Photocatalytic Regeneration of a Nicotinamide Adenine Nucleotide Mimic with Water-Soluble Iridium(III) Complexes

Abstract

Nicotinamide adenine nucleotide (NADH) is involved in many biologically relevant redox reactions, and the photochemical regeneration of its oxidized form (NAD+) under physiological conditions is of interest for combined photo- and biocatalysis. Here, we demonstrate that tri-anionic, water-soluble variants of typically very lipophilic iridium(III) complexes can photo-catalyze the reduction of an NAD+ mimic in a comparatively efficient manner. In combination with a well-known rhodium co-catalyst to facilitate regioselective reactions, these iridium(III) photo-reductants outcompete the commonly used [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) photosensitizer in water by up to 1 order of magnitude in turnover frequency. This improved reactivity is attributable to the strong excited-state electron donor properties and the good chemical robustness of the tri-anionic iridium(III) sensitizers, combined with their favorable Coulombic interaction with the di-cationic rhodium co-catalyst. Our findings seem relevant in the greater context of photobiocatalysis, for which access to strong, efficient, and robust photoreductants with good water solubility can be essential.

Effect of water-soluble zinc porphyrin on the catalytic activity of fumarase for l-malate dehydration to fumarate

“…The other chemicals were of analytical grade or the highest grade available obtained from FUJIFILM Wako Pure Chemical Corporation or NACALAI TESQUE, INC. ZnTCPP 4− , ZnTMAP 4+ and ZnTMPyP 4+ were synthesized by refluxing respective metal-free porphyrins with about 5 times molar equivalent of zinc acetate in the methanol solution according to the previous report. 38–42 The insertion of zinc into the porphyrin ring was confirmed by the change in the Q band of each porphyrin in the UV-visible absorption spectrum (SHIMADZU, MaltiSpec-1500).…”

Deciphering Photoinduced Catalytic Reaction Mechanisms in Natural and Artificial Photosynthetic Systems on Multiple Temporal and Spatial Scales Using X-ray Probes

“…Molecular catalysts, especially transition metal complexes (TMCs), play important roles as light sensitizers and catalytic redox centers in artificial photosynthesis that produces fuels from natural resources, e.g., water and CO 2 . ,− At the molecular level, these processes are initiated by fundamental light–matter interactions, converting photons to charges and providing driving forces for chemical transformations through energy dissipation pathways. X-ray transient spectroscopies, including X-ray transient absorption (XTA), X-ray transient emission (XTE), and resonant inelastic X-ray scattering (RIXS) as described in Section , are particularly suitable for capturing light induced chemical transformations during photocatalytic reactions involving TMCs to reveal the electronic structures of the metal centers, such as oxidation states, covalency, spin state, and orbital occupation, which are crucial for understanding the catalytic reaction mechanism and are difficult to obtain by other means.…”

NADH Photoregeneration in a Fully Automated Microfluidic Setup

“…15,16 Since a quarter of all enzymes is represented by oxidoreductases, 1,17 which mainly depend on β-nicotinamide adenine dinucleotide (NAD + ) or its phosphorylated form (NADP + ), the majority of regeneration systems is designed for the reduction of these specific molecules. 6,17 All proposed photocatalytic systems, either based on organic dyes, 18,19 metal complexes, 13,20 or semiconductors, 21−23 typically require a relay (the best one to date is the rhodium complex [Rh(Cp*)(bpy)Cl] + ) 7 and require an electron source to achieve the formation of the desired product. Generally, these sources are small organic molecules which undergo irreversible oxidation processes and for this, they are usually referred to as sacrificial electron donors (SEDs), considered the cost to pay to drive this type of reaction.…”

“…All proposed photocatalytic systems, either based on organic dyes, , metal complexes, , or semiconductors, − typically require a relay (the best one to date is the rhodium complex [Rh­(Cp*)­(bpy)­Cl] + ) and require an electron source to achieve the formation of the desired product. Generally, these sources are small organic molecules which undergo irreversible oxidation processes and for this, they are usually referred to as sacrificial electron donors (SEDs), considered the cost to pay to drive this type of reaction .…”