Small Transition Metal Research Articles

Stability and Dynamics of Zeolite-Confined Gold Nanoclusters.

Nanoengineered metal@zeolite materials have recently emerged as a promising class of catalysts for several industrially relevant reactions. These materials, which consist of small transition metal nanoclusters confined within three-dimensional zeolite pores, are interesting because they show higher stability and better sintering resistance under reaction conditions. While several such hybrid catalysts have been reported experimentally, key questions such as the impact of the zeolite frameworks on the properties of the metal clusters are not well understood. To address such knowledge gaps, in this study, we report a robust and transferable machine learning-based potential (MLP) that is capable of describing the structure, stability, and dynamics of zeolite-confined gold nanoclusters. Specifically, we show that the resulting MLP maintains ab initio accuracy across a range of temperatures (300-1000 K) and can be used to investigate time scales (>10 ns), length scales (ca. 10,000 atoms), and phenomena (e.g., ensemble-averaged stability and diffusivity) that are typically inaccessible using density functional theory (DFT). Taken together, this study represents an important step in enabling the rational theory-guided design of metal@zeolite catalysts.

Self-assembled methodologies for the construction of DNA nanostructures and biological applications.

Over the past decades, deoxyribonucleic acid (DNA), as a versatile building block, has been widely employed to construct functionalized nanostructures. Among the diverse types of materials, DNA related nanostructures have gained growing attention due to their intrinsic programmability, favorable biocompatibility, and strong molecular recognition capability. The conventional construction strategy for building DNA structures is based on Watson-Crick base-pairing rules, which are mainly driven by the hydrogen bonding of bases. However, hydrogen bonding-based DNA nanostructures cannot meet the requirements of specific morphology and multifunctionality. Currently, various functional elements have been introduced to expand the synthetic methodologies for constructing the DNA hybrid nanostructures, including small molecules, peptide polymers, organic ligands and transition metal ions. Besides, the potential applications for these DNA hybrid nanostructures have also been explored. It has been demonstrated that DNA hybrid structures with various properties can be extensively applied in the fields of magnetic resonance, luminescence imaging, biomedical detection, and drug delivery systems. In this review, we highlight the pioneering contributions to the methodologies of DNA-based nanostructure assembly. Furthermore, the recent advances in drug delivery systems and biomedical diagnosis based on DNA hybrid nanostructures are briefly summarized.

Synthesis and DNA Cleavage Activity of Cationic Methylene-Blue-Backboned Polymers.

Methods of DNA cleavage have broad bioapplications in gene editing, disease treatment, and biosensor design. The traditional method for DNA cleavage is mainly through oxidation or hydrolysis mediated by small molecules or transition metal complexes. However, DNA cleavage by artificial nucleases using organic polymers has been rarely reported. Methylene blue has been extensively studied in the fields of biomedicine and biosensing due to its excellent singlet oxygen yield, redox properties, and good DNA affinity. Methylene blue mainly relies on light and oxygen for DNA cleavage, and the cutting rate is slow. Here, we synthesize cationic methylene-blue-backboned polymers (MBPs) that can bind DNA efficiently and induce DNA cleavage through free radical mechanisms in the absence of light and exogenous reagents, showing high-efficiency nuclease activity. In addition, MBPs with different structures showed selectivity for DNA cleavage, and the cleavage efficiency of the flexible structure was significantly higher than that of the rigid structure. Studies on the DNA cleavage mechanism have shown that the cleavage mechanism of MBPs is not through the common ROS-mediated oxidative cleavage pathway, but through the radical of MBP• inducing DNA cleavage. Meanwhile, MBPs can simulate topoisomerase I (Topo I)-mediated topological rearrangement of superhelical DNA. This work paved a way for the application of MBPs in the field of artificial nucleases.

Geometrical and magnetic properties of small titanium and chromium clusters on monolayer hexagonal boron nitride.

Magnetic clusters on an insulating substrate are potential candidates for spin-based quantum devices. Here we investigate the geometric, electronic, and magnetic structures of small Ti and Cr clusters, from dimers to pentamers, adsorbed on a single-layer hexagonal boron nitride (h-BN) sheet within the framework of density functional theory. The stable adsorption configurations of the Ti clusters and Cr clusters composed of the same number of atoms are found to be totally different from each other. The difference in their bonding mechanisms has been revealed by the density of states and the charge density difference of the corresponding adsorption systems. While chemical bonds are formed between the Ti atoms and the supporting sheet, the Cr clusters are found in the physisorption state on the substrate. In addition, it is shown that the h-BN sheet is energetically favorable for building three-dimensional Ti clusters. These findings support the use of h-BN as a suitable decoupling substrate for manipulation of quantum spin states in small transition metal (TM) clusters and fabrication of devices based on them.

The effective regulation of heterogeneous N-heterocyclic carbenes: structures, electronic properties and transition metal adsorption.

Heterogeneous N-heterocyclic carbene materials have attracted increasing interest in the fields of materials science and catalysis due to their unique properties and potential applications. However, current heterogeneous systems primarily focus on a single class of carbene. In this work, we simultaneously introduce two classes of typical five-membered carbenes into a graphene lattice, forming a series of novel two-dimensional heterogeneous N-heterocyclic carbene nanomaterials (2D-NCMs) composed of multiple carbenes. First-principles calculations demonstrate the thermodynamic stability of the designed 2D-NCMs, as well as their diverse electronic properties ranging from metallic to semiconducting. The incorporation of carbenes in the 2D-NCMs enables them to adsorb both acidic BCl3 and basic CO molecules, thus exhibiting unique amphoteric properties. Furthermore, the 2D-NCMs exhibit remarkable adsorption capacities for ten transition metals, highlighting their promising potential for future catalytic applications. By adjusting the proportions of the two classes of carbenes, we can effectively regulate the electronic properties and adsorption capacities of small molecules and transition metals in the 2D-NCMs. This study presents a novel strategy for designing and regulating the properties of heterogeneous N-heterocyclic carbenes, offering significant implications in the fields of catalysis and materials science.

Probing the binding and activation of small molecules by gas-phase transition metal clusters via IR spectroscopy.

Isolated transition metal clusters have been established as useful models for extended metal surfaces or deposited metal particles, to improve the understanding of their surface chemistry and of catalytic reactions. For this objective, an important milestone has been the development of experimental methods for the size-specific structural characterization of clusters and cluster complexes in the gas phase. This review focusses on the characterization of molecular ligands, their binding and activation by small transition metal clusters, using cluster-size specific infrared action spectroscopy. A comprehensive overview and a critical discussion of the experimental data available to date is provided, reaching from the initial results obtained using line-tuneable CO2 lasers to present-day studies applying infrared free electron lasers as well as other intense and broadly tuneable IR laser sources.

Magnetic, Phonon and Optical Properties of Transition Metal and Rare Earth Ion Doped ZnS Nanoparticles.

The surface, size and ion doping effects on the magnetic, phonon and optical properties of ZnS nanoparticles are studied based on the s-d model including spin-phonon and Coulomb interaction, and using a Green's function theory. The changes of the properties are explained on a microscopic level, due to the different radii between the doping and host ions, which cause different strains-compressive or tensile, and change the exchange interaction constants in our model. The magnetization increases with increasing small transition metal (TM) and rare earth (RE) doping concentration. For larger TM dopants the magnetization decreases. The phonon energies increase with increasing TM, whereas they decrease by RE ions. The phonon damping increases for all doping ions. The changes of the band gap energy with different ion doping concentration is also studied. Band gap changes in doped semiconductors could be due as a result of exchange, s-d, Coulomb and electron-phonon interactions. We have tried to clarify the discrepancies which are reported in the literature in the magnetization and the band gap energy.

Expanding the scope of antenna–reactor photocatalysts for strong visible light absorption in small transition metal nanoparticles

The design of antenna–reactor photocatalysts has become a powerful strategy to covert transition metal reactors from traditional thermocatalysts to novel photocatalysts. Plasmonic metals are often used as the optical antenna. Here, we demonstrate that conventional dielectric supports with high refractive index are able to achieve comparable performance as the plasmonic antennas, giving rise to a huge enhancement of the visible light absorption in the small Pt nanoparticles (NPs) of the core–satellite antenna–reactor photocatalysts through resonance energy transfer. The absorption enhancement can be mediated not only by the electric resonances of the plasmonic antenna but also by the magnetic resonances of the dielectric antenna. A large enough dielectric antenna or a small plasmonic antenna is desired for the generation of strong optical resonances. Judged by those Pt NPs with strong visible light absorption enhancement, the potential catalytically active sites are mainly distributed at the back side of the dielectric antenna, while they may be widely distributed over the surface of the plasmonic antenna with probably lower activities. The expanding scope of antenna–reactor photocatalysts offers new opportunities for solar to chemical energy conversion using nonplasmonic catalytic transition metals.

Intermetallic Co-Pt/C Nanoparticles Synthesized Via Sonochemical Method As Enhanced Electrocatalysts for Cathode of PEMFC

For fuel cell stack of 80 kW, platinum for electrocatalyst requires around 10 g per fuel cell electric vehicle (FCEV). A large-scale synthesis method for the low-platinum catalyst is necessary for this field to reduce man-power. Ultrasound-assisted polyol synthesis (UPS) is a method for the preparation of small and uniform size transition metal core-platinum shell nanoparticles evenly distributed on the support. Platinum(Ⅱ) acetylacetonate, Cobalt(Ⅱ) acetylacetonate, and carbon support were dispersed in ethylene glycol which is reducing agent and irradiated by ultrasound for 3 h to reduce the precursor to metal nanoparticles, followed by washing and drying to obtain a powder. The characterization was observed by solution color visualization, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and electrocatalytic performance. Also, the synthesized samples were calcined at various temperatures to cause the atomic rearrangement to the most stable arrangement, and atomic accumulation of boundary between each atom and compression of platinum lattice that affects activity or durability of electrocatalyst has changed. Synthesized sample with optimized synthesis and treatment condition shows improved electrochemically active surface area (ECSA) and Oxygen reduction reaction (ORR) catalytic activity in the half-cell test and durable catalytic activity in the performance evaluation of membrane-electrode assembly (MEA) compared to existing Platinum catalyst. As renewable energy conversion and storage system is one of the main challenges, FCEV is developed to solve pollution from CO2 emission and oil depletion issues. Our low-platinum nanoparticle with uniform distribution synthesized using a sonochemical method will replace precious metal catalysts used in fuel cells instead of platinum catalysts.

Molecular Container and Metal Ion Sensor Chiral Cavitands

AbstractChiral macrocyclic cavitands prepared by a template free, high dilution methodology have been discovered to function as molecular containers accommodating small organic molecules and host transition metal ions with specific sensing ability while having an outstanding capability to sense Zn2+ with switch‐on fluorescence and also act as a selective colorimetric sensor for Cu2+. The cavitand acts as a unique two‐directional molecular tweezers for the guest molecules.

Hydrogen Evolution Reaction over Single-Atom Catalysts Based on Metal Adatoms at Defected Graphene and h-BN

In small transition and noble metal particles, commonly used as active parts of heterogeneous industrial catalysts, only a tiny fraction of metal atoms at their surfaces are utilized in relevant ch...

On the impact of multi-reference character of small transition metal compounds on their bond dissociation energies.

Determining the multi-reference character of a molecular system and its impact on the limits within which its properties may be calculated accurately by different quantum chemical methods remains a difficult yet important task in computational chemistry. Especially, transition metal compounds continue to frequently provide a challenge to quantum chemists in this regard. In this work, we construct, analyze, and evaluate different computational protocols to determine the impact of the multi-reference character of transition metal compounds on their bond dissociation energies using a set of reference data for 60 diatomic molecules. We find that the fractional orbital density approach allows to determine two global indicators on a physically sound basis. These can subsequently be used to classify the assessed set of molecules with high accuracy into categories of systems for which their multi-reference character matters substantially for their bond dissociation energies and for which it does not. A comparison with earlier suggested thresholds for classification of molecular systems due to their multi-reference character suggests that our approaches yield substantially better performance.

Дослідження методом рентгенівської фотоелектронної спектроскопії процесу синтезу ТіСпри відпалі ТiН2/ТiО2/С у вакуумі

Small dimensional transition metal carbides (MXenes) are promising materials for the development of photocatalysts and are highly efficient cocatalysts for industrial TiO_2 (P25). Thus, in the Ti_3C_2@TiО_2 nanocomposite obtained by layering Ti_3C_2 nanoplates, the ability to separate charge carriers increases due to the high electrical conductivity of TiC_{1-х}. The task of forming the TiC_{1-х}@TiО_{2-х} nanocomposite by direct synthesis with n-TiO_2 is promising, which allows to increase the quality of contact between the shell and the nanocomposite core and to reduce the number of intermediate stages of synthesis. In addition, highly dispersed TiC has high values of hardness, melting point, modulus of elasticity and shear and has the prospect of use in materials science in plasma spraying coatings. In work ТіС was synthesized on the surface of TiO_2 - the shell of the modified micropowder TiH_2/TiO_2/С during reductive annealing in vacuum using TiH_2 as a source of atomic hydrogen. After a series of annealing at 535 ºС - 600 ºС, the Ti2p- C1s- and O1s- spectra of surface atoms were obtained. The main stages of TiC synthesis in the TiO_2/С conversion reaction were established by the XPS method. The use of TiH_2 as a source of atomic hydrogen in nanosystems of the «core/shell» type is proposed for local synthesis on the surface of nanoobjects in a vacuum or inert atmosphere.

Understanding supported noble metal catalysts using first-principles calculations.

Heterogeneous catalysis on supported and nonsupported nanoparticles is of fundamental importance in the energy and chemical conversion industries. Rather than laboratory analysis, first-principles calculations give us an atomic-level understanding of the structure and reactivity of nanoparticles and supports, greatly reducing the efforts of screening and design. However, unlike catalysis on low index single crystalline surfaces, nanoparticle catalysis relies on the tandem properties of a support material as well as the metal cluster itself, often with charge transfer processes being of key importance. In this perspective, we examine current state-of-the-art quantum-chemical research for the modeling of reactions that utilize small transition metal clusters on metal oxide supports. This should provide readers with useful insights when dealing with chemical reactions on such systems, before discussing the possibilities and challenges in the field.

Jahn-Teller and Pseudo Jahn-Teller Effects: Influences on the Electronic Structures of Small Transition, Main Group and Mixed Metal Clusters

The present review article focuses on the impact of the Jahn-Teller effect (JTE) including hidden JTE and pseudo JTE on the ground and low-lying electronic structures of small transition, main group, and mixed metal clusters. The discussions are based on the results acquired from the quantum chemical analysis involving complete active space multiconfiguration self-consistent field (CASMCSCF or CASSCF) together with multireference singles and doubles configuration interaction (MRSDCI) theories. Related computational results from density functional (DFT) and coupled cluster (CC) theories, and the available experimental evidences on the JT-distorted structures are also included for comparative analysis. The role of the relativistic effects on several heavy metal clusters is discussed in detail, since these effects could lead to either enhancement or the quenching of the JTE. The final section of the review manifests the JT-distortion of several mixed metal clusters of icosahedral symmetry and they are explained through a much simpler shell structure (jellium) model.

Few-layer MoS2 dendrites as a highly active humidity sensor

Few-layer molybdenum disulfide (MoS2) transition metal chalcogenides (TMDCs) have been prepared, and their morphology has been widely investigated due to their moisture sensitivity properties. However, developing the design of MoS2 has made slow progress. This study introduces an improved chemical vapor deposition method to grow dendritic MoS2 nanomaterials. The grown MoS2 crystals have a dendritic shape with fractal and schedulable patterns. These morphologies are mainly initiated from the growth of double defects, and are regulated by S: Mo vapor ratio by characterizing their atomic structure. This study enhances the understanding of the growth mechanism of twin-derived crystals, extends their application from nanomaterials to 2D crystals, and provides a powerful and controllable method for small transition metal sulfide TMDCs. Shape engineering methods in electrochemical applications have evolved.

A magnetic study of the HoCo12-xFexB6 ferrimagnetic compounds

The effects of Fe substitution on the structural and magnetic properties of the HoCo12-xFexB6 (0 ≤ x ≤ 2) series of intermetallic compounds have been studied. All of the compounds form in the rhombohedral SrNi12B6-type structure, the lattice constants increasing linearly with x. These compounds are ferrimagnets with a small transition metal magnetic moment and exhibit a spin reorientation transition. The Curie temperature decreases from 147 K for x = 0–105 K for x = 2. The Fe for Co substitution leads also to a progressive decrease of the spontaneous magnetization. The spin reorientation transition temperature is significantly reduced upon Fe for Co substitution whereas the compensation temperature is much less sensitive to the Fe composition.

Engineering peroxiredoxin 3 to facilitate control over self-assembly

Oligomeric proteins are abundant in nature and are useful for a range of nanotechnological applications; however, a key requirement in using these proteins is controlling when and how they form oligomeric assemblies. Often, protein oligomerisation is triggered by various cellular signals, allowing for controllable oligomerisation. An example of this is human peroxiredoxin 3 (Prx), a stable protein that natively forms dimers, dodecameric rings, stacks, and tubes in response to a range of environmental stimuli. Although we know the key environmental stimuli for switching between different oligomeric states of Prx, we still have limited molecular knowledge and control over the formation and size of the protein's stacks and tubes. Here, we have generated a range of Prx mutants with either a decreased or knocked out ability to stack, and used both imaging and solution studies to show that Prx stacks through electrostatic interactions that are stabilised by a hydrogen bonding network. Furthermore, we show that altering the length of the polyhistidine tag will alter the length of the Prx stacks, with longer polyhistidine tags giving longer stacks. Finally, we have analysed the effect a variety of heavy metals have on the oligomeric state of Prx, wherein small transition metals like nickel enhances Prx stacking, while larger positively charged metals like tungstate ions can prevent Prx stacking. This work provides further structural characterisation of Prx, to enhance its use as a platform from which to build protein nanostructures for a variety of applications.

Adsorption Energy Shifts for Oxygen and Hydroxyl on 4-atom Metal-Decorated Graphene Catalysts Via Solvation, pH, and Substrate Dopants: Effects on ORR Activity

Recent literature results have highlighted the role of small transition metal and intermetallic nanoparticles supported on graphene as catalysts for many key applications in energy and commodity chemicals industries. Specifically, metal nanoparticle catalysts down to sizes of 4 and even 1 (single atom catalysts) on graphene have been studied for the Oxygen Reduction Reaction (ORR). A recent study showed that 4-atom transition metal intermetallic nanoparticles (NP) on graphene (metal-decorated graphene (MDG)) even generate a predictive Volcano Plot for ORR activity. Initial results from that study were not completely explained, and an expanded analysis and discussion built from that work is presented in this manuscript. Specifically, in this new work, the original Volcano Plot for 4-atom MDG NP catalysts for the ORR is analyzed for its counter-intuitive thermodynamic inversion between the rate limiting steps of O* hydrogenation and OH* hydrogenation. The Volcano Plot is then further studied for dependence on solvent correction energy, system pH, and with an initial probe on the sensitivity of descriptor values on doping of the graphene support via B and N atoms. Recommendations for optimum 4-atom MDG NP catalyst operation for the ORR are provided, and directions for future work and study are provided.

Small transition metal cluster adsorbed on graphene and graphene nanoribbons: A density functional based tight binding molecular dynamics study

Abstract The systemic study of the electronic properties of different transition metals (TMs-Sc, Ti, Fe, Co, Ni, Zn, Ag and Au) adsorbed in the surface of graphene was done with the aid of self-consistent charge density functional based tight binding method. Results show that the Silver metal adsorbed in the surface of graphene can open its gapless bandstructure. In addition, a single-gated field effect transistor based on Ag-adsorbed on zigzag graphene nanoribbon (zGNR) can act as a potential semiconductor for modern electronic applications. An important feature is that the Ag does not break the structure of zGNR on adsorption. Further, the resulting Ag/zGNR energy band gap is inversely proportional on the dimer lines across its width as predicted by tight-binding calculations.