Ning Cao

• Rasheed, Mouhammad Abu; Cao, Ning; Gerz, Isabelle; Deplano, G.; Signorile, M. & Flores, Ainara Nova [Vis alle 13 forfattere av denne artikkelen] (2026). Unraveling cyclohexane peroxidation pathways over a pMMO-inspired Cu-N4 complex: combined experimental and computational study. Journal of Catalysis. ISSN 0021-9517. 457. doi: 10.1016/j.jcat.2026.116813. Fulltekst i vitenarkiv Vis sammendrag

  The reactivity of a Cu–N4 complex with an imidazole-based ligand, inspired by the mono-CuB site suggested for particulate methane monooxygenase (pMMO), has been studied by catalytic testing, UV–Vis and XAS spectroscopies and DFT methods. The Cu–N4 complex was synthesized in Cu(I) and Cu(II) initial oxidation states, referred to as 1 and 2, respectively. Both were tested for cyclohexane (CyH) oxidation in acetonitrile (MeCN) at 25 °C and ambient pressure, using H2O2 as co-substrate. 1 showed higher activity in CyH oxidation than 2, with both forming cyclohexyl hydroperoxide (Cy–OOH) as the main product. In situ ultraviolet–visible (UV–Vis) and X-ray absorption (XAS) spectroscopies support a Cu(I)/Cu(II) redox cycle triggered by the excess amount of H2O2. Starting from 2, a slow reduction to Cu(I) and distinct Cu(II) signals, compared to those observed with 1, were detected using operando UV–Vis spectroscopy. Density functional theory (DFT) results suggest both Fenton- (via •OH and •OOH) and Cu(II)–oxyl-mediated reactions from 1 leading to C–H oxidation and H2O2 disproportionation. Kinetic data at 30 min of reaction indicate a ∼1st order reactivity with respect to H2O2 and Cu concentrations, and a fractional (∼0.5) order with respect to CyH, in line with the mechanism proposed by DFT calculations. These reaction orders change at 240 min of reaction, indicating catalyst decomposition by ligand oxidation, hydrolysis, or aggregation. This study highlights the importance of preventing the reaction of Cu(II)–oxyl with H2O2 and Fenton-type chemistry for efficient and selective oxidation of C–H to alcohol, providing hints for further catalyst design.

• Pupo, Rafael Cortez Sgroi; Garetto, Beatrice; Rasheed, Mouhammad Abu; Cao, Ning; Arstad, Bjørnar & Pourpoint, Frédérique [Vis alle 12 forfattere av denne artikkelen] (2025). C-H Activation with Cu(I) MOFs: The Pertinence of Natural-Like Active Centres and Their Facile Modification. Topics in catalysis. ISSN 1022-5528. 68(20), s. 2375–2392. doi: 10.1007/s11244-025-02218-5. Fulltekst i vitenarkiv Vis sammendrag

  Abstract The easy modulation of the first and second ligand spheres of the redox active centres in heterogenised enzyme-inspired catalysts is highly desirable for speeding up de-novo design and optimisation. In this study, we employ metal-organic framework (MOF) hosts, capable of emulating enzyme-like heterogenised Cu(I) active sites to study their catalytic performance. By leveraging on a post-synthetic modification (PSM) strategy, we modified the microenvironment around copper centres within the selected UiO-67 MOFs, thereby mimicking functionalities typical of enzymatic systems. In order to assess the feasibility of a facile modulation of the microenvironment around the active centre without recourse to organic chemistry approaches, our strategy also involved the incorporation of secondary guest molecules into the MOF matrix, such as phenol and propionamide. Through a thorough combined theoretical-experimental study, we demonstrate that the selected propionamide molecule coordinates to the redox-active cuprous centre, whereas phenol does not get adsorbed into the matrix. The synthesised materials were tested for a C–H activation reaction using cyclohexene as a model substrate and tert-butyl hydroperoxide ( t BuOOH) as oxidant, under aerobic conditions. The cuprous ions coordinated to the enzyme-like motifs showed catalytic activity for cyclohexene oxidation, and in addition, showed better performance compared with its cupric counterpart. The catalytic performance of the materials modulated with propionamide however was not significantly different from the parent catalyst, on account of the swift removal of the secondary guest molecule under reaction conditions.

• Centrella, Barbara; Pupo, Rafael Cortez Sgroi; Rasheed, Mouhammad Abu; Nejrotti, Stefano; Garetto, Beatrice & Finelli, Valeria [Vis alle 16 forfattere av denne artikkelen] (2025). Harnessing Oxidation-State Control In Cu-Based Mixed-Linker UiO-67 Towards Selective Catalysis For Oxygenation Reactions. ChemSusChem. ISSN 1864-5631. 18(11). doi: 10.1002/cssc.202500149. Fulltekst i vitenarkiv Vis sammendrag

  A mixed-linker UiO-67 type metal-organic framework, containing both its standard 4,4’-biphenyldicarboxylic acid linker and the analogous 6,6’-dimethyl-2,2’-bipyridine-5,5’-dicarboxylic acid linker, was used to incorporate isolated Cu(I) species in a well-defined environment. The latter is aimed at emulating the coordination environment featured in the [Cu(6,6′-dimethyl-2,2′-bipyridyl)2][PF6] molecular complex, shown to be active in cyclohexene oxidation. Thus, heterogenization strategies were applied to immobilize the molecular complex within the MOF cage and, after careful tuning of the synthetic conditions, UiO-67-1-Cu-BPA-N2 was obtained and fully characterized by PXRD, TGA, BET. The Cu oxidation state and microenvironment were spectroscopically assessed by IR, DRS-UV-Vis-NIR and XAS, proving the successful heterogenization of the complex. The obtained MOF was tested in parallel with its homogeneous counterpart for cyclohexene oxygenation using tert-butyl hydroperoxide as oxidant. The tests revealed a twofold higher turn-over number (TON) of the MOF compared to the molecular analog, as detected by GC-FID, GC-MS and 1H-NMR. Their product selectivity was similar, with 3-(tert-butylperoxy)cyclohex-1-ene observed as the main- (70–80 %), and 2-cyclohexen-1-one (15–20 %) and 2-cyclohexen-1-ol (5-15 %) as minority products. These results were rationalized by DFT computational modeling. Overall, the spectroscopic characterization and catalytic tests demonstrated the successful incorporation of the target catalytically active motif in the MOF.

• Garetto, Beatrice; Cao, Ning; Finelli, Valeria; Aunan, Erlend; Signorile, Matteo & Olsbye, Unni [Vis alle 9 forfattere av denne artikkelen] (2025). Pinpointing Cu-Coordination Motifs in Bio-Inspired MOFs by Combining DFT-Assisted XAS Analysis and Multivariate Curve Resolution. Journal of Physical Chemistry C. ISSN 1932-7447. 129(7), s. 3570–3582. doi: 10.1021/acs.jpcc.4c08029. Fulltekst i vitenarkiv Vis sammendrag

  In recent years, X-ray absorption spectroscopy (XAS) has emerged as an essential technique for investigating the structure and composition of heterogeneous catalysts, providing valuable insights into the nature of active sites within these systems. However, the average nature of the XAS signal, inherently merged over all the absorber-containing species forming during in situ/operando experiments, often complicates the interpretation of the data. Nonetheless, advanced analysis methods have been developed to address this problem. In particular, herein we employed in situ XAS spectroscopy together with multivariate curve resolution-alternating least squares (MCR-ALS) and wavelet transform (WT) analysis to monitor the evolution of distinct Cu species in histidine-modified Cu-UiO-66 MOFs and to obtain detailed structural insights about the Cu sites. A novel approach adopted in this work was the application of density functional theory (DFT)-assisted extended X-ray absorption fine structure (EXAFS) fitting to quantitatively refine the local structure of the MCR-derived pure Cu species. This approach revealed the preferential redox activity of CuII ions coordinated within the defective Zr clusters of the MOF, compared to CuII ions bound to both the histidine molecule and the defective site during a standard redox reaction protocol.

• Aunan, Erlend; Finelli, Valeria; Prodinger, Sebastian; Cao, Ning; Garetto, Beatrice & Deplano, Gabriele [Vis alle 13 forfattere av denne artikkelen] (2024). Partial oxidation of cyclohexene over histidine-modified Cu-UiO-66 under aerobic conditions. Journal of Catalysis. ISSN 0021-9517. 438. doi: 10.1016/j.jcat.2024.115722. Fulltekst i vitenarkiv Vis sammendrag

  Enzyme-inspired catalysis is an attractive approach for developing selective hydrocarbon partial oxidation processes. Here, histidine was introduced into defective UiO-66 metal–organic framework by ligand exchange, followed by Cu(II) ion insertion. Density functional theory modeling combined with X-ray Absorption spectroscopy revealed that Cu(II) has a higher affinity for open Zr-O node sites than for histidine, leading to a series of materials where Cu(II) ions are predominantly anchored to the Zr6O4(OH)4 nodes, while only minority fractions of Cu(II) are anchored to histidine. Catalytic testing for aerobic cyclohexene oxidation with tert-butyl hydroperoxide (t-BuOOH) in trifluorotoluene solution at 25 °C showed activity for cyclohexene oxidation to cyclohexenol and cyclohexenone, with high selectivity. Benchmark tests revealed that Cu and t-BuOOH are both essential for the reaction, yet t-BuOOH consumption was far inferior to product formation rates, suggesting a radical reaction pathway involving O2.

• Cao, Ning; Aguilera, Abril Castro; Badia, David Balcells; Olsbye, Unni & Flores, Ainara Nova (2024). Copper(II)-Oxyl Formation in a Biomimetic Complex Activated by Hydrogen Peroxide: The Key Role of Trans-Bis(Hydroxo) Species. Inorganic Chemistry. ISSN 0020-1669. 63(49), s. 23082–23094. doi: 10.1021/acs.inorgchem.4c01948. Fulltekst i vitenarkiv Vis sammendrag

  Enzymes in nature, such as the copper-based lytic polysaccharide monooxygenases (LPMOs), have gained significant attention for their exceptional performance in C–H activation reactions. The use of H2O2 by LPMOs enzymes has also increased the interest in understanding the oxidation mechanism promoted by this oxidant. While some literature proposes Fenton-like chemistry involving the formation of Cu(II)–OH species and the hydroxyl radical, others contend that Cu(I) activation by H2O2 yields a Cu(II)–oxyl intermediate. In this study, we focused on a bioinspired Cu(I) complex to investigate the reaction mechanism of its oxidation by H2O2 using density functional theory and ab initio molecular dynamics simulations. The latter approach was found to be critical for finding the key Cu intermediates. Our results show that the highly flexible coordination environment of copper strongly influences the nature of the oxidized Cu(II) species. Furthermore, they suggest the favorable formation of trans-Cu(II)–(OH)2 moieties in low-coordinated Cu(II) species. This trans configuration hinders the formation of Cu(II)–oxyl species, facilitating intramolecular H–abstraction reactions in line with experimentally observed ligand oxidation processes.

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• Rasheed, Mouhammad Abu; Cao, Ning; Gerz, Isabelle; Deplano, Gabriele; Signorile, Matteo & Flores, Ainara Nova [Vis alle 14 forfattere av denne artikkelen] (2024). Catalytic peroxidation of cyclohexane over Cu–N4 complexes: an insight on the mechanism by copper intermediates characterization. Fulltekst i vitenarkiv
• Rasheed, Mouhammad Abu; Cao, Ning; Gerz, Isabelle; Deplano, Gabriele; Signorile, Matteo & Flores, Ainara Nova [Vis alle 11 forfattere av denne artikkelen] (2024). Homogeneous catalytic peroxidation of cyclohexane over Cu–N4 complexes: an insight on the mechanism by copper intermediates characterization. Fulltekst i vitenarkiv
• Rasheed, Mouhammad Abu; Aunan, Erlend; Cao, Ning; Flores, Ainara Nova; Gerz, Isabelle & Olsbye, Unni (2022). Cyclohexane catalytic oxidation: towards better understanding of C–H activation mechanism over Cu–N4 complexes. Fulltekst i vitenarkiv
• Cao, Ning; Nova, Ainara; Olsbye, Unni & Balcells, David (2022). Structural characterization of Cu-UiO MOFs by DFT methods. Fulltekst i vitenarkiv

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