Time-, spin-, and angle-resolved photoemission spectroscopy with a 1-MHz 10.7-eV pulse laser.

We describe a setup of time-, spin-, and angle-resolved photoemission spectroscopy (tr-SARPES) employing a 10.7 eV (λ = 115.6 nm) pulse laser at a 1 MHz repetition rate as a probe photon source. This equipment effectively combines the technologies of a high-power Yb:fiber laser, ultraviolet-driven harmonic generation in Xe gas, and a SARPES apparatus equipped with very-low-energy-electron-diffraction spin detectors. A high repetition rate (1 MHz) of the probe laser allows experiments with the photoemission space-charge effects significantly reduced, despite a high flux of 1013 photons/s on the sample. The relatively high photon energy (10.7 eV) also brings the capability of observing a wide momentum range that covers the entire Brillouin zone of many materials while ensuring high momentum resolution. The experimental setup overcomes the low efficiency of spin-resolved measurements, which gets even more severe for the pump-probed unoccupied states, and affords the opportunity to investigate ultrafast electron and spin dynamics of modern quantum materials with energy and time resolutions of 25 meV and 360 fs, respectively.

Proving Nontrivial Topology of Pure Bismuth by Quantum Confinement.

The topology of pure Bi is controversial because of its very small (∼10 meV) band gap. Here we perform high-resolution angle-resolved photoelectron spectroscopy measurements systematically on 14-202 bilayer Bi films. Using high-quality films, we succeed in observing quantized bulk bands with energy separations down to ∼10 meV. Detailed analyses on the phase shift of the confined wave functions precisely determine the surface and bulk electronic structures, which unambiguously show nontrivial topology. The present results not only prove the fundamental property of Bi but also introduce a capability of the quantum-confinement approach.

An atomic seesaw switch formed by tilted asymmetric Sn-Ge dimers on a Ge (001) surface.

When tin (Sn) atoms are deposited on a clean germanium (Ge) (001) surface at room temperature, buckled dimers originating from the Sn atoms are formed at the Ge-dimer position. We identified the dimer as a heterogeneous Sn-Ge dimer by reversing its buckling orientation with a scanning tunneling microscope (STM) at 80 kelvin. An atomic seesaw switch was formed for one-dimensional electronic conduction in the Ge dimer-row direction by using the STM to reversibly flip the buckling orientation of the Sn-Ge dimer and to set up standing-wave states.

"Physiological" age as an outcome predictor for abdominal surgery in elderly patients.

It would seem that a large discrepancy exists between the "chronological" age and "apparent" age of elderly patients, and we often observe that the latter reflects the results of surgical procedures very well. In the present study, we reviewed 258 patients aged 70 years or older who underwent elective abdominal operations under general anesthesia, to evaluate an outcome predictor representing their "physiological" age. A total of 24 preoperative variables were compared between patients who left the hospital in a satisfactory condition, being survivors, and those who died in hospital despite the operative procedure performed, being nonsurvivors. In the group of patients aged between 70 and 79 years, there was no significant difference between the survivor and nonsurvivor groups for any of the variables examined; however, in the group of patients aged over 80 years old, the oldest of whom was 93 years, there were significant differences in the total lymphocyte count (TLC) and the performance status (PS), as well as in age, between the survivor and nonsurvivor groups. Utilizing the three variables of age, PS, and TLC, a computer-generated discriminant function analysis yielded an equation which discriminated survival with 97% accuracy, and mortality with 83% accuracy. These findings indicate that the PS and TLC scores added to the chronological age should be considered when deciding whether a surgical procedure is appropriate for an elderly patient.

1-Acetyl-7-deacetylforskolin: a potential non-specific inactive analog of forskolin for estimation of its specific high-affinity binding and adenylyl cyclase stimulation in vitro.

Labeled and unlabeled 1-acetyl-7-deacetylforskolin and forskolin were synthesized by acetylation of 7-deacetylforskolin with labeled and unlabeled acetyl chloride. The binding of 1-acetyl[1-acetyl-11C]-7-deacetylforskolin ([11C]1-acetyl-7-deacetylforskolin) and [7-acetyl-11C]forskolin ([11C]forskolin) to rat brain membranes was studied using filtration assay. The [11C]forskolin binding was decreased with an increasing load of unlabeled forskolin, whereas [11C]1-acetyl-7-deacetyl-forskolin binding was always very low, the level of which agreed with that of the non-specific binding in forskolin. However, binding of [7-acetyl-11C]1,9-dideoxyforskolin, which has been used as a non-specific inactive analog of forskolin, had a higher binding ratio than that of the non-specific binding of forskolin. The binding of [11C]forskolin was not affected by an increased load of cold 1-acetyl-7-deacetylforskolin. Forskolin activated adenylyl cyclase (AC) in cultured human endothelial cells, whereas 1-acetyl-7-deacetylforskolin did not. These data show that the 1-acetyl-7-deacetylforskolin lacks specific binding affinity and the ability to stimulate AC, while it has similar physical properties with forskolin. The compound 1-acetyl-7-deacetylforskolin would be a suitable "non-specific inactive analog" of forskolin with which to estimate its specific high-affinity binding capacity and to validate forskolin-specific AC stimulation in vitro.

Conformational rigidity of specific pyrimidine residues in tRNA arises from posttranscriptional modifications that enhance steric interaction between the base and the 2'-hydroxyl group.

In order to elucidate roles of the 2'-O-methylation of pyrimidine nucleotide residues of tRNAs, conformations of 2'-O-methyluridylyl(3'----5')uridine (UmpU), 2'-O-methyluridine 3'-monophosphate (Ump), and 2'-O-methyluridine (Um) in 2H2O solution were analyzed by one- and two-dimensional proton NMR spectroscopy and compared with those of related nucleotides and nucleoside. As for UpU and UmpU, the 2'-O-methylation was found to stabilize the C3'-endo form of the 3'-nucleotidyl unit (Up-/Ump-moiety). This stabilization of the C3'-endo form is primarily due to an intraresidue effect, since the conformation of the 5'-nucleotidyl unit (-pU moiety) was only slightly affected by the 2'-O-methylation of the 3'-nucleotide unit. In fact even for Up and Ump, the 2'-O-methylation significantly stabilizes the C3'-endo form by 0.8 kcal/.mol-1. By contrast, for nucleosides (U and Um), the C3'-endo form is slightly stabilized by 0.1 kcal/.mol-1. Accordingly, the stabilization of the C3'-endo form by the 2'-O-methylation is primarily due to the steric repulsion among the 2-carbonyl group, the 2'-O-methyl group and the 3'-phosphate group in the C2'-endo form. For some tRNA species, 2-thiolation of pyrimidine residues is found in positions where the 2'-O-methylation is found for other tRNA species.(ABSTRACT TRUNCATED AT 250 WORDS)

A study on conformationally restricted sangivamycins and their inhibitory abilities of protein kinases.

Conformational restrictions of sangivamycin, a rather selective inhibitor of PKC, could be achieved by the use of the steric effect and the gauche effect of the substituents on the ribofuranose moiety. The conformational deviations obtained by these methods were found to nicely correlate with the inhibitory ability of PKC.