Oxidation State Of Atoms Research Articles

Effects of Sulfur Amino Acids on Cardiodynamic Parameters of Isolated Rat Heart

Abstract Sulfur-containing amino acids are integral part of molecular mechanisms which underlie many aspects of cellular function and homeostasis, facilitated by reversible changes in oxidation states of sulfur atoms. Dysregulation of these pathways is associated with diverse pathologies, notably of the cardiovascular system, which are typically characterized by inappropriate plasma levels of sulfur-containing amino acids. The aim of this study was to assess the acute, direct effects of sulfur-containing amino acids and inorganic NaHS, as H2S donor, on cardiodynamic parameters in homocysteine treated rats. Moderate hyperhomocysteinemia did not cause significant decrease in myocardial contractility, but our findings suggest that NaHS and L-methionine cause negative effects on cardiac function in hearts of the rats treated with homocysteine, even in a single administration. Further investigations need to be carried out with purpose of better understanding and highlightening the impact of Hcy and sulphur amino acids on cardiac function.

Breakdown of the correlation between oxidation states and core electron binding energies at the sub-nanoscale

X-ray photoelectron spectroscopy is a powerful analytical tool to fingerprint the atomic oxidation state. However, the well-established trend that is found for bulk, ultra-thin films and surface oxides, which is usually characterized by an incremental binding energy shift upon increasing oxidation state, may not apply at the sub-nanoscale where reduced dimensionality and quantum size effects play a relevant role. Here we investigate through a combined experimental and theoretical approach the oxidation of size-selected Ag7 and Ag11 clusters supported on graphene, revealing an anomalous Ag 3d5/2 core level shift trend upon increasing O coverage. We show that the negative core level shift trend typical of Ag reverts back in the case of the highest Ag(III) oxidation state, an effect that is due to the peculiar electronic structure of Ag nano-oxides. Our results highlight the great care needed to extend at the zero-dimensional scale the knowledge acquired for the spectral interpretation of 3D and 2D materials.

Toward an efficient f-in-core/f-in-valence switchable description for DFTB calculations of Ce 4f states in ceria.

A computational protocol is developed for efficient studies of partially reduced redox-active oxides using the self-consistent charge density functional tight-binding method. The protocol is demonstrated for ceria, which is a prototypical reducible oxide material. The underlying idea is to achieve a consistent (and harmonized) set of Slater-Koster (SK) tables with connected repulsive potentials that enable switching on and off the in-valence description of the Ce 4f states without serious loss of accuracy in structure and energetics. The implicit treatment of the Ce 4f states, with the use of f-in-core SK-tables, is found to lead to a significant decrease in computational time. More importantly, it allows for explicit control of the oxidation states of individual Ce atoms. This makes it possible to "freeze" the electronic configuration, thereby allowing the exploration of the energetics for various meta-stable configurations. We anticipate that the outlined strategy can help to shed light on the interplay between the size, shape, and redox activity for nanoceria and other related materials.

Fine-tuning surface oxidation states of ruthenium nanoparticles to enhance hydrogen electrode reactions

The oxidation state of surface atoms on small-sized Ru-NPs can be precisely tuned by NP sizes. The intrinsic activities of the HER/HOR strongly depend on the surface Ru–O structure.

Synthesis and reactivity of alkali metal aluminates bearing bis(organoamido)phosphane ligand.

In this study, we report a group of alkali metal aluminates bearing bis(organoamido)phosphane ligand. The starting complex {[PhP(NtBu)2]AlMe2}Li·OEt2 (1) was prepared by stepwise deprotonation of the parent PhP(NHtBu)2 by nBuLi and AlMe3. Further derivatization of aluminate 1 was performed by the virtual substitution of lithium -{[PhP(NtBu)2]AlMe2}K (2), methyl substituents - {[PhP(NtBu)2]AlH2}Li·THF (3), modification of steric bulk and induction effects on the phosphorus atom - {[tBuP(N-2,6-iPr2C6H3)2]AlMe2}Li·(OEt2)2 (4), and phosphorus atom oxidation state {[Ph(Y)P(NtBu)2]AlMe2}Li (Y = O (5), S (6), Se (7), Te (8)). The structure causing non-covalent interactions in 1-4 were evaluated with the help of theoretical calculations and topological analysis ranging from π-electron system-metal to agostic interactions of various types. The further reactions of 1 with various nucleophiles were found to be a versatile tool for the preparation of iminophosphonamides via the formation of P-E bond (E = Si, Ge, Sn, Pb, P, and C) and followed by P(III) → P(V) tautomeric shift.

Effect of substrate on interfacial electronic properties of ferrocene thin films

Ferrocene molecular thin films on conducting substrates have potential for novel molecular electronic devices. Based on X-ray absorption spectroscopy and photoemission spectroscopic techniques, we have analyzed electronic properties of ferrocene thin films nano-junctions on layered highly oriented pyrolytic graphite (HOPG) and epitaxially grown graphene on Ni(1 1 1) substrates. Fe L edge analysis indicates that layered structure of HOPG has significant impact on room temperature desorption of ferrocene as compared to grapheme on Ni(1 1 1) substrate. C-K edge XAS spectrum reveal that ferrocene molecules do not have preferred orientation for adsorption on grapheme grown on Ni(1 1 1) substrate. In addition, X-ray absorption spectroscopy (XAS) reveals that there is no change in iron atom oxidation state suggesting that ferroence interaction is feeble with grapheme on Ni(1 1 1) substrate and HOPG.

Charge Distribution in Layered Lanthanide-Doped CuCr0.99Ln0.01S2 (Ln = Pr-Tb) Thermoelectric Materials.

The charge distribution study of metal atoms in CuCr0.99Ln0.01S2 (Ln = Pr-Tb) solid solutions was carried out using X-ray photoelectron spectroscopy (XPS). The analysis of the binding energy of S2p, Cu2p, Cr2p, Ln3d and Ln4d levels allows one to determine the oxidation state of atoms. Copper atoms were found to be monovalent. Chromium and lanthanide atoms were found to be in the trivalent state. Sulfur atoms were found to be in the divalent state. Cationic substitution was found to occur via an isovalent mechanism of Cr3+ to Ln3+. The obtained results were used for the interpretation of the Seebeck coefficient increase for CuCr0.99Ln0.01S2 solid solutions in contrast to the initial CuCrS2 matrix. The largest Seebeck coefficient values of 142 and 148 µV/K were observed at 500 K for CuCr0.99Sm0.01S2 and CuCr0.99Pr0.01S2, respectively. The obtained values are 1.4 times greater in comparison with those for the initial matrix (105 µV/K).

Advanced Electron Microscopy Techniques for PGM-Free Catalyst Characterization

Hydrogen fuel cells currently rely on expensive platinum group metal nanoparticle catalysts [1]. For green hydrogen production and utilization to become widely commercially viable, the cost of the devices that produce and utilize hydrogen must be significantly reduced. Platinum group metal-free (PGM-free) catalysts have the potential to greatly reduce this cost, and materials consisting of single transition metal atoms embedded in a nitrogen-doped graphitic carbon structure have shown particular promise for use as fuel cell cathodes [2]. A better understanding of the active site properties in these materials is still needed, however, to improve their stability and design new active site structures with enhanced properties [3]. Due to the atomic-scale nature of the active sites in these materials, scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) have proven invaluable for demonstrating their atomically dispersed nature and composition [4]. Conventional STEM techniques have limited ability to correlate the local bonding environment and oxidation state of the metal atoms, for example, or track changes in the catalyst structure both during synthesis and as a result of cycling, which would provide a deeper understanding of the relationship between active site and catalyst properties.Here, we demonstrate advanced electron microscopy techniques that provide both enhanced and previously inaccessible information about PGM-free catalysts and their active sites. We show developments in automated identification of metal atom positions, which we use both to generate statistics about interatomic distances and to automatically position the STEM probe on individual atoms for EELS data acquisition. The former allows information about the presence of dual-metal site structures to be extracted, for example, and the latter allows compositional information with improved SNR to be obtained. Rapid automatic probe positioning also presents the opportunity for measuring the effect of local bonding environment on metal atom oxidation state, which cannot be obtained manually since these sites are typically unstable under the beam. In addition, we will show identical-location STEM (IL-STEM) techniques that allow the evolution of catalyst morphology and properties to be tracked at high resolution across synthesis steps and accelerated stress tests [5]. In particular, we use IL-STEM imaging and EELS to track deposition of graphitic material on the surface of a PGM-free catalyst that significantly improves the material’s durability, as well as track the change in the nanoscale graphitic carbon structure of the material as a function of electrochemical cycling. By providing access to enhanced compositional and bonding state information, as well as the ability to track properties as a material evolves, these techniques will advance our knowledge of PGM-free catalysts and enable better control over their properties in the future, accelerating wide-spread use of hydrogen fuel cells [6].

Distribution and diversity of ROS-generating enzymes across the animal kingdom, with a focus on sponges (Porifera)

BackgroundReactive derivatives of oxygen (reactive oxygen species; ROS) are essential in signalling networks of all aerobic life. Redox signalling, based on cascades of oxidation–reduction reactions, is an evolutionarily ancient mechanism that uses ROS to regulate an array of vital cellular processes. Hydrogen peroxide (H2O2) and superoxide anion (O2•−) are employed as signalling molecules that alter the oxidation state of atoms, inhibiting or activating gene activity. Here, we conduct metazoan-wide comparative genomic assessments of the two enzyme families, superoxide dismutase (SOD) and NADPH oxidases (NOX), that generate H2O2 and/or O2•− in animals.ResultsUsing the genomes of 19 metazoan species representing 10 phyla, we expand significantly on previous surveys of these two ancient enzyme families. We find that the diversity and distribution of both the SOD and NOX enzyme families comprise some conserved members but also vary considerably across phyletic animal lineages. For example, there is substantial NOX gene loss in the ctenophore Mnemiopsis leidyi and divergent SOD isoforms in the bilaterians D. melanogaster and C. elegans. We focus particularly on the sponges (phylum Porifera), a sister group to all other metazoans, from which these enzymes have not previously been described. Within Porifera, we find a unique calcium-regulated NOX, the widespread radiation of an atypical member of CuZnSOD named Rsod, and a novel endoplasmic reticulum MnSOD that is prevalent across aquatic metazoans.ConclusionsConsidering the precise, spatiotemporal specificity of redox signalling, our findings highlight the value of expanding redox research across a greater diversity of organisms to better understand the functional roles of these ancient enzymes within a universally important signalling mechanism.

In-situ growth of iron oxides with MIL-100(Fe) enhances its adsorption for selenite

Composite materials of porous MIL-100(Fe) and bulk iron oxides, including MIL-100(Fe)@Aka and MIL-100(Fe)@Hem, were prepared through in-situ growth of iron oxides and MIL-100(Fe) using hydrothermal method. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric (TG) and pore analysis revealed two phases of crystal MIL-100(Fe) and akaganeite/hematite in the composite materials. Iron oxides were not only cemented with the surface of MIL-100(Fe) but also integrated into the pores of MIL-100(Fe). Especially, the hematite was likely to get more favor to in-situ grow with MIL-100(Fe) and form the well-crystallized composite. Compared with MIL-100(Fe), MIL-100(Fe)@Aka exhibited more stable surface charge in the pH range of 3.0–8.0, and MIL-100(Fe)@Hem displayed a higher density of active sites. Both MIL-100(Fe)@Aka and MIL-100(Fe)@Hem showed spontaneous and exothermal adsorption for Se(IV), which could be well described by the linear driven forces model. MIL-100(Fe)@Aka and MIL-100(Fe)@Hem had an obvious synergistic effect on Se(IV) adsorption. The introduction of akaganeite and hematite into MIL-100(Fe) could enhance its adsorption capacity for Se(IV) by a maximum of 154% and 153% respectively, and the saturated adsorption capacity of MIL-100(Fe)@Hem0.1 was up to 301.93 mg/g as fitted by Sips model. The X-ray photoelectron spectrum (XPS) of external-electron revealed that the oxidation state of Fe atoms decreased after adsorbing Se(IV). The findings in this study are expected to reveal the synergistic effect of porous MIL-100(Fe) and bulk iron oxides for greatly improving the adsorption capacity towards pollutants, and provide some guidance for the development of effective adsorbents to be used in environmental remediation.

A single-atom library for guided monometallic and concentration-complex multimetallic designs.

Atomically dispersed single-atom catalysts have the potential to bridge heterogeneous and homogeneous catalysis. Dozens of single-atom catalysts have been developed, and they exhibit notable catalytic activity and selectivity that are not achievable on metal surfaces. Although promising, there is limited knowledge about the boundaries for the monometallic single-atom phase space, not to mention multimetallic phase spaces. Here, single-atom catalysts based on 37 monometallic elements are synthesized using a dissolution-and-carbonization method, characterized and analysed to build the largest reported library of single-atom catalysts. In conjunction with in situ studies, we uncover unified principles on the oxidation state, coordination number, bond length, coordination element and metal loading of single atoms to guide the design of single-atom catalysts with atomically dispersed atoms anchored on N-doped carbon. We utilize the library to open up complex multimetallic phase spaces for single-atom catalysts and demonstrate that there is no fundamental limit on using single-atom anchor sites as structural units to assemble concentration-complex single-atom catalyst materials with up to 12 different elements. Our work offers a single-atom library spanning from monometallic to concentration-complex multimetallic materials for the rational design of single-atom catalysts.

Mining Knowledge from Crystal Structures: Oxidation States of Oxygen-Coordinated Metal Atoms in Ionic and Coordination Compounds.

We propose a universal scheme for predicting the oxidation states of metal atoms in ionic and coordination compounds with a small set of structural descriptors, which include the parameters of atomic Voronoi polyhedra. The scheme has been trained and checked with more than 35,000 crystal structures containing more than 90,000 metal atoms in the oxygen environment. The accuracy of the prediction exceeded 95%; we have detected a number of wrong oxidation states and incorrect chemical compositions in the crystallographic databases using this scheme. The scheme is easily extendable to any kind of atomic environment and can be used to search for correlations between geometrical and physical properties of crystal structures.

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Photoaging phenomena of biodegradable polybutylene succinate and conventional low density polyethylene by artificial weathering – A comparative surface study

Polybutylene succinate (PBS) is a promising eco-friendly alternative to many conventional plastics. It is not intended for outdoor use when a longer shelf life is desired. Research about the weatherability of PBS is important to expand its applicability. In the present study, the degree of aging on injection-molded sheets of biobased PBS and additive-free LDPE was investigated. These were subjected to accelerated photo-aging by 14-, 28-, and 56-days daylight exposure and 7-days UV irradiation. The comparison with LDPE confirmed that photo-initiated degradation processes occurred. The aging phenomena were monitored by atomic force microscopy, contact angle goniometry, Fourier-transform infrared spectroscopy, and synchrotron-assisted X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure. The results demonstrated effects in early stages of aging for PBS on surface morphology, roughness and wetting behavior. No significant chemical changes were detected on the surface of exposed PBS samples. For LDPE chemical changes in sp2/sp3 ratio, atomic oxidation state, and wetting behavior were observed for UV- and daylight weathered LDPE. However, no effects were apparent on the LDPE surface morphology. The biobased PBS is thus chemically more stable, but more surface-sensitive to accelerated photoaging than the LDPE used here.

Faraday law, oxidation numbers, and ionic conductivity: The role of topology.

Faraday's experiment measures-within a modern view-the charge adiabatically transported over a macroscopic distance by a given nuclear species in insulating liquids: the reason why it is an integer is deeply rooted in topology. Whole numbers enter chemistry in a different form: atomic oxidation states. They are not directly measurable and are determined instead from an agreed set of rules. Insulating liquids are a remarkable exception; Faraday's experiment indeed measures the oxidation numbers of each dissociated component in the liquid phase, whose topological values are unambiguous. Ionic conductivity in insulating liquids is expressed in terms of the autocorrelation function of the fluctuating charge current at a given temperature in a zero electric field; topology plays a major role in this important observable as well. The existing literature deals with the above issues by adopting the independent-electron framework; here, I provide the many-body generalization of all the above findings, which, furthermore, allows for compact and very transparent notations and formulas.

Multisublattice cluster expansion study of short-range ordering in iron-substituted strontium titanate

Owing to the challenges in obtaining realistic atomic configurations in large chemical phase spaces, it is not straightforward to describe structure–property relations in materials exhibiting configurational disorder. One example is iron-substituted strontium titanate (SrTi1−xFexO3−d, STF), a promising perovskite-derivative cathode material in solid oxide fuel cells that exhibits full solid solubility 0≤x≤1 and a tendency to exhibit short-range order. Here we demonstrate a multisublattice cluster expansion (CE) framework and apply it to STF across the full composition range. The CE approach is distinct from more traditional CE formulations in that clusters are defined explicitly by the chemical species distributed among multiple sublattices, rather than via cluster functions of occupation variables with decoration. The modified CE approach makes it easy to distinguish meaningful chemical interactions that are harder to extract from conventional CE, since for the latter chemical identity in a cluster is expressed as a product of site occupations. The least absolute shrinkage and selection operator (LASSO) is implemented as a regression analysis tool to select key clusters and avoid overfitting. We demonstrate this formulation on STF, and show that it can accurately predict configurational energies in comparison to conventional CE. From the key clusters, we identify that short-range ordering between substitutional Fe and oxygen vacancies (VO) results in the formation of Fe–VO strings. In addition, we consider the stability of STF through CE-based Monte Carlo (MC) simulations and confirm the presence of superstructures that were previously observed in transmission electron microscopy. Analysis of atomic configurations from MC samples reveals variations in the oxidation state of Fe atoms, which can be explained by the ordering tendency of Fe and VO. The cluster description and selection formalism described here may be applied to other disordered multisublattice systems for accurate and efficient material modeling.

Supercapacitor properties of V10O14(OH)2 and reduced graphene oxide hybrids: Experimental and theoretical insights

In this work, V10O14(OH)2 nanostructure and its hybrid with reduced graphene oxide (rGO/V10O14(OH)2) have been synthesized by a simple hydrothermal process, and the supercapacitance property has been explored. The material's crystal structure, surface morphology, elemental compositions, and oxidation state of metal atoms are properly characterized. The structure and electronic properties of V10O14(OH)2 and rGO/V10O14(OH)2 are presented using Density Functional Theory (DFT) investigations. Using the cyclic voltammetry (CV) technique, the capacitance of the rGO/V10O14(OH)2 hybrid was found to be 558 Fg−1 at a scan rate of 1 mV/s, which is 2.9 times greater than the capacitance of the V10O14(OH)2 material. The hybrid material provides 94% operational stability over 5000 cycles. From the Trassatti plot, the capacitance contribution of rGO/V10O14(OH)2 and V10O14(OH)2 are estimated, and found that the maximum capacitance contribution is due to diffusion-controlled pseudocapacitance phenomena, i.e., 87.5% and 95.9%, respectively. Enhanced electronic states near Fermi level and improved quantum capacitance for the hybrid structure justify the superior charge storage performance of the integrated structure (rGO/ V10O14(OH)2) as observed in the experiment. Also, the mobility of the electrolyte ions increases in the hybrid structure due to lower diffusion energy barrier leading to better charge transfer kinetics.

Invariance principles in the theory and computation of transport coefficients

In this work, we elaborate on two recently discovered invariance principles, according to which transport coefficients are, to a large extent, independent of the microscopic definition of the densities and currents of the conserved quantities being transported (energy, momentum, mass, charge). The first such principle, gauge invariance, allows one to define a quantum adiabatic energy current from density-functional theory, from which the heat conductivity can be uniquely defined and computed using equilibrium ab initio molecular dynamics. When combined with a novel topological definition of atomic oxidation states, gauge invariance also sheds new light onto the mechanisms of charge transport in ionic conductors. The second principle, convective invariance, allows one to extend the analysis to multi-component systems. These invariance principles can be combined with new spectral analysis methods for the current time series to be fed into the Green–Kubo formula to obtain accurate estimates of transport coefficients from relatively short molecular dynamics simulations.Graphic abstract

Mechanisms for Pressure-Induced Isostructural Phase Transitions in EuO.

We study pressure-induced isostructural electronic phase transitions in the prototypical mixed valence and strongly correlated material EuO using the global-hybrid density functional theory. The simultaneous presence in the valence of highly localized d- and f-type bands and itinerant s- and p-type states, as well as the half-filled f-type orbital shell with seven unpaired electrons on each Eu atom, have made the description of the electronic features of this system a challenge. The electronic band structure, density of states, and atomic oxidation states of EuO are analyzed in the 0-50GPa pressure range. An insulator-to-metal transition at about 12GPa of pressure was identified. The second isostructural transition at approximately 30-35GPa, previously believed to be driven by an oxidation from Eu(II) to Eu(III), is shown instead to be associated with a change in the occupation of the Eu d orbitals, as can be determined from the analysis of the corresponding atomic orbital populations. The Eu d band is confined by the surrounding oxygens and split by the crystal field, which results in orbitals of e_{g} symmetry (i.e., d_{x^{2}-y^{2}} and d_{2z^{2}-x^{2}-y^{2}}, pointing along the Eu-O direction) being abruptly depopulated at the transition as a means to alleviate electron-electron repulsion in the highly compressed structures.

Surface Pourbaix diagram of AgPd nanoalloys and its application in formate oxidation reaction

Surface Pourbaix diagrams for 38-atom AgPd nanoalloys with different Ag/Pd ratio are constructed based on the density functional theory calculations, with an increasing electrode potential, the adsorbed hydroxides increase on the surface of nanoparticle and convert to oxygen atoms partially sunk into subsurface. AgPd nanoalloys with a core-shell structure have an improved oxidation resistance compared with pure nanoparticle and Ag atoms on nanoalloys surface could suppress Pd dissolution and oxidation. It is newfound that a substitutional introduction of Pd atoms into the core of AgPd nanoalloys could suppress the oxide formations and increase the oxidation resistance, and a substitutional introduction of Ag atoms onto the surface of Pd38 nanoparticle could suppress Pd dissolution. Among all the calculated AgPd nanoalloys, Ag18Pd20 has an excellent durability against electrochemical dissolution and oxidation. Experimentally, the activity of as-synthesized Ag48Pd52 nanoalloy notably increases with increasing the upper limit potential from 0.3 to 0.5 V under cyclic voltammetry test of formate oxidation reaction (FOR). Increased oxidation state of Ag atoms on electrocatalyst surface, which is confirmed by Mulliken charge analysis, has been identified as the key to prompt the FOR activity enhancement.