catalytic cycle
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2022 ◽  
Author(s):  
Sebastian Gergel ◽  
Jordi Soler ◽  
Alina Klein ◽  
Kai Schülke ◽  
Bernhard Hauer ◽  
...  

The direct regioselective oxidation of internal alkenes to ketones could simplify synthetic routes and solve a longstanding challenge in synthesis. This reaction is of particular importance because ketones are predominant moieties in valuable products as well as crucial intermediates in synthesis. Here we report the directed evolution of a ketone synthase that oxidizes internal alkenes directly to ketones with several thousand turnovers. The evolved ketone synthase benefits from more than a dozen crucial mutations, most of them distal to the active site. Computational analysis reveals that all these mutations collaborate to facilitate the formation of a highly reactive carbocation intermediate by generating a confined, rigid and preorganized active site through an enhanced dynamical network. The evolved ketone synthase fully exploits a catalytic cycle that has largely eluded small molecule catalysis and consequently enables various challenging functionalization reactions of internal alkenes. This includes the first catalytic, enantioselective oxidation of internal alkenes to ketones, as well as the formal asymmetric hydration and hydroamination of unactivated internal alkenes in combination with other biocatalysts.


RSC Advances ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 378-388
Author(s):  
Wei Zhang ◽  
Yunhao Tang ◽  
Wei Xiao ◽  
Min Ruan ◽  
Yanshan Yin ◽  
...  

Probable surface NH3-SCR reaction mechanism over CuCe/TiO2-ZrO2 catalyst is proposed to follow the E–R mechanism and the L–H mechanism, while the E–R mechanism dominates in the reaction and the oxidation of NO closes the catalytic cycle.


2022 ◽  
Author(s):  
Takuya Akai ◽  
Mio Kondo ◽  
Yutaka Saga ◽  
Shigeyuki Masaoka

The first catalytic cycle for hydrogen production based on the photochemical two-electron reduction of carbon dioxide (CO2) and the dehydrogenation of formic acid at ambient temperature was demonstrated using a...


2021 ◽  
Author(s):  
Javier Bonet-Aleta ◽  
Miguel Encinas ◽  
Esteban Urriolabeitia ◽  
Pilar Martin-Duque ◽  
Jose L Hueso ◽  
...  

The present work sheds light on a generally overlooked issue in the emerging field of bio-orthogonal catalysis within tumor microenvironments (TMEs): the interplay between homogeneous and heterogeneous catalytic processes. In most cases, previous works dealing with nanoparticle-based catalysis in the TME, focus on the effects obtained (e.g. tumor cell death) and attribute the results to heterogeneous processes alone. The specific mechanisms are rarely substantiated and, furthermore, the possibility of a significant contribution of homogeneous processes by leached species –and the complexes that they may form with biomolecules- is neither contemplated nor pursued. Herein, we have designed a bimetallic catalyst nanoparticle containing Cu and Fe species and we have been able to describe the whole picture in a more complex scenario where both homogeneous and heterogeneous processes are coupled and fostered under TME relevant chemical conditions. We investigate the preferential leaching of Cu ions in the presence of a TME overexpressed biomolecule such as glutathione (GSH). We demonstrate that these homogeneous processes initiated by the released by Cu-GSH interactions are in fact responsible for the greater part of the cell death effects found (GSH, a scavenger of reactive oxygen species is depleted and highly active superoxide anions are generated in the same catalytic cycle). The remaining solid CuFe nanoparticle becomes an active catalase-mimicking surrogate able to supply oxygen from oxygen reduced species, such as superoxide anions (by-product from GSH oxidation) and hydrogen peroxide, another species that is enriched in the TME. This enzyme-like activity is essential to sustain the homogeneous catalytic cycle in the oxygen-deprived tumor microenvironment. The combined heterogeneous-homogeneous mechanisms revealed themselves as highly efficient in selectively killing cancer cells, due to their higher GSH levels compared to healthy cell lines.


Molecules ◽  
2021 ◽  
Vol 27 (1) ◽  
pp. 33
Author(s):  
Binlin Zhao ◽  
Tianxiang Zhu ◽  
Mengtao Ma ◽  
Zhuangzhi Shi

We report an efficient and practical iron-catalyzed hydrogen atom transfer protocol for assembling acetylenic motifs into functional alkenes. Diversities of internal alkynes could be obtained from readily available alkenes and acetylenic sulfones with excellent Markovnikov selectivity. An iron hydride hydrogen atom transfer catalytic cycle was described to clarify the mechanism of this reaction.


2021 ◽  
Author(s):  
Brandon Jolly ◽  
Nathalie Co ◽  
Ashton Davis ◽  
Paula Diaconescu ◽  
Chong Liu

Compartmentalization is an attractive approach to enhance catalytic activity by retaining reactive intermediates and mitigating deactivating pathways. Such a concept has been well explored in biochemical and more recently, organometallic catalysis to ensure high reaction turnovers with minimal side reactions. However, a scarcity of theoretical framework towards confined organometallic chemistry impedes a broader utility for the implementation of compartmentalization. Herein, we report a general kinetic model and offer design guidance for a compartmentalized organometallic catalytic cycle. In comparison to a non-compartmentalized catalysis, compartmentalization is quantitatively shown to prevent the unwanted intermediate deactivation, boost the corresponding reaction efficiency (γ), and subsequently increase catalytic turnover frequency (TOF). The key parameter in the model is the volumetric diffusive conductance (F_V) that describes catalysts’ diffusion propensity across a compartment’s boundary. Optimal values of F_V for a specific organometallic chemistry are needed to achieve maximal values of γ and TOF. As illustrated in specific reaction examples, our model suggests that a tailored compartment design, including the use of nanomaterials, is needed to suit a specific organometallic catalytic cycle. This work provides justification and design principles for further exploration into compartmentalizing organometallics to enhance catalytic performance. The conclusions from this work are generally applicable to other catalytic systems that need proper design guidance in confinement and compartmentalization.


2021 ◽  
Vol 449 ◽  
pp. 214191
Author(s):  
James A. Birrell ◽  
Patricia Rodríguez-Maciá ◽  
Edward J. Reijerse ◽  
Maria Alessandra Martini ◽  
Wolfgang Lubitz
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