Long hydrogen-bonded rod of molecular oxide: a hexatantalate tetramer

A tetra-n-butylammonium (TBA) salt of [H(4.5)(Ta(6)O(19))](3.5-) was synthesized by reacting hydrous tantalum oxide with TBAOH. X-ray structural analysis of TBA(3.5)[H(4.5)(Ta(6)O(19))]·2THF·5.5H(2)O (THF = tetrahydrofuran) revealed that this compound consists of a hydrogen-bonded, rod-shaped tetramer of hexatantalate that is almost 30 ? long together with TBA cations and solvent molecules of crystallization [a = 20.6354(5) ?, b = 25.5951(7) ?, c = 37.2058(8) ?, α = 77.092(1)°, β = 86.177(1)°, γ = 88.683(1)°, V = 19110.9(8) ?(3), Z = 8, and space group P ?1]. (1)H NMR spectra showed that this tetrameric structure is maintained in solution.     

Anion photoelectron spectroscopy of germanium and tin clusters containing a transition- or lanthanide-metal atom; MGe(n)- (n = 8-20) and MSn(n)- (n = 15-17) (M = Sc-V, Y-Nb, and Lu-Ta)

The electronic properties of germanium and tin clusters containing a transition- or lanthanide-metal atom from group 3, 4, or 5, MGe(n) (M = Sc, Ti, V, Y, Zr, Nb, Lu, Hf, and Ta) and MSn(n) (M = Sc, Ti, Y. Zr, and Hf), were investigated by anion photoelectron spectroscopy at 213 nm. In the case of the group 3 elements Sc, Y, and Lu, the threshold energy of electron detachment of MGe(n)(-) exhibits local maxima at n = 10 and 16, while in the case of the group 4 elements Ti, Zr, and Hf, it exhibits a local minimum only at n = 16, associated with the presence of a small bump in the spectrum. A similar behavior is observed for MSn(n)(-) around n = 16, and these electronic characteristics of MGe(n) and MSn(n) are closely related to those of MSi(n). Compared to MSi(n), however, the larger cavity size of a Ge(n) cage allows metal atom encapsulation at a smaller size n. A cooperative effect between the electronic and geometric structures of clusters with a large cavity of Ge(16) or Sn(16) is discussed together with the results of experiments that probe their geometric stability via their reactivity to H(2)O adsorption.     

Iron-catalyzed sulfonyl radical formations from sulfonylhydrazides and oxidative addition to alkenes

Generation of sulfonyl radicals from sulfonylhydrazides has been achieved in the presence of a non-toxic iron catalyst and oxygen. The intermolecular addition of resultant sulfonyl radicals to alkenes affords β-hydroxysulfone compounds.     

Preconcentration of Trace Elements in Water for Speciation Studies

Trace element speciation has recently become one of the most important problems in water analysis. Proper combination of preconcentration techniques with instrumental determination methods is essential to speciation analysis, because sensitivity and selectivity of direct determination methods are generally lacking. The present paper describes such preconcentration techniques as filtration, centrifugation, flotation and sorption, which have been developed in the author's laboratory for the speciation of heavy metals in river and pond waters by electron microscopy, X-ray microanalysis and chemical analysis. The application of freeze concentration to the speciation of silica in high-purity waters is also discussed.     

Vinyl polymerization. 275. Polymerization of vinyl monomers photosensitized by tetramethyltetrazene

A study of the photopolymerization of vinyl monomers in the presence of tetramethyltetrazene (TMT) was made. TMT was found to act as an effective sensitizer. In the photopolymerization of vinyl monomers such as methyl methacrylate or styrene the rate of polymerization was expressed by the equation: R_p = k[TMT]^1/2[monomer]. The chain-transfer constant of TMT under ultraviolet irradiation was estimated to be 3.8 × 10^?2 for the above monomers. A linear correlation was found to exist between the reactivity of dimethylamino radical toward the vinyl monomers and e values for the corresponding monomers.     

Visco-elastic properties of reentrant nematic liquid crystalline mixtures

The visco-elastic properties for binary mixtures of 4-n -hexyloxy-4′-cyanobiphenyl (6OCB) and 4-n-octyloxy-4′-cyanobiphenyl (8OCB) are investigated in detail by a light scattering technique. The mixtures exhibit a reentrant nematic (RN) phase between the smectic A (SmA) and crystal phases in the range 22.0–29.5 wt % of 6OCB. The viscosity and the elastic constant increase with cooling in both the nematic and reentrant nematic phases. It is also found that the mixtures exhibit anomalously large values of viscosity and elastic constant near the phase transition, i.e. a pretransitional phenomenon can be observed. The activation energy for viscosity is smaller in the RN phase than in the ordinary nematic phase appearing at higher temperatures, while the normalized elastic constant (defined as the ratio of the elastic constant to the square of the dielectric anisotropy) is larger. Moreover, the visco-elastic behaviour depends on the specific time during which the sample has been kept in the SmA phase. These results confirm that the SmA phase has a strong influence on the formation of molecular aggregates, which plays an important role in the reentrant phenomenon of these systems.     

Molecular weight between entanglements for linear d-glucans

Dynamic viscoelasticity measurements were carried out for concentrated solutions of linear d-glucans in BmimCl to examine the effect of the linkage between repeating units of glucose on the rheological properties. The values of molecular weight between entanglements (M _e) were determined for four d-glucans: curdlan, pullulan, cellulose, and amylose. From the concentration dependence of M _e, the value of M _e in the molten state (M _e,melt) for each d-glucan was estimated as a material constant. The order of M _e,melt became cellulose?<?pullulan?<?curdlan?<?amylose, indicating that the linkage is actually influential in M _e,melt for the linear d-glucans. The relationship between M _e,melt and the molecular structure of the d-glucans were discussed assuming that the values of M _e,melt for the d-glucans primarily reflect the chain stiffness such as the characteristic ratio C _∞ on the analogy of synthetic polymers. Although the trend was not so clear, it was shown that N _unit is a decreasing function of C _∞ .     

Phase-separation and distribution of phenyl groups for PhTES-TEOS coatings prepared on polycarbonate substrate

Phenyltriethoxysilane (PhTES) and tetraethoxysilane (TEOS) coatings [xPhTES·(100 − x)TEOS (mol%)] (x = 0 − 80) were prepared on polycarbonate (PC) substrate, and adhesion, surface hardness and distribution of phenyl groups were studied. The coatings with more than 60 mol% of PhTES showed good adhesion (≈ 100%), and the pencil hardness of PC substrate (4B) improved to 2B or B after the coatings. Bulk gels with the same compositions were also prepared, and distribution of phenyl groups were estimated using fourier transform infrared (FT-IR) spectroscopy (KBr method for bulk gels and attenuated total reflection (ATR) method for coatings). A significant difference for the distribution of phenyl groups was clearly observed between bulk gels and coatings, suggesting PC substrate affects the distribution of phenyl groups in coatings. The adhesion and FTIR results revealed that there is an interaction caused by π-electrons between benzene rings on PC substrate and phenyl groups of PhTES-TEOS coatings. It was found that the adhesion was strongly correlated with the phenylsilsesquioxane networks formed around PC substrate side.     

Photochromism of viologens included in crown ether cavity

The effect of a pi-electron-donating macrocyclic molecule on the photochromic behavior of viologen derivatives was investigated in a thin polymer film. The intermolecular interactions between the viologens and the macrocyclic molecule were investigated in a solution before photoirradiation. In acetone, benzylviologens, N,N'-dibenzyl-4,4'-bipyridinium hexafluorophosphate (1) and N,N'-dibenzyl-trans-1,2-bis(4-pyridinium)ethylene hexafluorophosphate (2) each derived from 4,4'-bipiyridine and trans-1,2-bis(4-pyridyl)ethylene, respectively, form an inclusion complex with p-benzocrown ether (3) with binding constants of ca 200 M-1, which was driven by a charge transfer interaction. The peak wavelength of the charge transfer absorption band was at 453 and 421 nm for the inclusion complexes of 1 and 2 with 3, respectively. Upon photoirradiation to the polymer film containing 1, the film changed color from colorless to blue, associated with the reduction of 1 from the dication to the radical cation. The original dication was recovered after 120 min. The addition of 3 into the film containing 1 caused not only the color change from colorless to yellow, associated with the charge transfer interaction between 1 and 3 before photoirradiation, but also an acceleration in the bleaching rate of the photoreduced 1. When p-dimethoxybenzene (4) was used as an acyclic analog of 3, a negligible change in the photochromic behavior of 1 was observed. Similar effect of 3 on the photochromic behavior of 2 was observed. These results imply that the pi-electron-donating macrocyclic molecule causes a faster bleaching of photoreduced viologens by forming the inclusion complex.     

Radiation-induced degradation of aqueous 2–chlorophenol assisted by zeolites

Journal of Radioanalytical and Nuclear Chemistry - This study aims to demonstrate that zeolite has the potential to increase the efficiency of radiolysis treatment of aqueous organic pollutants by...