Quasi-Periodic Growth of One-Dimensional Copper Boride on Cu(110).

An unexplored material of copper boride has been realized recently in two-dimensional form at a (111) surface of the fcc copper crystal. Here, one-dimensional (1-D) boron growth was observed on the Cu(110) surface, as probed by atomically resolved scanning probe microscopy. The 1-D copper boride was composed of quasi-periodic atomic chains periodically aligned parallel to each other, as confirmed by Fourier transform analysis. The 1-D growth unexpectedly proceeded across surface steps in a self-assembled manner and extended over several 100 nm. The long-range formation of a 1-D quasi-periodic structure on a surface has been theoretically modeled as a 1-D quasi-crystal and the predicted conditions matched the structural parameters obtained by the experimental work here. The quasi-periodic 1-D copper boride system enabled a way to examine 1-D quasi-crystallinity on an actual material.

Hydrogen Boride Sheets and Copper Nanoparticle Composites as a Visible-Light-Sensitive Hydrogen Release System.

Hydrogen boride (HB) sheet is a new class of 2D materials comprising hydrogen and boron, synthesized through ion-exchange and exfoliation techniques. HB sheets can release hydrogen (H2) under light irradiation and is predicted to be a promising H2 storage material. However, its application is limited to the UV region. One approach to enable a visible-light-driven system is the utilization of plasmonic metallic nanoparticles. The present study reports H2 release from copper (Cu) nanoparticle-modified HB sheet (HB/Cu) under visible-light irradiation. Copper nanoparticles possess unique and strong plasmonic responses in the visible-light range, making them ideal light absorbers in this system. HB/Cu nanocomposites are synthesized using a simple mixture of copper acetate and HB sheets in acetonitrile, where HB sheets reduced copper ions to metal copper nanoparticles. The photoirradiation results shows that HB/Cu nanocomposites released more H2 than the bare HB sheets under visible-light irradiation. This is probably due to the plasmonic photothermal effect of copper metal, which enhances H2 generation from the HB sheets. This material offers a viable and cost-effective approach for developing visible-light-sensitive systems.

Electrolytic Hydrogen Release from Hydrogen Boride Sheets.

Solid-state hydrogen storage materials are safe and lightweight hydrogen carriers. Among the various solid-state hydrogen carriers, hydrogen boride (HB) sheets possess a high gravimetric hydrogen capacity (8.5 wt%). However, heating at high temperatures and/or strong ultraviolet illumination is required to release hydrogen (H2) from HB sheets. In this study, the electrochemical H2 release from HB sheets using a dispersion system in an organic solvent without other proton sources is investigated. H2 molecules are released from the HB sheets under the application of a cathodic potential. The Faradaic efficiency for H2 release from HB sheets reached >90%, and the onset potential for H2 release is -0.445 V versus Ag/Ag+, which is more positive than those from other proton sources, such as water or formic acid, under the same electrochemical conditions. The total electrochemically released H2 in a long-time experiment reached ≈100% of the hydrogen capacity of HB sheets. The H2 release from HB sheets is driven by a small bias; thus, they can be applied as safe and lightweight hydrogen carriers with economical hydrogen release properties.

Ball-milled MoS2 with graphene shows enhanced catalytic activity for hydrogen evolution reaction.

The hydrogen evolution reaction (HER) is an important phenomenon in water splitting. Consequently, the development of an active, earth-abundant, and inexpensive HER catalyst is highly desired. MoS2 has drawn considerable interest as an HER catalyst because it is composed of non-precious metal and exhibits high catalytic activity in the nanosheet form. In this study, size-controlled MoS2 particles were synthesized by ball milling. The as-prepared samples exhibited significantly enhanced electrochemical and catalytic properties compared to those of pristine bulk MoS2. Furthermore, the HER activity improved further upon the introduction of graphene into the as-prepared ball-milled samples. In particular, the MoS2 sample ball-milled for 12 h mixed with graphene exhibited optimal performance, showing an overpotential (160 mV at 10 mA cm-2) that was ~ 335 mV lower than that of pristine bulk MoS2. The superior catalytic activity was ascribed to the exposed edge sites, sulfur vacancies, and 1T phase of MoS2, as well as the noteworthy fortifying effect of the electronically conductive flexible material, graphene. The results provide a promising strategy for its application as an efficient and stable HER catalyst.

Li et al. reported MoS₂-based electrocatalysts for the hydrogen evolution reaction. The superior catalytic activity was ascribed to exposed edge sites, sulfur vacancies, 1T phase, and the effect of graphene.

Direct Imaging of Band Structure for Powdered Rhombohedral Boron Monosulfide by Microfocused ARPES.

Boron-based two-dimensional (2D) materials are an excellent platform for nanoelectronics applications. Rhombohedral boron monosulfide (r-BS) is attracting particular attention because of its unique layered crystal structure suitable for exploring various functional properties originating in the 2D nature. However, studies to elucidate its fundamental electronic states have been largely limited because only tiny powdered crystals were available, hindering a precise investigation by spectroscopy such as angle-resolved photoemission spectroscopy (ARPES). Here we report the direct mapping of the band structure with a tiny (∼20 × 20 µm2) r-BS powder crystal by utilizing microfocused ARPES. We found that r-BS is a p-type semiconductor with a band gap of >0.5 eV characterized by the anisotropic in-plane effective mass. The present results demonstrate the high applicability of micro-ARPES to tiny powder crystals and widen an opportunity to access the yet-unexplored electronic states of various novel materials.

Effective treatment of hydrogen boride sheets for long-term stabilization.

Two-dimensional hydrogen boride (HB) sheets prepared via the ion-exchange reaction from magnesium diboride (MgB2) are known to possess several intriguing properties for a wide range of applications; however, previous reports have shown that the sheets prepared using this method contain small amounts of reactive components, making them unsuitable for certain applications. Therefore, developing a method for preparing HB sheets that exhibit long-term stability and do not contain reactive species is essential. In this study, we developed an effective treatment method for achieving long-term stabilization of HB sheets. We found that by pre-treating the HB sheets with water and then filtering the dried product from an acetonitrile dispersion, we could achieve excellent long-term stability over nine months. This stability was maintained even outside of a glovebox, with no H2 released by the decomposition and/or reaction. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) absorption spectroscopy measurements revealed that the sample exhibited pure HB characteristics with negatively charged boron and B-H-B and terminal B-H bonds, even after nine months of storage. Furthermore, based on thermal desorption spectroscopy (TDS) measurements, the presence of reactive species in the as-prepared HB sheets is attributed to fluctuating B-H bonds with relatively weak binding energies that can be removed using the method developed in this study.

Accelerated Synthesis of Borophane (HB) Sheets through HCl-Assisted Ion-Exchange Reaction with YCrB4.

We present an enhanced method for synthesizing sheets of borophane. Despite the challenges associated with low efficiency, we discovered that incorporating hydrochloric acid into the ion-exchange reaction significantly improved the production yield from 20% to over 50%. After a thorough examination of the reaction, we gained insight into the underlying mechanisms and found that the use of hydrochloric acid provides two key benefits: accelerated production of borophene and isolation of high-purity products. This method has the potential to pave the way for the production of novel topological 2D materials with potential industrial applications.

Prediction of a Cyclic Hydrogenated Boron Molecule as a Promising Building Block for Borophane.

We have extensively searched for a cyclic hydrogenated boron molecule that has a three-center two-electron bond at the center. Using first-principles calculations, we discovered a stable molecule of 2:4:6:8:-2H-1,5:1,5-µH-B8H10 and propose its existence. This molecule can be regarded as a building block for sheets of topological hydrogen boride (borophane), which was recently theoretically proposed and experimentally discovered. The electronic structure of the cyclic hydrogenated boron molecule is discussed in comparison with that of cyclic hydrogenated carbon molecules.

Rhombohedral Boron Monosulfide as a p-Type Semiconductor.

Two-dimensional materials have wide ranging applications in electronic devices and catalysts owing to their unique properties. Boron-based compounds, which exhibit a polymorphic nature, are an attractive choice for developing boron-based two-dimensional materials. Among them, rhombohedral boron monosulfide (r-BS) has recently attracted considerable attention owing to its unique layered structure similar to that of transition metal dichalcogenides and a layer-dependent bandgap. However, experimental evidence that clarifies the charge carrier type in the r-BS semiconductor is lacking. In this study, we synthesized r-BS and evaluated its performance as a semiconductor by measuring the Seebeck coefficient and photo-electrochemical responses. The properties unique to p-type semiconductors were observed in both measurements, indicating that the synthesized r-BS is a p-type semiconductor. Moreover, a distinct Fano resonance was observed in Fourier transform infrared absorption spectroscopy, which was ascribed to the Fano resonance between the E(2) (TO) phonon mode and electrons in the band structures of r-BS, indicating that the p-type carrier was intrinsically doped in the synthesized r-BS. These results demonstrate the potential future application prospects of r-BS.

Hydrogenation of Formate Species Using Atomic Hydrogen on a Cu(111) Model Catalyst.

The reaction mechanism of the CH3OH synthesis by the hydrogenation of CO2 on Cu catalysts is unclear because of the challenge in experimentally detecting reaction intermediates formed by the hydrogenation of adsorbed formate (HCOOa). Thus, the objective of this study is to clarify the reaction mechanism of the CH3OH synthesis by establishing the kinetic natures of intermediates formed by the hydrogenation of adsorbed HCOOa on Cu(111). We exposed HCOOa on Cu(111) to atomic hydrogen at low temperatures of 200-250 K and observed the species using infrared reflection absorption (IRA) spectroscopy and temperature-programmed desorption (TPD) studies. In the IRA spectra, a new peak was observed upon the exposure of HCOOa on Cu(111) to atomic hydrogen at 200 K and was assigned to the adsorbed dioxymethylene (H2COOa) species. The intensity of the new peak gradually decreased with heating from 200 to 290 K, whereas the IR peaks representing HCOOa species increased correspondingly. In addition, small amounts of formaldehyde (HCHO), which were formed by the exposure of HCOOa species to atomic hydrogen, were detected in the TPD studies. Therefore, H2COOa is formed via hydrogenation by atomic hydrogen, which thermally decomposes at ∼250 K on Cu(111). We propose a potential diagram of the CH3OH synthesis via H2COOa from CO2 on Cu surfaces, with the aid of density functional theory calculations and literature data, in which the hydrogenation of bidentate HCOOa to H2COOa is potentially the rate-determining step and accounts for the apparent activation energy of the methanol synthesis from CO2 on Cu surfaces.

Chemisorption of CO2 on Nitrogen-Doped Graphitic Carbons.

The adsorption of CO2 on nitrogen-doped graphitic carbon materials, such as graphene nanosheet (GNS) powder and highly oriented pyrolytic graphite (HOPG), was comparatively studied using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Desorption of CO2 was observed at approximately 380 K for both pyridinic-nitrogen (pyri-N)-doped GNS and pyri-N-doped HOPG samples in the TPD experiments, whereas no CO2 desorption was observed for graphitic nitrogen-doped HOPG. This indicated that only pyri-N species create identical CO2 adsorption sites on any graphitic carbon surface. The adsorption energies of CO2 on pyri-N-doped carbons were estimated between 101 and 108 kJ mol-1, indicating that chemisorption, rather than physisorption, took place. The CO2 adsorption/desorption process was reproducible in repeated measurements, and no CO2 dissociation occurred during the process, suggesting that it is a promising CO2 capturing material. The O 1s peak of the adsorbed CO2 clearly appeared at 531.5-532 eV in the XPS measurements. The N 1s peak of pyri-N did not change with CO2 adsorption, indicating that CO2 is not directly bound to pyri-N but is adsorbed on a carbon atom near the pyridinic nitrogen via the nonbonding pz orbital of the carbon atom.

Single-Pulsed SERS with Density-Based Clustering Analysis.

We developed a new method for obtaining surface-enhanced Raman scattering (SERS) spectra with extremely high sensitivity and spectral resolution. In this method, thousands of SERS spectra are acquired, followed by a data selection procedure based on density-based spatial clustering of applications with noise (DBSCAN). Each spectrum is recorded by exposure to a single nanosecond laser pulse to avoid the effect of time averaging. The reconstructed spectrum consists of the data that belong to the clusters. The method was applied to a crystal violet aqueous solution with a concentration of 10-7 mol/L. The results suggest that several minor Raman peaks were successfully recovered, which cannot be detected in conventional SERS measurements. Moreover, the method is also effective for separately observing Raman peaks that overlap with other neighboring peaks. This method extends the possibilities of SERS and will contribute to future high-resolution spectroscopy in condensed phases.

Highly Dispersed Ni Nanoclusters Spontaneously Formed on Hydrogen Boride Sheets.

Hydrogen boride (HB) sheets are two-dimensional materials comprising a negatively charged hexagonal boron network and positively charged hydrogen atoms with a stoichiometric ratio of 1:1. Herein, we report the spontaneous formation of highly dispersed Ni nanoclusters on HB sheets. The spontaneous reduction reaction of Ni ions by the HB sheets was monitored by in-situ measurements with an ultraviolet-visible spectrometer. Acetonitrile solutions of Ni complexes and acetonitrile dispersions of the HB sheets were mixed in several molar ratios (the HB:Ni molar ratio was varied from 100:0.5 to 100:20), and the changes in the absorbance were measured over time. In all cases, the results suggest that Ni metal clusters grow on the HB sheets, considering the increase in absorbance with time. The absorbance peak position shifts to the higher wavelength as the Ni ion concentration increases. Transmission electron microscopy images of the post-reaction products indicate the formation of Ni nanoclusters, with sizes of a few nanometers, on the HB sheets, regardless of the preparation conditions. These highly dispersed Ni nanoclusters supported on HB sheets will be used for catalytic and plasmonic applications and as hydrogen storage materials.

Ethanol-ethylene conversion mechanism on hydrogen boride sheets probed by in situ infrared absorption spectroscopy.

Two-dimensional hydrogen boride (HB) sheets were recently demonstrated to act as a solid acid catalyst in their hydrogen-deficient state. However, both the active sites and the mechanism of the catalytic process require further elucidation. In this study, we analyzed the conversion of ethanol adsorbed on HB sheets under vacuum during heating using in situ Fourier transform infrared (FT-IR) absorption spectroscopy with isotope labelling. Up to 450 K, the FT-IR peak associated with the OH group of the adsorbed ethanol molecule disappeared from the spectrum, which was attributed to a dehydration reaction with a hydrogen atom from the HB sheet, resulting in the formation of an ethyl species. At temperatures above 440 K, the number of BD bonds markedly increased in CD3CH2OH, compared to CH3CD2OH; the temperature dependence of the formation rate of BD bonds was similar to that of the dehydration reaction rate of ethanol on HB sheets under steady-state conditions. The rate-determining step of the dehydration of ethanol on HB was thus ascribed to the dehydrogenation of the methyl group of the ethyl species on the HB sheets, followed by the immediate desorption of ethylene. These results show that the catalytic ethanol dehydration process on HB involves the hydrogen atoms of the HB sheets. The obtained mechanistic insights are expected to promote the practical application of HB sheets as catalysts.

Diborane Concatenation Leads to New Planar Boron Chemistry.

Diborane has long been realized to be analogous to ethylene in terms of its bonding MOs, both as to symmetries and splitting patterns. This naturally suggests an investigation to see whether other similar conjugated hydrocarbons manifest a similar boron-substituted and H2 supplemented borane. That is, for a conjugated hydrocarbon structure with a neighbor-paired resonance pattern, we propose to look at boranes where each carbon atom is replaced by a boron atom, and an H-atom pair is added to each double bond of the resonance structure, with one H above the molecular plane and one below. This construction of concatenated diboranes is uniformly different than that for the previously known stable boranes of 4 or more B atoms. We find from quantum-chemical computations that our so constructed polyboranes are stable. All this suggests a possible novel new chapter in borane chemistry - a chapter with some promise of understandings related to that for (alternant) conjugated hydrocarbons.

Pharmacokinetic and pharmacodynamic modeling of the metastin/kisspeptin analog, TAK-448, for its anti-tumor efficacy in a rat xenograft model.

TAK-448 is the investigational metastin/kisspeptin analog, which is known to have an anti-tumor effect through suppression of androgen hormones (luteinizing hormone and testosterone) levels. This study developed pharmacokinetic-pharmacodynamic (PK/PD) models of TAK-448 and leuprorelin acetate (TAP-144) in a rat vertebral-cancer of the prostate (VCaP) androgen-sensitive prostate cancer xenograft model to quantitatively assess and compare the anti-tumor effects of both drugs. A potential contribution of the hormone-independent direct effects of TAK-448 to the tumor growth inhibition was also investigated in the in vivo rat xenograft model, because our in vitro experiments revealed that TAK-448 may also directly suppress VCaP cellular proliferation. The PK/PD model successfully described the time course of tumor growth inhibition after drug treatment as well as the development of resistance to the inhibition of androgen hormones, following drug treatment or castration. The EC50 of the hormone-dependent inhibitory effect of TAK-448 was much lower than that of TAP-144, and TAK-448 also has a faster onset of anti-tumor effect than TAP-144, demonstrating that TAK-448 has a stronger overall anti-tumor effect than TAP-144. In addition, model inference, by incorporating a hormone-independent inhibition pathway of TAK-448 into the PK-PD model, suggested that such a direct inhibition pathway for TAK-448 cannot be excluded, as also indicated by in vitro studies, but its EC50 would be approximately three orders of magnitude higher than that of the hormone-dependent pathway. This study helps to understand the potential and mechanism of TAK-448 as a prostate cancer treatment.

The Enhancement of Subcutaneous First-Pass Metabolism Causes Nonlinear Pharmacokinetics of TAK-448 after a Single Subcutaneous Administration to Rats.

2-(N-acetyl-D-tyrosyl-trans-4-hydroxy-L-prolyl-L-asparaginyl-L-threonyl-L-phenylalanyl) hydrazinocarbonyl-L-leucyl-Nω-methyl-L-arginyl-L-tryptophanamide monoacetate (TAK-448, RVT-602), a kisspeptin analog, has been developed as a therapeutic agent for prostate cancer. The purpose of the present study is to clarify the mechanism of the less than dose-proportional nonlinear pharmacokinetics of TAK-448 after subcutaneous administration to rats. The plasma pharmacokinetics of TAK-448 and radiolabeled TAK-448 ([14C]TAK-448) were examined after subcutaneous and intravenous administrations to rats. [14C]TAK-448 was also subcutaneously injected together with protease inhibitors. The effects of the protease inhibitors on the in vitro metabolism of [14C]TAK-448 were investigated using rat skin homogenates. In a dose-ascending study, less than dose-proportional nonlinear pharmacokinetics were observed after subcutaneous administration with limited absorption of TAK-448 at the highest dose level contrary to the linear pharmacokinetics following intravenous dosing, indicating enhancement of subcutaneous metabolism with dose escalation. The systemic absorption of unchanged TAK-448 recovered when protease inhibitors were subcutaneously coadministered, suggested the involvement of subcutaneous proteases in the first-pass metabolism. An in vitro metabolism study suggests that serine protease could be responsible for the subcutaneous metabolism of TAK-448. Dose-dependent enhancement of first-pass metabolism appears to contribute to the less than dose-proportional nonlinear pharmacokinetics of TAK-448 after subcutaneous administrations to rats.

Investigation of disposition for TAK-448, a synthetic peptide of kisspeptin analog, in rats and dogs using the radiolabeled TAK-448 suitable for pharmacokinetic study.

Disposition of 2-(N-acetyl-d-tyrosyl-trans-4-hydroxy-l-prolyl-l-asparaginyl-l-threonyl-l-phenylalanyl) hydrazinocarbonyl-L-leucyl-Nω-methyl-l-arginyl-l-tryptophanamide monoacetate (TAK-448, RVT-602), a synthetic kisspeptin analog, was investigated after parenteral dosing of radiolabeled TAK-448 ([d-Tyr-14C]TAK-448) to rats and dogs, and it was confirmed if the radiolabeling position at d-Tyr was eligible for assessment of in vivo disposition. Dosed radioactivity was rapidly and well absorbed after subcutaneous administration and an appreciable amount of unchanged TAK-448 (TAK-448F) and a hydrolyzed metabolite, M-I, were detected in the plasma of rats and dogs. After intravenous administration of [d-Tyr-14C]TAK-448 to rats, the radioactivity widely distributed to tissues with relatively higher concentrations in kidney and urinary bladder. The radioactivity was decreased rapidly from the tissues. After subcutaneous administration of [d-Tyr-14C]TAK-448 to rats and dogs, the dosed radioactivity was almost completely recovered by 48 and 72 h in rats and dogs, respectively, and most of the radioactivity was excreted in urine after extensive metabolism in the two species. These results suggest that TAK-448 has an acceptable pharmacokinetic profile for clinical evaluation and development, and demonstrate that the synthesized [D-Tyr-14C]TAK-448 used in this study represents a favorable labeling position to evaluate disposition properties of this compound.

Mechanism for Covalent Binding of MLN3126, an Oral Chemokine C-C Motif Receptor 9 Antagonist, to Serum Albumins.

N-{4-Chloro-2-[(1-oxidopyridin-4-yl)carbonyl]phenyl}-4-(propan-2-yloxy)benzenesulfonamide (MLN3126) is an orally available chemokine C-C motif receptor 9 selective antagonist. In nonclinical pharmacokinetic studies of MLN3126, nonextractable radioactivity was observed in plasma after oral administration of 14C-labeled MLN3126 ([14C]MLN3126) to Sprague-Dawley (SD) rats. In this study, the nonextractable radioactive component was digested with trypsin or a nonspecific protease, pronase, after chemical reduction to obtain drug-peptide adducts or drug-amino acid adducts. The chemical structure of these adducts was characterized by liquid chromatography/mass spectrometry. The results demonstrated that the major part of the nonextractable radioactivity was accounted for by covalent binding via the Schiff base formed specifically between the ε-amino group of lysine residue 199 in rat serum albumin and the carbonyl group of MLN3126. The half-life (t1/2) of the total radioactivity in plasma during and after 21 daily multiple oral administrations of [14C]MLN3126 to SD rats was approximately 5-fold shorter than the reported t1/2 of albumin in rats. The data indicated that the covalent binding was reversible under physiologic conditions. The formation of the covalent binding was also confirmed in in vitro incubations with serum albumins from rats, humans, and dogs in the same manner, indicating that there are no qualitative interspecies differences in the formation of the Schiff base.

Low-energy methane scattering from Pt(111).

We have measured the temperature dependence of angular distributions of CH4 from Pt(111) at an incident energy of 109 meV. A broad angular distribution has been observed along the two main symmetry directions, whereby the peak center shifts from the supra-specular position to the sub-specular position when the surface temperature increases from 120 K to 800 K. Different widths have been measured for the scattering patterns along the [ 1¯01 ] and the [ 2¯11 ] azimuthal directions. Based on calculations performed within the binary collision model, these differences have been ascribed to different corrugations of the CH4-Pt(111) interaction potential along the two high-symmetry directions. This corrugation has been estimated from the model calculations to amount ∼0.03 Å, a factor of three larger than the one measured with helium diffraction.