Asymmetric Epoxidation of α,β‐Unsaturated Aldehydes in Aqueous Media Catalyzed by Resin‐Supported Peptide‐ Containing Unnatural Amino Acids

The enantio‐ and diastereoselective epoxidation of α,β‐unsaturated aldehydes in aqueous media was realized using a resin‐supported peptide catalyst. Introducing the hydrophobic and bulky unnatural amino acid 3‐(1‐pyrenyl)alanine into the peptide sequence was effective for enhancing the reaction rate and enantioselectivity.     

含汽气流冷凝换热的实验研究

通过对130℃左右的含汽水流横向流过水平圆管表面冷凝换热过程的实验研究,详细拟定了实验方案和测量方法,整理出蒸汽凝结传质的薜伍德准则经验式,发现与罗斯数值解[4]的表达式相符合。汽——气混合物在冷凝过程中的质扩散,使含汽气流的对流换热得到了增强。     

Parallel Post‐Polyketide Synthase Modification Mechanism Involved in FD‐891 Biosynthesis in Streptomyces graminofaciens A‐8890

To isolate a key polyketide biosynthetic intermediate for the 16‐membered macrolide FD‐891 ( 1 ), we inactivated two biosynthetic genes coding for post‐polyketide synthase (PKS) modification enzymes: a methyltransferase (GfsG) and a cytochrome P450 (GfsF). Consequently, FD‐892 ( 2 ), which lacks the epoxide moiety at C8–C9, the hydroxy group at C10, and the O‐methyl group at O‐25 of FD‐891, was isolated from the gfsF/gfsG double‐knockout mutant. In addition, 25‐O‐methyl‐FD‐892 ( 3 ) and 25‐O‐demethyl‐FD‐891 ( 4 ) were isolated from the gfsF and gfsG mutants, respectively. We also confirmed that GfsG efficiently catalyzes the methylation of 2 and 4 in vitro. Further, GfsF catalyzed the epoxidation of the double bond at C8‐C9 of 2 and 3 and subsequent hydroxylation at C10, to afford 4 and 1 , respectively. These results suggest that a parallel post‐PKS modification mechanism is involved in FD‐891 biosynthesis.     

Fractal analysis of electrical trees

Recently, fractal characteristics in pattern formation have been attracting much attention. A number of books and papers have been published on the fractal analysis of random patterns or structures occurring in nature. The geometrical patterns of dielectric breakdown, which include lightning, surface discharges and electrical trees, are known to be of a fractal nature. Their fractal patterns can be analyzed numerically using fractal dimensions. In this paper, a survey of the fractal analysis of electrical trees, both in experiment and in computer simulation, is given. Several methods for estimating the fractal dimension are summarized. The stochastic models for discharge patterns based on computer simulation are also summarized. Fractal analysis of real electrical trees in polymeric insulating materials is reviewed. For the experimental tree patterns, the fractal analysis of the projected 2-D and the reconstructed 3-D patterns is presented     

Gd@C82 metallofullerenes for neutron capture therapy—fullerene solubilization by poly(ethylene glycol)-block-poly(2-(N,N-diethylamino)ethyl methacrylate) and resultant efficacy in vitro

Poly(ethylene glycol)-block-poly(2-(N,N-diethylamino)ethyl methacrylate) (PEG-b-PAMA) was found to solubilize fullerenes such as C₆₀, and this technique was applied to metallofullerenes. Gd@C₈₂ was easily dissolved in water in the presence of PEG-b-PAMA without any covalent derivatization, forming a transparent complex about 20–30 nm in diameter. Low cytotoxicity was confirmed in vitro. Neutron irradiation of cultured cells (colon-26 adenocarcinoma) with Gd@C₈₂-PEG-b-PAMA-complexed nanoparticles showed effective cytotoxicity, indicating the effective emission of gamma rays and internal conversion electrons produced from the neutron capture reaction of Gd. This result suggests a potentially valuable approach to gadolinium-based neutron capture therapy.     

Fine tuning of frontier orbital energy levels in dithieno[3,2-b:2′,3′-d]silole-based copolymers based on the substituent effect of phenyl pendants

A series of dithieno[3,2-b:2′,3′-d]silole-based π-conjugated copolymers containing thieno[3,4-c]pyrrole-4,6-dione or thieno[3,4-b]thiophene units bearing 4-substituted phenyl pendants were synthesized and their thermal stability, optical properties and frontier orbital energy levels were systematically investigated. The introduction of electron-withdrawing substituents on the phenyl rings lowered their frontier orbital energy levels without deteriorating their thermal and optical properties. By replacing an electron-donating methoxy group with an electron-withdrawing trifluoromethyl group, both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital energy levels of the polymers were deepened by more than 0.3 eV. A relatively linear relationship was observed between the HOMO energy levels and the Hammett substituent constants.     

Orientational control of pentacene crystals on SiO2 by graphoepitaxy to improve lateral carrier transport

We controlled the in-plane orientation of pentacene grains by graphoepitaxy using patterned amorphous-SiO₂/Si substrates on which periodic grooves with slope edges had been formed. Pentacene crystals exhibited a clear tendency to align their b-axes perpendicular to the groove edges. Organic thin-film transistors were fabricated on the patterned and flat substrates and their transistor characteristics were compared. Although the patterned substrates increased the apparent mobility by only 10–20%, the number of grain boundaries with high potential barriers to carrier transport was reduced to half of that on flat substrates. This improvement is expected to enhance the response speed of pentacene organic thin-film transistors and suppress the sensitivity of their characteristics to the operating temperature.     

Bayesian hemodynamic parameter estimation by bolus tracking perfusion weighted imaging

A delay-insensitive probabilistic method for estimating hemodynamic parameters, delays, theoretical residue functions, and concentration time curves by computed tomography (CT) and magnetic resonance (MR) perfusion weighted imaging is presented. Only a mild stationarity hypothesis is made beyond the standard perfusion model. New microvascular parameters with simple hemodynamic interpretation are naturally introduced. Simulations on standard digital phantoms show that the method outperforms the oscillating singular value decomposition (oSVD) method in terms of goodness-of-fit, linearity, statistical and systematic errors on all parameters, especially at low signal-to-noise ratios (SNRs). Delay is always estimated sharply with user-supplied resolution and is purely arterial, by contrast to oSVD time-to-maximum TMAX that is very noisy and biased by mean transit time (MTT), blood volume, and SNR. Residue functions and signals estimates do not suffer overfitting anymore. One CT acute stroke case confirms simulation results and highlights the ability of the method to reliably estimate MTT when SNR is low. Delays look promising for delineating the arterial occlusion territory and collateral circulation.