Formation of hydrogenated boron clusters in an external quadrupole static attraction ion trap

We report the formation of icosahedral B(12)H(8) (+) through ion-molecule reactions of the decaborane ion [B(10)H(x)(+) (x=6-14)] with diborane (B(2)H(6)) molecules in an external quadrupole static attraction ion trap. The hydrogen content n of B(12)H(n)(+) is determined by the analysis of the mass spectrum. The result reveals that B(12)H(8)(+) is the main product. Ab initio calculations indicate that B(12)H(8)(+) preferentially forms an icosahedral structure rather than a quasiplanar structure. The energies of the formation reactions of B(12)H(14)(+) and B(12)H(12)(+) between B(10)H(x)(+) (x=6,8) ions, which are considered to be involved in the formation of B(12)H(n)(+), and a B(2)H(6) molecule are calculated. The calculations of the detachment pathway of H(2) molecules and H atoms from the product ions, B(12)H(14)(+) and B(12)H(12) (+), indicate that the intermediate state has a relatively low energy, enabling the detachment reaction to proceed owing to the sufficient reaction energy. This autodetachment of H(2) accounts for the experimental result that B(12)H(8)(+) is the most abundant product, even though it does not have the lowest energy among B(12)H(n)(+).     

Ultrafast dynamics of the carbonyl stretching vibration in acetic acid in aqueous solution studied by sub-picosecond infrared spectroscopy

Vibrational energy relaxation of the carbonyl CO stretching modes of CH3COOD and CD3COOD in D2O is studied by frequency-resolved infrared pump-probe spectroscopy. The spectral change caused by the vibrational excitation includes two dynamical components with the time constants of 450 and 980 fs for CH3COOD and 390 and 930 fs for CD3COOD. The two dynamical components exhibit different spectral properties. There are two species of acetic acid forming different complexes with solvent water molecules. The time constants are almost the same for CH3COOD and CD3COOD, suggesting that the vibrational energy deposited to the carbonyl group is first distributed among vibrational modes not related to the methyl group.     

Effect of pressure on colloidal behavior in hydrothermal water

The pressure dependence of the colloidal phenomena of nanoparticles in hydrothermal water was investigated by both experiment and theory. Dynamic light scattering experiments show that diamond nanoparticles, which are highly stable in ambient water, easily aggregate in high-temperature and high-pressure water. Although the stability of nanoparticles in ambient pure water does not depend on pressure, it is interestingly found that at constant temperature particles aggregate faster in the hydrothermal regime when the pressure is higher. A theoretical interpretation is proposed to predict the stability of colloids in water as a function of temperature and pressure. Numerical analysis shows that the repulsive interparticle potential barrier, which stabilizes particles in the dispersion, decreases dramatically in high-temperature and high-pressure water. The decrease in the potential barrier arises from the temperature and the pressure dependencies of the dielectric constant (epsilon) and the ion product (p K w) of water. Numerical analysis shows that the pressure dependence of epsilon is negligible in the temperature range of 20-300 degrees C, whereas the pressure dependence of p K w is significant at temperatures of T > 150 degrees C. The theory reveals that the pressure dependence of the rate of size increment in the hydrothermal regime results from the pressure dependence of p K w. An increase in pressure in the hydrothermal water enhances the ionization of water molecules which reduces the surface potential of the particles. This effect lowers the interparticle repulsive potential barrier, which accelerates aggregation of the particles.     

Observation of molecular ordering at the surface of trimethylpropylammonium bis(trifluoromethanesulfonyl)imide using high-resolution rutherford backscattering spectroscopy

The surface structure of trimethylpropylammonium bis(trifluoromethanesulfonyl)imide ([TMPA] [TFSI]) is studied by high-resolution Rutherford backscattering spectroscopy at room temperature. The results provide direct evidence of the molecular ordering at the surface. The C1 conformer of the [TFSI] anion is dominant among two stable conformers, and the anions are oriented with their CF3 groups pointing toward the vacuum in the outermost molecular layer. The anions in the second molecular layer also show preferred orientation although it is rather weak.     

Durinskiol A: a long carbon-chain polyol compound from the symbiotic dinoflagellate Durinskia sp.

A long carbon-chain polyol compound with a molecular weight of 2128 mu, durinskiol A (1) was isolated from the cultured symbiotic dinoflagellate Durinskia sp. Its planar structure was elucidated based on 2D-NMR and MS/MS analysis. Durinskiol A (1) caused a short body length, abnormal pigment pattern, and pericardiac and yolk-sac edema in zebrafish.     

Spontaneous formation of fractal structures on triglyceride surfaces with reference to their super water-repellent properties

Alkylketene dimer (AKD), a kind of wax, has been known to form fractal surfaces spontaneously and show super water-repellency. Such formation of water-repellent and fractal surfaces was also found in this work for triglycerides. Since the crystal phase transitions of these waxes were well studied, we studied the formation of their fractal surfaces through contact angle measurements, differential scanning calorimetry (DSC), and X-ray diffraction (XRD). From time-dependent contact angle measurements, it was found that the formation of super water-repellent surfaces with fractal structures occurred spontaneously also on the triglyceride surfaces at different temperatures. The freshly solidified triglyceride surfaces were almost transparent, and their initial contact angles of water were close to 110 degrees. The surfaces then became rough and clouded after being incubated for a certain time at a specified temperature. The super water-repellent surfaces were quite rough and showed fractal structures with the dimension of ca. 2.2 calculated from the scanning electron microscopic (SEM) images by the box-counting method. The phase transformation from a metastable state to a stable cystalline one after the solidification from the melt of triglycerides was clearly observed by DSC and XRD measurements. The fractal crystalline structures and the super water-repellency resulted from this phase transformation and the crystal growth. Ensuring the initial sample solidified into the metastable state and curing the surface at an appropriate temperature are key factors for the successful preparation of fractal triglyceride surfaces by the solidification method.     

Recent advances in the structural determination of endohedral metallofullerenes

The structural determination of endohedral metallofullerenes has attracted special attention in disclosing the formation mechanism and developing new routes to bulk production. Recent advances in the theoretical and experimental studies are summarized with representative mono- and dimetallofullerenes such as M@C₈₂ (M=Ca, Sc, Y, and La), Sc₂@C₈₄, and La₂@C₈₀. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 232–239, 1998     

K-Mo基催化剂的表面酸性与其合成醇选择性

对500℃和800℃焙烧制得的氧化态K－MoO3／γ－AlO3，K－MoO3／SiO2及非负载K－Mo催化剂进行硫化后，测试其合成醇活性．结果表明500℃焙烧制得的负载型催化剂显示较高的合成低碳烃活性和较低的合成低磷醇选择性，经800℃焙烧后，合成低磷醇的选择性大幅度提高．500℃焙烧的非负载K－Mo催化剂显示较高的合成醇选择性，经800℃焙烧后，促碳醇的选择性保持不变．用氨的吸附及TPD方法测定了各样品的酸性，并与催化剂活性对照，发现催化剂酸性越强，酸量越大，则其合成醇选择性越低．催化剂上的乙醇分解实验证实，催化剂的酸量大小与它的醇分解活性成正变关系，这些结果说明催化剂酸性对其合成醇性能有直接的影响．     

The polycarbosilane-to-SixC1−x conversion studied by inelastic neutron scattering and infrared absorption

Polycarbosilane (PC) is a precursor which is converted to Si_xC_1−x fibers by pyrolysis in an inert gas atmosphere. The changes in the atomic vibrational spectrum during the conversion process from PC to Si_xC_1−x have been examined by means of inelastic neutron scattering (INS) and infrared absorption (IR). The existence of transverse-optical(TO)- and longitudinal-optical(LO)-like phonon modes due to amorphous SiC clusters was established in the original and pyrolyzed PC by INS measurements. After pyrolyzing at 700–800°C, these modes appear distinctly around 730 and 930 cm⁻¹, respectively, in the INS spectra. Pyrolysis at 1000°C makes these TO- and LO-like phonon modes sharper.