Photocatalytic Reduction of Artificial and Natural Nucleotide Co-factors with a Chlorophyll-Like Tin-Dihydroporphyrin Sensitizer

Abstract

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.

Visible light-driven photophysics and photochemistry of water-soluble metalloporphyrins

“…Kinetically inert in-plain metalloporphyrins, in which the metal center is coplanarly located in the cavity of the ligand, may offer promising possibilities for realization of photocatalytic systems based on outer-sphere electron transfer [5]. The so-called hyper-porphyrins can be particularly interesting in this respect, due to their distorted structure, which may increase the (photo)redox reactivity of these complexes.…”

Photophysical and photocatalytic behavior of nickel(II) 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin

“…Water-soluble metallporphyrins are promising for utilization in environmentally friendly procedures. Kinetically inert in-plain metalloporphyrins, in which the metal center coplanarly fits into the cavity of the ligand, were successfully applied in photocatalytic systems based on outersphere electron transfer [4,5]. This type of metalloporphyrins can be formed with the ions of the iron group, such as Fe(III), Co(III), and Ni(II).…”

Photophysical and photocatalytic behavior of cobalt(III) 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin

“…Water-soluble derivatives can be utilized in environmentally benign systems not containing organic solvents. Kinetically inert in-plain metalloporphyrins, in which the metal center coplanarly fits into the cavity of the ligand, may offer promising possibilities for realization of photocatalytic systems based on outer-sphere electron transfer [2]. The so-called hyper-porphyrins can be especially interesting in this respect, due to their distorted structure, which may increase the (photo)redox reactivity of these complexes.…”