Microstructure of Highly Syndiotactic “Living” Poly(propylene)s Produced from a Titanium Complex with Chelating Fluorine‐Containing Phenoxyimine Ligands (an FI Catalyst)

Highly syndiotactic “living” poly(propylene)s were synthesized at 25°C using a bis[N‐(3‐tert‐butylsalicylidene)‐2,3,4,5,6‐pentafluoroanilinato]titanium (IV) dichloride/MAO catalyst system, and microstructures of the polymer were analyzed by means of ¹³C NMR spectroscopy. The syndiotactic poly(propylene) contains isobutyl, isopentyl and propyl end groups, suggesting that the living polymerization of propylene was initiated via 1,2‐insertion, followed by 2,1‐insertion as the principal mode of polymerization. Pentad distribution analysis revealed that the syndiospecific polymerization proceeds under chain‐end control.     

Na2O overlayers epitaxially prepared on Pd(100) and structure-sensitive CO2 adsorption

Sodium oxide overlayers prepared on Pd(100) were examined with AES, LEED and XPS. The oxides were grown by cycles of Na deposition followed by oxidation, maintaining the composition of Na₂O. The surface structure of the deposited oxide was sensitive to the annealing temperature after oxidation. The Na₂O/Pd(100) surfaces gave rise to a (3 × 3) LEED pattern when annealed at 600 K under vacuum. A model based on Na₂O(100) was proposed for the (3 × 3) overlayers, where the oxide was epitaxially aligned in a square periodicity on the substrate. Multilayered Na₂O was prepared maintaining the (3 × 3) pattern, by repeated cycles of preparation. Annealing at 700 K caused a c(4 × 6) pattern, for which a model based on Na₂O(110) was proposed. CO₂ was adsorbed on the (3 × 3) oxide of various thickness to form carbonate at 350 K, whereas the c(4 × 6) oxide was inert. The relationship of structure and reactivity is discussed in relation to the microscopic design of metal-oxide surfaces for base-catalysis.     

Electronic effects on enantioselectivity in epoxidation catalyzed by D4-symmetric chiral porphyrins

Asymmetric epoxidation of various aromatic olefins was examined with our D₄-symmetric chiral porphyrin. The enantioselectivity was greatly improved upon when the substrates contained electron-deficient groups. Moreover, examination of electronic effects in the porphyrin catalyst revealed that electron-deficient groups lowered and electron-donating groups raised the enantioselectivity. Hammett plot analysis suggested that these electronic effects could be interpreted in terms of the Hammond postulate.     

Recent Progress of Optical Fibers

This paper reviews recent progress of advanced optical fibers that are expected to be as candidates for the future trunk-line systems, metropolitan networks and access lines for subscribers.     

Slow positron study on dielectric-coated mirror for free-electron-laser experiments

A positron lifetime study has been done on dielectric multilayer cavity mirrors for free-electron-laser experiments by the use of a variable-energy pulsed positron beam. A long-lived ortho-positronium component has been observed at low positron energy region, corresponding to the depth of the top amorphous SiO₂ layer. The intensity of the positronium component correlates with the degradation and restoration of the mirrors. We discuss the relation between the positronium intensity and degradation mechanism of the mirrors. The present studies revealed that the slow positron lifetime technique is highly sensitive to the properties of the mirrors and is useful for the evaluation of the mirrors.     

Spectrophotometric determination of scandium with arsenazo

Arsenazo is used for the spectrophotometric determination of scandium in the range 10 to 50 μg. The absorbance is measured at 570 mμ and pH 6.1. A method is proposed for the successive determination of scandium and thorium. Scandium is separated from magnesium, calcium, rare earths, zirconium, fluoride, phosphate, and some other metals by extraction with TTA in xylene. Copper, aluminum, and iron(III) are removed by 8-quinolinol-chloroform extraction. Uranium(VI) is removed by anion exchange using hydrochloric acid. Thorium is separated from scandium by anion exchange using nitric acid.     

Synthesis and properties of bisdehydro[4n+2]annulenediones

Bisdehydro[14]- and [18]annulenediones have been synthesized by cyclic dimerization of corresponding -ethynyl acid chlorides in the presence of palladium-copper catalyst in triethylamine-benzene and fully characterized by analyses and their ¹H-NMR, mass, electronic and IR spectroscopic evidences.     

Asymmetric synthesis of a xanthine dehydrogenase inhibitor (S)-(−)-BOF-4272: Utility of chiral alkoxysulfonium salts

A practical synthetic method for a xanthine dehydrogenase inhibitor, (S)-(−)-BOF-4272, was established utilizing an asymmetric oxidation of diaryl sulfide BOF-4269. The oxidation of the sulfide with 1-chlorobenzotriazole carried out in the presence of 4-cyanopyridine and chiral 2-phenylcyclohexanol gave a high enantiomeric excess (73%ee). The sulfoxides in each enantiomerically pure form could be obtained by treating with alkaline hydrolysis or thermolysis of one the diastereomeric intermediate sulfonium salts (>99%de). Thus the transformation into the sulfoxides occur with virtually perfect inversion (alkaline hydrolysis) or retention (thermolysis). It is therefore possible to obtain the target sulfoxide, (S)-(−)-BOF-4272, from both the two diastereomeric sulfonium intermediates.     

Measurement of inclusion complex formation between cyclophane and biological relevant amino acids using electrospray ionization, cold-spray ionization and fast atom bombardment mass spectrometry

The investigation of the host-guest complex formations between cyclophane (TGDMAP) (1) as a host and L-acidic amino acids such as L-glutamic acid (Glu) and L-aspartic acid (Asp) as guests was carried out using fast atom bombardment (FAB), electrospray ionization (ESI) and cold-spray ionization (CSI) mass spectrometry (MS). The stability constant (K(s)) values obtained by the three different MS methods almost agreed. However, the complex ion peaks of a novel cyclophane (CPCn) (2) with Glu and Asp were not observed in FAB-MS. Then, these host-guest complex formations by use of CSI-MS and ESI-MS was examined, as the results, these complex ion peaks were observed clearly and the measurement values by the two MS methods are mostly in agreement. It was concluded that ESI-MS and CSI-MS are available for the determination of K(s) value as well as FAB-MS.