Caroline Marchi-Delapierre

A new chiral diiron catalyst for enantioselective epoxidation

The dinuclear chiral complex Fe(2)O(bisPB)(4)(X)(2)(ClO(4))(4) (X = H(2)O or CH(3)CN) catalyzes with high efficiency (up to 850 TON) and moderate enantioselectivity (63%) the epoxidation of electron deficient alkenes at 0 degrees C by a peracid.

The Protein Environment Drives Selectivity for Sulfide Oxidation by an Artificial Metalloenzyme

Magic Mn–salen metallozyme: The design of an original, artificial, inorganic, complex‐protein adduct, has led to a better understanding of the synergistic effects of both partners. The exclusive formation of sulfoxides by the hybrid biocatalyst, as opposed to sulfone in the case of the free inorganic complex, highlights the modulating role of the inorganic‐complex‐binding site in the protein.

Crystallographic snapshots of the reaction of aromatic C–H with O 2 catalysed by a protein-bound iron complex

Chemical reactions inside single crystals are quite rare because crystallinity is difficult to retain owing to atomic rearrangements. Protein crystals in general have a high solvent content. This allows for some molecular flexibility, which makes it possible to trap reaction intermediates of enzymatic reactions without disrupting the crystal lattice. A similar approach has not yet been fully implemented in the field of inorganic chemistry. Here, we have combined model chemistry and protein X-ray crystallography to study the intramolecular aromatic dihydroxylation by an arene-containing protein-bound iron complex. The bound complex was able to activate dioxygen in the presence of a reductant, leading to the formation of catechol as the sole product. The structure determination of four of the catalytic cycle intermediates and the end product showed that the hydroxylation reaction implicates an iron peroxo, generated by reductive O(2) activation, an intermediate already observed in iron monooxygenases. This strategy also provided unexpected mechanistic details such as the rearrangement of the iron coordination sphere on metal reduction.

The structure of the periplasmic nickel-binding protein NikA provides insights for artificial metalloenzyme design

Understanding the interaction of a protein with a relevant ligand is crucial for the design of an artificial metalloenzyme. Our own interest is focused on the synthesis of artificial monooxygenases. In an initial effort, we have used the periplasmic nickel-binding protein NikA from Escherichia coli and iron complexes in which N2Py2 ligands (where Py is pyridine) have been varied in terms of charge, aromaticity, and size. Six “NikA/iron complex” hybrids have been characterized by X-ray crystallography, and their interactions and solution properties have been studied. The hybrids are stable as indicated by their Kd values, which are all in the micromolar range. The X-ray structures show that the ligands interact with NikA through salt bridges with arginine residues and π-stacking with a tryptophan residue. We have further characterized these interactions using quantum mechanical calculations and determined that weak CH/π hydrogen bonds finely modulate the stability differences between hybrids. We emphasize the important role of the tryptophan residues. Thus, our study aims at the complete characterization of the factors that condition the interaction of an artificial ligand and a protein and their implications for catalysis. Besides its potential usefulness in the synthesis of artificial monooxygenases, our approach should be generally applicable in the field of artificial metalloenzymes.

Vanadium Thiolate Complexes for Efficient and Selective Sulfoxidation Catalysis: A Mechanistic Investigation

The structural and electronic properties as well as the catalytic activity toward sulfoxidation of two new vanadium complexes have been investigated. They both possess in their coordination sphere two alkyl thiolate ligands: a dioxido V(V) complex [VO2L(NS2)](HNEt3) (1) (L(NS2) = 2,2-(pyridine-2,6-diyl)bis(1,1-diphenylethanethiol)) and an oxido V(IV) complex [VOL(N2S2)] (2) (L(N2S2) = 2,2-(2,2-bipyridine-6,6-diyl)bis(1,1-diphenylethanethiol)). The X-ray structure of 1 has revealed that the V(V) metal ion is at the center of a distorted trigonal bipyramid. The optimized structure of 2 obtained by DFT calculations displays a square-pyramidal geometry, consistent with its EPR spectrum characterized by an axial S = 1/2 signal (g⊥ = 1.988, g∥ = 1.966, Ax(V) = 45 × 10(-4) cm(-1), Ay(V) = 42 × 10(-4) cm(-1), Az(V) = 135 × 10(-4) cm(-1)). DFT calculations have shown that the HOMO (highest occupied molecular orbital) of 1 is notably localized on the two thiolate sulfur atoms (56% and 22%, respectively), consistent with the expected covalent character of the V(V)-S bond. On the other hand, the SOMO (singly occupied molecular orbital) of 2 is exclusively localized at the V(IV) ion (92%). Complexes 1 and 2 have shown an ability to catalytically oxidize sulfide into sulfoxide. The oxidation reactions have been carried out with thioanisole as substrate and hydrogen peroxide as oxidant. Yields of 80% and 75% have been obtained in 10 and 15 min for 1 and 2, respectively. However, in terms of conversion, 1 is more efficient than 2 (81% and 44%, respectively). More importantly, the reaction is completely selective with no trace of sulfone produced. While 1 displays a poor stability, catalyst 2 shows the same efficiency after five successive additions of oxidant and substrate. The difference in reactivity and stability between both complexes has been rationalized through a mechanism study performed by means of experimental data ((51)V NMR and EPR spectroscopy) combined with theoretical calculations. It has been shown that the structure of the cis-oxo peroxo V(V) intermediate species, which is related to its stability, can partly explain these discrepancies.

Cross-Linked Artificial Enzyme Crystals as Heterogeneous Catalysts for Oxidation Reactions

Designing systems that merge the advantages of heterogeneous catalysis, enzymology, and molecular catalysis represents the next major goal for sustainable chemistry. Cross-linked enzyme crystals display most of these essential assets (well-designed mesoporous support, protein selectivity, and molecular recognition of substrates). Nevertheless, a lack of reaction diversity, particularly in the field of oxidation, remains a constraint for their increased use in the field. Here, thanks to the design of cross-linked artificial nonheme iron oxygenase crystals, we filled this gap by developing biobased heterogeneous catalysts capable of oxidizing carbon-carbon double bonds. First, reductive O2 activation induces selective oxidative cleavage, revealing the indestructible character of the solid catalyst (at least 30u202f000 turnover numbers without any loss of activity). Second, the use of 2-electron oxidants allows selective and high-efficiency hydroxychlorination with thousands of turnover numbers. This new technology by far outperforms catalysis using the inorganic complexes alone, or even the artificial enzymes in solution. The combination of easy catalyst synthesis, the improvement of omic technologies, and automation of protein crystallization makes this strategy a real opportunity for the future of (bio)catalysis.