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The strong C-H bond activation of hydrocarbons is a difficult reaction in environmental and biological chemistry. Herein, a high-valent manganese(IV)-hydroxo complex, [Mn

Contains fulltext : 293925.pdf (Publisher’s version ) (Open Access) 05 juni 2023

The structure of the title salt, [Ag(C7H12N2)2][CdCl(C44H28N4)], at 150 K has triclinic symmetry. One of the phenyl rings bonded to the porphyrin molecule and the propyl groups of both ylidene molecules coordinating to silver are disordered over two positions.

Photocatalytic generation of nitrenes and radicals can be used to tune or even control their reactivity. Photocatalytic activation of sulfonyl azides leads to the elimination of N

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Pd-catalyzed C–H functionalization reactions of non-directed substrates have recently emerged as an attractive alternative to the use of directing groups. Key to the success of these transformations has been the discovery of new ligands capable of increasing both the reactivity of the inert C–H bond and the selectivity of the process. Among them, a new type of S,O-ligand has been shown to be highly efficient in promoting a variety of Pd-catalyzed C–H olefination reactions of non-directed arenes. Despite the success of this type of S,O-ligand, its role in the C–H functionalization processes is unknown. Herein, we describe a detailed mechanistic study focused on elucidating the role of the S,O- ligand in the Pd-catalyzed C–H olefination of non-directed arenes. For this purpose, several mechanistic tools, including isolation and characterization of reactive intermediates, NMR and kinetic studies, isotope effects and DFT calculations have been employed. The data from these experiments suggest that the C–H activation is the rate-determining step in both cases with and without the S,O-ligand. Furthermore, the results indicate that the S,O-ligand triggers the formation of more reactive Pd cationic species, which explains the observed acceleration of the reaction. Together, these studies shed light on the role of the S,O-ligand in promoting Pd-catalyzed C–H functionalization reactions We acknowledge nancial support from NWO through a VIDI grant (723.013.006) and from MCIN-PID2019-110008GB-I00. E. G.-B. thanks SGIker (UPV/EHU) for providing human and computational resources.

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Here we describe a photoswitchable iron(III) salen phosphate catalyst, which is able to catalyze the enantiodivergent oxidation of prochiral aryl alkyl sulfides to chiral aryl alkyl sulfoxides. The stable (S)-axial isomer of the catalyst produced enantioenriched sulfoxides with the (R)-configuration in up to 75 % e.e., whereas the photoisomerized metastable (R)-axial isomer of the catalyst favored the formation of (S)-sulfoxides in up to 43 % e.e. The maximum Δe.e. value obtained in the enantiodivergent sulfoxidation was 118 %, which is identical to the maximum Δe.e. value that was measured in the enantiodivergent epoxidation of alkenes by a related recently described Mn1 catalyst. This iron-based catalyst broadens the scope of photoswitchable enantiodivergent catalysts and may be used in the future to develop a photoswitchable catalytic system that can write digital information on a polymer chain in the form chiral sulfoxide functions.

Contains fulltext : 292792.pdf (Publisher’s version ) (Open Access) 01 mei 2023

Living systems use enzymatic reaction networks to process biochemical information and make decisions in response to external or internal stimuli. Here, we present a modular and reusable platform for molecular information processing using enzymes immobilised in hydrogel beads and compartmentalised in a continuous stirred tank reactor. We demonstrate how this setup allows us to perform simple arithmetic operations, such as addition, subtraction and multiplication, using various concentrations of substrates or inhibitors as inputs and the production of a fluorescent molecule as the readout.

Contains fulltext : 287543.pdf (Publisher’s version ) (Open Access) 28 november 2022

Cells continuously sense external forces from their microenvironment, the extracellular matrix (ECM). In turn, they generate contractile forces, which stiffen and remodel this matrix. Although this bidirectional mechanical exchange is crucial for many cell functions, it remains poorly understood. Key challenges are that the majority of available matrices for such studies, either natural or synthetic, are difficult to control or lack biological relevance. Here, we use a synthetic, yet highly biomimetic hydrogel based on polyisocyanide (PIC) polymers to investigate the effects of the fibrous architecture and the nonlinear mechanics on cell-matrix interactions. Live-cell rheology was combined with advanced microscopy-based approaches to understand the mechanisms behind cell-induced matrix stiffening and plastic remodeling. We demonstrate how cell-mediated fiber remodeling and the propagation of fiber displacements are modulated by adjusting the biological and mechanical properties of this material. Moreover, we validate the biological relevance of our results by demonstrating that cellular tractions in PIC gels develop analogously to those in the natural ECM. This study highlights the potential of PIC gels to disentangle complex bidirectional cell-matrix interactions and to improve the design of materials for mechanobiology studies. ispartof: Proc Natl Acad Sci U S A vol:120 issue:15 pages:e2216934120- ispartof: location:United States status: published

Macrocyclic metal porphyrin complexes can act as shape-selective catalysts mimicking the action of enzymes. To achieve enzyme-like reactivity, a mechanistic understanding of the reaction at the molecular level is needed. We report a mechanistic study of alkene epoxidation by the oxidant iodosylbenzene, mediated by an achiral and a chiral manganese(V)oxo porphyrin cage complex. Both complexes convert a great variety of alkenes into epoxides in yields varying between 20-88 %. We monitored the process of the formation of the manganese(V)oxo complexes by oxygen transfer from iodosylbenzene to manganese(III) complexes and their reactivity by ion mobility mass spectrometry. The results show that in the case of the achiral cage complex the initial iodosylbenzene adduct is formed on the inside of the cage and in the case of the chiral one on the outside of the cage. Its decomposition leads to a manganese complex with the oxo ligand on either the inside or outside of the cage. These experimental results are confirmed by DFT calculations. The oxo ligand on the outside of the cage reacts faster with a substrate molecule than the oxo ligand on the inside. The results indicate how the catalytic activity of the macrocyclic porphyrin complex can be tuned and explain why the chiral porphyrin complex does not catalyze the enantioselective epoxidation of alkenes.

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The development of enantiodivergent catalysts capable of preparing both enantiomeric products from one substrate in a controlled fashion is challenging. Introducing a switching function into the catalyst can address this challenge, allowing the chiral reaction environment to reversibly change during catalysis. Here we report a photoswitchable phosphate ligand, derived from 2,2'-biphenol, which axially coordinates as the counter ion to an achiral manganese(III) salen catalyst, providing the latter with the ability to switch stereoselectivity in the epoxidation of alkenes. The enantiomers of the chiral ligand exist as a pair of pseudo-enantiomers, which can be interconverted by irradiation with light of different wavelengths. The opposite axial chirality of these pseudo-enantiomers is efficiently transferred to the manganese(III) salen catalyst. With this switchable supramolecular catalyst, the enantioselectivity of the epoxidation of a variety of alkenes can be controlled, resulting in opposite enantiomeric excesses of the epoxide products. This transfer of chirality from a photoswitchable anionic ligand to a metal complex broadens the scope of supramolecular catalysts.

Paramagnetic metallohost systems can bind guest molecules and find application as biomimetic catalysts. Due to the presence of the paramagnetic metal center, rigorous characterization of these systems by NMR spectroscopy can be very difficult. We report here that metallohost-guest systems can be studied by using the paramagnetic relaxation enhancement (PRE) effect. Manganese(III) porphyrin cage compounds are shown through their PRE to thread and bind viologen guests, including a polymeric one. The binding constants and dethreading activation parameters are lower than those of the metal-free porphyrin cage compounds, which is proposed to be a result of charge repulsion of the trivalent metal center and dicationic viologen guest. The threading rate of the manganese(III) porphyrin cage onto the polymer is more than 10 times faster than that of the non-metallated one, which is ascribed to initial binding of the cage to the polymer chain prior to threading, and to an entron effect.

The copper(I), silver(I), and gold(I) metals bind π-ligands by σ-bonding and π-back bonding interactions. These interactions were investigated using bidentate ancillary ligands with electron donating and withdrawing substituents. The π-ligands span from ethylene to larger terminal and internal alkenes and alkynes. Results of X-ray crystallography, NMR, and IR spectroscopy and gas phase experiments show that the binding energies increase in the order AgCuAu and the binding energies are slightly higher for alkynes than for alkenes. Modulation of the electron density at the metal using substituents on the ancillary ligands shows that the π-back bonding interaction plays a dominant role for the binding in the copper and gold complexes.

Gold(II) complexes are rare and their application for catalysis of chemical transformations is unexplored. The reason is their easy oxidation or reduction to the more stable gold(III) or gold(I) complexes, respectively. We explored the thermodynamics of the formation of the [(L)AuIIX]+ complexes (L = ligand, X = halogen) from their gold(III) precursors and investigated the stability and the spectral properties in the IR and VIS range of the formed gold(II) complexes in the gas phase. The results show that the best ancillary ligands L for stabilizing gaseous [(L)AuIIX]+ complexes are bidentate and tridentate ligands with nitrogen donor atoms. The electronic structure and spectral properties of the investigated gold(II) complexes were correlated with the quantum chemical calculations. The results show that the molecular and electronic structure of the gold(II) complexes as well as their spectroscopic properties are very similar to the analogous stable copper(II) complexes.

This perspective gives an overview of the action spectroscopy methods for measurements of electronic, vibrational, and rotational spectra of mass-selected ions in the gas phase. We classify and give a short overview of the existing experimental approaches in this field. There is currently a plethora of names used for, essentially, the same techniques. Hence within this overview, we scrutinized the notations and suggested terms to be generally used. The selection was either driven by making the name unique and straightforward or the term being the most broadly used one. We believe that a simplification and a unification of the notation in ion spectroscopy can make this field better accessible for experts outside the mass spectrometry community where the applications of gas-phase action ion spectroscopy can make a large impact.

Contains fulltext : 253441.pdf (Publisher’s version ) (Open Access) 25 augustus 2022

Enantioselective reactions are at the core of chemical synthesis. Their development mostly relies on prior knowledge, laborious product analysis and post-rationalization by theoretical methods. Here, we introduce a simple and fast method to determine enantioselectivities based on mass spectrometry. The method is based on ion mobility separation of diastereomeric intermediates, formed from a chiral catalyst and prochiral reactants, and delayed reactant labeling experiments to link the mass spectra with the reaction kinetics in solution. The data provide rate constants along the reaction paths for the individual diastereomeric intermediates, revealing the origins of enantioselectivity. Using the derived kinetics, the enantioselectivity of the overall reaction can be predicted. Hence, this method can offer a rapid discovery and optimization of enantioselective reactions in the future. We illustrate the method for the addition of cyclopentadiene (CP) to an α, β-unsaturated aldehyde catalyzed by a diarylprolinol silyl ether.

Molecular motors change conformation under the influence of light and when attached to host molecules, they may find applications as sensors and switchable catalysts. Here, we present a porphyrin macrocyclic host functionalized with two motor appendages for future catalytic applications. The compound is formed as a mixture of six stereoisomers (three sets of enantiomers), which have been separated by (chiral) chromatography. 1H NMR and chiral spectroscopy revealed that in one set of enantiomers, the two motors interact with the cavity of the host (bound‐bound), whereas in a second set, one interacts and the other one does not (bound‐loose). In the third set, both motors do not interact with the host compound (loose‐loose). The motorized hosts bind guest molecules in the order: (loose‐loose) > (bound‐loose) > (bound‐bound). They can be switched with light to pseudoidentical diastereomers, leading to orthogonal behavior in the light‐gated binding of guest molecules. Although the photoisomerization of the diastereomer set loose‐loose significantly lowers the binding affinity for viologen guests, the opposite is true for the diastereomer set bound‐bound, that is, the binding affinity increases. For the diastereomer set bound‐loose, no influence on guest binding is observed as the effect of photoisomerization on the motors is cancelled out. Key Points We present a porphyrin cage compound with two light‐switchable molecular motors for future catalytic applications The double‐motorized porphyrin cage compound is formed as a mixture of six stereoisomers (three sets of enantiomers), which could be separated, and by photoswitching converted to pseudoidentical stereoisomers The stereoisomers display different binding affinities for guest molecules, which reverse on photoswitching, leading to orthogonal guest binding behavior

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Pyridine-functionalized hemithioindigo photoswitches (Z)-6-(Z)-8 were obtained by an aldol condensation of benzothiophenone 5 with the appropriate pyridinecarbaldehyde. These compounds were methylated with methyl iodide or methyl triflate to obtain pyridinium-functionalized hemithioindigo photoswitches (Z)-2-(Z)-4. The resulting compounds (Z)-2-(Z)-4 and (Z)-6-(Z)-8 could be isomerized to the (E)-isomer with light of λ = 470 nm, with relative abundances of the photoisomers up to 96%. All photoswitches except (Z)-2 could be isomerized back to the (Z)-state with light of longer wavelengths. For (Z)-2 this process of adopting a new photostationary state was slower compared to the thermal relaxation. Switches (Z)-2-(Z)-4 were capable of binding in a porphyrin cage host (H21) with association constants that increased with the distance between the positive charge and the central double bond of the switch: ((Z)-2