Synthesis and Characterization of a Binuclear Iron(III) Complex Bridged by 1-Aminocyclopropane-1-carboxylic Acid. Ethylene Production in the Presence of Hydrogen Peroxide

Magnetic exchange interactions in binuclear and tetranuclear iron(III) complexes described by spin-flip DFT and Heisenberg effective Hamiltonians

Low-energy spectra of single-molecule magnets (SMMs) are often described by Heisenberg Hamiltonians. Within this formalism, exchange interactions between magnetic centers determine the ground-state multiplicity and energy separation between the ground and excited states. In this contribution, we extract exchange coupling constants (J) for a set of iron (III) binuclear and tetranuclear complexes from all-electron calculations using non-collinear spin-flip time-dependent density functional theory (NC-SF-TDDFT). For 12 binuclear complexes with J-values ranging from -6 to -132 cm^-1 , our benchmark calculations using the short-range hybrid ωPBEh functional and 6-31G(d,p) basis set agree well with the experimentally derived values (mean absolute error of 4.7 cm^-1 ). For the tetranuclear SMMs, the computed J constants are within 6 cm^-1 from the experimentally derived values. We explore the range of applicability of the Heisenberg model by analyzing bonding patterns in these Fe(III) complexes using natural orbitals (NO), their occupations, and the number of effectively unpaired electrons. The results illustrate the efficiency of the spin-flip protocol for computing the exchange couplings and the utility of the NO analysis in assessing the validity of effective spin Hamiltonians.

Biomimetic 1-Aminocyclopropane-1-Carboxylic Acid Oxidase Ethylene Production by MIL-100(Fe)-Based Materials

A novel core@shell hybrid material based on biocompatible hydroxyapatite nanoparticles (HA) and the well-known MIL-100(Fe) (Fe₃O(H₂O)₂F(BTC)₂·nH₂O, BTC: 1,3,5-benzenetricarboxylate) has been prepared following a layer-by-layer strategy. The core@shell nature of the studied system has been confirmed by infrared, X-ray powder diffraction, N₂ adsorption, transmission electron microscopy imaging, and EDS analyses revealing the homogeneous deposition of MIL-100(Fe) on HA, leading to HA@MIL-100(Fe) rod-shaped nanoparticles with a 7 nm shell thickness. Moreover, both MIL-100(Fe) and HA@MIL-100(Fe) have demonstrated to act as efficient heterogeneous catalysts toward the biomimetic oxidation of 1-aminocyclopropane-1-carboxylic acid into ethylene gas, a stimulator that regulates fruit ripening. Indeed, the hybrid material maintains the catalytic properties of pristine MIL-100(Fe) reaching 40% of conversion after only 20 min. Finally, the chemical stability of the catalyst in water has also been monitored for 21 days by inductively coupled plasma-mass spectrometry confirming that only ca. 3% of Ca is leached.

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.

Synthesis and characterization of [Fe(BPMEN)ACC]SbF6: a structural and functional mimic of ACC-oxidase

Miming plants: an original synthesis led to the preparation of the first model of the active site of the ethylene-forming enzyme ACC-oxidase. The prepared complex is a structural and a functional model as it reacts with hydrogen peroxide to produce the phytohormone ethylene.

A unique 1-amino-1-cyclopropane carboxylate cupric-cryptate hosting sodium

The first cluster containing acc was prepared via supramolecular self-assembly. This Cu(II) cluster traps Na(+), as shown in the solid state by the crystal structure and in solution by ESI-MS. Further characterisations revealed a ferromagnetic intracluster exchange and an irreversible reduction with a rapid intracluster electron transfer.