Specific Binding Energy Research Articles

Targeting an Old Foe for Cancer: A Molecular Dynamics Perspective to Unravel the Specific Binding Nature of 2-Methoxy Estradiol to Human β-Tubulin Isotypes.

Microtubules, composed of α- and β-tubulin subunits are crucial for cell division with their dynamic tissue-specificity which is dictated by expression of isotypes. These isotypes differ in carboxy-terminal tails (CTTs), rich in negatively charged acidic residues in addition to the differences in the composition of active site residues. 2-Methoxy estradiol (2-ME) is the first antimicrotubule agent that showed less affinity toward hemopoietic-specific β1 isotype consequently preventing myelosuppression toxicity. The present study focuses on the MD-directed conformational analysis of 2-ME and estimation of its binding affinity in the colchicine binding pocket of various β-tubulin isotypes combined with the α-tubulin isotype, α1B. AlphaFold 2.0 was used to predict the 3D structure of phylogenetically divergent human β-tubulin isotypes in dimer form with α1B. The dimeric complexes were subjected to induced-fit docking with 2-ME. The statistical analysis of docking showed differences in the binding characteristics of 2-ME with different isotypes. The replicas of atom-based molecular dynamic simulations of the best conformation of 2-ME provided insights into the molecular-level details of its binding pattern across the isotypes. Furthermore, the MM/GBSA analyses revealed the specific binding energy profile of 2-ME in β-tubulin isotypes. It also highlighed, 2-ME exhibits the lowest binding affinity toward the β1 isotype as supported by experimental study. The present study may offer useful information for designing next-generation antimicrotubule agents that are more specific and less toxic.

Oxygen vacancy healing boosts the piezoelectricity of bone scaffolds.

Although barium titanate (BaTiO3) presented tremendous potential in achieving self-powered stimulation to accelerate bone repair, pervasive oxygen vacancies restricted the full play of its piezoelectric performance. Herein, BaTiO3-GO nanoparticles were synthesized by the in situ growth of BaTiO3 on graphene oxide (GO), and subsequently introduced into poly-L-lactic acid (PLLA) powders to prepare PLLA/BaTiO3-GO scaffolds by laser additive manufacturing. During the synthesis process, CO and C-OH in GO would respectively undergo cleavage and dehydrogenation at high temperature to form negatively charged oxygen groups, which were expected to occupy positively charged oxygen vacancies in BaTiO3 and thereby inhibit the formation of oxygen vacancies. Moreover, GO could be partially reduced to reduced graphene oxide, which could act as a conductive phase to facilitate polarization charge transfer, thus further improving the piezoelectric performance. The results showed that the oxygen peak at the specific electron binding energy in O 1s declined from 54.4% to 14.6% and the Ti3+ peak that was positively correlated with oxygen vacancies apparently weakened for BaTiO3-GO, illustrating that the introduced GO significantly decreased the oxygen vacancy. As a consequence, the piezoelectric current of PLLA/BaTiO3-GO increased from 80 to 147.3 nA compared with that of PLLA/BaTiO3. The enhanced piezoelectric current effectively accelerated cell differentiation by upregulating alkaline phosphatase expression, calcium salt deposition and calcium influx. This work provides a novel insight for the design of self-powered stimulation scaffolds for bone regeneration.

Temperature effects, energy shifts, and band entropies of Si semiconductors

AbstractUnderstanding the electronic properties of silicon semiconductors is important for the preparation of high‐performance semiconductor materials. We calculated the band entropies, electronic structures, and bonding properties of a silicon semiconductor using density functional theory and the binding‐energy and bond‐charge model. The relationship between Si energy and temperature was studied using the tight binding (TB) approximation and bond‐order‐length‐strength (BOLS) theory (BOLS‐TB), with the Si (111) surface as an example. The specific binding energies and bonding properties of Si atoms in different surface atomic layers are discussed by analyzing the X‐ray photoelectron spectra of the Si (111) surface at 953 and 1493 K. This study improves our understanding of how surface properties reflect local bonding states and deepens our understanding of how atomic‐relaxation‐derived Hamiltonian perturbations and temperature influence the binding energy of the surface region. It also contributes to the development of Si‐based semiconductor materials by providing new ideas and methods.

Mechanical activation of coal gasification fine slag and mechanical and thermal properties of coal gasification fine slag–poly(vinyl chloride) composites

To facilitate the high-value utilization of activate coal gasification fine slag (CGFS), a wet mechanical activation process was used. As a result of this treatment, CGFS samples with different particle size distributions were obtained. The effects of mechanical activation on various physical and chemical properties of CGFS were investigated, including its particle size distribution, mineral composition, specific surface area, pore size, crystallinity, particle morphology, chemical bonding, and binding energy. Poly(vinyl chloride) (PVC)/CGFS composites were prepared via a melt blending process, and their mechanical and thermal properties were evaluated. It was found that with increasing levels of mechanical activation, the CGFS particle size distribution became more concentrated and the particle spacing became more uniform. With the increasing mechanical activation, the crystallinity was found to decrease and the content of amorphous mineral matter (such as SiO2 and Al2O3) increased. The observed increase in specific surface area and decrease in average pore diameter due to the mechanical activation was seen to lead to an increase in the number of active sites. The produced PVC/CGFS composite materials were found to exhibit good mechanical properties and dynamic thermal stability. The thermal stability of the PVC composites was also found to improve relative to the composites produced without the use of mechanical activation.

Enhanced hole mobility-lifetime product in selenium-added CdTe compounds

An improved detector performance for 2% selenium-added CdZnTe(CZT) was observed and explained by the reduced concentration of a deep-level hole trap, which was confirmed by photoluminescence measurements of CdZnTeSe(CZTS) and CdTeSe(CTS). The hole lifetime in CZTS was found to be 2.18μs in the selenium-containing material, which is much longer than that typically measured by 10–100 times. The prolonged lifetime of hole carriers is likely caused by the disappearance of hole trapping at a specific binding energy of 1.1-eV below the conduction band. Also, the enhanced pulse height spectra of CZTS gamma-ray detectors were explained in terms of the ratio of electron and hole mobility-lifetime products. Cu-migrated patterns are used for the first time to reveal sub-grains and their networks in CZT and CZTS. Based on qualitative analysis, the Cu-migrated patterns in CZT and CZTS showed similar results.

Biophysical modeling indicates a high affinity of ethyl esters of omega-3 polyunsaturated fatty acids to the enzymes of the pro-inflammatory arachidonic acid cascade

Background. Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) are widely used in modern cardiology. The anti-inflammatory effect of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is realized, in particular, by modulating the activity of the arachidonic acid (ARA) cascade.Objective: to conduct biophysical analysis of the interactions of various forms of PUFAs (ARA, EPA, DHA, EPA and DHA ethyl esters) with three target proteins-enzymes of the ARA cascade (cyclooxygenase-1 (COX-1), COX-2, 5-lipoxygenase (5-LPOG)).Material and methods. The minimization of the energy of the ligand-receptor complexes at various initial positions of the molecule relative to the receptor pocket and the molecular energy profiles of the protein (the energy of side chain transfer from solvent to protein) were calculated using the ECMMS package.Results. EPA and DHA ethyl esters were characterized by significantly higher absolute values of specific binding energies of target proteins than ARA or simply EPA/DHA. For example, in the case of COX-2, EPA, DHA and EPA ethyl ester had similar ∆∆G values (–3.0...–3.1 kcal/mol), while the COX-2 complex with DHA ethyl ester was somewhat more stable (∆∆G = –3.4 kcal/mol). In the case of the 5-LPOG enzyme, the complex with EPA ethyl ester was the most stable (∆∆G = –1.62 kcal/mol). Higher absolute binding energies indicate a higher affinity of EPA and DHA ethyl esters to enzymes of the ARA cascade.Conclusion. The results suggest that the high affinity of EPA and DHA ethyl esters to the enzymes of the ARA cascade is one of the molecular bases of therapeutic efficacy of ω-3 PUFAs with high degree of standardization.

Measurement of the specific and non-specific binding energies of Mg2+ to RNA

Determining the non-specific and specific electrostatic contributions of magnesium binding to RNA is a challenging problem. We introduce a single-molecule method based on measuring the folding energy of a native RNA in magnesium and at its equivalent sodium concentration. The latter is defined so that the folding energy in sodium equals the non-specific electrostatic contribution in magnesium. The sodium equivalent can be estimated according to the empirical 100/1 rule (1 M NaCl is equivalent to 10 mM MgCl2), which is a good approximation for most RNAs. The method is applied to an RNA three-way junction (3WJ) that contains specific Mg2+ binding sites and misfolds into a double hairpin structure without binding sites. We mechanically pull the RNA with optical tweezers and use fluctuation theorems to determine the folding energies of the native and misfolded structures in magnesium (10 mM MgCl2) and at the equivalent sodium condition (1 M NaCl). While the free energies of the misfolded structure are equal in magnesium and sodium, they are not for the native structure, the difference being due to the specific binding energy of magnesium to the 3WJ, which equals ΔG≃ 10 kcal/mol. Besides stabilizing the 3WJ, Mg2+ also kinetically rescues it from the misfolded structure over timescales of tens of seconds in a force-dependent manner. The method should generally be applicable to determine the specific binding energies of divalent cations to other tertiary RNAs.

Relative Stability of Boron Planar Clusters in Diatomic Molecular Model.

In the recently introduced phenomenological diatomic molecular model imagining the clusters as certain constructions of pair interatomic chemical bonds, there are estimated specific (per atom) binding energies of small all-boron planar clusters Bn, n = 1–15, in neutral single-anionic and single-cationic charge states. The theoretically obtained hierarchy of their relative stability/formation probability correlates not only with results of previous calculations, but also with available experimental mass-spectra of boron planar clusters generated in process of evaporation/ablation of boron-rich materials. Some overestimation in binding energies that are characteristic of the diatomic approach could be related to differences in approximations made during previous calculations, as well as measurement errors of these energies. According to the diatomic molecular model, equilibrium binding energies per B atom and B–B bond lengths are expected within ranges 0.37–6.26 eV and 1.58–1.65 Å, respectively.

Understanding the Energetic Components Influencing the Thermodynamic Quantities of Carbonic Anhydrase Protein upon Ligand Binding

AbstractWe perform structural analysis and calculate the vibrational energy diffusivities, represented as heat‐communication map, between a carbonic anhydrase II and its binding inhibitor benzosulfonamide, to identify critical residues involved in the secondary and tertiary adaptations surrounding the active site, such as HID95, HIE118, HID93, THR197, and HIE198. Notably, the water molecules surrounding the active sites play an essential part in the energy flow. The stability of the docked ligand is assessed using its structural deviation and free energy calculation. Additionally, density functional theory calculations are used to evaluate specific binding energies, resulting in prominent residues such as THR197, THR198, and HIE118 with high binding potential to the benzosulfonamide ligand.

OBTAINING NEUTRON MATTER AND HYPERHEAVY NUCLEI: POSSIBLE QUANTUM-TECHNOLOGICAL INSTRUMENTAL APPROACHES

Possible mechanisms of creation of both hyperheavy nuclei by electron-nuclear collapse and neutron matter by condensation of ultracold neutrons are discussed. The fundamental possibility of the existence of such objects was previously substantiated by A.B.Migdal, who suggested that the known set of proton-neutron nuclei with mass numbers from 0 to 300 and a maximum specific binding energy of about 8 MeV / nucleon at A≈60 corresponds to the first region, beyond which (starting from about the charge Z≈ ( hc/e2 )3/2 ≈1600 ) there is an additional region describing a possible state of nuclear matter, stabilized by a pion condensate. In this region, the maximum specific energy corresponds to ≈15 MeV / nucleon at A ≈ 100000. It is shown that neutron matter can be obtained under certain conditions, and its systematization can be realized as an addition to the Periodic Table. When solving such problems, it becomes quite real to study not only physical, but also chemical, and possibly engineering and technical properties. Analysis shows that the stability of neutron matter at the microlevel is ensured by the Tamm interaction and the Hund beta equilibrium. Such matter can be quite stable not only on the mega-level (neutron stars) due to gravitational interaction, as was a priori assumed earlier, but also on the scale of "ordinary" matter. The process of neutronization is possible not only with critical gravitational interaction, but also by other mechanisms (supercritical increase in the atomic number of elements due to electron-nuclear collapse and condensation of ultracold neutrons), which opens the way to the fundamental possibility of obtaining both neutron matter in laboratory conditions and superheavy nuclei. Based on the works of Migdal, Tamm and Hund, the possibility of the existence of stable neutron matter (with Z >> 175, N >> Z, A> 10 3 -10 5 and a size of 200-300 femtometers and more) is argued at the microlevel, and not only at the mega-level, as is now considered in astrophysics. A critical analysis of the well-established concept of the minimum possible mass of neutron stars is carried out. The following quantum technological approaches to the realization of UCN condensation are proposed: 1. Slow isothermal compression; 2. Refrigerator for dissolving helium-3 and helium-4; 3. Use of a conical concentrator for UCN focusing (Vysotskii cone); 4. Magnetic trap; 5. Additional UCN laser cooling. Neutron matter is considered as a potential cosmological candidate for dark matter. One should take into account the possibility of the formation of fragments of neutron matter as dark matter (neutral, femto-, pico- and nanoscale, the cooling of relics makes it difficult to detect them by now) already at the initial origin of the Universe, which is the dominant process. The observable part of the Universe is formed by the residual part of protons, and then by decayed single neutrons and unstable fragments of neutron matter (with Z> 175, N >> Z, but A <10 3 -10 5 ).

Role of F124 in the inhibition of Bacillus firmus K-1 Xyn11A by monomeric aromatic phenolic compounds

This study aimed to investigate the inhibitory effect of monomeric aromatic phenolic compounds on Xyn11A and its F124A mutant. The inhibitory assay showed gallic acid as the most potent inhibitor for the WT. Conversely, gallic acid completely lost its inhibitory effect and resistance to the other compounds increased significantly in the F124A mutant. Molecular docking revealed that phenolic compounds inhibited WT by simultaneously binding to E78, R112, and F124. The pi-pi stacking of F124 and aromatic rings of phenolic compounds mediated the hydrogen bonds formed between phenolic inhibitors and E78. Gallic acid's strongest inhibitory effects in WT may be due to the high number of hydroxyl groups. However, in F124A, the phenolic compounds bound tyrosine residues sitting far from the catalytic site. Gallic acid's binding to Y69, which is furthest away from the catalytic site and highest specific binding energy, may have contributed to gallic acid's loss of inhibitory effects in F124A.

Computer simulation of dealloying in Cu-Pt nanoparticles

Two basic alternative atomistic simulation methods (molecular dynamics and Monte-Carlo) have been used to reproduce the dealloying phenomenon in Cu-Pt nanoalloys. Using the Gupta (tight-binding) potential, we simulated nanoparticles consisting initially of 1500 Cu and 1500 Pt atoms. The involved programs propose search and following removing Cu atoms with the lowest specific binding energies. We have found that as a result of dealloying the particle surface layer is really enriched with Pt atoms. However the particle core keeps in general the structure of the initial nanoalloy. This effect is especially noticeable in molecular dynamics simulation. We have also established that dealloying results in formation of a defected particle structure (vacancies, first of all). Presumably, just such an effect yields the porous structure of bigger Cu-Pt particles in laboratory experiments on dealloying.

Energetics and kinetics of substrate analog-coupled staphylococcal nuclease folding revealed by a statistical mechanical approach

Protein conformational changes associated with ligand binding, especially those involving intrinsically disordered proteins, are mediated by tightly coupled intra- and intermolecular events. Such reactions are often discussed in terms of two limiting kinetic mechanisms, conformational selection (CS), where folding precedes binding, and induced fit (IF), where binding precedes folding. It has been shown that coupled folding/binding reactions can proceed along both CS and IF pathways with the flux ratio depending on conditions such as ligand concentration. However, the structural and energetic basis of such complex reactions remains poorly understood. Therefore, we used experimental, theoretical, and computational approaches to explore structural and energetic aspects of the coupled-folding/binding reaction of staphylococcal nuclease in the presence of the substrate analog adenosine-3',5'-diphosphate. Optically monitored equilibrium and kinetic data, combined with a statistical mechanical model, gave deeper insight into the relative importance of specific and Coulombic protein-ligand interactions in governing the reaction mechanism. We also investigated structural aspects of the reaction at the residue level using NMR and all-atom replica-permutation molecular dynamics simulations. Both approaches yielded clear evidence for accumulation of a transient protein-ligand encounter complex early in the reaction under IF-dominant conditions. Quantitative analysis of the equilibrium/kinetic folding revealed that the ligand-dependent CS-to-IF shift resulted from stabilization of the compact transition state primarily by weakly ligand-dependent Coulombic interactions with smaller contributions from specific binding energies. At a more macroscopic level, the CS-to-IF shift was represented as a displacement of the reaction "route" on the free energy surface, which was consistent with a flux analysis.

Understanding hydrogen retention in damaged tungsten using experimentally-guided models of complex multispecies evolution

Fuel retention in plasma facing tungsten components is a critical phenomenon affecting the mechanical integrity and radiological safety of fusion reactors. It is known that hydrogen can become trapped in small defect clusters, internal surfaces, dislocations, and/or impurities, and so it is common practice to seed W subsurfaces with irradiation defects in an attempt to precondition the system to absorb hydrogen. The amount of H can later be tallied by performing careful thermal desorption tests where released temperature peaks are mapped to specific binding energies of hydrogen to defect clusters and/or microstructural features of the material. While this provides useful information about the potential trapping processes, modeling can play an important role in elucidating the detailed microscopic mechanisms that lead to hydrogen retention in damaged tungsten. In this paper, we develop a detailed kinetic model of hydrogen penetration and trapping inspired by recent experiments combining ion irradiation, hydrogen plasma exposure, and thermal desorption. We use the stochastic cluster dynamics method to solve the system of coupled partial differential equations representing the mean field description of the multispecies system. The model resolves the spatial distribution of defects and hydrogen clusters during the three processes carried out experimentally and is parameterized with information from atomistic calculations. We find that the calculated thermal desorption spectra are broadly characterized by three H emission regions: (i) a low temperature one where dislocations are the main contributors to the release peaks; (ii) an intermediate one governed by hydrogen release from small overpressurized clusters with multiple overlapping peaks, and (iii) a high temperature one defined by clean isolated emission peaks from large underpressurized bubbles. These three temperature intervals are seen to largely correlate with the depth at which the clusters are found. The relevance of the ‘super abundant’ vacancy mechanism is assessed, finding that its main role is to transfer more clusters from the intermediate to the high temperature regions as its relevance increases. We find this picture to be in very good agreement with the experiments, adding confidence to the predictive potential of the models and their useto understand irradiation damage and plasma exposure effects in plasma facing components.

Promising compounds from natural sources against COVID-19

The epidemic associated with the new Sars-CoV-2 coronavirus has affected almost all countries of the world and no reliable treatment for this infection exists yet. Many laboratories in the world are currently conducting intensive experimental and theoretical/in silico studies to find effective drugs specific for this disease (COVID-19), but unfortunately, it may take a long time before new drugs appear in the clinical practice. One of the currently widely accepted approaches for finding active compounds is based on the possibility of using existing drugs approved by government medical organizations (as the FDA). Their choice is based on screening, based on the use of computer models that evaluate the specific binding (energy minimization) of such drugs to target molecules that are important for the life cycle. Thus, a few well-known antiviral drugs against HIV, hepatitis C and others selected on this basis exerted an antiviral effect in vitro, but their real effectiveness was far from expected. It should be emphasized that the severe clinical manifestation of the disease is an acute respiratory distress syndrome, mediated by oxidative stress and an aggressive immune attack on its own cells. In this regard, the use of compounds with high antioxidant activity could have advantages both prophylactically and medically. There is a huge range of natural compounds, including official and traditional medicine, which represent valuable unlimited potential for COVID-19 therapy, the advantage of such compounds in their low toxicity. In this review, we tried to focus on the clinical and pharmacological properties of natural substances, mainly flavonoids, which can become promising drugs for the treatment and prevention of COVID-19. The review includes information on possible virus targets and antiviral drugs. Much attention is paid to the question of inhibition of viral activity. Based on published data, including structural features of various compounds, a prediction is made about the prospects of using these compounds as inhibitors of viral activity, as well as anti-inflammatory drugs for the treatment of COVID-19. An important step in the analysis of compounds was the study of the possibility of their interaction with cellular targets of the virus, as well as the ability to bind to the proteins of the Sars-CoV-2 virus itself.

Relative stability of planar clusters B11, B12, and B13 in neutral- and charged-states

Theoretically, within the diatomic model, the relative stability of most abundant boron clusters B11, B12, and B13 with planar structures in neutral, positive and negative charged-states is studied. According to the specific (per atom) binding energy criterion, B12+ (6.49 eV) is found to be the most stable boron cluster, while B11– + B13+ (5.83 eV) neutral pair is expected to present the preferable ablation channel for boron-rich solids. Obtained results would be applicable in production of boron-clusters-based nanostructured coating materials with super-properties such as lightness, hardness, conductivity, chemical inertness, neutron-absorption, etc., making them especially effective for protection against cracking, wear, corrosion, neutron- and electromagnetic-radiations, etc.

Strain and Charge Doping Fingerprints of the Strong Interaction between Monolayer MoS2 and Gold.

Gold-mediated exfoliation of MoS2 has recently attracted considerable interest. The strong interaction between MoS2 and Au facilitates preferential production of centimeter-sized monolayer MoS2 with near-unity yield and provides a heterostructure system noteworthy from a fundamental standpoint. However, little is known about the detailed nature of the MoS2–Au interaction and its evolution with the MoS2 thickness. Here, we identify the specific vibrational and binding energy fingerprints of this interaction using Raman and X-ray photoelectron spectroscopy, which indicate substantial strain and charge doping in monolayer MoS2. Tip-enhanced Raman spectroscopy reveals heterogeneity of the MoS2–Au interaction at the nanoscale, reflecting the spatial nonconformity between the two materials. Micro-Raman spectroscopy shows that this interaction is strongly affected by the roughness and cleanliness of the underlying Au. Our results elucidate the nature of the MoS2–Au interaction and guide strain and charge doping engineering of MoS2.

Tannic acid modified single nanopore with multivalent metal ions recognition and ultra-trace level detection

• A reliable single glass nanopore system that possess specific binding affinities has been developed. • This system could achieve metal ions recognitions and ultra-trace level detection (limit of our detection on Fe 3+ ion can reach 10 −15 M). • Theoretical modeling and experiments demonstrate that the specific binding energies between the functional polyphenol groups and metal ions play an important role in metal ions recognition, which promote a systematical study of polyphenol chemistry in nanoconfined space. Artificial single nanopore as a promising tool for chemical and biological studies, such as ionic detection, DNA sequencing, molecular sensing/separation, nanofluidics and biomimetics, has been attracting great attention. Here we show a reliable functional single glass nanopore system with tannic acid to provide polyphenolic functional groups that possess specific binding affinities able to achieve metal ions recognition and ultra-trace level detection (e.g., limit of Fe 3+ detection is down to 10 −15 M). This system displays fast and high sensing ability features for detecting multivalent metal ions. Theoretical calculation (Gaussian 16) and experiments demonstrate that the specific binding energy between the trihydroxy phenolic groups of the inner surface of the nanopore and multiple metal ions can effectively distinguish trivalent, divalent, and monovalent metal ions. Therefore, our new system could promote a potential to conveniently recognize multivalent metal ions in nanoconfined space, and spark efforts to mimic ionic transport in biological nanopore systems and exploit smart nanofluidic devices.

Applications of density functional theory to heavy metal binding to magnetic-cored dendrimer

Magnetic-cored dendrimer (MD) is a nano-material composed with the magnetite nanoparticle in the core and dendritic branches developed on the surface of the core. Due to the unique structure and magnetic property of the MD, it has been studied for various environmental applications including the adsorption. With a large number of the terminal group, the poly (amidoamine) dendrimer provides many possible binding positions to various kind of contaminants. It has been reported that the heavy metal adsorption shows different affinity depending on heavy metal species in the aqueous phase. In this study, the MD was synthesized and their binding efficiency experimented with four different dissolved heavy metals of Pb (II), Cu (II), Zn (II), and Cr (VI). The maximum adsorption capacity of heavy metal was in the following order: Pb2+ > HCrO4- > Zn2+ > Cu2+. The interaction between the MD and the targeted heavy metal was calculated using the density functional theory (DFT). A pseudo-potential code SIESTA model was used. The calculated enthalpy of each metal indicated an agreement with the experimental result. A specific binding position and energies of different heavy metal species were confirmed through DFT calculations. The calculated enthalpy demonstrates structural and dynamical characteristics between MD and heavy metals. The binding preference of MD to a different kind of heavy metal provides useful information for the environmental applications.

Operando observations of reactive metal–Oxide structure formation on the Pt3Ni(111) surface at near-ambient pressure

The formation of interfacial metal–oxide structures on the Pt3Ni(111) bimetallic surface was investigated using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) techniques at near-ambient pressure (NAP). Direct observation of surface images clearly shows the occurrence of surface segregation of the sub-surface Ni depending on the surrounding gas-phase conditions. Especially, the prepared topmost Pt-skin layer of the Pt3Ni(111) is altered by Ni oxide segregation that makes an interfacial Pt-NiO1−x nanostructure with dissociated oxygen. This metal–oxide interface could provide active sites for more-efficient carbon monoxide (CO) conversion processes under mixed CO/O2 gas environments; the associated specific chemical binding energy was identified using NAP-XPS. The combined operando observations from the NAP-STM and NAP-XPS on the Pt3Ni(111) surface reveal that the interfacial metal–oxide structure is strongly correlated with the origin of the enhanced catalytic activity at thermodynamic equilibrium.