Nonclassical Urea Oligomers. VII. Binding Specificity of Carbanilido-ethylenimine Oligomer: Absorption Behavior in Suspension

Polyester elastomers were prepared by block copolymerization of dimethyl terephthalate (DMT), butanediol (BDO), and polytetramethylene glycol (PTMG). Polyester from DMT and butanediol forms a high-melting hard segment in block copolyester to prevent undue chain slippage when fibers are stretched. High elongation was provided by soft segment which consisted of condensation product from DMT and PTMG.

Experiments were carried out to determine the effect of composition variables on the properties of these elastomers, such as glass transition temperature, elongation at break, tenacity, and elastic recovery. The study on molecular characteristics of the elastic polyester showed that a leather-like region exists between glassy and rubbery regions. These elastomers were melt-spun to give elastic fibers which are competitive with commercially available Spandex-type fibers.     

Complexation of acyclic ligands having two terminal quinoline units with alkali metal cations

Abstract

Acyclic multidentate ligands consisting of an oligooxyethylene chain (di-, tri-, tetra-, and penta-) and two terminal rigid quinaldate end groups were newly prepared and their complexation properties with alkali metal cations were estimated by the solvent extraction method to indicate a better affinity for K⁺. Among them, the tetraethylene glycol derivative showed the highest K⁺ binding on about the same level as 18-crown-6. Their conformations in solution and in the solid state were examined by using ¹H- and ¹³C-NMR spectroscopy and X-ray crystal analyses, respectively. The better binding of K⁺ in comparison with the corresponding glymes or analogues having the same donor sites was reasonably explained by considering the effective co-ordination of the carbonyl oxygen of the ester groups and the parallel π-stacking interaction between two quinaldate surfaces.     

Thermal behavior and dismantlability of adhesives containing various inorganic salts

As a fundamental study on the development of dismantlable adhesives containing chemically reactive materials, the thermal behavior and dismantlability of an epoxy adhesive containing one of the twenty-seven inorganic salts (chlorides, perchlorates, and nitrates) were observed. In the thermal behavior measured by the differential scanning calorimetry, epoxy adhesives with inorganic salts containing iron, copper, zinc, and aluminum cations released heats of reaction at lower temperatures than the adhesive alone or the adhesives with other inorganic salts. Since such inorganic salts were considered to be effective candidates as fillers in dismantlable adhesives, the adhesion strengths of their mixtures with the adhesive were observed after heat aging at 270 °C for 30 min. The results showed that both chloride and perchlorate salts specifically decreased the adhesion strength after heating. On the other hand, the effect of nitrate salts on the decrease in adhesion strength was low in comparison with the chloride and perchlorate salts.     

Thermal oxidative degradation of additive-free polypropylene pellets investigated by multichannel Fourier-transform chemiluminescence spectroscopy

Thermal oxidative degradation of additive-free polypropylene pellets heated isothermally in dry air at 150 and 180 °C (below and above the melting point of 163 °C) was investigated by multichannel Fourier-transform chemiluminescence spectroscopy. The initial peak wavelength of chemiluminescence emission at 490 nm remained constant during the early stages of thermal degradation, but new emissions developed with time in the red spectral region over an extended oxidation period. The time-dependent luminescence spectra were deconvoluted into three emission bands by least-squares fitting using Gaussian curves. We concluded that at least three groups of luminescent species (luminophores), having different conjugation lengths, were generated by thermal oxidation over extended periods and show luminescence around 490, 660, and 740 nm.     

Study on excited states of hexamethoxybenzene-NO+ charge-transfer complex: incorporation of excited radical cation

A charge-transfer (CT) complex of NOBF₄ and hexamethoxybenzene (HMB), which gives out HMB^?+ as a “fluorescent radical cation probe,” upon one-electron oxidation, has been designed to explore the excited state dynamics of contact radical ion pairs by laser-induced fluorescence and femtosecond transient absorption spectroscopic techniques. The acetonitrile solution of the CT complex showed weak fluorescence with a similar spectrum to that observed for free excited HMB radical cation (HMB^?+*), suggesting the formation of HMB^?+* upon the one-photonic excitation of the CT complex. The laser-power dependence of the fluorescence intensity supported the one-photonic excitation event. We have also observed a short-lived transient species but no long-lived species by femtosecond laser flash photolysis of the CT complex. The lifetime (6.5 ps) was in good accordance with its fluorescence quantum yield (2.5 × 10^?5) and was able to assign the transient species to the fluorescent state, an excited radical ion pair [HMB ^?+*/NO^?]. All the events were completed within the inner sphere and the short lifetime of the transient species could be attributed to rapid back-electron transfer. It is concluded that the excited radical cation character in the excited state of the CT complex originates from the radical ion character in the CT complex in the ground state and that a relatively long lifetime of HMB^?+* facilitates its observation even in the contact ion pair.     

Synthetic study of kosinostatin aglycone: synthesis of BCDE rings using alkoxycarbonylmethylation of diazonaphthoquinone

A synthetic study of kosinostatin aglycone is reported. Synthesis of key intermediate lactone 3, which corresponds to the BCDE ring fragment, was accomplished, and the precursor BCD ring fragment 5 was synthesized via two routes. First, 5 was synthesized from 2,5-dimethoxybenzaldehyde 16 by the combination of typical known transformations including efficient application of non-aqueous OsO₄ oxidation in the presence of PhB(OH)₂. However the synthesis required 15 long steps, and its main difficulty was ortho-alkoxycarbonylmethylation of 1-naphthol. Next we attempted to apply our recently developed alkoxycarbonylmethylation of diazonaphthoquinone for the synthesis of 5, and 5 was successfully synthesized in 9 steps from the same starting compound 16. Finally, 5 was stereoselectively converted to lactone 3 via trifluoroacetic acid-mediated cyclization of the 3,4-epoxycylohexanecarboxylic acid derivative.     

Characterization of flower-inducing compound in Lemna paucicostata exposed to drought stress

A flower-inducing compound, LDS1, was isolated from a free-floating aquatic plant, Lemna paucicostata. The chemical structure and the absolute stereochemistry of LDS1 were determined as (9R,13R,11E,15Z)-9,13-dihydroxy-10-oxooctadeca-11,15-dienoic acid for its most abundant diastereomer. LDS1 was enzymatically produced when the plant was exposed to drought stress, and induced flowering at a concentration of 10 nM.     

Recognition of caffeine by a water-soluble acyclic phane compound

Caffeine (1,3,7-trimethylxanthine) is a chemical substance associated with everyday human life. In order to recognize caffeine in water, six water-soluble acyclic phane compounds composed of three aromatic rings were examined as artificial receptors. ¹H NMR titration experiments revealed that 6,6′-[1,3-phenylenebis(carbonylimino)]bis-1,3-naphthalenedisulfonate had the highest binding ability for caffeine, with a binding constant (K_b) of 127±5 M⁻¹ at 300 K. While this phane compound also formed a complex with theophylline (1,3-dimethylxanthine) at around half the value of the binding constant for caffeine (K_b=64±4 M⁻¹), it showed weak or little complexation for adenosine, guanosine, inosine, and their 5′-phosphates (sodium salts of adenylic acid, guanylic acid, and inosinic acid).     

Rate constant measurements for initial addition reactions of radicals at the propagation step of photo‐polymerization as studied by pulsed EPR spectroscopy

Pulsed EPR spectroscopy was employed to determine reaction rate constants at an early stage of addition reactions in radical polymerizations triggered by four initiator radicals, which were generated by photodissociation of four parent molecules. Two monomers (tert‐butylacrylate and tert‐butylmethacrylate) were examined as reactant. Stern–Volmer analysis on the measured decay time of electron spin echo intensity of reacting radicals provides rate constants for addition reactions. We focused on rate constants for the second step reaction between monomer and adduct radical that is produced by the first step addition reaction between initiator radical and monomer. The rate constant measured by pulsed EPR was evaluated by theoretical calculations in the light of (1) enthalpy difference between product radical and reactants and (2) charge transfer interaction between reacting radical and monomer. Copyright © 2016 John Wiley & Sons, Ltd.     

Third-order aberration analysis of an off-axial optical system

The aberration theory applied to co-axial optical systems is extended to off-axial systems, for which third-order aberration coefficients are considered. The derived aberrations are analyzed using three-dimensional ray bundles, spot diagrams, and image charts, and classified in relation to the system symmetry. This theory is very useful for optical designers, allowing them to clarify the relationship between the structures of off-axial optical systems and the corresponding off-axial aberrations.