Formation, Characterization, and Reactivity of a Nonheme Oxoiron(IV) Complex Derived from the Chiral Pentadentate Ligand asN4Py

The chiral pentadentate low-spin (S = 1) oxoiron(IV) complex [Fe^IV(O)(asN4Py)]²⁺ (2) was synthesized and spectroscopically characterized. Its formation kinetics, reactivity, and (enantio)selectivity in an oxygen-atom-transfer reaction was investigated in detail and compared to a similar pentadentate ligand-containing system.

Changing the chemical and physical properties of high valent heterobimetallic bis-(μ-oxido) Cu–Ni complexes by ligand effects

Two new heterobimetallic [LNiO₂Cu(RPY2)]⁺ (RPY2 = N-substituted bis 2-pyridyl(ethylamine) ligands with R = indane, 3a or R = Me, 3b) complexes have been spectroscopically trapped at low temperatures.

Visible-Light-Driven Oxidation of Organic Substrates with Dioxygen Mediated by a [Ru(bpy)3 ](2+) /Laccase System

Oxidation reactions are highly important chemical transformations that still require harsh reaction conditions and stoichiometric amounts of chemical oxidants that are often toxic. To circumvent these issues, olefins oxidation is achieved in mild conditions upon irradiation of an aqueous solution of the complex [Ru(bpy)3 ](2+) and the enzyme laccase. Epoxide formation is coupled to the light-driven reduction of O2 by [Ru(bpy)3 ](2+) /laccase system. The reactivity can be explained by dioxygen acting both as an oxidative agent and as renewable electron acceptor, avoiding the use of a sacrificial electron acceptor.

A structural and functional model for the 1-aminocyclopropane-1-carboxylic acid oxidase

The hitherto most realistic low-molecular-weight analogue for the 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO) is reported. The ACCOs 2-His-1-carboxylate iron(II) active site was mimicked by a TpFe moiety, to which the natural substrate ACC could be bound. The resulting complex [Tp(Me,Ph) FeACC] (1), according to X-ray diffraction analysis performed for the nickel analogue, represents an excellent structural model, featuring ACC coordinated in a bidentate fashion-as proposed for the enzymatic substrate complex-as well as a vacant coordination site that forms the basis for the first successful replication also of the ACCO function: 1 is the first known ACC complex that reacts with O2 to produce ethylene. As a FeOOH species had been suggested as intermediate in the catalytic cycle, H2 O2 was tested as the oxidant, too, and indeed evolution of ethylene proceeded even more rapidly to give 65 % yield.

Laccases as palladium oxidases

The first example of a coupled catalytic system involving an enzyme and a palladium(ii) catalyst competent for the aerobic oxidation of alcohol in mild conditions is described. In the absence of dioxygen, the fungal laccase LAC3 is reduced by a palladium(0) species as evidenced by the UV/VIS and ESR spectra of the enzyme. During the oxidation of veratryl alcohol performed in water, at room temperature and atmospheric pressure, LAC3 regenerates the palladium catalyst, is reduced and catalyzes the four-electron reduction of dioxygen into water with no loss of enzyme activity. The association of a laccase with a water-soluble palladium complex results in a 7-fold increase in the catalytic efficiency of the complex. This is the first step in the design of a family of renewable palladium catalysts for aerobic oxidation.

Comparison of heme and nonheme iron-based 1-aminocyclopropane-1-carboxylic acid oxidase mimics: kinetic, mechanistic and computational studies

Kinetic, mechanistic and computational studies of the H₂O₂oxidation of 1-aminocyclopropane-1-carboxylic acid to ethylene by heme- and nonheme-type iron complexes are described as biomimics of 1-aminocyclopropane-1-carboxylic acid oxidase.

Gram-scale production of a basidiomycetous laccase in Aspergillus niger

We report on the expression in Aspergillus niger of a laccase gene we used to produce variants in Saccharomyces cerevisiae. Grams of recombinant enzyme can be easily obtained. This highlights the potential of combining this generic laccase sequence to the yeast and fungal expression systems for large-scale productions of variants.

1-Aminocyclopropane-1-carboxylic acid oxidase: insight into cofactor binding from experimental and theoretical studies

1-Aminocyclopropane-1-carboxylic acid oxidase (ACCO) is a nonheme Fe(II)-containing enzyme that is related to the 2-oxoglutarate-dependent dioxygenase family. The binding of substrates/cofactors to tomato ACCO was investigated through kinetics, tryptophan fluorescence quenching, and modeling studies. α-Aminophosphonate analogs of the substrate (1-aminocyclopropane-1-carboxylic acid, ACC), 1-aminocyclopropane-1-phosphonic acid (ACP) and (1-amino-1-methyl)ethylphosphonic acid (AMEP), were found to be competitive inhibitors versus both ACC and bicarbonate (HCO(3)(-)) ions. The measured dissociation constants for Fe(II) and ACC clearly indicate that bicarbonate ions improve both Fe(II) and ACC binding, strongly suggesting a stabilization role for this cofactor. A structural model of tomato ACCO was constructed and used for docking experiments, providing a model of possible interactions of ACC, HCO(3)(-), and ascorbate at the active site. In this model, the ACC and bicarbonate binding sites are located close together in the active pocket. HCO(3)(-) is found at hydrogen-bond distance from ACC and interacts (hydrogen bonds or electrostatic interactions) with residues K158, R244, Y162, S246, and R300 of the enzyme. The position of ascorbate is also predicted away from ACC. Individually docked at the active site, the inhibitors ACP and AMEP were found coordinating the metal ion in place of ACC with the phosphonate groups interacting with K158 and R300, thus interlocking with both ACC and bicarbonate binding sites. In conclusion, HCO(3)(-) and ACC together occupy positions similar to the position of 2-oxoglutarate in related enzymes, and through a hydrogen bond HCO(3)(-) likely plays a major role in the stabilization of the substrate in the active pocket.