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1.
Nat Mater ; 21(4): 423-429, 2022 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-35190656

RESUMEN

Charge neutrality and their expected itinerant nature makes excitons potential transmitters of information. However, exciton mobility remains inaccessible to traditional optical experiments that only create and detect excitons with negligible momentum. Here, using angle-resolved photoemission spectroscopy, we detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide, TaSe3. The low density of conduction electrons and the low dimensionality in TaSe3 combined with a polaronic renormalization of the conduction band and the poorly screened interaction between these polarons and photo-induced valence holes leads to various excitonic bound states that we interpret as intrachain and interchain excitons, and possibly trions. The thresholds for the formation of a photo-hole together with an exciton appear as side valence bands with dispersions nearly parallel to the main valence band, but shifted to lower excitation energies. The energy separation between side and main valence bands can be controlled by surface doping, enabling the tuning of certain exciton properties.


Asunto(s)
Electrones
2.
Proc Natl Acad Sci U S A ; 119(20): e2122063119, 2022 May 17.
Artículo en Inglés | MEDLINE | ID: mdl-35533271

RESUMEN

SignificanceThe chemical reduction of unsaturated bonds occurs by hydrogenation with H2 as the reductant. Conversely, in biology, the unavailability of H2 engenders the typical reduction of unsaturated bonds with electrons and protons from different cofactors, requiring olefin hydrogenation to occur by proton-coupled electron transfer (PCET). Moreover, the redox noninnocence of tetrapyrrole macrocycles furnishes unusual PCET intermediates, including the phlorin, which is an intermediate in tetrapyrrole ring reductions. Whereas the phlorin of a porphyrin is well established, the phlorin of a chlorin is enigmatic. By controlling the PCET reactivity of a chlorin, including the use of a hangman functionality to manage the proton transfer, the formation of a chlorinphlorin by PCET is realized, and the mechanism for its formation is defined.


Asunto(s)
Electrones , Protones , Transporte de Electrón , Hidrogenación , Oxidación-Reducción
3.
Sci Rep ; 12(1): 7253, 2022 May 04.
Artículo en Inglés | MEDLINE | ID: mdl-35508509

RESUMEN

The radical Friedländer hetero-annulation of 2-aminoaryl ketone and -methylene carbonyl compound was used to develop a green tandem approach for the metal-free synthesis of polysubstitutedquinolines. At room temperature in an ethanol solvent, photo-excited state functions generated from MB+ were used as single-electron transfer (SET) and energy transfer (EnT) catalysts, utilizing visible light as a renewable energy source in the air atmosphere. The purpose of this research is to increase the use of a nonmetal cationic dye that is both inexpensive and widely available. High yields, energy-effectiveness, high atom economy, time-saving features of the reaction, and operational simplicity, and the least amount of a catalyst are the benefits of this study. As a result, a wide range of ecological and long-term chemical properties are obtained. Polysubstitutedquinolines' turnover number (TON) and turnover frequency (TOF) have been calculated. Surprisingly, such cyclization can be accomplished on a gram scale, indicating that the process has industrial potential.


Asunto(s)
Electrones , Azul de Metileno , Catálisis , Transporte de Electrón , Transferencia de Energía
4.
Acta Crystallogr A Found Adv ; 78(Pt 3): 200-211, 2022 May 01.
Artículo en Inglés | MEDLINE | ID: mdl-35502712

RESUMEN

Single-particle imaging with X-ray free-electron lasers depends crucially on algorithms that merge large numbers of weak diffraction patterns despite missing measurements of parameters such as particle orientations. The expand-maximize-compress (EMC) algorithm is highly effective at merging single-particle diffraction patterns with missing orientation values, but most implementations exhaustively sample the space of missing parameters and may become computationally prohibitive as the number of degrees of freedom extends beyond orientation angles. This paper describes how the EMC algorithm can be modified to employ Metropolis Monte Carlo sampling rather than grid sampling, which may be favorable for reconstruction problems with more than three missing parameters. Using simulated data, this variant is compared with the standard EMC algorithm.


Asunto(s)
Algoritmos , Electrones , Rayos Láser , Método de Montecarlo
5.
Sci Rep ; 12(1): 7417, 2022 May 06.
Artículo en Inglés | MEDLINE | ID: mdl-35523838

RESUMEN

The presented paper fundamentally investigates the influence of different electron transfer mechanisms, various metal-based electrodes, and a static magnetic field on the overall performance of microfluidic microbial fuel cells (MFCs) for the first time to improve the generated bioelectricity. To do so, as the anode of microfluidic MFCs, zinc, aluminum, tin, copper, and nickel were thoroughly investigated. Two types of bacteria, Escherichia coli and Shewanella oneidensis MR-1, were used as biocatalysts to compare the different electron transfer mechanisms. Interaction between the anode and microorganisms was assessed. Finally, the potential of applying a static magnetic field to maximize the generated power was evaluated. For zinc anode, the maximum open circuit potential, current density, and power density of 1.39 V, 138,181 mA m-2 and 35,294 mW m-2 were obtained, respectively. The produced current density is at least 445% better than the values obtained in previously published studies so far. The microfluidic MFCs were successfully used to power ultraviolet light-emitting diodes (UV-LEDs) for medical and clinical applications to elucidate their application as micro-sized power generators for implantable medical devices.


Asunto(s)
Fuentes de Energía Bioeléctrica , Fuentes de Energía Bioeléctrica/microbiología , Electricidad , Electrodos , Electrones , Campos Magnéticos , Microfluídica , Zinc
6.
Yakugaku Zasshi ; 142(5): 479-485, 2022.
Artículo en Japonés | MEDLINE | ID: mdl-35491153

RESUMEN

Three-dimensional structural information is indispensable to understand the function of proteins in living organisms and X-ray crystallography plays a major role in determining the three-dimensional structure. X-ray free-electron laser (XFEL), which is intense and femtosecond X-ray pulses, enables us to obtain X-ray diffraction intensity data before the destruction of protein molecules, and is expected to be a technology to obtain dynamic structural information. This year marks the 10th anniversary of SPring-8 Angstrom Compact Free Electron Laser (SACLA), Japan's X-ray free electron laser facility. In this review, I describe the damage-free crystal structure analysis, de novo crystal structure determination using single wavelength anomalous dispersion by serial femtosecond crystallography (SFX), and time-resolved X-ray crystallography that have been performed at SACLA.


Asunto(s)
Electrones , Rayos Láser , Cristalografía por Rayos X , Proteínas/química , Difracción de Rayos X , Rayos X
7.
STAR Protoc ; 3(2): 101304, 2022 Jun 17.
Artículo en Inglés | MEDLINE | ID: mdl-35496778

RESUMEN

Myelin provides physical, neurotrophic, and metabolic support for axonal integrity. The thickness of CNS (central nervous system) myelin sheath is usually < one micrometer, which is under or near the detection threshold of the conventional light microscopy. Here, we present a high-resolution transmission electron microscopy-based protocol to assess myelination at the ultrastructural level. We describe sample preparation from mouse tissue, followed by electron microscopic imaging and CNS myelination analysis. This protocol is also useful for analyzing murine PNS myelination. For complete details on the use and execution of this protocol, please refer to Wang et al. (2021).


Asunto(s)
Sistema Nervioso Central , Electrones , Animales , Axones/metabolismo , Sistema Nervioso Central/diagnóstico por imagen , Ratones , Microscopía Electrónica de Transmisión , Vaina de Mielina/metabolismo
8.
J Chem Phys ; 156(12): 124111, 2022 Mar 28.
Artículo en Inglés | MEDLINE | ID: mdl-35364877

RESUMEN

The ground state and excited state electronic properties of chlorophyll (Chl) a and Chl b in diethyl ether, acetone, and ethanol solutions are investigated using quantum mechanical and molecular mechanical calculations with density functional theory (DFT) and time-dependent DFT (TDDFT). Although the DFT/TDDFT methods are widely used, the electronic structures of molecules, especially large molecules, calculated with these methods are known to be strongly dependent on the functionals and the parameters used in the functionals. Here, we optimize the range-separated parameter, µ, of the CAM-B3LYP functional of Chl a and Chl b to reproduce the experimental excitation energy differences of these Chl molecules in solution. The optimal values of µ for Chl a and Chl b are smaller than the default value of µ and that for bacteriochlorophyll a, indicating the change in the electronic distribution, i.e., an increase in electron delocalization, within the molecule. We find that the electronic distribution of Chl b with an extra formyl group is different from that of Chl a. We also find that the polarity of the solution and hydrogen bond cause the decrease in the excitation energies and the increase in the widths of excitation energy distributions of Chl a and Chl b. The present results are expected to be useful for understanding the electronic properties of each pigment molecule in a local heterogeneous environment, which will play an important role in the excitation energy transfer in light-harvesting complex II.


Asunto(s)
Electrones , Clorofila A , Teoría Funcional de la Densidad , Transferencia de Energía
9.
Rev Sci Instrum ; 93(3): 033302, 2022 Mar 01.
Artículo en Inglés | MEDLINE | ID: mdl-35364983

RESUMEN

This paper reviews the main microwave diagnostic techniques and tools adopted in electron cyclotron resonance (ECR) (and others) ion source laboratories, with a special focus on techniques and instruments developed at INFN-LNS. Along with the tools used for optimization of microwave launching (power monitors, spectral analysis, and network analyzers), this paper deals, in particular, with more recent devices on-purpose developed to perform in-plasma analysis, such as absolute density measurements and density profiles retrieval. Among these, the first example of microwave interferometry for ECR compact machines (the VESPRI interferometer at INFN-LNS) will be briefly discussed, in combination with microwave polarimetric techniques based on Faraday rotation detection. More sophisticated microwave techniques are going to be designed and are now at a numerical study stage, e.g., profilometry and imaging via inverse scattering methods (this paper will offer short theoretical bases and first numerical results on 1D profilometry). In the end, the relevance about the implications and interplays of microwave techniques in multidiagnostic systems (microwave, optical, and x-ray domains) will be commented, with a special focus on time resolved microwave measurements and advanced signal processing via wavelet transform, useful for characterization of plasma instabilities.


Asunto(s)
Ciclotrones , Electrones , Microondas , Vibración
10.
Chem Commun (Camb) ; 58(36): 5502-5505, 2022 May 03.
Artículo en Inglés | MEDLINE | ID: mdl-35416818

RESUMEN

The normal 1,3-dipolar cycloaddition between the carbonates of 4-hydroxy-2-cyclopentenones and C,N-cyclic azomethine imines can be switched to an inverse-electron-demand version under Pd(0) catalysis, by in situ generation of HOMO-raised η2-Pd(0)-cyclopentadienone complexes. An array of fused heterocyclic architectures are constructed with high levels of diastereo and enantioselectivity, and diastereodivergent synthesis is well realised by tuning the bifunctional phosphine ligands. In addition, similar reaction with in situ formed thiophene-1,1-dioxide is compatible by using a chiral bisphosphine ligand, and the fused cyclic sulfone frameworks are afforded with high stereoselectivity.


Asunto(s)
Electrones , Iminas , Compuestos Azo , Reacción de Cicloadición , Ligandos , Estereoisomerismo , Tiofenos , Tiosemicarbazonas
11.
J Phys Chem Lett ; 13(16): 3529-3533, 2022 Apr 28.
Artículo en Inglés | MEDLINE | ID: mdl-35420036

RESUMEN

The influence of incremental hydration (≤4) on the electronic resonances of the pyrene anion is studied using two-dimensional photoelectron spectroscopy. The photoexcitation energies of the resonances do not change; therefore, from the anion's perspective, the resonances remain the same, but from the neutral's perspective of the electron-molecule reaction, the resonances decrease in energy by the binding energy of the water molecules. The autodetachment of the resonances shows that hydration has very little effect, showing that even the dynamics of most of the resonances are not impacted by hydration. Two specific resonances do show changes that are explained by the closing of specific autodetachment channels. The lowest-energy resonance leads to efficient electron capture as observed through thermionic emission and evaporation of water molecules (dissociative electron attachment). The implications of low-energy electron capture in dense molecular interstellar clouds are discussed.


Asunto(s)
Electrones , Agua , Aniones/química , Espectroscopía de Fotoelectrones , Pirenos , Agua/química
12.
J Hazard Mater ; 431: 128616, 2022 06 05.
Artículo en Inglés | MEDLINE | ID: mdl-35359112

RESUMEN

The harmful effects of antibiotics on biological denitrification have attracted widespread attention due to their excessive usage. Polymyxin B (PMB) as the typical antimicrobial peptides having been regarded as the "last hope" for treatment of multidrug-resistance bacteria, has also been detected in wastewater. However, little is known about the influence of PMB on aerobic denitrification. In this study, the impact of PMB on aerobic denitrification performance was investigated. Results showed 0.50 mg/L PMB decreased nitrate removal efficiency from 97.4% to 85.3%, and drove denitrifiers to transform more nitrate to biomass instead of producing gas-N. The live/dead staining method showed PMB damaged bacterial membrane. Transcriptome analysis further indicated the key enzymes participating in denitrification and aerobic respiratory chains were suppressed by PMB. To resist the PMB stress, denitrifiers formed thicker biofilm to protect cells from PMB damaging and thus remodeling the central carbon metabolism. Further investigation revealed denitrifiers have different preference on various carbon sources when PMB is present. Subsequently, the underlying mechanism of the distinctive carbon sources preference was explored by the combination of transcriptome and metabolism analysis. Overall, our data suggested denitrifiers have distinctive carbon sources preference under PMB treatment conditions, reminding us that carbon source selection should be cautious in practical applications.


Asunto(s)
Carbono , Desnitrificación , Antibacterianos/farmacología , Carbono/metabolismo , Electrones
13.
Ultramicroscopy ; 237: 113510, 2022 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-35367900

RESUMEN

We investigate potential improvements in using electron cryomicroscopy to image thick specimens with high-resolution phase contrast imaging. In particular, using model experiments, electron scattering theory, Monte Carlo and multislice simulations, we determine the potential for improving electron cryomicrographs of proteins within a cell using chromatic aberration (Cc) correction. We show that inelastically scattered electrons lose a quantifiable amount of spatial coherence as they transit the specimen, yet can be used to enhance the signal from thick biological specimens (in the 1000 to 5000 Å range) provided they are imaged close to focus with an achromatic lens. This loss of information quantified here, which we call "specimen induced decoherence", is a fundamental limit on imaging biological molecules in situ. We further show that with foreseeable advances in transmission electron microscope technology, it should be possible to directly locate and uniquely identify sub-100 kDa proteins without the need for labels, in a vitrified specimen taken from a cell.


Asunto(s)
Electrones , Microscopía por Crioelectrón/métodos , Microscopía Electrónica , Microscopía de Contraste de Fase , Método de Montecarlo
14.
J Chem Theory Comput ; 18(5): 3099-3110, 2022 May 10.
Artículo en Inglés | MEDLINE | ID: mdl-35404607

RESUMEN

Cationic cobaltocenium derivatives are promising components of the anion exchange membranes because of their excellent thermal and alkaline stability under the operating conditions of a fuel cell. Here, we present an efficient modeling approach to assessing the chemical stability of substituted cobaltocenium CoCp2+, based on the computed electronic structure enhanced by machine learning techniques. Within the aqueous environment, the positive charge of the metal cation is balanced by the hydroxide anion through formation of the CoCp2+OH- complexes, whose dissociation is studied within the implicit solvent employing the density functional theory. The data set of about 118 the CoCp2+OH- complexes based on 42 substituent groups characterized by a range of electron-donating (ED) and electron-withdrawing (EW) properties is constructed and analyzed. Given 12 carefully chosen chemistry-informed descriptors of the complexes and relevant fragments, the stability of the complexes is found to strongly correlate with the energies of the highest occupied and lowest unoccupied molecular orbitals, modulated by a switching function of the Hirshfeld charge. The latter is used as a measure of the electron-withdrawing-donating character of the substituents. On the basis of this observation from the conventional regression analysis, two fully connected, feed-forward neural network (FNN) models with different unit structures, called the chemistry-informed (CINN) and the quadratic (QNN) neural networks, together with a support vector regression (SVR) model are developed. Both deep neural network models predict the bond dissociation energies of the cobaltocenium complexes with mean relative errors less than 10.56% and average absolute errors less than 1.63 kcal/mol, superior to the conventional regression and the SVR model prediction. The results show the potential of QNN to efficiently capture more complex relationships. The concept of incorporating the domain (chemical) knowledge/insight into the neural network structure paves the way to applications of machine learning techniques with small data sets, ultimately leading to better predictive models compared to the classical machine learning method SVR and conventional regression analysis.


Asunto(s)
Cobalto , Anticonceptivos Orales Combinados , Electrones , Femenino , Humanos , Aprendizaje Automático , Redes Neurales de la Computación
15.
J Comput Chem ; 43(15): 1000-1010, 2022 Jun 05.
Artículo en Inglés | MEDLINE | ID: mdl-35411548

RESUMEN

The equilibrium between keto and enol forms in acetylacetone and its derivatives is studied using electron delocalization indices and delocalization tensor density. We demonstrate how electron delocalization governs the equilibrium between keto and enol forms. The less stable enols have more distinct double and single bond character in the CCC fragment, while electron delocalization in this fragment is more pronounced in more stable enols. Looking for the origin of such behavior, we considered the one-electron potentials entering the Euler equation for the electron density. We found that electron delocalization is mainly governed by the static exchange potential, which depends on the three-dimensional atomic structure. It, however, does not distinguish differences in electron delocalization in more and less stable enols, the effect arising from the kinetic exchange contribution, which reflects spin-dependent effects in the electron motion. The local depletion of kinetic exchange in the conjugated fragment yields the enhanced electron delocalization along the CCC bonds in more stable enols. Thus, a combination of considered descriptors allowed us to reveal the influence of electron delocalization on the equilibrium between keto and enol forms and showed the significant features of this phenomenon.


Asunto(s)
Alcoholes , Electrones , Cinética
16.
Acc Chem Res ; 55(9): 1290-1300, 2022 May 03.
Artículo en Inglés | MEDLINE | ID: mdl-35414170

RESUMEN

ConspectusCyclometalated iridium(III) complexes are frequently employed in organic light emitting diodes, and they are popular photocatalysts for solar energy conversion and synthetic organic chemistry. They luminesce from redox-active excited states that can have high triplet energies and long lifetimes, making them well suited for energy transfer and photoredox catalysis. Homoleptic tris(cyclometalated) iridium(III) complexes are typically very hydrophobic and do not dissolve well in polar solvents, somewhat limiting their application scope. We developed a family of water-soluble sulfonate-decorated variants with tailored redox potentials and excited-state energies to address several key challenges in aqueous photochemistry.First, we aimed at combining enzyme with photoredox catalysis to synthesize enantioenriched products in a cyclic reaction network. Since the employed biocatalyst operates best in aqueous solution, a water-soluble photocatalyst was needed. A new tris(cyclometalated) iridium(III) complex provided enough reducing power for the photochemical reduction of imines to racemic mixtures of amines and furthermore was compatible with monoamine oxidase (MAO-N-9), which deracemized this mixture through a kinetic resolution of the racemic amine via oxidation to the corresponding imine. This process led to the accumulation of the unreactive amine enantiomer over time. In subsequent studies, we discovered that the same iridium(III) complex photoionizes under intense irradiation to give hydrated electrons as a result of consecutive two-photon excitation. With visible light as energy input, hydrated electrons become available in a catalytic fashion, thereby allowing the comparatively mild reduction of substrates that would typically only be reactive under harsher conditions. Finally, we became interested in photochemical upconversion in aqueous solution, for which it was desirable to obtain water-soluble iridium(III) compounds with very high triplet excited-state energies. This goal was achieved through improved ligand design and ultimately enabled sensitized triplet-triplet annihilation upconversion unusually far into the ultraviolet spectral range.Studies of photoredox catalysis, energy transfer catalysis, and photochemical upconversion typically rely on the use of organic solvents. Water could potentially be an attractive alternative in many cases, but photocatalyst development lags somewhat behind for aqueous solution compared to organic solvent. The purpose of this Account is to provide an overview of the breadth of new research perspectives that emerged from the development of water-soluble fac-[Ir(ppy)]3 complexes (ppy = 2-phenylpyridine) with sulfonated ligands. We hope to inspire the use of some of these or related coordination compounds in aqueous photochemistry and to stimulate further conceptual developments at the interfaces of coordination chemistry, photophysics, biocatalysis, and sustainable chemistry.


Asunto(s)
Iridio , Compuestos Organometálicos , Aminas , Electrones , Transferencia de Energía , Iridio/química , Ligandos , Compuestos Organometálicos/química , Fotoquímica , Solventes , Agua
17.
FEMS Microbiol Ecol ; 98(5)2022 May 06.
Artículo en Inglés | MEDLINE | ID: mdl-35416241

RESUMEN

Cable bacteria (CB) perform electrogenic sulfur oxidation (e-SOx) by spatially separating redox half reactions over centimetre distances. For freshwater systems, the ecology of CB is not yet well understood, partly because they proved difficult to cultivate. This study introduces a new 'agar pillar' approach to selectively enrich and investigate CB populations. Within sediment columns, a central agar pillar is embedded, providing a sediment-free gradient system in equilibrium with the surrounding sediment. We incubated freshwater sediments from a streambed, a sulfidic lake and a hydrocarbon-polluted aquifer in such agar pillar columns. Microprofiling revealed typical patterns of e-SOx, such as the development of a suboxic zone and the establishment of electric potentials. The bacterial communities in the sediments and agar pillars were analysed over depth by PacBio near-full-length 16S rRNA gene amplicon sequencing, allowing for a precise phylogenetic placement of taxa detected. The selective niche of the agar pillar was preferentially colonized by CB related to Candidatus Electronema for surface water sediments, including several potentially novel species, but not for putative groundwater CB affiliated with Desulfurivibrio spp. The presence of CB was seemingly linked to co-enriched fermenters, hinting at a possible role of e-SOx populations as an electron sink for heterotrophic microbes. These findings add to our current understanding of the diversity and ecology of CB in freshwater systems, and to a discrimination of CB from surface and groundwater sediments. The agar pillar approach provides a new strategy that may facilitate the cultivation of redox gradient-dependent microorganisms, including previously unrecognized CB populations.


Asunto(s)
Electrones , Sedimentos Geológicos , Agar , Bacterias/genética , Sedimentos Geológicos/microbiología , Lagos , Oxidación-Reducción , Filogenia , ARN Ribosómico 16S/genética
18.
World J Microbiol Biotechnol ; 38(5): 90, 2022 Apr 15.
Artículo en Inglés | MEDLINE | ID: mdl-35426517

RESUMEN

Pseudomonas aeruginosa (PA) is an electrogenic bacterium, in which extracellular electron transfer (EET) is mediated by microbially-produced phenazines, especially pyocyanin. Increasing EET rate in electrogenic bacteria is key for the development of biosensors and bioelectrofermentation processes. In this work, the production of pyocyanin, Nicotinamide Adenine Dinucleotide (NAD) and NAD synthetase by the electrogenic strain PA-A4 is determined using a Microbial Fuel Cell (MFC). Effects of metabolic inhibition and enhancement of pyocyanin and NAD synthetase on NAD/NADH levels and electrogenicity was demonstrated by short chronoamperometry measurements (0-48 h). Combined overexpression of two intermediate NAD synthetase production genes-nicotinic acid mononucleotide adenyltransferase (nadD) and quinolic acid phosphoribosyltransferase (nadC) genes, which are distant on the PA genomic map, enabled co-transcription and increased NAD synthetase activity. The resulting PA-A4 nadD + nadC shows increases in pyocyanin concentration, NAD synthetase activity, NAD/NADH levels, and MFC potential, all significantly higher than its wild type. Extracellular respiratory mechanisms in PA are linked with NAD metabolism, and targeted increased yield of NAD could directly lead to enhanced EET. A previous attempt at enhancing NAD synthetase for electrogenicity by targeting the terminal NAD synthetase gene (nadE) in standard P. aeruginosa PA01 had earlier been reported. Our work however, poses another route to electrogenicity enhancement in PA using; a combination of nadD and nadC. Further experiments are needed to understand specific intracellular mechanisms governing how over-expression of nadD and nadC induced activity of NadE protein. These findings significantly advance the knowledge of the versatility of NAD biosynthetic genes in PA electrogenicity.


Asunto(s)
NAD , Pseudomonas aeruginosa , Amida Sintasas , Electrones , Ligasas/metabolismo , NAD/metabolismo , Pseudomonas aeruginosa/genética , Pseudomonas aeruginosa/metabolismo , Piocianina
19.
Inorg Chem ; 61(18): 7153-7164, 2022 May 09.
Artículo en Inglés | MEDLINE | ID: mdl-35475617

RESUMEN

Iron complexes with nitrido ligands are of interest as molecular analogues of key intermediates during N2-to-NH3 conversion in industrial or enzymatic processes. Dinuclear iron complexes with a bridging nitrido unit are mostly known in relatively high oxidation states (III/IV or IV/IV), originating from the decomposition of azidoiron precursors via high-valent Fe≡N intermediates. The use of a tetra-NHC macrocyclic scaffold ligand (NHC = N-heterocyclic carbene) has now allowed for the isolation of a series of organometallic µ-nitridodiiron complexes ranging from the mid-valent FeIII-N-FeIII (1) via mixed-valent FeIII-N-FeIV (type 4) to the high-valent FeIV-N-FeIV (type 5) species that are interconverted at moderate potentials, accompanied by axial ligand binding at the FeIV sites. Magnetic measurements and electron paramagnetic resonance spectroscopy showed the homovalent complexes to be diamagnetic and the mixed-valent system to feature an S = 1/2 ground state due to very strong antiferromagnetic coupling. The bonding in the Fe-N-Fe moiety has been further probed by crystallographic structure determination, 57Fe Mössbauer and UV-vis spectroscopies, as well as density functional theory computations, which revealed high covalency and nearly identical Fe-N distances across this redox series. The latter has been rationalized in terms of the nonbonding nature of the combination of Fe dz2 atomic orbitals from which electrons are successively removed upon oxidation, and these redox processes are best described as being metal-centered. The tetra-NHC-ligated µ-nitridodiiron series complements a set of related complexes with single-atom µ-oxido and µ-phosphido bridges, but the Fe-N-Fe core exhibits a comparatively high stability over several oxidation states. This promises interesting applications in view of the manifold catalytic uses of µ-nitridodiiron complexes based on macrocyclic N-donor porphinato(2-) or phthalocyaninato(2-) ligands.


Asunto(s)
Compuestos Férricos , Hierro , Electrones , Compuestos Férricos/química , Hierro/química , Ligandos , Oxidación-Reducción
20.
Phys Chem Chem Phys ; 24(16): 9051-9081, 2022 Apr 20.
Artículo en Inglés | MEDLINE | ID: mdl-35389399

RESUMEN

Important contemporary biological and materials problems often depend on interactions that span orders of magnitude differences in spatial and temporal dimensions. This Tutorial Review attempts to provide an introduction to such fascinating problems through a series of case studies, aimed at beginning researchers, graduate students, postdocs and more senior colleagues who are changing direction to focus on multiscale aspects of their research. The choice of specific examples is highly personal, with examples either chosen from our own work or outstanding multiscale efforts from the literature. I start with various embedding schemes, as exemplified by polarizable continuum models, 3-D RISM, molecular DFT and frozen-density embedding. Next, QM/MM (quantum mechanical/molecular mechanical) techniques are the workhorse of pm-to-nm/ps-to-ns simulations; examples are drawn from enzymes and from nanocatalysis for oil-sands upgrading. Using polarizable force-fields in the QM/MM framework represents a burgeoning subfield; with examples from ion channels and electron dynamics in molecules subject to strong external fields, probing the atto-second dynamics of the electrons with RT-TDDFT (real-time - time-dependent density functional theory) eventually coupled with nuclear motion through the Ehrenfest approximation. This is followed by a section on coarse graining, bridging dimensions from atoms to cells. The penultimate chapter gives a quick overview of multiscale approaches that extend into the meso- and macro-scales, building on atomistic and coarse-grained techniques to enter the world of materials engineering, on the one hand, and cell biology, on the other. A final chapter gives just a glimpse of the burgeoning impact of machine learning on the structure-dynamics front. I aim to capture the excitement of contemporary leading-edge breakthroughs in the description of physico-chemical systems and processes in complex environments, with only enough historical content to provide context and aid the next generation of methodological development. While I aim also for a clear description of the essence of methodological breakthroughs, equations are kept to a minimum and detailed formalism and implementation details are left to the references. My approach is very selective (case studies) rather than exhaustive. I think that these case studies should provide fodder to build as complete a reference tree on multiscale modelling as the reader may wish, through forward and backward citation analysis. I hope that my choices of cases will excite interest in newcomers and help to fuel the growth of multiscale modelling in general.


Asunto(s)
Electrónica , Electrones , Humanos , Modelos Moleculares , Simulación de Dinámica Molecular
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