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961.
Kenji Hanabusa Kuniko Yanagisawa Jun-Ichi Higashi Hirofusa Shirai Tadao Hayakawa Nobumasa Hojo 《Journal of polymer science. Part A, Polymer chemistry》1990,28(4):825-835
Poly(L -glutamate) esters ( 3a – 3d ) with long alkyl side chains containing a mesogenic aromatic segment at the terminal position were synthesized. The superstructure of these polypeptides in solution and film were found to hold a α-helical conformation which was confirmed by CD, IR, and dichroic IR spectroscopy. The thermotropic liquid crystalline behavior was investigated by DSC, x-ray diffraction, and polarizing microscopy with hot stage. Polymers 3a and 3b , having transesterification over 60%, were assumed at least to have two liquid crystalline states. Polymer 3c-H-95 exhibited one crystalline state and two liquid crystalline states; however, 3d-H-97 did not show distinct liquid crystalline states. 相似文献
962.
Hideaki Tsunematsu Shizuko Nakashima Magobei Yamamoto 《Journal of mass spectrometry : JMS》1989,24(10):943-945
Fragmentations of N-benzyloxycarbonyl-protected tripeptide ethyl esters containing proline were compared with those of the corresponding peptide derivatives not containing proline in negative-ion fast atom bombardment mass spectrometry. The fragment ion [M – 109]? due to loss of the benzyloxy group followed by dehydrogenation from the peptide molecule was the base peak in the negative-ion mass spectra for the peptides not containing proline, whilst it was a very weak fragment ion or not observed at all in those for the peptides containing proline. These results suggest that the fragmentations of the peptide derivatives in negative-ion fast atom bombardment mass spectrometry depend on the conformational difference of the peptide derivatives owing to the existence of proline in the derivative. 相似文献
963.
Free radicals in crosslinked PTFE which formed by 60Co γ-rays irradiaion at 77 K and at room temperature were studied by electron spin resonance (ESR) spectroscopy. The crosslinked PTFE specimens with different crosslinking density were prepared by electron beam irradiation in the molten state. The ESR spectra observed in the irradiated crosslinked PTFE are much different from those in non-crosslinked PTFE (virgin); a broad singlet component increases with increasing the crosslinking density, G-value of radicals is much higher in crosslinked PTFE than in non-crosslinked one. Free radicals related to the broad component are trapped in the non-crystalline region of crosslinked PTFE and rather stable at room temperature, whereas radicals trapped in amorphous non-crosslinked PTFE are unstable at room temperature. It is thought that most of free radicals trapped in the crosslinked PTFE are formed in the crosslinked amorphous region. The trapped radicals decays around 383 K (110°C) due to the molecular motion of -relaxation. 相似文献
964.
Michihiko Noguchi Masashi ShiraiKuniko Nakashima Ichiro AraiAkiko Nishida Hidetoshi YamamotoAkikazu Kakehi 《Tetrahedron》2003,59(25):4581-4590
The thermal reaction of N-benzyl-N-[3-(N-substituted imino)methyl-4-oxo-4H-pyrido[1,2-a]pyrimidin-2-yl]amino acid esters, generated from aldehyde esters and primary amines, provides 2,3-dihydropyrido[1,2-a]pyrrolo[2,3-d]pyrimidin-4(1H)-one derivatives effectively and stereoselectively. Therein, the stereoselective generation of conjugated azomethine ylides from the imine esters and their cyclization is essential for the pyrroline-ring formation. 相似文献
965.
[structure; see text] An iterative synthetic route to organic-soluble ureido-naphthyridine oligomers has been developed. Use of this protocol allowed synthesis of a short ureido-naphthyridine oligomer, which presents a self-complementary DDAADDAA hydrogen bonding array (D = hydrogen bond donor, A = hydrogen bond acceptor). Strong self-association via eight hydrogen bonds was observed in organic solution. 相似文献
966.
The pH value in the gel-sol system for the preparation of uniform anatase TiO2 nanoparticles, as a decisive factor for controlling the size and shape of the final product, was found to be significantly changed during the formation process of the anatase TiO2 particles from a condensed Ti(OH)4 gel. The dramatic evolution of pH with the progress of the synthetic process has clearly been explained in terms of the adsorption and desorption of a hydroxide ion (OH-) ora proton (H+) on the solids transforming with time. The adsorption and desorption of OH- or H+ were enhanced by the presence of an inert electrolyte such as NaClO4, as explained by its shielding effect on the electrical interactions between the electrically charged precipitates and free OH- and H+ ions. The electrolyte also hampered the phase transformation of Ti(OH)4 precipitate to anatase TiO2. This effect of electrolytes was explained in terms of the inhibited nucleation of anatase TiO2 by enhanced adsorption of OH- ions toTiO2 embryos. The points of zero charge (PZC) of the amorphous Ti(OH)4 precipitate and the anatase TiO2 particles at 25 degrees C were obtained from the change in pH associated with the adsorption and desorption of OH- or H+, i.e., 4.6 for Ti(OH)4 precipitate and 6.0 for anatase TiO2 in the presence of 0.1 mol dm(-3) NaClO4. The PZCof the Ti(OH)4 precipitate measured at 25 degrees C after additional aging at 100 degrees C for 30 min was shifted to 4.1, owing to the promoted adsorption of OH-. 相似文献
967.
Matsuda T Watanabe K Harada T Nakamura K Arita Y Misumi Y Ichikawa S Ikariya T 《Chemical communications (Cambridge, England)》2004,(20):2286-2287
A novel continuous-flow scCO(2) process for kinetic resolution of racemic alcohols can be performed with an immobilized lipase to lead to a quantitative mixture of the corresponding optically active acetates with up to 99% ee and unreacted alcohols with up to 99% ee, in which the productivity of the optically active compounds was improved by over 400 times compared to the corresponding batch reaction using scCO(2). 相似文献
968.
Racemic and optically active hepialone, a new sex-pheromonal component produced by the male moth, Hepialus californicus Bvd., was synthesized and thus confirmed the structure of the pheromone as (2R)-2,3-dihydro-2-ethyl-6-methyl-4H-pyran-4-one (1). 相似文献
969.
G. Sugihara A. A. Nakamura T. -H. Nakashima Y. -I. Araki T. Okano M. Fujiwara 《Colloid and polymer science》1997,275(8):790-796
For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, the differential
conductivity (∂κ/∂C)
T
,
P
vs. square root of concentration (√C) was employed in order to determine not only CMC but also the limiting molar conductance (Λ0) and the molar conductance of micellar species (ΛM).
Based on the data of the degree of counterion binding to micelles (β) determined previously at different temperatures ranging
15–50 °C at every 5 °C, the experimental values of the degree of dissociation (ionization) of a micelle (αEX) were calculated by regarding as αEX=1−β. The ratio ΛM/Λ0 corresponding to the ratio of slopes below and above CMC in the curve of specific conductivity (κ) vs. concentration (C), which has been often assumed to be the degree of ionization of micelles (α), was compared with the present αEX. However, the ratio ΛM/Λ0 (=α) was found to have a correlationship with αEX (=1−β) as αEX≈0.40×(ΛM/Λ0), or strictly, αEX=0.40 (ΛM/Λ0)+0.08, indicating that the simple ratio of the slopes below and above CMC in κ vs. C curve is not true for αEX=1−β. On the other hand, the method proposed by Evans gave a value closer to αEX compared with the simple ratio.
Received: 17 September 1996 Accepted: 8 April 1997 相似文献
970.
Takada T Kawai K Cai X Sugimoto A Fujitsuka M Majima T 《Journal of the American Chemical Society》2004,126(4):1125-1129
Charge transfer in DNA is of current interest because of the involvement of charge transfer in oxidative DNA damage and electronic molecular devices. We have investigated the charge separation process via the consecutive adenine (A)-hopping mechanism using laser flash photolysis of DNA conjugated with naphthaldiimide (NDI) as an electron acceptor and phenothiazine (PTZ) as a donor. Upon the 355-nm laser flash excitation of NDI, the charge separation and recombination process between NDI and PTZ was observed. The yields of the charge separation via the consecutive A-hopping were slightly dependent upon the number of A bases between the two chromophores, while the charge recombination rate was strongly dependent upon the distance. The charge-separated state persisted over 300 micros when NDI was separated from PTZ by eight A bases. Furthermore, the rate constant of the A-hopping process was determined to be 2 x 10(10) s(-1) from an analysis of the yield of the charge separation depending on the number of A-hopping steps. 相似文献