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41.
Summary In the aqueous solutions of poly(N-vinylacetamide) in the presence of Na2SO4 or (NH4)2SO4, the intrinsic viscosities were small and the Huggins constants were large compared with those in water. Similar but much
less effects were observed for NaF. Opposite effects were found, however, for NaSCN. The poor solvent quality of aqueous sulfate
solutions was significantly improved by the addition of guanidine hydrochloride to 3 M or higher. Urea was much less effective
in improving the solvent quality. The different M28.8neffects observed between urea and GdnHCl may be explained by their different
binding affinities to amide group. Solubilization of PNVA flocculates induced by the presence of 0.8 M Na2SO4 took place by adding urea to 1 M, although only small changes were detected in the viscosity behavior accompanying the addition
of 1 M urea.
Received: 12 June 1997 Accepted: 4 August 1997 相似文献
42.
Maeda H 《Journal of colloid and interface science》2003,258(2):390-395
A simple analytical expression is presented to describe the dependence of the degree of counterion binding beta of ionic-nonionic mixed micelles on the composition x(I) (the micelle mole fraction of the ionic species): 1/(1-beta)=1-x(I)+x(I)/[1-beta(x(I)=1)]. In the application of the relation, the value of beta for the pure ionic micelle, beta(x(I)=1), should be known in advance. An equivalent expression was first proposed by Hall et al. on purely empirical grounds but in the present study the relation is derived on the basis of the Poisson-Boltzmann equation of the plate model of micelles in a salt-free medium. The insensitive nature of beta toward a change in micelle concentration as well as to the addition of a salt is also derived under reasonable approximations. When the relation was applied to 12 mixed micelles both with and without added salt, it described quite well the observed composition dependencies of all examples examined. Two other simple analytical expressions are also derived, but they are much less satisfactory in describing the experimental data. 相似文献
43.
Utilizing a commercially available helium-purging device and PEEK tubes for all tubing, especially for connection between the mobile phase and pump, high performance liquid chromatography with an electrochemical detector (ECD/HPLC) at the cathodic mode is a simple and precise method for the determination of p-nitrophenol (NP). Studies with cyclic and hydrodynamic voltammetry indicated that 25% aqueous MeOH containing 0.1% (v/v) CF(3)CO(2)H and -0.8 V vs. Ag/AgCl are the best mobile phase and detection potential for cathodic ECD/HPLC. With the present system, the limits of detection and determination were 0.2 and 0.25 microM, respectively, and up to 50 microM, a linear calibration curve was afforded. Within-day precisions for the analysis of 5 and 50 microM NP were 0.8 and 0.7% (n=6), respectively, and between-day precisions (n=6) for these samples were 3.5 and 2.2%, respectively. Compared with the commonly used Bessey-Lowry-Brock method, cathodic ECD/HPLC was useful for the assay of acid phosphatase in urine samples with p-nitrophenyl phosphate disodium salt as a substrate. 相似文献
44.
Kenji Maeda Ross A. Miller Ali Shafiee Joseph D. Armstrong III 《Tetrahedron letters》2005,46(9):1545-1549
Highly diastereoselective (>20:1) bromo-lactonization of N-sulfonyl-2-allyl-2-phenylglycine methyl ester (11) was observed. Successive treatment of the chiral lactone with MeONa gave the desired (2S,4R)-4-hydroxy-2-phenylproline derivative in high yield without erosion of the diastereoselectivity. The starting chiral non-racemic compound (5) was prepared from the racemic 2-phenylglycine using a classical kinetic resolution (crystallization), an asymmetric phase transfer alkylation, and an enzyme-catalyzed kinetic resolution. 相似文献
45.
Zhang X Furutachi H Fujinami S Nagatomo S Maeda Y Watanabe Y Kitagawa T Suzuki M 《Journal of the American Chemical Society》2005,127(3):826-827
(mu-Hydroxo or oxo)(mu-1,2-peroxo)diiron(III) complexes having a tetradentate tripodal ligand (L) containing a carboxylate sidearm [Fe2(mu-OH or mu-O)(mu-O2)(L)2]n+ were synthesized as models for peroxo-intermediates of non-heme diiron proteins and characterized by various physicochemical measurements including X-ray analysis, which provide fundamental structural and spectroscopic insights into the peroxodiiron(III) complexes. 相似文献
46.
Alfred Trautwein Yutaka Maeda Frank E. Harris Helmuth Formanek 《Theoretical chemistry accounts》1974,36(1):67-76
Experimental Mössbauer spectra of the Fe57-enriched CO complex of sperm whale myoglobin (MbCO) at T= 4.2 K with and without applied magnetic field (H⊥γ) were measured to derive the sign of the electric field gradient (EFG), the quadrupole splitting ΔE Q, and the isomer shift δ of the heme iron. We find a positive EFG, δE Q = 0.363 mm/sec, and δ + 0.266 mm/sec. Molecular orbital calculations were carried out to obtain theoretical estimates of EFG and ΔE Q for several steric arrangements of the CO ligand relative to the heme group. Our results are most consistent with the conclusion that the iron is situated in the heme plane, and that a bent geometry with a Fe-C-O angle of about 135 ° is more favorable than a more symmetric structure with a linear Fe-C-O geometry. 相似文献
47.
Y. Akiyama F. Mizukami H. Izutsu M. Sato K. Maeda Y. Kiyozumi K. Sakaguchi 《Journal of Sol-Gel Science and Technology》1998,13(1-3):421-425
A novel organic-inorganic composite was prepared by a sol-gel process using hydrolysis and condensation of tetraethoxysilane (TEOS) reacted with a saccharide. During the process, ethoxy groups of the TEOS were replaced with hydroxyl groups of the saccharide and, consequently, saccharide molecules were combined with silica through their hydroxyl groups. Samples obtained under different reaction conditions were used for optical resolution of a metal chelate compound. The resolution ability of the composites was affected by the amount of water added for hydrolysis and of the saccharide. In particular, the amount of water drastically influenced the optical resolution performance. Composites obtained at the lower H2O/TEOS ratio gave the metal chelate compound a higher optical rotation. Three types of composites with the same composition were prepared by kneading, impregnation and by the sol-gel method, and were compared. The sol-gel composite showed the best optical resolution ability. It was concluded that the optical resolution ability was closely related to dispersibility of saccharide in the silica matrix. 相似文献
48.
49.
Beker H Boggild H Boissevain J Cherney M Dodd J Esumi S Fabjan CW Fields DE Franz A Hansen KH Holzer EB Humanic TJ Jacak BV Jayanti R Kalechofsky H Kobayashi T Kvatadze R Lee YY Leltchouk M Lörstad B Maeda N Medvedev A Miake Y Miyabayashi A Murray M Nagamiya S Nishimura S Noteboom E Pandey SU Piuz F Polychronakos V Potekhin M Poulard G Sakaguchi A Sarabura M Shigaki K Simon-Gillo J Sondheim W Sugitate T Sullivan JP Sumi Y van Hecke H Willis WJ Wolf K Xu N 《Physical review letters》1995,74(17):3340-3343
50.
W. K. A. Kumuduni Y. Nakata T. Okada M. Maeda 《Applied physics. B, Lasers and optics》1994,58(4):289-294
One-dimensional imaging laser-induced fluorescence spectroscopy has been used for in-situ measurements of spatial distributions of YO molecules produced during the ArF-laser ablation of YBa2 Cu3 O
7–x
in vacuum and oxygen gas environment. The time-integrated angular distribution of particles ejected in vacuum has a cos
n
form, where 11 <n < 13. When oxygen gas was introduced, YO molecules were confined in a smaller volume, and temporal changes of their spatial distribution were interpreted in terms of blast-wave formation. 相似文献