Kinetics of the dehydration of boehmites prepared under different hydrothermal conditions

The kinetics of the dehydration of five boehmites, which were prepared under different hydrothermal conditions (300°C, 85 atm, 20 h — 150°C, 4.5 atm, 5 h), were studied by means of isothermal TG at an air pressure of 150 mm Hg and at a constant flow rate of nitrogen (30 ml min^?1) containing water vapor of partial pressures between 10^?4 and 23.8 mm Hg. It was found that the dehydration temperature of boehmites was lowered as the preparation conditions became more mild. Moreover, the rate-controlling step of the dehydration of boehmites varied with their preparation conditions. The water vapor pressure led to decreases in the rate of dehydration.     

Helical rosette nanotubes with tunable stability and hierarchy

The design of nanostructured materials with tunable dimensions and properties that maintain their structural integrity under physiological conditions is a major challenge in biomedical engineering and nanomedicine. Helical rosette nanotubes (HRN) are a new class of materials produced through a hierarchical self-assembly process of low molecular weight synthetic organic modules in water. Here, we describe a synthetic strategy to tune their stability and hierarchy by preorganization of the self-assembling units, control of net charge per unit of nanotube surface area, amphiphilicity, and number of H-bonds per self-assembling module, and through peripheral steric (de)compression. Using these criteria, HRNs with tunable stability and hierarchical architecture were produced from self-assembling modules that (a) persist as individual molecules in solution, (b) self-assemble into HRN but denature at high temperature (<85 degrees C), (c) self-assemble into HRN whose structural integrity persists even in boiling water (>95 degrees C), and (d) self-assemble into well-dispersed short nanotubes, long nanotubes, ribbons, or superhelices. Given the biocompatibility, synthetic accessibility, and chemical and physical tunability of these materials, numerous applications in biomedical engineering, materials science, and nanoscience and technology are envisioned.     

Monomer-isomerization polymerization. XIII. Monomer-isomerization polymerization of 1,4-cyclohexadiene with Ziegler-Natta catalyst

1,4-Cyclohexadiene underwent monomer-isomerization polymerization to yield poly(1,3-cyclohexadiene) with a Ziegler-Natta catalyst comprising TiCl₄–Al(C₂H₅)₃ catalyst with Al/Ti molar ratios of 0.5–3.0 at 60°C for 96 hr. Good yields of polymer were obtained (49.5% yield at Al/Ti = 3.0; [η] = 0.04 dl/g). The infrared and NMR spectra of the polymer were identical to those of poly-(1,3-cyclohexadiene), confirming that 1,4-cyclohexadiene first isomerizes to 1,3-cyclohexadiene and then homopolymerizes to give poly-1,3-cyclohexadiene. 1,3-Cyclohexadiene polymerized without isomerization easily in the presence of TiCl₃–Al(C₂H₅)₃ catalyst at Al/Ti molar ratios of 0.5–3.0 at 60°C for 3 hr (76.3% yield at Al/Ti = 3.0; [η] = 0.06 dl/g).     

Evaluation of photoinduced changes in stability constants for metal-ion complexes of crowned spirobenzopyran derivatives by electrospray ionization mass spectrometry

The photoinduced changes of metal-ion complexing ability of crowned spirobenzopyran derivatives were studied by using electrospray ionization mass spectrometry (ESI-MS). Stability constants for the complexation with various metal ions in methanol under visible-irradiation conditions were determined for the first time by ESI-MS. It was found that the stability constants of crowned bis(spirobenzopyran) derivatives with metal ions are decreased dramatically by visible irradiation due to the disappearance of powerful ionic interaction between phenolate anion(s) of the merocyanine form of their spirobenzopyran moiety and a metal ion bound to their crown ether moiety, and the decrease in the stability constants is more pronounced for the multivalent metal-ion complexes. A theoretical consideration was also made to attain reliable values of stability complexes for metal-ion complexes of crown compounds.     

Synthetic scope and mechanistic studies of Ru(OH)x/Al2O3-catalyzed heterogeneous hydrogen-transfer reactions

Three kinds of hydrogen-transfer reactions, namely racemization of chiral secondary alcohols, reduction of carbonyl compounds to alcohols using 2-propanol as a hydrogen donor, and isomerization of allylic alcohols to saturated ketones, are efficiently promoted by the easily prepared and inexpensive supported ruthenium catalyst Ru(OH)x/Al2O3. A wide variety of substrates, such as aromatic, aliphatic, and heterocyclic alcohols or carbonyl compounds, can be converted into the desired products, under anaerobic conditions, in moderate to excellent yields and without the need for additives such as bases. A larger scale, solvent-free reaction is also demonstrated: the isomerization of 1-octen-3-ol with a substrate/catalyst ratio of 20,000/1 shows a very high turnover frequency (TOF) of 18,400 h(-1), with a turnover number (TON) that reaches 17,200. The catalysis for these reactions is intrinsically heterogeneous in nature, and the Ru(OH)x/Al2O3 recovered after the reactions can be reused without appreciable loss of catalytic performance. The reaction mechanism of the present Ru(OH)x/Al2O3-catalyzed hydrogen-transfer reactions were examined with monodeuterated substrates. After the racemization of (S)-1-deuterio-1-phenylethanol in the presence of acetophenone was complete, the deuterium content at the alpha-position of the corresponding racemic alcohol was 91%, whereas no deuterium was incorporated into the alpha-position during the racemization of (S)-1-phenylethanol-OD. These results show that direct carbon-to-carbon hydrogen transfer occurs via a metal monohydride for the racemization of chiral secondary alcohols and reduction of carbonyl compounds to alcohols. For the isomerization, the alpha-deuterium of 3-deuterio-1-octen-3-ol was selectively relocated at the beta-position of the corresponding ketones (99% D at the beta-position), suggesting the involvement of a 1,4-addition of ruthenium monohydride species to the alpha,beta-unsaturated ketone intermediate. The ruthenium monohydride species and the alpha,beta-unsaturated ketone would be formed through alcoholate formation/beta-elimination. Kinetic studies and kinetic isotope effects show that the Ru-H bond cleavage (hydride transfer) is included in the rate-determining step.     

VUV/SOFT-X-RAY SPECTROSCOPIC FACILITIES AT THE SYNCHROTRON RADIATION LABORATORIES IN JAPAN

The present status is described of the vacuum ultraviolet/soft-X-ray spectroscopic facilities at the synchrotron radiation laboratories in Japan. An overview is presented of the spectroscopic instruments available and under development at the SOR-RING at the Institute for Solid State Physics, University of Tokyo, the Photon Factory-ring at the National Laboratory for High Energy Physics, the UVSOR at the Institute for Molecular Science, and the TERAS at the Electrotcchnical Laboratory. Emphasis is placed upon the unique features of the instruments developed in Japan.     

Theoretical study of the photoinduced transfer among the ground state and two metastable states in [Fe(CN)5NO]2-

Ab initio calculations were performed to investigate photoinduced transfers among the ground state (GS) and two metastable states (MS1 and MS2) of [Fe(CN)5NO]2-. We obtained the global potential energy surface of the electronic ground state by a scheme of multireference singly and doubly excited configuration interaction followed by a Davidson-type quadruple correction (MRSDCI+Q). The ground state surface has three local minima corresponding to GS, MS1, and MS2. The character of bond between Fe and the nitrosyl group are discussed. We carried out calculations of the lower five electronic excited states by MRSDCI+Q. The main configurations of these lower five excited states were represented by the dFe-->pi*NO transition accompanied by considerable back-donation. The potential energy surfaces of the six states, including the ground state, were obtained by state averaged complete active space self-consistent field calculations. The surfaces have several conical intersections and avoided crossings in the reaction pathway. The photoinduced transfers among GS, MS1, and MS2 are caused by the nonadiabatic effect near these crossings.     

Consecutive thin-layer chromatographic separation of Au(III), Pt(IV), Pd(II) and large amounts of associated base metals

Summary The TLC system composed of ECTEOLA-cellulose and 2.5 mol/l HCl–2.5 mol/l NaCl–0.6% (w/v) H₂O₂ solution allows consecutive separations of Au(III), Pt(IV), Pd(II) and a number of associated base metals such as Cr(III), Mn(II), Fe(III), Co(II) Ni(II), Cu(II), Mg, Ca, Ba, Al, Bi(III), Pb(II), Zn(II) and Ag(I) coexisting in an extremely wide range of amounts and ratios, to be conducted completely in a single run. The effectiveness of the present system is verified by applying it to various synthesized samples containing the three noble metals and one of the base metals, Pt-metal powder and two kinds of Au-alloys.     

Intense fluorescence of metal-to-ligand charge transfer in [Pt(0)(binap)(2)] [binap = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl

[Pt(0)(binap)(2)] (binap = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) is found to exhibit a luminescence from metal-to-ligand charge transfer state (MLCT) with a quantum yield of 0.12 and a lifetime of 1.2 micros in toluene at an ambient temperature. Prompt fluorescence with a quantum yield of 1.6 x 10(-)(4) is observed by means of a picosecond time-correlated single photon counting technique. The spectrum of the steady-state luminescence is almost identical to that of the prompt fluorescence, indicating that the intense luminescence is mainly delayed fluorescence from thermally activated (1)MLCT. The analysis of the temperature-dependent emission indicates that the energy difference between the (1)MLCT and (3)MLCT is 1.15 x 10(3) cm(-)(1). The lifetime of the prompt fluorescence is determined to be 3.2 ps from the decay of stimulated emission overlapped on subpicosecond transient absorption spectra. The lifetime of the (1)MLCT is much longer than expected from the large spin-orbit coupling constant of 5d (Pt) electrons (4000 cm(-)(1)). Theoretical analysis based on density functional theory reveals that structural distortion in the MLCT states causes large energy splitting between HOMO and HOMO - 1, which prevents a very fast ISC induced by strong spin-orbit interactions between these orbitals. The relatively slow ISC is therefore induced by weak spin-orbit interactions (ca. 50 cm(-)(1)) between ligand-centered molecular orbitals. Theoretical calculations indicate that the phosphorescence observed at lower temperatures is due to intensity borrowing from 4(1)B(2) --> GS transition. However, the large energy difference between HOMO and HOMO - 2 reduces the extent of mixing between the lowest (3)MLCT and 4(1)B(2) due to spin-orbit interaction, thereby decreasing the radiative rate of the phosphorescence.