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991.
Synthesis and Structure/Property Relationships of Regioselective 2‐O‐, 3‐O‐ and 6‐O‐Ethyl Celluloses
Hiroshi Kamitakahara Toshihiro Funakoshi Shinji Nakai Toshiyuki Takano Fumiaki Nakatsubo 《Macromolecular bioscience》2010,10(6):638-647
Regioselectively ethylated celluloses, 2‐O‐ ( 1 ), 3‐O‐ ( 2 ), and 6‐O‐ethyl‐ ( 3 ) celluloses were synthesized via ring‐opening polymerization of glucopyranose orthopivalate derivatives. The number‐average degrees of polymerization (DPns) of compounds 1 and 2 were calculated to be 10.6 and 49.4, respectively. Three kinds of compound 3 with different DPns were prepared: DPns = 12.9 ( 3‐1 ), 60.3 ( 3‐2 ), and 36.1 ( 3‐3 ). The 2‐O‐, 3‐O‐, and 6‐O‐ethylcelluloses were soluble in water, confirmed by NMR analysis. Furthermore, the 3‐O‐ ( 2 ), and 6‐O‐ethyl‐ ( 3‐2 ) celluloses showed thermo‐responsive aggregation behavior and had a lower critical solution temperature (LCST) at about 40 °C and 70 °C, respectively, based on the results from turbidity tests and DSC measurements. The 6‐O‐ethyl‐cellulose ( 3‐3 ) with DPn = 36.1 and DPw = 54.6 showed gelation behavior over approx 70 °C, whereas the 6‐O‐ethyl‐celluloses 3‐1 and 3‐2 with lower and higher molecular weight, such as DPns 12.9 and 60.3, did not show gelation behavior at this temperature. It was revealed that the position of ethyl group affected the phase transition temperature. According to our experiments, the 3‐O‐ethyl and 6‐O‐ethyl groups along the cellulose chains caused the thermo‐responsive property of their aqueous solutions. The appropriate DP of the regioselective 6‐O‐ethyl‐cellulose existed for gelation of the aqueous solution.
992.
A substituent at the 3-position on a pyridine ring significantly affects the regioselectivity during the addition of alkynes to pyridinium salts. When the substituent is an electron-withdrawing group, 1,6-adducts are predominantly produced, whereas, 1,2-adducts become the major products when the substituent is an electron-donating group. The changes in the regioselectivity depending on the substituent can be explained by the difference in the product stabilities. The produced dihydropyridines are easily aromatized into disubstituted pyridines with chloranil in quantitative yields. 相似文献
993.
Hong-Tao Sun Fumiaki Shimaoka Jian Ruan Yuji Miwa Minoru Fujii Jianrong Qiu Minoru Mizuhata Shigehito Deki Shinji Hayashi 《Journal of Non》2009,355(48-49):2425-2428
We report on highly efficient broadband near-infrared photoluminescence (PL) in Ni2+-doped glass ceramics (GCs) films fabricated by annealing Si/Ni2+-doped glass superlattices (SNGS). Over two orders of magnitude enhancement of PL can be achieved in comparison with that from the annealed glass film. The PL lifetime of the annealed SNGS is several milliseconds, which is much longer than those of bulk GCs. The strong PL enhancement results from the formation of high-quality cordierite nanocrystals because the Si layers act as Si source for the crystal growth. This technique can be extended to fabricate other types of high-quality GCs films. 相似文献
994.
Let f1,…,fd be an orthogonal basis for the space of cusp forms of even weight 2k on Γ0(N). Let L(fi,s) and L(fi,χ,s) denote the L-function of fi and its twist by a Dirichlet character χ, respectively. In this note, we obtain a “trace formula” for the values at integers m and n with 0<m,n<2k and proper parity. In the case N=1 or N=2, the formula gives us a convenient way to evaluate precisely the value of the ratio L(f,χ,m)/L(f,n) for a Hecke eigenform f. 相似文献
995.
Shinji Tanimoto 《Annals of Combinatorics》2010,14(3):355-366
This paper introduces subgroups of the symmetric group and studies their combinatorial properties. Their elements are called
parity alternating, because they are permutations with even and odd entries alternately. The objective of this paper is twofold.
The first is to derive several properties of such permutations by subdividing them into even and odd permutations. The second
is to discuss their combinatorial properties; among others, relationships between those permutations and signed Eulerian numbers.
Divisibility properties by prime powers are also deduced for signed Eulerian numbers and several related numbers. 相似文献
996.
Shinji Watanabe Atsushi Tsuruta Jacques Flouquet 《Physica B: Condensed Matter》2009,404(19):2942-2945
The mechanism of how the magnetic field controls the critical end point of the first-order valence transition is clarified, which is essentially ascribed to charge degrees of freedom. It is shown that the quantum critical point is induced by applying the magnetic field, which explains a peculiar magnetic response in CeIrIn5 and sharp contrast between X=Ag and Cd for YbXCu4. Significance of the proximity of the first-order valence transition in the Ce- and Yb-based heavy fermions is pointed out. 相似文献
997.
Dr. Katsuhiko Takeuchi Ming-Yu Chen Dr. Hao-Yu Yuan Dr. Hiroki Koizumi Dr. Kazuhiro Matsumoto Dr. Norihisa Fukaya Dr. Yoong-Kee Choe Shinji Shigeyasu Seiji Matsumoto Dr. Satoshi Hamura Prof. Dr. Jun-Chul Choi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(72):18066-18073
We have successfully isolated and characterized the zinc carbamate complex (phen)Zn(OAc)(OC(=O)NHPh) ( 1 ; phen=1,10-phenanthroline), formed as an intermediate during the Zn(OAc)2/phen-catalyzed synthesis of organic carbamates from CO2, amines, and the reusable reactant Si(OMe)4. Density functional theory calculations revealed that the direct reaction of 1 with Si(OMe)4 proceeds via a five-coordinate silicon intermediate, forming organic carbamates. Based on these results, the catalytic system was improved by using Si(OMe)4 as the reaction solvent and additives like KOMe and KF, which promote the formation of the five-coordinated silicon species. This sustainable and effective method can be used to synthesize various N-aryl and N-alkyl carbamates, including industrially important polyurethane raw materials, starting from CO2 under atmospheric pressure. 相似文献
998.
The growth rate of silicon carbide whiskers grown from polycarbosilane was measured and the growth morphology was investigated. The plot of whisker length vs. growth time was almost linear up to a certain growth time but tended to become time-saturated, independent of growth temperature. Cessation of whisker growth was caused by a change of the growth process from vapor–liquid–solid (VLS) to vapor–solid (VS). Decrease in whisker length with growth time was observed in the higher temperature range. Arrhenius plots of growth rate were almost linear in the lower temperature range, but deviated markedly from linearity in the higher temperature range. This deviation was caused by the coexistence of the VS process and the VLS process during whisker growth. 相似文献
999.
Dr. Xiao Liu Dr. Shinji Inagaki Prof.Dr. Jinlong Gong 《Angewandte Chemie (International ed. in English)》2016,55(48):14924-14950
Artificial photosynthesis—reduction of CO2 into chemicals and fuels with water oxidation in the presence of sunlight as the energy source—mimics natural photosynthesis in green plants, and is considered to have a significant part to play in future energy supply and protection of our environment. The high quantum efficiency and easy manipulation of heterogeneous molecular photosystems based on metal complexes enables them to act as promising platforms to achieve efficient conversion of solar energy. This Review describes recent developments in the heterogenization of such photocatalysts. The latest state‐of‐the‐art approaches to overcome the drawbacks of low durability and inconvenient practical application in homogeneous molecular systems are presented. The coupling of photocatalytic CO2 reduction with water oxidation through molecular devices to mimic natural photosynthesis is also discussed. 相似文献
1000.
The catalysts having a conformation switch system induced by acylation and deacylation serve as asymmetric acylating catalysts of sec-alcohols. The kinetic resolution of various sec-alcohols resulted in good to excellent selectivities in the presence of 0.5 to 0.05 mol % of catalyst 1a. The conformation switch system plays a key role to attain both good selectivity and high catalytic activity. 相似文献