Transverse excitations in liquid Sn.

Transverse acoustic (TA) excitation modes were observed in inelastic x-ray scattering (IXS) spectra of liquid Sn. The excitation energies and widths of the TA modes are in good agreement with results of an ab initio molecular dynamics simulation. By comparing current correlation spectra between the experimental and theoretical results quantitatively, we have concluded that the TA modes can be detected experimentally through the quasi-TA branches in the longitudinal current correlation spectra. The lifetime and propagation length of the TA modes were determined to be ~0.7 ps and 0.8-1.0 nm, respectively, corresponding to the size of cages formed instantaneously in liquid Sn.

Surface waves on non-Newtonian viscoelastic liquids.

In the present work, we study the dynamics of thermally excited fluctuations on the surface of non-Newtonian viscoelastic liquids, which shows complex behaviors such as crossover between the capillary wave and the elastic wave, and the coexistence of several modes. We show that the power spectrum is separated into surface localized modes and the bulk shear modes, and they are decomposed further into several modes using the partial fraction expansion. The peak positions of these modes are characterized by roots of a polynomial equation. We calculate the decomposition of the surface wave spectra numerically, and discuss evolution of constituent peaks with liquid parameters.

Bulk shear-mode contribution to thermally generated capillary waves on a room-temperature ionic-liquid surface.

In the present work, we show that the autocorrelation function of the capillary-wave displacement is expressed by the sum of the ordinary oscillator and the bulk shear-mode terms. The former is expressed by a simple damped oscillator form or a sum of exponentially damping functions depending on the extent of damping. The latter is also written by superposition of exponentially damping modes, and an analytically exact formulation is obtained. We performed surface dynamic light-scattering experiment for the surface of an ionic liquid, 1-butyl- 3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, and compared the experimental autocorrelation function with the theoretical one. We observed for the first time the bulk shear-mode contribution, and confirmed that the experimental data is well explained by the theoretical autocorrelation function.

Surface tension of room temperature ionic liquids measured by dynamic light scattering.

Using dynamic light scattering techniques, we obtained the surface tension sigma, surface excess entropy S(sigma), surface excess enthalpy H(sigma), and viscosity eta for the following seven room temperature ionic liquids in a wide temperature range from 30 to around 140 degrees C: 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methyl imidazolium hexafluorophosphate. We have found that sigma increases systematically with decreasing the anion size and the alkyl side chain length. On the other hand, S(sigma) and eta increase with decreasing the anion size but decrease with decreasing the alkyl chain length. H(sigma) seems to decrease with increasing the anion size, but it has no clear dependence on the alkyl chain length. We discuss the bulk and surface properties, referring to the Coulomb interactions and van der Waals interactions.

Dispersion relation of capillary waves on ionic liquids: observation of the fast overdamped mode.

We measured the capillary wave spectra on the surface of ionic liquids using dynamic light scattering techniques. Empirical dispersion relations deduced from the time domain analysis clearly reveal the transition from oscillating to overdamped behavior with changing temperature and the wave vector. In particular, not only slow but also fast modes were observed in the overdamped regime. The empirical dispersion relations coincide with the theoretical dispersion relations deduced from the linearized Navier-Stokes equation when experimentally determined density, viscosity, and surface tension are assigned to the latter.

Electron-ion-coincidence spectra of K-shell excited Ne, Ar, and Kr clusters.

Electron-ion-coincidence spectra were recorded for K-shell excited krypton, argon, and neon clusters covering the size range from 1 atom to about 3000 atoms by utilizing hard x-ray undulator beamlines. Multiply charged ions Rz+(z>or=2) and singly charged ions Rn+(n>or=1) are observed as cluster fragments, and their relative abundance exhibits a characteristic dependence on the average cluster size N. It is expected from these results that the charges generated on the cluster surface are strongly localized while those in the cluster core are more delocalized. The estimated charge separation distance increases with N, and it is longer for lighter elements.

Coulomb explosion of K-shell ionized krypton clusters studied by multiple-ion coincidence momentum imaging.

The Coulomb explosion of K-shell ionized krypton clusters with an average size N of 160 has been studied by electron-multiple-ion-coincidence measurements in which the time-of-flight (TOF) of ions was measured by using a position sensitive detector. The authors have sorted the TOF spectra by the number of coincidence ion signals, Ncoin, and found that singly charged fragment ions such as Kr+, Kr2+, and Kr3+ are dominant for Ncoin>or=2, and that multiply charged ions are detected mainly for Ncoin=1. The Ncoin dependence of the peak widths in the TOF spectra reveals that the average momentum of the Kr+ ions increases with Ncoin, while those of Kr2+ and Kr3+ decrease. These results have been more directly confirmed by the momentum imaging measurements. The authors propose that the heavier ions are produced in the central part of clusters where the Coulomb interactions from the surrounding ions are more effectively canceled out due to the higher symmetry.

Critical point dewetting observed in the liquid Se-Tl system on a quartz substrate.

We have studied the wetting phenomena of the liquid Se-Tl system on a quartz substrate by photography and ellipsometry, and found that a thin layer of the Se-rich liquid phase intrudes between the Tl-rich liquid phase and the quartz substrate in the temperature region far below the critical temperature. Surprisingly, neither the Se-rich nor the Tl-rich wetting film is formed near the critical temperature, indicating the critical point dewetting. In addition, we found that the temperature difference between the surface and the bulk liquid induces the transition between the wetting and non-wetting states. In order to interpret the observation, we constructed a model grand potential, incorporating the long-range interaction, the temperature difference and gravity. From this analysis, it is suggested that the combination of the long-range force and gravity plays an important role in overcoming the critical point wetting phenomena.

Size-selective extended X-ray absorption fine structure spectroscopy of free selenium clusters.

In a recent paper [M. Yao et al., J. Synchrotron Radiat. 8, 542 (2001)]], we proposed a new method for the size-selective EXAFS (extended x-ray absorption fine structure) of neutral-free clusters, in which not only the x-ray absorption process but also the deexcitation processes are utilized as the structural information. In order to verify this method experimentally, we have developed the synchronous measurements of EXAFS and photoelectron photoion coincidence and carried them out for a Se cluster beam by utilizing the third-generation intense x-ray source. The EXAFS spectra for Se small clusters have been obtained and compared critically with theoretical predictions.

A new method for the size-selective EXAFS of neutral free clusters.

Recently we have measured Photoelectron Photoion Coincidence (PEPICO) spectra for selenium dimer Se2 and larger species such as Se5 at the beamline BL-12C in Photon Factory. The PEPICO spectra reveal that the multiply charged ions, Se(z+), are produced as a result of de-excitation processes following the inner-shell excitation and fragmented to atomic ions owing to the Coulomb explosion. The branching ratios from the parent clusters to the daughter ions exhibit clear dependence on the size of the parent clusters. In particular, the branching ratios in the non-resonant absorption region are well reproduced by assuming that the charges are randomly distributed within the clusters before the Coulomb explosion. Based upon these findings, we propose a new method for the size-selective EXAFS of neutral free clusters by utilizing the PEPICO measurements.

Mercury wetting film on sapphire.

We have measured optical properties of a mercury wetting film on sapphire under high temperature and high pressure near the liquid-gas critical point of mercury by using a newly developed 45 degrees reflection technique. We have analyzed the experimental data to deduce the density, the thickness, and the coverage of the wetting film quantitatively as functions of pressure and temperature. As a first approximation, we have assumed a slab model for the density profile of the wetting film, and found that the density of the wetting film dslab is much smaller than that of bulk liquid at the liquid-vapor coexistence curve. This result is consistent with the Lifshitz theory, from which we may predict that the sapphire substrate prefers wetting film with density lower than the metal-nonmetal transition. When the temperature is close enough to the prewetting critical temperature Tpw(c), the effective slab density dslab shows a sharp decrease as the pressure approaches the liquid-gas coexistence. This indicates that the slab model is not sufficient to describe the shape of the wetting film, and a smooth variation of the density has to be taken into account. In the prewetting supercritical region, two anomalies are observed in the reflectances. Possible mechanisms of these anomalies are discussed.

Genomic structure of mouse copper chaperone, COX17.

Coxl7p was first cloned as a cytoplasmic copper chaperone from yeast mutant and recent works suggested the existence of mammalian homologues. Previous report has shown that a gel filtration fraction of heart extract containing porcine Coxl7p peptide promoted the survival of NIH3T3 fibroblast cells. In the present study, we first cloned DNA fragments of the mouse COX17 gene. The mouse COX17 spans approximately 6kb and consists of three exons. It was mapped to the center of chromosome 16, using a radiation hybrid-mapping panel. The major transcription start site is 80 bp upstream of the ATG initiation codon as determined by rapid amplification of cDNA ends (5'-RACE) analysis. Two potential polyadenylation sites are 3233 and 3293 bp downstream of the termination codon, respectively. Transient transfection of reporter plasmids containing portions of the mouse COX17 5'-flanking region into AtT-20 and NIH3T3 cells allowed the localization of the essential promoter to a 0.8 kb region upstream of the transcription starting site. Furthermore, the transfected luciferase activity was much higher in AtT-20 than NIH3T3. According to sequence analysis of the approximately 0.8kb 5'-flanking region, GC rich segments including consensus sequences for binding of the transcription factor Sp1, but no TATA/CAAT boxes, exist in the region of the transcription start site. Besides the GC box, binding sites for NRF-1 and 2 known as specific transcription factors for COX subunits are also localized around the transcription starting site.

The expression of Cox17p in rodent tissues and cells.

Previous works have reported the isolation of a novel polypeptide from porcine heart. Structural analysis has shown that it is a mammalian homologue of Cox17p, believed essential for the assembly of functional cytochrome c oxidase and delivery of copper ions to the mitochondrion for insertion into the enzyme in yeast. Although the human, mouse and porcine homologs of this small protein have already been cloned or purified, the function of Cox17p in the mammalian system has not yet been elucidated. To investigate the physiological function of Cox17p in mammals, we performed Northern blot analysis using probes containing the mouse and rat sequences obtained by RT-PCR. The hybridization signals were detected in all mouse tissues, but notably intense signals were observed in heart, brain and kidney RNA samples. Some of the neuroendocrine and endocrine cell lines showed higher expression levels than fibroblasts. The highest expression level of Cox17p mRNA in mouse brain was observed in the pituitary sample. While in rat heart, Cox17p mRNA expression was detected from early development, in rat brain, embryonic and postnatal changes in the expression were observed. Immunocytochemical analysis showed that Cox17p immunoreactivity was strong in the pituitary cell line, AtT-20. These findings suggested that Cox17p is not only part of the respiratory chain but also involved in brain and endocrine functions.

Chiral HPLC resolution of monoepoxides derived from 6,9-dienes and its application to stereochemistry assignment of fruit-piercing noctuid pheromone.

The resolution of insect pheromonal cis-monoepoxy racemates derived from (Z,Z)-6,9-dienes was examined employing chiral HPLC columns, and the results showed that a normal-phase column (Chiralpak AD) was suitable for both 6,7- and 9,10-epoxides with a C(17)-C(23) straight chain, as was a reversed-phase column (Chiralcel OJ-R) for the 6, 7-epoxides. To determine the absolute configuration of each separated enantiomer applying a modified Mosher's method, the epoxy ring was opened by methanolysis, and the (1)H-NMR data of (S)- and (R)-MTPA esters of the methoxyalcohols produced were analyzed. Further, the hydrogenated product of each enantiomer was chromatographed on the OJ-R column referring to the corresponding authentic chiral compounds with a saturated chain, which were prepared by a Sharpless epoxidation reaction. These analyses showed that the levorotatory 6,7- and 9,10-epoxides with shorter t(R)s possess 6S,7R and 9R,10S configuration, respectively, and the dextrorotatory enantiomers with longer t(R)s possess the opposite configuration. Utilizing this chiral HPLC, it was revealed that an abdominal tip extract of the fruit-piercing moth, Oraesia excavata Butler (Lepidoptera: Noctuidae), included (9S,10R)-(Z)-9, 10-epoxy-6-henicosene as a main sex pheromone component. The synthetic 9,10-epoxide with this configuration, which was separated from the racemate, exhibited stronger activity in electrophysiological and field tests against male moths than the enantiomer.