Radiation-induced polymerization of glass-forming systems. VII. Polymerization in supercooled state under high pressure

Radiation-induced polymerization of glass-forming monomers such as 2-hydroxyethyl methacrylate and glycidyl methacrylate under high pressure was studied. The glass transition temperature of these monomers was heightened by increased pressure. The temperature dependence of polymerizability showed a characteristic relation; similar to those in supercooled-phase polymerization under normal pressure, that had a maximum at T_v which shifted to higher levels of temperature as well as to T_g under high pressure. Polymerizability in the supercooled state also increased under increased pressure.     

Synthesis and duplex formation of the reverse amidohelicene tetramer

The reverse amidohelicene (P)-tetramer containing (P)-helicenediamine and m-phenylenedicarboxylate was synthesized. The circular dichroism (CD) and vapor pressure osmometry (VPO) analysis revealed the dimeric aggregate formation in THF. It is notable that the reverse amide tetramer formed a duplex, as well as the original amidohelicene oligomers. In various solutions, mixtures of the reverse (P)-tetramer and amidohelicene (P)/(M)-tetramer formed homoaggregates instead of heteroaggregates.     

Direct Carboxylation of Electron-Rich Heteroarenes Promoted by LiO-tBu with CsF and [18]Crown-6

We herein demonstrate that the combination of LiO-tBu, CsF, and [18]crown-6 efficiently promotes the direct C−H carboxylation of electron-rich heteroarenes (benzothiophene, thiophene, benzofuran, and furan derivatives). A variety of functional groups, including methyl, methoxy, halo, cyano, amide, and keto moieties, are compatible with this system. The reaction proceeds via the formation of a tert-butyl carbonate species.     

Phosphazene Base tBu-P4 Catalyzed Methoxy–Alkoxy Exchange Reaction on (Hetero)Arenes

The organic superbase tBu-P4 catalyzes methoxy-alkoxy exchange reactions on (hetero)arenes with alcohols. The catalytic reaction proceeded efficiently with electron-deficient methoxy(hetero)arenes as well as with a variety of alcohols, including 3-amino-1-propanol, β-citronellol, menthol, and cholesterol. An intramolecular version of this reaction furnished six- and seven-membered ring compounds.     

Palladium-catalyzed sequential carbon-carbon bond cleavage/formation producing arylated benzolactones

3-(2-Hydroxyphenyl)cyclobutanones react with aryl bromides in the presence of palladium catalysts to afford 4-arylmethyl-3,4-dihydrocoumarins in high yields through a sequence involving carbon-carbon bond cleavage and formation. In the case of the reaction with 2-(2-hydroxyphenyl)cyclobutanones, five- or seven-membered lactones were produced depending on the presence of an additional substituent at the 2-position.     

Diastereo- and enantioselective synthesis of nitroso Diels-Alder-type bicycloketones using dienamine: mechanistic insight into sequential nitroso Aldol/Michael reaction and application for optically pure 1-amino-3,4-diol synthesis

This article presents complete diastereo- and highly enantioselective synthesis of nitroso Diels-Alder-type bicycloketones using dienamine. With the hydrogen bonding of two hydroxyls in the bulky binaphthol 1c, high enantioselectivities and complete diastereoselectivity are realized in 2-oxa-3-aza-bicycloketone synthesis. On the other hand, alpha,beta-unsaturated ketone can be employed as diene precursor, utilizing readily available tetrazole catalyst 3b, to provide the 3-oxa-2-aza-bicycloketones in moderate yields with complete enantioselectivities. Investigation into the reaction utilizing 2-morpholino-4,4-diphenylcyclohexadiene 2d clearly indicated that cyclization with the bulky binaphthol 1c is involved in the sequential process, the N-nitroso aldol reaction, followed by Michael addition. In addition, optically pure 1-amino-3,4-diol is synthesized from 2-oxa-3-aza-bicycloketones. Use of p-phenoxynitrosobenzene allows access to protected amino diol via cleavage of the N-Ph bond.     

Electron Spin Resonance Spectroscopy of Gamma-Irradiated Glucose Polymers

Using electron spin resonance (ESR) spectroscopy, we revealed the irradiation-induced radicals in cellulose and starch. Before gamma-ray irradiation, no ESR signals were observed in both the glucose polymers. However, after gamma-ray irradiation, a singlet at g = 2.0 was observed, and a pair of side signals appeared simultaneously. The side signals were found at the symmetric field positions at both sides of the singlet signal. The side signals were visible in cellulose but not in starch. The side signals are found to be a precise indicator for irradiation effects in cellulose. They are originated from neither the peroxide radical of glucose polymer nor the so-called cellulosic radicals. By the simulation method, we found that the side signals are originated from a triplet due to a hyperfine interaction with two protons. By the theoretical simulation, we revealed that the signal undergo the rotational motions rather than rigid limit state (or no motion).     

Power-law analysis of surface-plasmon-enhanced electromagnetic field dependence of blinking SERS of thiacyanine or thiacarbocyanine adsorbed on single silver nanoaggregates

Blinking statistics in surface-enhanced Raman scattering (SERS) of thiacyanine or thiacarbocyanine adsorbed on single Ag nanoaggregates were analyzed by a power law. A power law reproduces the probability distributions of both the bright and dark SERS occurrences against their duration times. As the localized surface plasmon resonance (LSPR) wavelength of a single Ag nanoaggregate approached the excitation wavelength or the excitation laser intensity increases, the power-law exponents were close to -1.5, a value derived from a one-dimensional random walk model. When the LSPR wavelength left the excitation wavelength or the excitation laser intensity decreases, the power-law exponents deviated from -1.5. The decrease in the power-law exponents in the bright SERS, which indicates a decrease in the probabilities of the long-lived bright SERS, and the increase in the power-law exponents in the dark SERS coincide with the increasing shallowness and narrowing of a optical trapping potential well due to a surface-plasmon-enhanced electromagnetic field around a junction of the Ag nanoaggregates excited at a wavelength apart from the LSPR wavelength or under the low laser intensity, i.e., the low original electromagnetic field, respectively.     

Global minimum structure search in Li(x)CoO(2) composition using a hybrid evolutionary algorithm

The global minimum structures for Li(x)CoO(2) compositions where 0 ≤ x ≤ 1 were probed by using a hybrid evolutionary algorithm with an underlying ab initio structural relaxation scheme. The method successfully predicted experimentally observed variants of layered configurations at various degrees of lithiation and the spinel (Fd3[combining macron]m) phase at x = 1/2. New low-energy non-layered host structures at x < 1/2 were also revealed. These structures can be formed from the usual layered configuration through coherent stacking faults along the c-axis and the migration of Co ions into the Li-poor intercalation layer.     

Maximum network flows with concave gains

This paper deals with a generalized maximum flow problem with concave gains, which is a nonlinear network optimization problem. Optimality conditions and an algorithm for this problem are presented. The optimality conditions are extended from the corresponding results for the linear gain case. The algorithm is based on the scaled piecewise linear approximation and on the fat path algorithm described by Goldberg, Plotkin and Tardos for linear gain cases. The proposed algorithm solves a problem with piecewise linear concave gains faster than the naive solution by adding parallel arcs. Supported by a Grant-in-Aid for Scientific Research (No. 13780351 and No.14380188) from The Ministry of Education, Culture, Sports, Science and Technology of Japan.