Switching the Mechanism of NADH Photooxidation by Supramolecular Interactions

Abstract

A series of three Ru(II) polypyridine complexes was investigated for the selective photocatalytic oxidation of NAD(P)H to NAD(P) + in water. A combination of (timeresolved) spectroscopic studies and photocatalysis experiments revealed that ligand design can be used to control the mechanism of the photooxidation: For prototypical Ru(II) complexes a 1 O 2 pathway was found. Rudppz ([(tbbpy) 2 Ru(dppz)]Cl 2 , tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine), instead, initiated the cofactor oxidation by electron transfer from NAD(P)H enabled by supramolecular binding between substrate and catalyst. Expulsion of the photoproduct NAD (P) + from the supramolecular binding site in Rudppz allowed very efficient turnover. Therefore, Rudppz permits repetitive selective assembly and oxidative conversion of reduced naturally occurring nicotinamides by recognizing the redox state of the cofactor under formation of H 2 O 2 as additional product. This photocatalytic process can fuel discontinuous photobiocatalysis.

TransformingEscherichia coliProteomembranes into Artificial Chloroplasts Using Molecular Photocatalysis

“… [60] Thus, it enables the bacterium to generate a pmf and consequently also ATP even in the absence of oxygen, conditions that are necessary for the photocatalytic NADH formation utilizing photocatalyst 1 . [61] For comparison, using membrane vesicles originating from the strictly aerobic Pseudomonas putida resulted in no photocatalytic ATP formation using 1 as catalyst (data not shown). This is rationalized by the observation that also no ATP was formed when NADH was simply added to these vesicles under exclusion of oxygen.…”

Compartmentalization Accelerates Photosensitized NADH to NAD+ Conversion

“…It also highlights the beneficial effect of compartmentalization at high local concentration within liposomes, especially when working with a poorly watersoluble gas as co-reagent. [25] ; [c] Same NADH bulk concentration as within the liposomes.…”

“…[a] Same overall conc. of NADH as in liposome experiments; [b] Same NADH bulk concentration as reported in bulk experiments [25] ; [c] Same NADH bulk concentration as within the liposomes.…”

“…To benchmark our NADH conversion experiments with reported bulk experiments we performed the photoinduced NADH conversion under homogeneous conditions as reported by Mengele et.al. who worked with a PS : NADH ratio of 1 : 500 using PS=Ru( t bbpy) 3 2+ ( t bbpy=4,4’‐di‐ tert ‐butyl‐2,2’‐bipyridine) at 1 mM NADH concentration [25] . While the reported rate constant is 0.032±0.002 min −1 , [25] we obtained a slightly smaller rate constant of k=0.021±0.003 min −1 using PS=RuC 0 under otherwise identical conditions which we attribute to the electronic differences in PS properties.…”

A targeted and efficient CDT system with photocatalytic supplement of H2O2 and hydroxyl radical production at a neutral pH

“…Moreover, the extended aromatic structure of the PIP-OCH 3 ligand in Ru3 may facilitate π-π interactions with NADH. 49 Upon titration with NADH, the chemical shift of Ru3 at 7.10 ppm, which can be ascribed to the ortho protons of the methoxy group on the PIP-OCH 3 ligand, gradually moved to 6.89 ppm (Fig. S7 †).…”