Applications of spectral-Representation model as a potential method for Cu clusters

We applied the spectral-representation technique developed by Katsuki and Huzinaga as a model potential in calculating the electronic structure of Cu clusters. The characteristics of this potential were closely investigated in Cu and Cu₂. For Cu, Cu₂, Cu₅, Cu₉, and Cu₁₃, we performed all-electron ab initio self-consistent field calculations and model-potential calculations where 3p, 3d, and 4s electrons, and 3d and 4s electrons are treated as valence electrons. The ionization potentials (IPs) given by the all-electron calculations were 6.26, 5.55, 4.52, 4.02, and 4.08 eV for Cu, Cu₂, Cu₅, Cu₉, and Cu₁₃, respectively. The IPs given by the model-potential calculations were 6.25, 5.56, 4.62, 4.09, and 4.23 eV for the 3p-, 3d-, and 4s-valence electrons, and 6.26, 5.68, 4.71, 4.07, and 4.19 eV for the 3d- and 4s-valence electrons. The IPs given by the model-potential calculations agree well with those of the all-electron calculations. We also performed model-potential calculations where only the 4s electrons were treated as valence electrons. The calculated IPs were 6.47, 5.98, 5.38, 4.63, and 4.88 eV for Cu, Cu₂, Cu₅, Cu₉, and Cu₁₃, respectively. These are ca. 0.8 eV higher than the IPs by the all-electron calculation for the larger clusters of Cu₅, Cu₉, and Cu₁₃. The higher IPs originate from the expulsion of the 3d electrons from the valence electrons. We also performed model-potential calculations with 4s electrons for Cu₇₄. The calculated IP is 4.61 eV, which is estimated to be 0.8 eV larger than that obtained by the all-electron calculation. The IPs with correlation corrections are 7.7, 7.4, 6.3, 5.8, 5.9, and 5.6 eV for Cu, Cu₂, Cu₅, Cu₉, Cu₁₃, and Cu₇₄, respectively. Experimental values are 7.73, 7.37, 6.30, 5.37, 5.67, and 5.26 eV. The agreement between the two is fairly good. The electron affinities are also discussed. © 1996 by John Wiley & Sons, Inc.     

Synthesis of nitrogen‐containing heterocycles 9. Preparation and carbon‐carbon bond cleavage of spiro[cycloalkane[1′,2′,4′]‐triazolo[1′,5′‐a][1′,3′,5′]triazine] derivatives and related compounds

Diaminomethylenehydrazones of cyclic ketones 1–5 reacted with ethyl N‐cyanoimidate (I) at room temperature or with bis(methylthio)methylenecyanamide (II) under brief heating to give directly the corresponding spiro[cycloalkane[1′,2′,4′]triazolo[1′,5′,‐a][1′,3′‐5′]triazine] derivatives 7–12 in moderate to high yields. Ring‐opening reaction of the spiro[cycloalkanetriazolotriazine] derivatives occurred at the cycloalkane moiety upon heating in solution to give 2‐alkyl‐5‐amino[1,2,4]triazolotriazines 13–16. Diaminomethylenehydrazones 17–19, of hindered acyclic ketones, gave 2‐methyl‐7‐methylthio[1,2,4]‐triazolo[1,5‐a][1,3,5]triazines 21–23 by the reaction with II as the main products with apparent loss of 2‐methylpropane from the potential precursor, 2‐tert‐butyl‐2‐methyl‐7‐methylthio[1,2,4]triazolo[1,5‐a]‐[1,3,5]triazines 20, in good yields. In general, bis(methylthio)methylenecyanamide II was found to be a favorable reagent to the one‐step synthesis of the spiro[cycloalkanetriazolotriazine] derivatives from the diaminomethylenehydrazones. The spectral data and structural assignments of the fused triazine products are discussed.     

Facile synthesis of 2,4-dioxo-1,2,3,4-tetrahydroquinazolines by sulfur-assisted carbonylation with carbon monoxide

2,4-Dioxo-1,2,3,4-tetrahydroquinazolines were easily synthesized in excellent yields by sulfur-assisted carbonylation of 2′-aminobenzamides with carbon monoxide in the presence of a base, such as DBU or DBN.     

Atomic force microscopy: Bombyx mori silk fibroin molecules and their higher order structure

We performed atomic force microscopy measurements on fibroin molecules from the domestic silkworm, Bombyx mori. At low concentrations, we could observe single protein molecules. The shape of the observed molecules is a rod with long smaller chains extending from the ends. The size of the rod is 60 nm in length and 15 nm in width. At high concentrations, we observed long threadlike aggregates of fibroin molecules, their chains entangled with one another. These results provide insight into the microscopic mechanism of silk‐fiber formation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1436–1439, 2000     

A Measurement Technique for Organic Nitrates and Halocarbons in Ambient Air

A cryogenic preconcentration/high-resolution gas chromatographic technique has been developed for the rapid, simultaneous quantitation of C₁–C₄ organic nitrates and halocarbons in ambient air. Whole-air samples are collected in Tedlar^TM bags by an evacuated-chamber method. Samples were stable in 0.010-cm-thick bags for 24 h if they were immediately stored in a freezer at −25°C. Analytes in a 50-cm³ air sample were efficiently preconcentrated on fused-silica beads at −180°C and thermally desorbed at 30°C. High-resolution gas chromatography with a cross-linked polydimethylsiloxane fused-silica capillary column and an electron-capture detector were used for separation and quantitation of the analytes. An analysis time of about 12 min was facilitated by sample cryofocusing at −180°C and oven temperature programming. Recoveries of the analytes by the evacuated-chamber method were better than 95%. The sensitivity of the technique for sample volumes of 50 cm³ is in the sub-parts-per-trillion by volume (ppt[v]) range for many of the analytes, with an average precision of about ±5% for analytes at levels of about 10 ppt(v).     

Perceptual discrimination of very high frequency components in wide frequency range musical sound

Subjective evaluation tests on perceptual discrimination between musical sounds with and without very high frequency (above 20 kHz) components were conducted. To make a precise evaluation, the test system was designed to exclude any influence from very high frequency components in the audible frequency range. Moreover, a newly developed very wide frequency range microphone was used to record various sound stimuli that contained enough components in the very high frequency range. Tests showed that the subjects could discriminate between musical sounds with and without very high frequency components. This paper describes these subjective evaluations in terms of reproducing such very high frequency components in musical sound.