Stereospecific Synthesis of Enantiopure [6]Helicene Containing a Seven-Membered Ring and [7]Helicene by Acid-Promoted Stepwise Alkyne Annulations of Doubly Axial-Chiral Precursors**

Enantiopure [6]helicene containing an embedded seven-membered ring and carbo[7]helicene (>99 % ee) with opposite helicity were simultaneously and quantitatively (>99 %) synthesized with a perfect stereospecificity through stepwise acid-promoted intramolecular alkyne annulations of doubly axial-chiral cyclization precursors. The helical handedness of the [6]- and [7]helicenes was fully stereocontrolled by the doubly axial chirality of the precursors as a result of complete axial-to-helical chirality transfer. The cyclizations proceeded in a stepwise manner; the first six-membered ring formation was followed by the kinetically controlled seven- or six-membered ring formation with or without helix-inversion of a [4]helicene intermediate generated during the first cyclization step, thus quantitatively producing enantiopure circularly polarized luminescent [6]- and [7]helicenes with opposite helicity.     

Nanostructured Manganese Oxides within a Ring-Shaped Polyoxometalate Exhibiting Unusual Oxidation Catalysis

Nanosized manganese oxides have recently received considerable attention for their synthesis, structures, and potential applications. Although various synthetic methods have been developed, precise synthesis of novel nanostructured manganese oxides are still challenging. In this study, using a structurally defined nanosized cavity inside a ring-shaped polyoxometalate, we succeeded in synthesizing two types of discrete 18 and 20 nuclear nanostructured manganese oxides, Mn18 and Mn20 , respectively. In particular, Mn18 showed much higher catalytic activity than other manganese oxides for the oxygenation of alkylarenes including electron-deficient ones, and the reaction proceeded through a unique reaction mechanism due to its unusual manganese oxide structure.     

Synthesis of various end‐functionalized polyesters by controlled/living ring‐opening polymerization of lactones using pentafluorophenylbis(triflyl)methane

The ring‐opening polymerizations (ROPs) of ε‐caprolactone (ε‐CL) and δ‐valerolactone (δ‐VL) with pentafluorophenylbis(triflyl)methane (C₆F₅CHTf₂) as the organocatalyst and alcohol initiators were carried out. For the ROP using 3‐phenyl‐1‐propanol (PPA) as the initiator in CH₂Cl₂ at room temperature with the [ε‐CL or δ‐VL]₀/[PPA]₀/[C₆F₅CHTf₂] ratio of 50/1/0.1, the polymerization homogeneously proceeded to afford poly(ε‐caprolactone) (PCL) and poly(δ‐valerolactone) (PVL) having narrow polydispersity indices. The molecular weights of the obtained polymers determined from ¹H NMR spectra showed good agreement with those estimated from the initial ratio of [ε‐CL or δ‐VL]₀/[PPA]₀ and monomer conversions. The ¹H NMR, size exclusion chromatography, and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry measurements strongly indicated that PCL and PVL possessed the 3‐phenylpropoxy group as the α‐chain‐end and the hydroxy group as the ω‐chain‐end. In addition, the controlled/living nature for the C₆F₅CHTf₂‐catalyzed ROP of lactones was confirmed by kinetic and chain‐extension experiments. The block copolymerization of PCL and PVL successfully proceeded to afford PCL‐b‐PVL and PVL‐b‐PCL. In addition, various end‐functionalized PCLs and PVLs with narrow molecular weight distributions were synthesized by the ROP of ε‐CL and δ‐VL using functional initiators, such as 6‐azido‐1‐hexanol, 2‐hydroxyethyl methacrylate, propargyl alcohol, N‐(2‐hydroxyethyl)maleimide, 4‐vinylbenzyl alcohol, 5‐hexen‐1‐ol, and 5‐norbornene‐2‐methanol. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Total synthesis and morphogenesis-inducing activity of (±)-thallusin and its analogues

Total synthesis of (±)-thallusin was achieved using Hg(OTf)₂·PhNMe₂-induced olefin cyclization, and Suzuki coupling with a pyridylboronic acid derivative. Hg(OTf)₂ also acted as a catalyst to isomerize the double bond into the more thermodynamically stable isomer when treated in toluene. Synthetic (±)-thallusin as well as an analogue showed morphogenesis-inducing activity.     

Early intermediate in human prion protein folding as evidenced by ultrarapid mixing experiments

An important step toward understanding the mechanism of the PrP(C)-to-PrP(Sc) conversion is to elucidate the folding pathway(s) of the prion protein. On the basis of stopped-flow measurements, we recently proposed that the prion protein folds via a transient intermediate formed on the submillisecond time scale, and mutations linked to familial diseases result in a pronounced increase in the population of this intermediate. Here, we have extended these studies to continuous-flow measurements using a capillary mixing system with a time resolution of approximately 100 micros. This allowed us to directly observe two distinct phases in folding of the recombinant human prion protein 90-231, providing unambiguous evidence for rapid accumulation of an early intermediate (with a time constant of approximately 50 micros), followed by a rate-limiting folding step (with a time constant of approximately 700 micros). The present study also clearly demonstrates that the population of the intermediate is significantly increased at mildly acidic pH and in the presence of urea. A similar three-state folding behavior was observed for the Gerstmann-Straussler-Scheinker disease-associated F198S mutant, in which case the population of an intermediate was greatly increased as compared to that of the wild-type protein. Overall, the present data strongly suggest that this partially structured intermediate may be a direct monomeric precursor of the misfolded PrP(Sc) oligomer.     

In operando quantitation of Li concentration for a commercial Li‐ion rechargeable battery using high‐energy X‐ray Compton scattering

Compton scattering is one of the most promising probes for quantitating Li under in operando conditions, since high‐energy X‐rays, which have high penetration power, are used as the incident beam and the Compton‐scattered energy spectrum has specific line‐shapes for each element. An in operando quantitation method to determine the Li composition in electrodes has been developed by using line‐shape (S‐parameter) analysis of the Compton‐scattered energy spectrum. In this study, S‐parameter analysis has been applied to a commercial coin cell Li‐ion rechargeable battery and the variation of the S‐parameters during the charge/discharge cycle at the positive and negative electrodes has been obtained. By using calibration curves for Li composition in the electrodes, the change in Li composition of the positive and negative electrodes has been determined using the S‐parameters simultaneously.     

Structural study of Si(1 1 1)-6 × 1-Ag surface using surface X-ray diffraction

The surface structure of Si(1 1 1)-6 × 1-Ag was investigated using surface X-ray diffraction techniques. By analyzing the CTR scattering intensities along 00 rod, the positions of the Ag and reconstructed Si atoms perpendicular to the surface were determined. The results agreed well with the HCC model proposed for a 3 × 1 structure induced by alkali-metals on a Si(1 1 1) substrate. The heights of the surface Ag and Si atoms did not move when the surface structure changed from Si(1 1 1)-√3 × √3-Ag to Si(1 1 1)-6 × 1-Ag by the desorption of the Ag atoms. From the GIXD measurement, the in-plane arrangement of the surface Ag atoms was determined. The results indicate that the Ag atoms move large distances at the phase transition between the 6 × 1 and 3 × 1 structures.     

Compensation for the thermal effect in the second-harmonic generation of a Q-switched nanosecond-kilohertz Nd:YVO4 laser

We report the quantitative relationship between the phase-matching condition and the surrounding temperature in a critical phase-matching second-harmonic generation of a Q-switched Nd:YVO₄ laser with a high repetition rate. The thermal effect can be effectively compensated for by appropriately changing the phase-matching angle with respect to the surrounding temperature of a nonlinear optical crystal. A stable wavelength conversion from the 1064 nm fundamental to the 532 nm second harmonic in a type-I critical phase-matching lithium triborate crystal is experimentally achieved and the corresponding conversion efficiency up to 70% is obtained.