Iron pentacarbonyl (Fe(CO)5) is a versatile material that is utilized as an inhibitor of flame, shows soot suppressibility, and is used as a precursor for focused electron-beam-induced deposition ...(FEBID). X-ray absorption near-edge structure (XANES) of the K edge, which is a powerful technique for monitoring the oxidation states and coordination environment of metal sites, can be used to gain insight into Fe(CO)5-related reaction mechanisms in in situ experiments. We use a finite difference method (FDM) and molecular-orbital-based time-dependent density functional theory (TDDFT) calculations to clarify the Fe K-edge XANES features of Fe(CO)5. The two pre-edge peaks P1 and P2 are mainly the Fe(1s) → Fe–C(σ*) and Fe(1s) → Fe–C(π*) transitions, respectively. When the geometry transformed from D 3h to C 4v symmetry, a ∼30% decrease of the pre-edge P2 intensity was observed in the simulated spectra. This implies that the π bonding of Fe and CO is sensitive to changes in geometry. The following rising edge and white line regions are assigned to the Fe(1s) → Fe(4p)(mixing C(2p)) transitions. Our results may provide useful information to interpret XANES spectra variations of in situ reactions of metal–CO or similar compounds with π acceptor ligandlike metal–CN complexes.
Nitric oxide (NO),
a pro-neurogenic and antineuroinflammatory gasotransmitter,
features the potential to develop a translational medicine against
neuropathological conditions. Despite the extensive ...efforts made on
the controlled delivery of therapeutic NO, however, an orally active
NO prodrug for a treatment of chronic neuropathy was not reported
yet. Inspired by the natural dinitrosyl iron unit (DNIU) Fe(NO)
2
, in this study, a reversible and dynamic interaction between
the biomimetic (NO)
2
Fe(μ-SCH
2
CH
2
OH)
2
Fe(NO)
2
(
DNIC-1
) and serum
albumin (or gastrointestinal mucin) was explored to discover endogenous
proteins as a vehicle for an oral delivery of NO to the brain after
an oral administration of
DNIC-1
. On the basis of the
in vitro and in vivo study, a rapid binding of
DNIC-1
toward gastrointestinal mucin yielding the mucin-bound dinitrosyl
iron complex (DNIC) discovers the mucoadhesive nature of
DNIC-1
. A reversible interconversion between mucin-bound DNIC and
DNIC-1
facilitates the mucus-penetrating migration of
DNIC-1
shielded in the gastrointestinal tract of the stomach
and small intestine. Moreover, the NO-release reactivity of
DNIC-1
induces the transient opening of the cellular tight
junction and enhances its paracellular permeability across the intestinal
epithelial barrier. During circulation in the bloodstream, a stoichiometric
binding of
DNIC-1
to the serum albumin, as another endogenous
protein vehicle, stabilizes the DNIU Fe(NO)
2
for a subsequent
transfer into the brain. With aging mice under a Western diet as a
disease model for metabolic syndrome and cognitive impairment, an
oral administration of
DNIC-1
in a daily manner for 16
weeks activates the hippocampal neurogenesis and ameliorates the impaired
cognitive ability. Taken together, these findings disclose the synergy
between biomimetic
DNIC-1
and endogenous protein vehicles
for an oral delivery of therapeutic NO to the brain against chronic
neuropathy.
•Novel ZIF67-derived perovskite fluorides were synthesized using ammonium fluoride.•Perovskite fluoride shows particle-aggregated particle with less grain boundaries.•Highest CF of 490.4 F/g is got ...for a ZIF67-derived perovskite fluoride electrode.•The untreated ZIF67 electrode only shows CF value of 3.5 F/g at 20 mV/s.•Replace 2-methylimidazole with F− in ZIF67 can improve electrical conductivity.
Oxidation, carbonization, sulfurization and selenization are commonly used to enhance electrical conductivity and electroactivity of metal–organic frameworks. However, extra costs on time and money are required for post treatments. In this work, ammonium fluoride (NH4F) is incorporated in precursor solution for synthesizing perovskite ZIF67 derivatives as electroactive material. Novel particle-aggregated particle is obtained with largely reduced sizes and less grain boundaries. A highest specific capacitance (CF) of 490.4 F/g is attained at 20 mV/s for the optimized ZIF67 derivative electrode prepared using NH4F and Co:Ni ratio of 2:1 (CoNi21-NH4F), while the untreated, oxidized, carbonized, sulfurized and selenized bimetallic ZIF67 electrodes synthesized without NH4F only show the smaller CF values of 3.5, 363.9, 28.7, 85.9 and 103.2 F/g at 20 mV/s, respectively. Replacing 2-methylimidazole with F− in ZIF67 can improve electrical conductivity due to smaller size and higher electronegativity of F− than 2-methylimidazole. Largely enhanced CF value for CoNi21-NH4F electrode strongly indicates success of improving energy storage via simply adding NH4F in precursor solution without post treatments. Maximum energy density of 22.7 Wh/kg at power density of 0.6 W/kg, CF retention of 94% and Coulombic efficiency of 99% in 10.000 cycles charge/discharged process are obtained for supercapacitor with CoNi21-NH4F electrodes.
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An imidazolate-bridged Cu(II)–Zn(II) model compound, Cu(II)-diethylenetriamino-μ-imidazolato-Zn(II)-tris(aminoethyl)amine perchlorate (CZS), was synthesized and encapsulated into various mesoporous ...silicas (MPSs) to mimic the structure and functionalities of copper zinc superoxide dismutase (CuZnSOD). Two encapsulation methods were studied: covalent bonding and ionic exchange. The encapsulated CZS yielded good thermal stability and enhanced superoxide disproportionation activity in various designed MPS solids mimicking the environment and functionality of native CuZnSOD enzyme. Ionic exchange method generally gave better SOD-like catalytic activities than covalent bonding because the local attraction of SiO– to Cu(II) opens up the active axial position. We employed several spectroscopic techniques: UV–vis, EPR, and EXAFS to characterize the active site-Cu(II) ion of the immobilized CZS and to obtain the structural information of Cu(II) and Zn(II) centers confined in MPS. In the analyses of EPR and EXAFS spectra, we established the geometry of confined copper center changed to a more distorted square planar symmetry than free-form CZS, which can accommodate superoxide anion radical (O2 –•) coordinating to copper center in the proper manner. As the result of confinement in MPS, the active site of Cu(II) center gives rise to much increased SOD activities. Inspired by the local environments of guanidinium group in the native CuZnSOD enzyme in facilitating the superoxide dismutation, we further modified the silanol surface of MPS with N-trimethoxysilylpropyl-N,N,N-trimethyl-ammonium chloride (TMAC) preparing MPS-N+ to facilitate the transport of superoxide anion radicals. Optimized activities are associated with fine-tuning of pore size, surface acidity, and positively charged functional group. The spectroscopic studies allow us to establish the structure–reactivity relationship between the nanostructure of MPS and the efficacy of the superoxide dismutation in MPS and to elucidate the mechanism of the SOD-like activity of immobilized model compound in MPS.
Co‐crystallization of a cyanide‐bridged tetranuclear complex Co2Fe2 with 4‐cyanophenol (CP) gave a hydrogen bonding donor–acceptor system, Co2Fe2(bpy*)4(CN)6(tp*)2(PF6)2⋅2 CP⋅8 BN (1). 1 exhibited a ...three‐step phase transition between HT, IM1, IM2, and LT phases upon temperature variation. Variable temperature magnetic measurements and structural analyses revealed that the three‐step spin transition is caused by electron‐transfer‐coupled spin transitions (ETCSTs) accompanied with alteration of the hydrogen bonding interactions.
Wasserstoffbrücken‐Walzer: Ein dreistufiger Spinübergang wurde in einem Wasserstoffbrücken‐Donor‐Akzeptor‐System beobachtet, das einen quadratischen Co2Fe2‐Komplex enthält. Die Stabilisierung der Zwischenphasen beruht auf einem dynamischen Wechsel der Wasserstoffbrücken, gekoppelt mit dem Spinübergangsverhalten.
X‐ray absorption spectroscopy (XAS) becomes one of the important techniques to characterize the active metal site of crystalline or non‐crystalline materials. The x‐ray absorption near structure ...(XANES) of Fe K‐edge is often used to monitor the variation of the oxidation states and the local geometric structures in a series of Fe complexes or in situ reactions such as synthetic catalysts and metalloproteins. We provide a detailed interpretation of Fe K‐edge XANES features on the mononitrosyl iron complex, (NO)Fe(S2C6H4)2PPN, based on the theoretical calculation results of FDM (finite difference method) and TDDFT (time‐dependent density functional theory). The pre‐edge peak is mainly the transition of 1s(Fe) → 3dz2(Fe)(mixing with 3pz(S)). The following rising edge to white line region is related to Fe‐S and Fe‐N bonding. To apply the results, we have studied the variation of XANES features with systematically changing of Fe‐N bond lengths. The increasing of Fe‐N bond lengths leads to the XANES feature shifting to lower energy owing to reducing the orbitals overlapped between Fe and N.
The Fe K‐edge XANES features marked by P, A, B, and C are elucidated by FDM and TDDFT calculations. The pre‐edge peak P is mainly the transition of 1s(Fe) → 3dz2(Fe)(mixing with 3pz(S)), and feature A is related to the Fe‐S bonding. The feature B and C are corresponding to π* and σ* antibonding orbital of Fe‐N bond, respectively.
Nitric oxide (NO) is an essential endogenous signaling molecule regulating multifaceted physiological functions in the (cardio)vascular, neuronal, and immune systems. Due to the short half-life and ...location-/concentration-dependent physiological function of NO, translational application of NO as a novel therapeutic approach, however, awaits a strategy for spatiotemporal control on the delivery of NO. Inspired by the magnetic hyperthermia and magneto-triggered drug release featured by Fe3O4 conjugates, in this study, we aim to develop a magnetic responsive NO-release material (MagNORM) featuring dual NO-release phases, namely, burst and steady release, for the selective activation of NO-related physiology and treatment of bacteria-infected cutaneous wound. After conjugation of NO-delivery Fe(μ-S-thioglycerol)(NO)22 with a metal–organic framework (MOF)-derived porous Fe3O4@C, encapsulation of obtained conjugates within the thermo-responsive poly(lactic-co-glycolic acid) (PLGA) microsphere completes the assembly of MagNORM. Through continuous/pulsatile/no application of the alternating magnetic field (AMF) to MagNORM, moreover, burst/intermittent/slow release of NO from MagNORM demonstrates the AMF as an ON/OFF switch for temporal control on the delivery of NO. Under continuous application of the AMF, in particular, burst release of NO from MagNORM triggers an effective anti-bacterial activity against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). In addition to the magneto-triggered bactericidal effect of MagNORM against E. coli-infected cutaneous wound in mice, of importance, steady release of NO from MagNORM without the AMF promotes the subsequent collagen formation and wound healing in mice.
Regarding dihydrogen as a clean and renewable energy source, ammonia borane (NH3BH3, AB) was considered as a chemical H2-storage and H2-delivery material due to its high storage capacity of ...dihydrogen (19.6 wt %) and stability at room temperature. To advance the development of efficient and recyclable catalysts for hydrolytic dehydrogenation of AB with parallel insight into the reaction mechanism, herein, ZIF-67-derived fcc-Co@porous carbon nano/microparticles (cZIF-67_nm/cZIF-67_μm) were explored to promote catalytic dehydrogenation of AB and generation of H2(g). According to kinetic and computational studies, zero-order dependence on the concentration of AB, first-order dependence on the concentration of cZIF-67_nm (or cZIF-67_μm), and a kinetic isotope effect value of 2.45 (or 2.64) for H2O/D2O identify the Co-catalyzed cleavage of the H–OH bond, instead of the H–BH2NH3 bond, as the rate-determining step in the hydrolytic dehydrogenation of AB. Despite the absent evolution of H2(g) in the reaction of cZIF-67 and AB in the organic solvents (i.e., THF or CH3OH) or in the reaction of cZIF-67 and water, Co-mediated activation of AB and formation of a Co-H intermediate were evidenced by theoretical calculation, infrared spectroscopy in combination with an isotope-labeling experiment, and reactivity study toward CO2-to-formate/H2O-to-H2 conversion. Moreover, the computational study discovers a synergistic interaction between AB and the water cluster (H2O)9 on fcc-Co, which shifts the splitting of water into an exergonic process and lowers the thermodynamic barrier for the generation and desorption of H2(g) from the Co-H intermediates. With the kinetic and mechanistic study of ZIF-67-derived Co@porous carbon for catalytic hydrolysis of AB, the spatiotemporal control on the generation of H2(g) for the treatment of inflammatory diseases will be further investigated in the near future.
Continued efforts are made on the development of earth-abundant metal catalysts for dehydrogenation/hydrolysis of amine boranes. In this study, complex ...K-18-crown-6-ether(NO)2Fe(μ-MePyr)(μ-CO)Fe(NO)2 (3-K-crown, MePyr = 3-methylpyrazolate) was explored as a pre-catalyst for the dehydrogenation of dimethylamine borane (DMAB). Upon evolution of H2(g) from DMAB triggered by 3-K-crown, parallel conversion of 3-K-crown into (NO)2Fe(N,N′-MePyrBH2NMe2)− (5) and an iron-hydride intermediate (NO)2(CO)Fe(μ-H)Fe(CO)(NO)2− (A) was evidenced by X-ray diffraction/nuclear magnetic resonance/infrared/nuclear resonance vibrational spectroscopy experiments and supported by density functional theory calculations. Subsequent transformation of A into complex (NO)2Fe(μ-CO)2Fe(NO)2− (6) is synchronized with the deactivated generation of H2(g). Through reaction of complex Na-18-crown-6-ether(NO)2Fe(η2-BH4) (4-Na-crown) with CO(g) as an alternative synthetic route, isolated intermediate Na-18-crown-6-ether(NO)2(CO)Fe(μ-H)Fe(CO)(NO)2 (A-Na-crown) featuring catalytic reactivity toward dehydrogenation of DMAB supports a substrate-gated transformation of a pre-catalyst (NO)2Fe(μ-MePyr)(μ-CO)Fe(NO)2− (3) into the iron-hydride species A as an intermediate during the generation of H2(g).
Lord of the Dance Dynamic hydrogen‐bonding interactions and spin‐transition behavior play a key role in stabilizing intermediate phases in a multi‐step spin transition. In their Communication on page ...595 ff., M. Nihei, H. Oshio, et al. present a hydrogen‐bonding donor–acceptor system, comprising a spin transition‐active square complex Co2Fe2 and aromatic hydrogen‐bond‐donor molecules, which exhibits a three‐step spin transition in response to temperature.
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