Periodic Reporting for period 3 - CUBE (Unravelling the secrets of Cu-based catalysts for C-H activation)
Reporting period: 2023-05-01 to 2024-10-31
Catalysis is key to sustainable production of commodity products, and to life itself. While industrial catalysts are generally robust and provide high turn-over rates, they are less selective than their enzymatic analogues, which are, on the other hand, quite fragile. The successful combination of the advantages of each catalysis field would have tremendous societal impact. Among prime target reactions, selective C-H activation has been vigorously pursued for more than 70 years in all areas of catalysis – homogeneous, heterogeneous and biological – yet with scarce cross-fertilization. CUBE will bridge this gap, by synergistically disclosing the secrets of Cu-containing biological and synthetic catalysts and by translating the acquired knowledge into rationally designed new synthetic and biological catalysts with unprecedented activity, selectivity and turn-over numbers. The work includes development and implementation of novel spectroscopic and computational tools (WP1) to obtain the deeper understanding of oxidant activation (WP2) and C-H bond activation (WP3) that will enable catalyst evolution and design (WP4). The consortium studies synthetic copper complexes, free or incorporated in metal-organic frameworks (MOFs), copper-zeolites, and enzymes called lytic polysaccharide monooxygenases (LPMOs).
New spectroscopic methods have been developed. In particular, a combination of XAS and VtC XES was applied to a series of copper model complexes spanning formal oxidation states from Cu(I) to Cu(III). By combining these experimental data with computations, it was shown that the spectroscopic oxidation states may be robustly assessed and that experimental evidence for the controversial Cu(III) oxidation state assignment could be supported. The method is currently applied to CUBE-relevant samples. In the area of Cu-zeolites, a relevant achievement was the development of a new approach to quantify the amount of Cu(I) with a standard volumetric apparatus bypassing the use of a facilities such as XAS measurements.
A much-needed collection of natural and engineered LPMO variants has been completed and members are currently being scrutinized using a combination of highly advanced biochemical, spectroscopic and theoretical methods, leading to new insights into the determinants of copper reactivity, enzyme redox stability and enzyme functionality. The emerging insights are now being used to generate LPMO variants with novel catalytic properties. This includes both engineered LPMOs, engineered LPMOs immobilized on specifically tailored solid surfaces to create catalytic hybrid materials, and de novo designed PMO-like proteins. For the generation of the hybrid materials, proof-of-concept has been achieved in the second reporting period in a collaboration between NMBU and UNITO.
Biomimetic N4-Cu, N3-Cu and N2-Cu motifs have been synthesized and incorporated into MOFs. The motifs show peroxygenation activity, yet with modest turn-over rates compared to the enzymatic analogs.
Second-sphere modification is in progress. Reaction mechanisms are studied by computational and experimental methods.
A much-needed collection of natural and engineered LPMO variants has been completed and members are currently being scrutinized using a combination of highly advanced biochemical, spectroscopic and theoretical methods, leading to new insights into the determinants of copper reactivity, enzyme redox stability and enzyme functionality. The emerging insights are now being used to generate LPMO variants with novel catalytic properties. This includes both engineered LPMOs, engineered LPMOs immobilized on specifically tailored solid surfaces to create catalytic hybrid materials, and de novo designed PMO-like proteins. For the generation of the hybrid materials, proof-of-concept has been achieved in the second reporting period in a collaboration between NMBU and UNITO.
Biomimetic N4-Cu, N3-Cu and N2-Cu motifs have been synthesized and incorporated into MOFs. The motifs show peroxygenation activity, yet with modest turn-over rates compared to the enzymatic analogs.
Second-sphere modification is in progress. Reaction mechanisms are studied by computational and experimental methods.
In the second project period we have managed to move the front of the field through several breakthroughs. Key breakthroughs on the enzyme side are the unraveling of second sphere copper coordination effects on copper reactivity, the full mapping of protective hole hopping pathways in LPMOs that not only protect but also affect catalytic efficiency, and the development of advanced stopped-flow and electrochemical sensor techniques that allow generation of unprecedented kinetic data. The latter will give the Cube consortium a unique possibility to productively combine spectroscopy, theory and biochemical data. Key breakthrough on the synthetic catalyst side is the successful incorporation of biomimetic catalytic motifs in MOFs, verified by extensive characterization using ex-situ and in-situ DFT-assisted XAS, XRD, NMR, FT-IR and UV-VIS methods, and tested for peroxygenation reactions in liquid phase. The MOF backbone offers versatile opportunities for second sphere modification, and efforts in this direction will be intensified in the next reporting period.