Highly selective and simple synthesis of C(2)(m)--X--C(2)(n) fullerene dimers

Energetic-radiation-induced dimerization reaction of fullerenes was found to be a simple and highly selective method for synthesis of C2m-X-C2n (m = n or m not equal n) type molecules without formation of other products. Utilizing the new method, C70-C-C70, C60-C-C70, C60-C-C60, and C70-O-C70 were prepared and characterized. The method is capable of synthesizing new C2m-X-C2n molecules by introducing X (different atoms) into the reaction system. Energetic radiation created reactive sites for covalently bonded bridges between fullerene molecules originally only weakly bound by van der Waals force. This observation may open a new subject and practicable approach for polymer sciences of fullerenes.     

Adlayers of C60-C60 and C60-C70 fullerene dimers formed on au(111) in benzene solutions studied by STM and LEED

Scanning tunneling microscopy (STM) and low-energy electron diffraction were used to reveal the structures of ordered adlayers of [2+2]-type C60-C60 fullerene dimer (C120) and C60-C70 cross-dimer (C130) formed on Au(111) by immersingit in abenzene solution containing C120 or C130 molecules. High-resolution STM images clearly showed the packing arrangements and the electronic structures of C120 and C130 on the Au(111) surface in ultrahigh vacuum. The (2 square root3 x 4square root3)R30 degrees, (2square root3 x 5square root3)R30 degrees, and (7 x 7) structures were found for the C120 adlayer on the Au(111) surface, whereas C130 molecules were closely packed on the surface. Each C60 or C70 monomer cage was discerned in the STM image of a C130 molecule.     

Fluorinated polyimide nanocomposites for CO2/CH4 separation

The purpose of this project was to synthesize fluorinated polyimide (PI) nanocomposite membranes in order to study the gas permeation rates and selectivity of carbon dioxide and methane. PIs were synthesized from 2,2‐bis(3,4‐anhydrodicarboxyphenyl)hexafluoropropane (6F dianhydride, 6FDA) and 4,4′‐diaminodiphenyl ether (oxydianiline, ODA) into which were incorporated nanoparticulate additives as follows: in situ TiO_2, both plain and treated with dodecyl sulfate surfactant, and organo‐clay (Cloisite®‐10 Å) at loads of 1, 3, and 5 wt% to the polyamic acid. Polyamic acid films were solvent cast, cured at 200°C then post‐cured at 300°C and measured for permeation data and for thermal properties. Glass transition temperatures ranged from 124 to 140°C for the cured PIs and from 142 to 147°C for the post‐cured materials, the nano‐inclusions having little discernable effect on this property. Thermogravimetric analysis (TGA) data show that the inclusion of Cloisite® or TiO₂ caused a small decrease of thermal stability from 555°C to about 532 to 541°C. The inclusion of clay causes a decreased permeation rate while the addition of TiO₂ improves the rate and selectivity. Treating the nanofillers with surfactant decreases selectivity and marginally increases rate of permeation of CO₂. Post‐curing caused a darkening of the composites, but not the neat PI. This heat treatment also resulted in a significantly decreased permeation rate, but a significantly increased selectivity. The resulting material shows superior gas separation properties to the commercially available PI, Matrimid® produced by Ciba‐Geigy. Copyright © 2008 John Wiley & Sons, Ltd.     

Lucidumol D,a new lanostane-type triterpene from fruiting bodies of Reishi (Ganoderma lingzhi)

A new lanostane-type triterpenoid, lucidumol D (1) was isolated from the fruiting bodies of Ganoderma lingzhi. Its structure was elucidated on the basis of extensive 1D- and 2D-NMR studies as well as mass spectrometry. The cytotoxicity of lucidumol D against proliferation of several cancer cells were assayed by using MTT method and the obtained result suggested selective anti-proliferative and cytotoxic effects against MCF-7, HepG2, HeLa, Caco-2, and HCT-116. In comparison to lucidumol C (2) isolated previously by our group, the structure-activity relationship indicated that carbonyl function at C-11 is necessary to enhance the cytotoxicity.     

Spongipyran synthetic studies. Evolution of a scalable total synthesis of (+)-spongistatin 1

Three syntheses of the architecturally complex, cytotoxic marine macrolide (+)-spongistatin 1 (1) are reported. Highlights of the first-generation synthesis include: use of a dithiane multicomponent linchpin coupling tactic for construction of the AB and CD spiroketals, and their union via a highly selective Evans boron-mediated aldol reaction en route to an ABCD aldehyde; introduction of the C(44)-C(51) side chain via a Lewis acid-mediated ring opening of a glucal epoxide with an allylstannane to assemble the EF subunit; and final fragment union via Wittig coupling of the ABCD and EF subunits to form the C(28)-C(29) olefin, followed by regioselective Yamaguchi macrolactonization and global deprotection. The second- and third-generation syntheses, designed with the goal of accessing 1 g of (+)-spongistatin 1 (1), maintain both the first-generation strategy for the ABCD aldehyde and final fragment union, while incorporating two more efficient approaches for construction of the EF Wittig salt. The latter combine the original chelation-controlled dithiane union of the E- and F-ring progenitors with application of a highly efficient cyanohydrin alkylation to append the F-ring side chain, in conjunction with two independent tactics to access the F-ring pyran. The first F-ring synthesis showcases a Petasis-Ferrier union/rearrangement protocol to access tetrahydropyrans, permitting the preparation of 750 mg of the EF Wittig salt, which in turn was converted to 80 mg of (+)-spongistatin 1, while the second F-ring strategy, incorporates an organocatalytic aldol reaction as the key construct, permitting completion of 1.009 g of totally synthetic (+)-spongistatin 1 (1). A brief analysis of the three syntheses alongside our earlier synthesis of (+)-spongistatin 2 is also presented.     

Effects of substitutional impurity Au and Si atoms on antiphase boundary energies in Ti3Al: A first principles study

Effects of substitutional impurity atoms Au and Si on the energies of antiphase boundaries (APBs) on {1100} and (0001) planes in a Ti₃Al intermetallic compound were examined using first principles calculations. Au additions reduce the energies of APBs on both {1100} and (0001) planes by up to more than 40%. The reduction tends to be more remarkable especially when the added Au atom has larger number of Al atoms on its second-nearest neighbor sites rather than on first-nearest neighbor ones. In addition, in the case of Si addition, a significant energy reduction was found only for APBs on (0001) planes, and no remarkable dependence of APB energies on the coordinating atoms was found even for APBs on (0001) planes. These results are crucial to both understanding of the effect of APBs on the impurity diffusivity and predicting the ability of impurity atoms to stabilize antiphase domain structure that increases the strength of Ti₃Al dramatically.     

First-principles molecular dynamics simulation of O2 reduction on nitrogen-doped carbon

Density-functional calculations were performed to examine oxygen reduction reactions (ORRs) on N-doped graphene sheets. We found that O₂ adsorption becomes energetically favorable as the number of N around a CC bond increases. Pathways for both 4e⁻ and 2e⁻ reductions were identified. The possibility of O poisoning was suggested after calculating the reversible potential of each reduction step.     

Ionic conductivity of complexes of novel multiarmed polymers with phosphazene core and LiClO4

Novel multiarmed polymers with ethylene oxide units, [( CH₂CH₂O)_n : 7, n = 3; 8, n= 7.2; 9, n = 11.8, and 12, n = 11.8] were prepared from the reaction of polyethylene glycol monomethyl ethers with acid chlorides of hexakis(3,5-dicarboxyphenoxy)-( 6 ) and hexakis(4-carboxyphenoxy)cyclotriphosphazenes ( 11 ) and conductivities of their Li⁺ salt complexes were investigated. The glass transition temperatures of the salt-free polymers are in the temperature range −59 to −54°C, indicative of a high degree of reorientational mobility of the arms. When LiClO₄ was added to the multiarmed polymers, the T_g values raised monotonically. The extent of T_g elevation was affected by the length of arms and the number of oxygen atoms around cyclotriphosphazene core and increased in the order 7 > 8 > 12 > 9 . The conductivities increased in the order 9 > 8 = 12 > 7 and the maximum conductivities of 4.0 × 10⁻⁵ S/cm at 30°C and 6.0 × 10⁻⁴ S/cm at 90°C have been achieved for the 9 -Li⁺ complex with Li⁺/O = 0.03. Interestingly, the conductivity of 9 -Li⁺ complexes at constant reduced temperatures increased in the whole concentrations of LiClO₄ examined (Li⁺/O = 0.01–0.2), although the degree of increase in conductivity above Li⁺/O = 0.06 became small. From the behaviors of T_g and the conductivity of multiarmed polymer–LiClO₄ complexes, it appears that the conductivity is governed by relative concentrations of inter- and intramolecular complexes in the polymer matrix. The influence of structural change of the comb-shaped to multiarmed polymers on the conductivity is described. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1839–1847, 1997     

The temperature dependence of the threshold current of GaInAsP/InP DH lasers

The temperature dependence of the threshold current of GaInAsP/InP lasers was considered in terms of linear gain, loss, and carder lifetime. The linear gain was calculated taking into account electronic intraband relaxation effects. The carrier lifetime, intraband relaxation time, loss in the active region, and dipole moment, all of which determine the threshold condition, were estimated from the experiments. The main loss mechanism which determines the temperature dependence of the differential quantum efficiency appears to be the absorption due to transitions between the split-off and heavy-hole valence bands. The temperature dependence of the theoretical threshold current Ithcalculated in terms of these parameters was compared with the measured results and reasonable agreement was obtained.