Structure and electronic properties of quinone dimers connected with acetylene and diacetylene linkages

Quinone dimers connected with acetylene (QAQ) and diacetylene linkages (QAAQ) have been synthesized and their structure and electronic properties studied. X-ray analysis, DFT calculations, and UV-vis measurements showed that, unlike directly connected quinone dimers (QQ), they had planar and thus efficiently extended π conjugation systems. The respective reduction potentials of QAQ and QAAQ were considerably raised, and QAQ thereby behaved as a mild oxidizing agent.     

Total Synthesis of (−)‐FR182877 through Tandem IMDA–IMHDA Reactions and Stereoselective Transition‐Metal‐Mediated Transformations

Intelligent design : The total synthesis of the cytotoxic (?)‐FR182877 relies on 1) tandem Diels–Alder reactions to close rings A–D (see scheme), 2) a palladium‐mediated 7‐exo‐trig reaction, and 3) an iridium‐mediated isomerization followed by epimerization and stereoselective reduction.

     

Oxidation Reactivity of Bis(μ‐oxo) Dinickel(III) Complexes: Arene Hydroxylation of the Supporting Ligand

In the nick(el) of time : Bis(μ‐oxo) dinickel(III) complexes 2 (see scheme), generated in the reaction of 1 with H₂O₂, are capable of hydroxylating the xylyl linker of the supporting ligand to give 3 . Kinetic studies reveal that hydroxylation proceeds by electrophilic aromatic substitution. The lower reactivity than the corresponding μ‐η²:η²‐peroxo dicopper(II) complexes can be attributed to unfavorable entropy effects.

     

Tuning of Electronic Properties of Single‐Walled Carbon Nanotubes under Homogenous Conditions

Reversible and non‐bonding interaction between SWNTs and ODCB is observed from the analyses of visible near‐infrared absorption data and Raman spectroscopies (see spectra). The solvent effect on SWNTs effectively controls the electronic structure of SWNTs under homogeneous conditions.

     

A study on the role of gelatin in methacrylic-acid-based gel dosimeters

In radiotherapy treatment, polymer gel dosimetry can be used for verifying three-dimensional (3D) dose distributions. Gelatin is generally used as a gelling agent in the dosimeters. In this paper, another role of gelatin in a methacrylic-acid-based gel dosimeter (MAGAT) is investigated. Temperature increases due to exothermic polymerization in the irradiated gel are measured directly. Dose–R₂ responses are also obtained using MRI. It is shown that no appreciable increases in either temperature or R₂ are observed in MAGAT dosimeters made without gelatin, and that significant temperature and R₂ increases are observed when very low gelatin concentrations are used. These results indicate that gelatin is an important enabler for radiation-induced free-radical polymerization in methacrylic-acid-based gels. When gelatin is replaced by amino acids, changes in temperature are observed, along with small changes in R₂. The resulting dosimeter solutions remain transparent because the polymer does not precipitate as it does in regular MAGAT dosimeters containing gelatin. When the amino acids are replaced by acids without amino groups, no temperature or R₂ changes are observed, indicating that no polymer forms. These results show that amino groups (and possibly other functional groups) on the gelatin catalyze the radiation-induced free-radical polymerization that occurs in MAGAT dosimeters.     

Multiscale Lagrangian fluid dynamics simulation for polymeric fluid

We have developed a simulation technique of multiscale Lagrangian fluid dynamics to tackle hierarchical problems relating to historical dependency of polymeric fluid. We investigate flow dynamics of dilute polymeric fluid by using the multiscale simulation approach incorporating Lagrangian particle fluid dynamics technique (the modified smoothed particle hydrodynamics) with stochastic coarse‐grained polymer simulators (the dumbbell model). We have confirmed that our approach is well in agreement with the macroscopic results obtained by a constitutive equation corresponding to the dumbbell model, and observed that microscopic thermal fluctuation appears in macroscopic fluid dynamics as dispersion phenomena. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 886–893, 2010     

9,9′‐spirobifluorene‐containing polycarbonates: Transparent polymers with high refractive index and low birefringence

Syntheses of 2,2′‐bisalcoholic group‐substituted 9,9′‐spirobifluorene monomers 2 were performed by the reaction of 2,2′‐dihydroxy‐9,9′‐spirobifluorene 2a with haloalcohols. Polycarbonates consisting of 9,9′‐spirobifluorene skeleton in the main chain (PC 4 ) were synthesized by the polycondensation of 2,2′‐bisalcoholic monomers 2 and triphosgene or diphenyl carbonate. PC 4 showed good thermal stability: the 5% weight loss temperature was over 330 °C under both nitrogen and air atmospheres. The glass transition temperature was in a range of 16–269 °C estimated by differential scanning calorimetry, depending on the flexibility of the alkylene or oxyethylene chains of 2 . PC 4 showed high solubility toward ordinary organic solvents such as CHCl₃, benzene, and THF, making possible the preparation of the flexible thin films. Very high refractive index in a range of 1.62–1.66 at 589 nm was observed although PC 4 consists only of C, H, and O atoms, whereas very low degree of birefringence was confirmed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3658–3667, 2010     

Nano-biphasic ionic liquid systems composed of hydrophobic phosphonium salts and a hydrophilic ammonium salt

A combination of a phosphonium-type-zwitterions-lithium bis(trifluoromethanesulfonyl)imide complex and a hydrophilic ammonium salt provides a nanosegregated liquid-crystalline matrix consisting of hydrophilic ionic liquid (IL) domains and hydrophobic IL domains.     

Structure–Activity Studies on the Fluorescent Indicator in a Displacement Assay for the Screening of Small Molecules Binding to RNA

A series of xanthone and thioxanthone derivatives with aminoalkoxy substituents were synthesized as fluorescent indicators for a displacement assay in the study of small‐molecule–RNA interactions. The RNA‐binding properties of these molecules were investigated in terms of the improved binding selectivity to the loop region in the RNA secondary structure relative to 2,7‐bis(2‐aminoethoxy)xanthone (X2S) by fluorimetric titration and displacement assay. An 11‐mer double‐stranded RNA and a hairpin RNA mimicking the stem loop IIB of Rev response element (RRE) RNA of HIV‐1 mRNA were used. The X2S derivatives with longer aminoalkyl substituents showed a higher affinity to the double‐stranded RNA than the parent molecule. Introduction of a methyl group on the aminoethoxy moiety of X2S effectively modulated the selectivity to the RNA secondary structure. Methyl group substitution at the C1′ position suppressed the binding to the loop regions. Substitution with two methyl groups on the amino nitrogen atom resulted in reducing the affinity to the double‐stranded region by a factor of 40 %. The effect of methyl substitution on the amino nitrogen atom was also observed for a thioxanthone derivative. Titration experiments, however, suggested that thioxanthone derivatives showed a more prominent tendency of multiple binding to RNA than xanthone derivatives. The selectivity index calculated from the affinity to the double‐stranded and loop regions suggested that the N,N‐dimethyl derivative of X2S would be suitable for the screening of small molecules binding to RRE.