Field ion image qualities of Ga,In and Sn on W and work functions

It has been found previously that Ga, In and Sn form a pseudomorphic monolayer on W which maximizes the work function of the covered surface. In the present work the bright and sharp field ion images of the pseudomorphic monolayer are shown comparing the images of the substrate tungsten. The interesting finding is that the images of the covering layer are most distinct for Sn which gives rise to the largest increment in the work function, and are least for In which has the smallest work function increment. A simple calculation on the penetration probaility of an electron into the potential barrier between an imaging gas atom and a metal surface indicates that the probability increases significantly with the work function and consequently the covered area would be images brightly. The calculation also suggests that the work function, that is the surface charge distribution, is one of the key factors controlling the quality of the field ion images.     

Improvement of the high-speed log D assay using an injection marker for the water plug aspiration/injection method

An improved method for the high-speed assay for log D (HSLogD) employing an injection marker is described. The critical process of HSLogD is automated sampling of the water phase, which prevents contamination from the octanol phase. However, deployment of HSLogD sometimes produces incorrect and inaccurate values compared with data from closely related methods due to low solubility of compounds or instrument problems. Therefore, careful manual inspection of data is needed to confirm the results obtained by this method. To solve this problem, compounds were screened for suitability as injection markers and 2-(4-methoxyphenoxy)-4,8-dimethylquinoline was the most suitable compound examined. Introduction of the injection marker into the process successfully eliminated the need for the tedious and time-consuming manual inspection process.     

Control of the Transition between Ni‐C and Ni‐SIa States by the Redox State of the Proximal Fe?S Cluster in the Catalytic Cycle of [NiFe] Hydrogenase

[NiFe] hydrogenase catalyzes the reversible cleavage of H₂. The electrons produced by the H₂ cleavage pass through three Fe–S clusters in [NiFe] hydrogenase to its redox partner. It has been reported that the Ni‐SI_a, Ni‐C, and Ni‐R states of [NiFe] hydrogenase are involved in the catalytic cycle, although the mechanism and regulation of the transition between the Ni‐C and Ni‐SI_a states remain unrevealed. In this study, the FT‐IR spectra under light irradiation at 138–198 K show that the Ni‐L state of [NiFe] hydrogenase is an intermediate between the transition of the Ni‐C and Ni‐SI_a states. The transition of the Ni‐C state to the Ni‐SI_a state occurred when the proximal [Fe₄S₄]_p^2+/+ cluster was oxidized, but not when it was reduced. These results show that the catalytic cycle of [NiFe] hydrogenase is controlled by the redox state of its [Fe₄S₄]_p^2+/+ cluster, which may function as a gate for the electron flow from the NiFe active site to the redox partner.     

Total Synthesis of Chiriquitoxin,an Analogue of Tetrodotoxin Isolated from the Skin of a Dart Frog

The first total synthesis of chiriquitoxin, the most structurally complex analogue of tetrodotoxin isolated from a Costa Rican dart frog, has been accomplished from a newly designed intermediate for a variety of tetrodotoxin derivatives. The synthesis includes the third total synthesis of tetrodotoxin in this laboratory, and its intermediate was transformed into chiriquitoxin by a stereocontrolled aldol reaction with a D ‐camphor‐derived lactone for installation of the unique side chain, and a new deprotection of methylthiomethyl (MTM) ether by using a Pummerer rearrangement.     

Synthesis of Tetrodotoxin,a Classic but Still Fascinating Natural Product

Tetrodotoxin, a toxic principle of puffer fish intoxication, is one of the most famous marine natural products due to its densely functionalized structure and potent toxicity. Despite its small molecular size (MW 319 g mol^?1), tetrodotoxin has long been well known as a formidable molecule in natural product synthesis. We have devoted more than twenty years to developing synthetic strategies for this molecule, resulting in the preparation of a variety of analogues of tetrodotoxin for biological experiments. This account describes a brief history of tetrodotoxin research and an overview of our synthetic efforts toward tetrodotoxin with the underlying logic and strategy.     

Calculation of quasiparticle energy of molecular systems by the GW method

The quasiparticle energy of the H₂ molecule is calculated by using the GW method, in which the self‐energy operator fully depends on the frequency. The initial Green function G₀ is constructed from the wave function obtained by the Hartree–Fock approximation (HFA) and local density approximation (LDA) in the framework of the density functional theory (DFT). From the results obtained we have shown that the wave function from the DFT–LDA is more effective than that from the HFA for G₀. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 348–353, 2001     

New organic superconductors beta-(BDA-TTP)2X [BDA-TTP + 2,5-bis(1,3-dithian-2ylidene)-1,3,4,6-tetrathiapentalene; X(-) = SbF6(-), AsF6(-), and PF6(-)].

The synthesis, electrochemical properties, and molecular structure of a new pi-electron donor, 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP), is described. In contrast to the hitherto-known tetrachalcogenafulvalene pi-donors providing organic superconductors, this donor contains only the bis-fused 1,3-dithiole-2-ylidene unit as a pi-electron system, yet produces a series of ambient-pressure superconductors beta-(BDA-TTP)2X [X = SbF6 (magnetic T(c) = 6.9 K, resistive T(c) = 7.5 K), AsF6 (magnetic T(c) = 5.9 K, resistive T(c) = 5.8 K), and PF6 (magnetic T(c) = 5.9 K)], which are isostructural. The values of the intermolecular overlap integrals calculated on the donor layers of these superconductors suggest a two-dimensional (2D) electronic structure with loose donor packing. Tight-binding band calculations also indicate that these superconductors have the 2D band dispersion relations and closed Fermi surfaces.     

New mesogens with cubic phases: hydrogen-bonded bipyridines and siloxane-containing benzoic acids II. Structural studies

The supramolecular structure of new hydrogen-bonded mesogens composed of dipyridyl and 4-(oligodimethylsiloxyl)alkoxybenzoic acids was investigated by X-ray diffraction and deuterium NMR. These H-bonded mesogens exhibit a cubic thermotropic liquid crystalline phase at a temperature below a smectic A phase. Moreover, above the smectic A phase two optically isotropic, low viscosity phases (I₁ and I₂) exist with the lower temperature I₁ phase comprising aggregated mesogens. Two broad, temperature-independent, wide angle X-ray reflections suggest that the aggregation is driven by nanophase-separation; the aggregate adopts a structure with one domain siloxane rich and the other hydrocarbon rich. In the isotropic melt near the I₁-to-I₂ phase transition, a very weak small angle reflection, indicates incipient lamellar-like clustering of the aggregated mesogens. With decreasing temperature the intensity of the small angle reflection increases and in the smectic A phase, the reflection becomes very sharp. In the cubic phase the small angle reflection splits into two peaks which can be indexed with a face-centred cubic (FCC) structure. The deuterium NMR measurements in the isotropic and smectic A phases are indicative of aggregation and an oriented, lamellarlike structure, respectively. In the cubic phase, the collapse of quadrupolar splittings is consistent with an isotropic average of the quadrupole interaction caused by mesogen translational diffusion through a cubic supramolecular structure.     

Very simple,carbuncle-free,boundary-layer-resolving,rotated-hybrid Riemann solvers

In this paper, we propose new Euler flux functions for use in a finite-volume Euler/Navier–Stokes code, which are very simple, carbuncle-free, yet have an excellent boundary-layer-resolving capability, by combining two different Riemann solvers into one based on a rotated Riemann solver approach. We show that very economical Euler flux functions can be devised by combining the Roe solver (a full-wave solver) and the Rusanov/HLL solver (a fewer-wave solver), based on a rotated Riemann solver approach: a fewer-wave solver automatically applied in the direction normal to shocks to suppress carbuncles and a full-wave solver applied, again automatically, across shear layers to avoid an excessive amount of dissipation. The resulting flux functions can be implemented in a very simple and economical manner, in the form of the Roe solver with modified wave speeds, so that converting an existing Roe flux code into the new fluxes is an extremely simple task. They require only 7–14% extra CPU time and no problem-dependent tuning parameters. These new rotated fluxes are not only robust for shock-capturing, but also accurate for resolving shear layers. This is demonstrated by an extensive series of numerical experiments with standard finite-volume Euler and Navier–Stokes codes, including various shock instability problems and also an unstructured grid case.     

Cysteine SH and Glutamate COOH Contributions to [NiFe] Hydrogenase Proton Transfer Revealed by Highly Sensitive FTIR Spectroscopy

A [NiFe] hydrogenase (H₂ase) is a proton‐coupled electron transfer enzyme that catalyses reversible H₂ oxidation; however, its fundamental proton transfer pathway remains unknown. Herein, we observed the protonation of Cys546‐SH and Glu34‐COOH near the Ni–Fe site with high‐sensitivity infrared difference spectra by utilizing Ni‐C‐to‐Ni‐L and Ni‐C‐to‐Ni‐SI_a photoconversions. Protonated Cys546‐SH in the Ni‐L state was verified by the observed SH stretching frequency (2505 cm^?1), whereas Cys546 was deprotonated in the Ni‐C and Ni‐SI_a states. Glu34‐COOH was double H‐bonded in the Ni‐L state, as determined by the COOH stretching frequency (1700 cm^?1), and single H‐bonded in the Ni‐C and Ni‐SI_a states. Additionally, a stretching mode of an ordered water molecule was observed in the Ni‐L and Ni‐C states. These results elucidate the organized proton transfer pathway during the catalytic reaction of a [NiFe] H₂ase, which is regulated by the H‐bond network of Cys546, Glu34, and an ordered water molecule.