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51.
T. Miki T. Higashimura S. Okamura 《Journal of polymer science. Part A, Polymer chemistry》1967,5(1):95-106
In the solution polymerization of trioxane catalyzed by BF3 · O(C2H5)2 at 30°C. the amount of the methanol-insoluble polyoxymethylene is less than the amount of monomer consumed. This difference was much larger than the amount of formaldehyde determined in the polymerized system and could not also be explained in terms of the amount of the methanol-soluble oligomer. Tetraoxane was detected in large quantities by gas chromatography in the polymerized solution of trioxane. Therefore, the difference between the amounts of the methanol-insoluble polymer and the monomer consumed was ascribed partly to the formation of tetraoxane. In spite of the fact that tetraoxane was polymerized more easily than trioxane by BF3 · O(C2H5)2, an almost constant amount of tetraoxane was produced, independent of the kind of solvent and the polymer yield. This suggests the existence of an equilibrium concentration of tetraoxane. On the other hand, the formation of trioxane was observed in the solution polymerization of tetraoxane by BF3 · O(C2H5)2. This suggests that the formation of tetraoxane during the trioxane polymerization is due to a back-biting reaction in which the growing chain end of trioxane attacks the oxygen atom in its own chain with depolymerization of tetraoxane. 相似文献
52.
K. Norisuye K. Okamura Y. Sohrin H. Hasegawa T. Nakanishi 《Journal of Radioanalytical and Nuclear Chemistry》2005,267(1):183-193
Summary The present paper describes a new analytical method for determining the 240Pu/239Pu isotopic ratio and 238Pu/239+240Pu α -activity ratio in seawater, both of which are important parameters for determining Pu sources in the ocean. Plutonium
isotopes were preconcentrated from a large volume of seawater (4700-10800 liter) by solid phase extraction using MnO2-impregnated fibers and eluted into 3M HCl. After the elution, the Pu species of all oxidation states were converted to Pu(IV)
using NaNO2, purified by solvent extraction using thenoyltrifluoroacetone (TTA)-benzene, and concentrated in 5 ml of 0.2M HNO2. The 240Pu/239Pu and 238Pu/239+240Pu ratios in the 5-ml final solution were determined by inductively coupled plasma-mass spectrometry (ICP-MS) and α-spectrometry,
respectively. A pg level of Pu, which was a sufficiently large amount for the determination, was obtained by the solid phase
extraction. Through the redox conversion and solvent extraction, the Pu species, such as Pu(III), Pu(IV) and Pu(VI), were
collected at a high recovery of 96±2% (n=3) despite the presence of large amounts of Mn, and interfering 238U (3.3 μg. l-1in seawater) was effectively removed with a decontamination factor of 1.7·107. The accuracy of the method for the 240Pu/239Pu ratio was verified using reference materials of seawater and a terrestrial soil sample. The present technique was applied
to the determination of the 240Pu/239Pu and 238Pu/239+240Pu ratios in coastal and oceanic water. 相似文献
53.
A new metal complex[MnL2](NO3)2·CH3CN(1) was synthesized by reaction of 4’-4-(l,2,4-triazol-l-yl)phenyl -2,2’:6’,2"-terpyridine(L) with manganese nitrate.The structure of the complex was determined by X-ray crystallography.The results of UV-vis studies showed that the complex exhibits colorimetric sensing ability for Fe3+,which can be observed by naked eye. 相似文献
54.
Two supramolecular complexes, [Cd(bimb)2Cl2] (1) and [Cd(bimb)(DMF)Cl2]·DMF (2) [bimb=4,4′-bis(imidazol-1-ylmethyl)biphenyl], were synthesized by reactions of CdCl2·2.5H2O with bimb ligand in ethanol and N,N′-dimethylformamide (DMF), respectively, and their structures were determined by X-ray crystallography. Complex 1 is an infinite 2D grid network bridged by bimb ligands, and the 2D sheets were further linked by C–H ?Cl hydrogen bonds to form a polycatenated 3D framework. Complex 2 has dicadmium(II) di-μ-chloride units which are connected by bimb bridging ligands to form an infinite non-interpenetrating 2D network. The results provide a nice example of the solvent system exerting a great effect on the construction of supramolecular frameworks. 相似文献
55.
56.
Hidenori Okamura Antony Crisp Sarah Hübner Sidney Becker Petra Rov Thomas Carell 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(51):18864-18869
The RNA world hypothesis assumes that life on Earth began with nucleotides that formed information‐carrying RNA oligomers able to self‐replicate. Prebiotic reactions leading to the contemporary nucleosides are now known, but their execution often requires specific starting materials and lengthy reaction sequences. It was therefore proposed that the RNA world was likely proceeded by a proto‐RNA world constructed from molecules that were likely present on the early Earth in greater abundance. Herein, we show that the prebiotic starting molecules bis‐urea (biuret) and tris‐urea (triuret) are able to directly react with ribose. The urea‐ribosides are remarkably stable because they are held together by a network of intramolecular, bifurcated hydrogen bonds. This even allowed the synthesis of phosphoramidite building blocks and incorporation of the units into RNA. Investigations of the nucleotides’ base‐pairing potential showed that triuret:G RNA base pairs closely resemble U:G wobble base pairs. Based on the probable abundance of urea on the early Earth, we postulate that urea‐containing RNA bases are good candidates for a proto‐RNA world. 相似文献
57.
Toshimitsu Yamazaki M.J.A. Yoshinori Akaishi 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2007,83(5):144-150
We have studied the structure of K−pp comprehensively by solving this threebody system in a variational method, starting from the Ansatz that the Λ(1405) resonance (≡Λ*) is a K−p bound state. The structure of K−pp reveals a molecular feature, namely, the K− in Λ* as an “atomic center” plays a key role in producing strong covalent bonding with the other proton. We point out that strongly bound nuclear systems are formed by “super strong” nuclear force due to migrating real bosonic particles a la Heitler-London-Heisenberg, whereas the normal nuclear force is caused by mediating virtual mesons. We have shown that the elementary process, p + p → K+ + Λ* + p, which occurs in a short impact parameter and with a large momentum transfer, leads to unusually large self-trapping of Λ* by the involved proton, since the Λ*-p system exists as a compact doorway state propagating to K−pp. 相似文献
58.
Yuki Kataoka Dr. Naoya Kanbayashi Naoka Fujii Dr. Taka-aki Okamura Prof. Takeharu Haino Prof. Kiyotaka Onitsuka 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(26):10372-10377
π-Stacked polymers, which consist of layered π-electron systems in a polymer, can be expected to be used in molecular electronic devices. However, the construction of a stable π-stacked structure in a polymer is considerably challenging because it requires sophisticated designs and precise synthetic methods. Herein, we present a novel π-stacked architecture based on poly(quinolylene-2,3-methylene) bearing alanine derivatives as the side chain, obtained through the living cyclo-copolymerization of an o-allenylaryl isocyanide. In the resulting polymer, the neighboring quinoline rings of the main chain form a layered structure with π–π interactions, which is stabilized by intramolecular hydrogen bonds. The vicinal quinoline units form two independent helices and the whole molecule is a twisted-tape structure. This structure is established on the basis of UV/CD spectra, theoretical calculations, and atomic-force microscopy. 相似文献
59.
Yuki Kataoka Naoya Kanbayashi Naoka Fujii Taka‐aki Okamura Takeharu Haino Kiyotaka Onitsuka 《Angewandte Chemie (International ed. in English)》2020,59(26):10286-10291
π‐Stacked polymers, which consist of layered π‐electron systems in a polymer, can be expected to be used in molecular electronic devices. However, the construction of a stable π‐stacked structure in a polymer is considerably challenging because it requires sophisticated designs and precise synthetic methods. Herein, we present a novel π‐stacked architecture based on poly(quinolylene‐2,3‐methylene) bearing alanine derivatives as the side chain, obtained through the living cyclo‐copolymerization of an o‐allenylaryl isocyanide. In the resulting polymer, the neighboring quinoline rings of the main chain form a layered structure with π–π interactions, which is stabilized by intramolecular hydrogen bonds. The vicinal quinoline units form two independent helices and the whole molecule is a twisted‐tape structure. This structure is established on the basis of UV/CD spectra, theoretical calculations, and atomic‐force microscopy. 相似文献
60.
A. Toshimitsu YOKOBORI Jr. 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2020,96(9):373
In this work, the mesoscale mechanics of metals, which links their microscopic physics and macroscopic mechanics, was established. For practical applications, the laws for quantitatively predicting life of cycle and time-dependent fracture behavior such as fatigue, hydrogen embrittlement, and high-temperature creep were derived using particle transport phenomena theories such as dislocation group dynamics, hydrogen diffusion, and vacancy diffusion. Furthermore, these concepts were also applied for estimating the degree of viscoelastic deterioration of blood vessel walls, which is dominated by a time-dependent mechanism, and for the diagnosis of aneurysm accompanied by the viscoelastic deterioration of the blood vessel wall. In these theories, new mechanical indexes were derived as dominant factors for predicting the life of fatigue crack growth and the time-dependent fracture of notched specimens of materials such as hydrogen embrittlement and high-temperature creep. Furthermore, as an example of a practical application, these theories were applied to estimate the degree of viscoelastic deterioration and chaotic motions of blood vessel walls, which are closely related to blood vessel diseases such as atherosclerosis and aneurysm. Moreover, new indexes to diagnose them were also proposed for clinical applications. 相似文献