Structural Engineering of Porphyrin-(N^N)Rh(III) Systems for Photocatalytic Nicotinamide Cofactor Regeneration

Project: Research project

Project Details

Description

We propose the concept how to use structural engineering of Porphyrin-(N^N)Rh(III) photocatalysts (N^N = bidentate ligand with two N atoms) for nicotinamide cofactor regeneration. The use of light energy in the synthesis of chemicals and fuels, so called artificial photosynthesis, is a promising, cost effective and inherently sustainable process. Although many artificial photocatalytic systems have been explored, e.g. for photocatalytic H2 production, CO2 reduction and photoredox catalysis, their practical applications in chemical and pharmaceutical industries has been hindered by the intrinsic problems of low conversion efficiency, inferior selectivity of products, and photocatalyst instability.

Biocatalysis has been widely applied in the sophisticated syntheses with high activity, selectivity, and low energy consumption. Generally, they require a stoichiometric amount of a cofactor as the hydrogen source, notably reduced nicotinamide adenine dinucleotide (NADH). We proposed to construct Porphyrin-(N^N)Rh(III) photocatalytic systems, in which porphyrin acts as photosensitizer to produce electrons, (N^N)Rh(III) complex as catalyst center to facilitate NADH regeneration. The product of NADH will serves as a reductant to reduce certain substrates into the target products by an appropriate enzyme in a green, sustainable, economical, and efficient way. To our knowledge, current photocatalysts combine those components in a separated way. Therefore, there is a lack of any spatial structuring, which is a key feature of the natural photosynthetic system.
Porphyrin are not only a strongly absorbing photosensitizer but also an ideal scaffold for diversified functionalization at eight β- and four meso-positions. And Zn(II)-porphyrin is preferred for its facile preparation and high stability. On the other side, rhodium complexes [(N^N)Rh(III)Cp*Cl]+ are almost the only successful non-enzymatic regeneration catalysts for NADH regeneration. In proof-of-concept experiments, we prepared Zn(II)-10,15,20-triphenyl- 5-(4-pyridinyltriazol-2-phenyl)porphyrin and further coordinated to Rh(III) ion to create a new photocatalyst. Its photocatalytic NADH regeneration yield has been demonstrated to be superior to the separated Zn(II)-tetra(phenyl)porphyrin and [(N^N)Rh(III)Cp*Cl]Cl.

We will synthesize series of new Porphyrin-(N^N)Rh(III) photocatalysts with a modified porphyrin as the photosensitizer and (N^N)Rh(III) complexes as the catalytic center. In the photocatalysts, the inter-ring dihedral angle between the photosensitizer and the Rh-complex will be finely engineered by varying the steric of different linker spaces. The distance between the photosensitizer and the electron mediator can also be regulated by varying the spacer length. Such changes will directly affect the electron transfer efficiency between the photosensitizer and catalytic center. Specifically, the light-harvesting ability are expected to be improved by the conjugation of different chromophores.

Moreover, covalent-organic-frameworks (COFs) can provide a highly tunable platform to combine photosensitizer and transition-metal catalysts to drive photocatalytic NADH regeneration. Therefore, some COF-based porphyrin-(N^N)Rh(III) photocatalysts will be prepared from porphyrins and rhodium complex building blocks. The periodic arrangements in COFs definitely facilitate an efficient electron transfer to accelerate the catalytic cycle. Moreover, COFs photocatalysts can be readily recycled and reused.

In parallel with computational modeling methods, we will apply several techniques to investigate structure-property relationships including photophysical, electrochemical, electron transfer and NADH regeneration properties. We aim therefore to develop the most efficient Porphyrin-(N^N)Rh(III) photocatalysts photocatalysts for NADH regeneration and subsequent enzymatic production of chemicals and fuels with high efficiency and selectivity (eg. regio- and enantioselectivity). In the medium term, NADH regeneration process will be sought that reach sufficient activity to be considered for commercial exploitation.
StatusFinished
Effective start/end date1/01/2131/12/23

UN Sustainable Development Goals

In 2015, UN member states agreed to 17 global Sustainable Development Goals (SDGs) to end poverty, protect the planet and ensure prosperity for all. This project contributes towards the following SDG(s):

  • SDG 7 - Affordable and Clean Energy

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