Chiral aggregates formed from methylated tetraenoic fatty acids: formation of both antipodes of chiral aggregates from a single enantiomer and time-dependent stereomutation

Formation and behaviors of chiral aggregates of methylated tetraenoic fatty acids (TE-FAs) were reported. In the C-24 TE-FA series, the aggregate prepared by dispersing an ethanol stock solution of C-24 TE-FA 1b into sodium phosphate buffer gave a strong positive Cotton effect, whereas the aggregate prepared from a methanol stock solution gave a negative Cotton effect. In the C-20 TE-FA series, the aggregate prepared from an ethanol stock solution of C-20 TE-FA 2b exhibited time-dependent chirality inversion. [see text].     

Electron transfer promoted regioselective ring-opening reaction of cyclopropyl silyl ethers

Oxidative ring-opening reactions of cyclopropyl silyl ethers incorporated into bicyclo[m.1.0]alkane framework were investigated. The results show that the regioselectivities for ring-opening of intermediate radical cations, formed by single electron transfer, are governed by the nature of the nucleophile as well as oxidizing species.     

Constituents of the green tea seeds of Camellia sinensis

Green tea (Camellia sinensis) leaves are known to contain active ingredients such as catechins and caffeine, and are widely useful materials. Recently, green tea flowers also have been in the spotlight. However, little attention has been paid to the tea seeds. In this work, the constituents of green tea seeds and green tea leaves were compared. Caffeine was found in the seeds, whereas catechins (usually obtained from green tea leaves) were not observed. Next, we investigated the constituents of hexane extracts and methanol extracts of green tea seeds. We found that the hexane extracts contained high amounts of oleic glyceride (79.9%) in addition to linoleic glyceride (20%). We confirmed the structures of these glycerides by NMR spectroscopy and by synthesis from a fatty acid and glycerol. The methanol extract was found to contain naringenin glucosides by mass spectrometry and NMR spectroscopic analysis.     

Auger recombination dynamics in hybrid silica-coated CdTe nanocrystals

CdTe quantum dots coated with a silica layer containing CdS-like clusters exhibit intense photoluminescence and a spectral red-shift. Biexciton Auger recombination of these particles is examined by transient absorption spectroscopy. A lengthening of the Auger recombination lifetime by a factor of ～3.5 in the presence of the CdS-like clusters is observed and may contribute to the good PL properties of these nanostructures.     

Asymmetric alkynylation of aldehydes with propiolates without high reagent loading and any additives

The asymmetric alkynylation of aliphatic and aromatic aldehydes with propiolates was mediated by dialkylzinc and a novel prolinol catalyst without high reagent loading and any additives, such as Ti(Oi-Pr)(4), to give the corresponding γ-hydroxy-α,β-acetylenic esters with high enantiomeric excess of up to 95%.     

Total synthesis of broussonetine F: the orthoamide Overman rearrangement of an allylic diol

A first total synthesis of broussonetine F from diethyl L-tartrate was achieved. The cornerstone of our synthesis was an orthoamide Overman rearrangement, which provided an allylic amino alcohol with complete diastereoselectivity.     

Limiting size index distributions for ball-bin models with Zipf-type frequencies

We consider a random ball-bin model where balls are thrown randomly and sequentially into a set of bins. The frequency of choices of bins follows the Zipf-type (power-law) distribution; that is, the probability with which a ball enters the ith most popular bin is asymptotically proportional to 1/i ^α , α > 0. In this model, we derive the limiting size index distributions to which the empirical distributions of size indices converge almost surely, where the size index of degree k at time t represents the number of bins containing exactly k balls at t. While earlier studies have only treated the case where the power α of the Zipf-type distribution is greater than unity, we here consider the case of α ≤ 1 as well as α > 1. We first investigate the limiting size index distributions for the independent throw models and then extend the derived results to a case where bins are chosen dependently. Simulation experiments demonstrate not only that our analysis is valid but also that the derived limiting distributions well approximate the empirical size index distributions in a relatively short period.     

Synthesis and properties of 1,1′-bis(diacetylene-group) connected ferrocene-thiophene derivative: a cooperatively functional behavior of diacetylene-group connected constituents

An extended π-electronic conjugation system of 1,1′-bis(diacetylene-group) connected ferrocene-thiophene derivative has been synthesized, with our integrated reaction between the corresponding TMS-protected acetylenes in one-pot. Its electronic properties have been examined, suggesting a cooperatively functional behavior of the diacetylene-group connected constituents.     

Enhanced performance of photorefractive poly(N‐vinyl carbazole) composites

We present the enhanced photorefractive performance of high molecular weight poly(N‐vinyl carbazole) (PVCz)‐based composites. Higher diffraction efficiency with faster speed of grating build‐up was obtained by optimizing the composition of the PVCz composites. At relatively low applied electric field of E = 45 V μm^?1, diffraction efficiency of 26% for p‐polarized probe beam and corresponding that of 5.1% for s‐polarized probe beam were measured with faster grating build‐up speed of 48.3 s^?1 for the composite with 2,4,7‐trinitrofluorenone (TNF) as a sensitizer. Fastest speed of grating build‐up of 100 s^?1 and large optical gain up to 110 cm^?1 were measured at E = 80 V μm^?1 for the composite with fullerene derivative of PCBM as a sensitizer. These improved performances are due to a large orientational enhancement effect with faster response speed in addition to Pockels effect for the samples with appropriate glass transition temperature. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011