleotide co-factors with a chlorophyll-like tin-dihydroporphyrin sensitizer
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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.
- Oppelt, Kerstin T.,W??, Eva,Stiftinger, Martin,Sch?fberger, Wolfgang,Buchberger, Wolfgang,Kn?r, Günther
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supporting information
p. 11910 - 11922
(2013/11/19)
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- A simple alternative method for preparing Sn(IV) porphyrins
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Sn(IV) porphyrins are highly desirable for various applications because of their stability, their preference for oxygen-donor ligands and because they possess properties which can be easily characterized using various spectroscopic techniques. The most established method for the preparation of the Sn(IV) porphyrins is refluxing the porphyrin with SnCl 2·2H 2O in pyridine as solvent. Although this method works efficiently, we found that the work-up results in a lot of unwanted materials and using large quantities of pyridine as solvent is not good under laboratory conditions. In this paper, we show that the Sn(IV) porphyrins can be prepared easily by treating porphyrin with SnCl 2·2H 2O in chloroform, di chloromethane and toluene as solvent containing 25-50% ethanol as co-solvent. The reaction works smoothly and involves simple work-up and straightforward chromatographic purification. The method works efficiently for meso and β-substituted porphyrins. The spectral and electrochemical properties of various Sn(IV) were studied and our studies showed that the properties are sensitive to the nature of substituent present at the meso-position. Copyright
- Shetti, Vijayendra S.,Ravikanth, Mangalampalli
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experimental part
p. 361 - 370
(2010/11/21)
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- Redox Chemistry of Metalloporphyrins in Aqueous Solution
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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.
- Harriman, A.,Richoux, M. C.
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p. 4957 - 4965
(2007/10/02)
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