Stereoselective synthesis of cis- and trans-oligo(phenylenevinylene)s via palladium-catalyzed cross-coupling reactions

cis-Oligo(phenylenevinylene)s (OPVs) are synthesized by Suzuki-Miyaura coupling of arylboronic acids with (Z)-bromoalkenes in over 96% geometrical purity. On the other hand, trans-oligo(phenylenevinylene)s can be synthesized by Hiyama coupling of aryl iodide with (E)-alkenylsilanes in almost perfect purities. Effect of pi-conjugation chain length on photoisomerization behavior of OPVs is described.     

Fractal growth mechanism of sp3-bonded 5H-BN microcones by plasma-assisted pulsed-laser chemical vapor deposition

Here we propose a repetitive photochemical reaction and diffusion model for the fractal pattern formation of sp(3)-bonded 5H-BN microcones in laser-assisted plasma chemical vapor deposition, which was observed experimentally and reported previously. This model describing the behavior of the surface density of precursor species gave explanations to (1) the "line-drawing" nature of the patterns, (2) the origin of the scale-invariant self-similarity (fractality) of the pattern, and (3) the temperature-dependent uniform to fractal transition. The results have implications for controlling the self-organized arrangements of electron-emitter cones at the micro-and nanoscale by adjusting macroscopically the boundary condition (L(X),L(Y)) for the deposition, which will be very effective in improving the electron field emission properties.     

Infrared spectra of the (H2O)n-SO2 complexes in argon matrices

The infrared spectra of the (H(2)O)n-SO(2) complexes trapped in argon matrices have been investigated using Fourier transform infrared spectroscopy. In addition to the 1:1 and 2:1 complexes, the first spectroscopic evidence for the 3:1 complex has been obtained from the spectra of the SO stretching and the OH stretching modes. The observed frequency shifts in the bonded OH stretching region indicate that the hydrogen bonds of the 2:1 and 3:1 complexes are strengthened compared to that of the 1:1 complex, which suggests the cyclic structure of the complexes.     

Modeling and spectral simulation of matrix-isolated molecules by density functional calculations: a case study on formic acid dimer

The supermolecule approach has been used to model molecules embedded in solid argon matrix, wherein interaction between the guest and the host atoms in the first solvation shell is evaluated with the use of density functional calculations. Structural stability and simulated spectra have been obtained for formic acid dimer (FAD)-Ar(n) (n = 21-26) clusters. The calculations at the B971∕6-31++G(3df,3pd) level have shown that the tetrasubstitutional site on Ar(111) plane is likely to incorporate FAD most stably, in view of consistency with the matrix shifts available experimentally.     

Facile and selective deallylation of allyl ethers using diphosphinidenecyclobutene-coordinated palladium catalysts

(pi-Allyl)palladium triflate bearing a 1,2-bis(4-methoxyphenyl)-3,4-bis(2,4,6-tri-tert-butylphenylphosphinidene)cyclobutene ligand (DPCB-OMe), [Pd(eta(3)-C(3)H(5))(DPCB-OMe)]OTf, efficiently catalyzes deallylation of a variety of allyl ethers in aniline to give corresponding alcohols in high yields under mild conditions. The reactions can be performed in air without loss of a variety of functionalities including vinyl, alkynyl, hydroxy, acetoxy, silyloxy, and acetal groups. Allyl 2-allyloxybenzoate selectively undergoes deallylation of the allyloxy group to give allyl salicylate in quantitative yield.     

New sesquiterpene hydroperoxides with trypanocidal activity from Pogostemon cablin

Trypanocidal constituents of Pogostemon cablin were investigated. Activity guided isolation of the acetone extract resulted in isolation of three new sesquiterpene hydroperoxides 1-3, together with a known sesquiterpene, patchouli alcohol (4). In vitro minimum lethal concentrations of the hydroperoxides 1-3 against epimastigotes of Trypanosoma cruzi were 0.84 microM (1), 1.7 microM (2) and 1.7 microM (3). The activity of the corresponding alcohols and patchouli alcohol was very weak (MLC>200 microM).     

Modified five-layer asymmetric coupled quantum well (M-FACQW) for giant negative refractive index change

We have analyzed the electrorefractive properties of a GaAs/AlGaAs modified five-layer asymmetric coupled quantum well (M-FACQW). The theoretical analyses show that the M-FACQW is expected to exhibit a giant negative electrorefractive index change Δn in the transparent-wavelength region away from the absorption edge. The influence of fluctuations in layer thickness on the electrorefractive properties of the M-FACQW was also investigated. Although the fluctuation in layer thickness deteriorates the characteristics of Δn in the M-FACQW, the M-FACQW still maintains a very giant Δn compared with that of a conventional rectangular quantum well without thickness fluctuation. In addition, we have fabricated the M-FACQW with monolayer accuracy by solid-source molecular beam epitaxy, and measured its photoabsorption current. The experimental results are in good agreement with the calculated properties. This indicates that the M-FACQW has great potential for use in ultra-wideband and low-voltage optical modulators and switches.     

Removal of structurally different dyes in submerged membrane fungi reactor—Biosorption/PAC-adsorption,membrane retention and biodegradation

The long-term performance of a submerged membrane fungi reactor was observed while a synthetic textile wastewater containing either or both of the two structurally different azo dyes was continuously fed. Compared to the Acid Orange II dye (simpler structure), higher biosorption but slower biodegradation of the polymeric dye (Poly S119) was observed in sterile batch tests. In the membrane bioreactor (MBR), although a relative abundance of fungi (66%) without any specific control of bacterial contamination could be maintained, unlike in pure fungus culture, enzymatic activity was below detection limit. Nevertheless, >99% removal of Poly S119 was consistently achieved under a dye loading of 0.1 g L⁻¹ d⁻¹ (HRT = 1 d). Comparison of the reactor-supernatant (SQ) and the membrane-permeate (PQ) qualities (31% improvement) revealed the significant contribution of the membrane to the overall removal (biosorption, cake layer filtration, biodegradation) of Poly S119. Contrary to the faster removal of Orange II in batch test, membrane-permeate quality revealed 93% removal of the dye in MBR (corresponding SQ = 82%). However, excellent (>99%) stable removal of Orange II or of both the dyes together, as well as stable enzymatic activity was observed following addition of powdered activated carbon (PAC) in the MBR. In accordance with real textile wastewater, dye contributed only 5% of the TOC loading (0.944 g L⁻¹ d⁻¹) in this study. In contrast to low TOC removal by fungi alone, the MBR containing mixed microbial community steadily achieved >98% removal, which improved further to >99% after PAC addition.     

A Square‐Planar Complex of Platinum(0)

The Pt⁰ complex [Pt(PPh₃)(Eind₂‐BPEP)] with a pyridine‐based PNP‐pincer‐type phosphaalkene ligand (Eind₂‐BPEP) has a highly planar geometry around Pt with ∑(Pt)=358.6°. This coordination geometry is very uncommon for formal d¹⁰ complexes, and the Pd and Ni homologues with the same ligands adopt distorted tetrahedral geometries. DFT calculations reveal that both the Pt and Pd complexes are M⁰ species with nearly ten valence electrons on the metals whereas their atomic orbital occupancies are evidently different from one another. The Pt complex has a higher occupancy of the atomic 6s orbital because of strong s–d hybridization due to relativistic effects, thereby adopting a highly planar geometry reflecting the shape and orientation of the partially unoccupied orbital.     

Fine tuning of the orifice size of an open-cage fullerene by placing selenium in the rim: insertion/release of molecular hydrogen

A newly synthesized open-cage fullerene containing selenium in the rim of the 13-membered-ring orifice allows milder conditions for hydrogen insertion, and the rate for hydrogen release is ca. three times faster than its sulfur analogue.