How Heme Metabolism Occurs in Heme Oxygenase: Computational Study of Oxygen-Donation Ability of the Oxo and Hydroperoxo Species

We report a density functional theory study on the heme metabolism in heme oxygenase using iron−hydroperoxo and −oxo models. The activation energies for heme oxidation at the α-carbon by the iron−hydroperoxo and −oxo species are calculated to be 42.9 and 39.9 kcal/mol, respectively. These high activation barriers lead us to reconsider the catalytic mechanism of heme oxygenas

Conjugated Ladder-Type Polymer with Hexaazatriphenylene Units as a Cathode Material for Lithium, Sodium, and Potassium Batteries

A ladder-type conjugated polymer with hexaazatriphenylene moieties is reported, and its application as a cathode material for Li-, Na-, and K-based batteries is assessed. The material demonstrates specific capacities of 170–180 mA h g–1 at 0.1 A g–1, and up to 113 mA h g–1 at 5 A g–1 (charge/discharge in ∼80 s). It also shows superior cycling stability, especially in potassium cells that show no capacity fade after 4000 cycles at 5 A g–1. Charge–discharge processes of the material are probed using operando Raman spectroscopy

Formation of H₂O₂ on Au₂₀ and Au₁₉Pd Clusters: Understanding the Structure Effect on the Atomic Level

Supported gold nanoparticles are promising catalysts for production of H₂O₂ from O₂ and H₂. Size, structure, and palladium doping effects play the key role in activity and selectivity of a gold catalyst. We performed a study of the influence of Au₂₀ and Au₁₉Pd structure features on the main steps of H₂O₂ formation on the atomic level, using the DFT/PBE approach with relativistic all electron basis set. The top, edge, and facet atoms of the tetrahedral Au₂₀ cluster as well as a palladium atom of Au₁₉Pd located on the top, edge, and facet of a tetrahedron have been considered as active sites of steps involved in H₂O₂ synthesis. The thermodynamic and kinetic data including Gibbs free energies and the activation Gibbs free energies were calculated for the steps determining the formation of H₂O₂ (H_(s) + OOH_(s) = H₂O_2(s), H₂O_2(s) = H₂O_2(g)) and for one step decreasing the selectivity (H₂O_2(s) = OH_(s) + OH_(s)). Gold tends to have low activity and high selectivity in H₂O₂ synthesis regardless of the structure of active site. Low coordinated palladium atoms promote H₂O₂ formation as well as its dissociation. Pd on a facet of a cluster facilitates H₂O₂ production with high activity and selectivity

Formation of H₂O₂ on Au₂₀ and Au₁₉Pd Clusters: Understanding the Structure Effect on the Atomic Level

Supported gold nanoparticles are promising catalysts for production of H₂O₂ from O₂ and H₂. Size, structure, and palladium doping effects play the key role in activity and selectivity of a gold catalyst. We performed a study of the influence of Au₂₀ and Au₁₉Pd structure features on the main steps of H₂O₂ formation on the atomic level, using the DFT/PBE approach with relativistic all electron basis set. The top, edge, and facet atoms of the tetrahedral Au₂₀ cluster as well as a palladium atom of Au₁₉Pd located on the top, edge, and facet of a tetrahedron have been considered as active sites of steps involved in H₂O₂ synthesis. The thermodynamic and kinetic data including Gibbs free energies and the activation Gibbs free energies were calculated for the steps determining the formation of H₂O₂ (H_(s) + OOH_(s) = H₂O_2(s), H₂O_2(s) = H₂O_2(g)) and for one step decreasing the selectivity (H₂O_2(s) = OH_(s) + OH_(s)). Gold tends to have low activity and high selectivity in H₂O₂ synthesis regardless of the structure of active site. Low coordinated palladium atoms promote H₂O₂ formation as well as its dissociation. Pd on a facet of a cluster facilitates H₂O₂ production with high activity and selectivity

Negatively Charged Iron-Bridged Fullerene Dimer {Fe(CO)₂‑μ₂‑η²,η²‑C₆₀}₂^2–

The interaction of {Cryptand(K+)}(C60•–) with Fe3(CO)12 produced {Cryptand(K+)}2{Fe(CO)2-μ2-η2,η2-C60}22–·2.5C6H4Cl2 (1) as the first negatively charged iron-bridged fullerene C60 dimer. The bridged iron atoms are coordinated to two 6–6 bonds of one C60 hexagon with short and long C(C60)–Fe bonds with average lengths of 2.042(3) and 2.088(3) Å. Fullerenes are close to each other in the dimer with a center-to-center interfullerene distance of 10.02 Å. Optical spectra support the localization of negative electron density on the Fe2(CO)4 units, which causes a 50 cm–1 shift of the CO vibration bands to smaller wavenumbers, and the C60 cages. Dimers are diamagnetic and electron paramagnetic resonance silent and have a singlet ground state resulting from the formation of an Fe–Fe bond in the dimer with a length of 2.978(4) Å. According to density functional theory calculations, the excited triplet state is higher than the ground state by 6.5 kcal/mol. Compound 1 shows a broad near-infrared band with a maximum at 970 nm, which is attributable to the charge transfer from the orbitals localized mainly on iron atoms to the C60 ligand

Spin Crossover in Anionic Cobalt-Bridged Fullerene (Bu₄N⁺){Co(Ph₃P)}₂(μ₂‑Cl^–)(μ₂‑η²,η²‑C₆₀)₂ Dimers

A spin crossover phenomena is observed in an anionic (Bu₄N⁺)­{Co­(Ph₃P)}₂(μ₂-Cl^–)­(μ₂-η²,η²-C₆₀)₂·2C₆H₁₄ (<b>1</b>) complex in which two cobalt atoms bridge two fullerene molecules to form a dimer. The dimer has a triplet ground state with two weakly coupling Co⁰ atoms (<i>S</i> = 1/2). The spin transition realized above 150 K is accompanied by a cobalt-to-fullerene charge transfer that forms a quintet excited state with a high spin Co^I (<i>S</i> = 1) and C₆₀^•– (<i>S</i> = 1/2)

Advanced Nonvolatile Organic Optical Memory Using Self-Assembled Monolayers of Porphyrin–Fullerene Dyads

Photo-switchable organic field-effect transistors (OFETs) represent an important platform for designing memory devices for a diverse array of products including security (brand-protection, copy-protection, keyless entry, etc.), credit cards, tickets, and multiple wearable organic electronics applications. Herein, we present a new concept by introducing self-assembled monolayers of donor–acceptor porphyrin–fullerene dyads as light-responsive triggers modulating the electrical characteristics of OFETs and thus pave the way to the development of advanced nonvolatile optical memory. The devices demonstrated wide memory windows, high programming speeds, and long retention times. Furthermore, we show a remarkable effect of the orientation of the fullerene–polymer dyads at the dielectric/semiconductor interface on the device behavior. In particular, the dyads anchored to the dielectric by the porphyrin part induced a reversible photoelectrical switching of OFETs, which is characteristic of flash memory elements. On the contrary, the devices utilizing the dyad anchored by the fullerene moiety demonstrated irreversible switching, thus operating as read-only memory (ROM). A mechanism explaining this behavior is proposed using theoretical DFT calculations. The results suggest the possibility of revisiting hundreds of known donor–acceptor dyads designed previously for artificial photosynthesis or other purposes as versatile optical triggers in advanced OFET-based multibit memory devices for emerging electronic applications

Paramagnetic {[Fe(CO)₂]₂-μ₂‑η²:η²‑η²:η²‑(C₆₀)₂}^2– Dimer Bridged by Iron Atoms and C–C Bonds: Effect of Starting Iron Carbonyls on Structures and Properties of Negatively Charged Iron-Bridged Fullerene Dimers

The reaction between an excess of Fe­(CO)5 with {Cryptand­(K+)}­(C60•–) produced the salt {Cryptand­(K+)}2{[Fe­(CO)2]2-μ2-η2:η2-η2:η2-(C60)2}2–·4C6H4Cl2 (1) containing negatively charged iron-bridged fullerene dimers. In these dimers, the C60 cages are linked via two Fe­(CO)2 fragments, forming short Fe–C­(C60) bonds with a length of 2.070(3) Å and via two intercage C–C bonds with a length of 1.566(3) Å. Interfullerene center-to-center distance is short, being 9.02 Å. Thus, the coordination-induced dimerization of fullerenes is observed in 1. The dimer is negatively charged, with additional negative electron density mainly localized on iron atoms and, to a lesser extent, on the C60 cages, as revealed by optical and electron paramagnetic resonance spectra. These dimers have a diamagnetic singlet ground state with a small singlet–triplet gap of 25 K; consequently, they transfer to a paramagnetic state with two S = 1/2 spins per dimer above 50 K. Previously, different dimers with isomeric structures were obtained starting from {Cryptand­(K+)}­(C60•–) and Fe3(CO)12. However, these dimers exhibit diamagnetic properties, owing to the formation of a Fe–Fe bond. In contrast, in dimer 1, the Fe atoms are positioned too far apart to form such a bond, preserving the spin on Fe. We assume that both dimers are formed through the same [Fe­(CO)3]­(C60•–) intermediate, but the subsequent interaction of this intermediate with Fe3(CO)12 or its dimerization yields different dimers. Therefore, the starting carbonyls can control the structures and properties of the resulting dimers

Spin Crossover in Anionic Cobalt-Bridged Fullerene (Bu₄N⁺){Co(Ph₃P)}₂(μ₂‑Cl^–)(μ₂‑η²,η²‑C₆₀)₂ Dimers

A spin crossover phenomena is observed in an anionic (Bu₄N⁺)­{Co­(Ph₃P)}₂(μ₂-Cl^–)­(μ₂-η²,η²-C₆₀)₂·2C₆H₁₄ (<b>1</b>) complex in which two cobalt atoms bridge two fullerene molecules to form a dimer. The dimer has a triplet ground state with two weakly coupling Co⁰ atoms (<i>S</i> = 1/2). The spin transition realized above 150 K is accompanied by a cobalt-to-fullerene charge transfer that forms a quintet excited state with a high spin Co^I (<i>S</i> = 1) and C₆₀^•– (<i>S</i> = 1/2)

Formation of {Co(dppe)}₂{μ₂‑η²:η²‑η²:η²‑[(C₆₀)₂]} Dimers Bonded by Single C–C Bonds and Bridging η²‑Coordinated Cobalt Atoms

Coordination of two bridging cobalt atoms to fullerenes by the η² type in {Co­(dppe)}₂{μ₂-η²:η²-η²:η²-[(C₆₀)₂]}·3C₆H₄Cl₂ [<b>1</b>; dppe = 1,2-bis­(diphenylphosphino)­ethane] triggers fullerene dimerization with the formation of two intercage C–C bonds of 1.571(4) Å length. Coordination-induced fullerene dimerization opens a path to the design of fullerene structures bonded by both covalent C–C bonds and η²-coordination-bridged metal atoms