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41.
Jean Ravez Annie Perron Jean Pierre Chaminade Paul Hagenmuller Loïc Rivoallan 《Journal of solid state chemistry》1974,10(3):274-281
Two series of phases with tetragonal bronze-like structure and composition BaxLi5?2xT5O15 (T = Nb, Ta) have been isolated in the systems BaNb2O6LiNbO3 and BaTa2O6LiTaO3. All these phases show ferroelectric-paraelectric transitions. The Curie temperature increases with the lithium content. The value of TC for Ba2.03Li0.94Nb5O15 is the highest ever observed for this type of structure: the obtained phases are potentially good materials for the harmonic generation of the 0.53-μm radiation. The optical yield of the niobate Ba2.14Li0.71Nb5O15 is about 2.5 times that of Ba2NaNb5O15 and 250 times that of the K.D.P. The crystallographic and dielectric data of the system Ba2.14Li0.71Nb5O15Ba2.14Li0.71Ta5O15 characterize three domains, which are respectively antiferroelectric, ferroelectric, and paraelectric. The Curie temperature and the optical yield decrease with increasing tantalum content. 相似文献
42.
Piotr Kujawa Annie Audibert‐Hayet Joseph Selb Franoise Candau 《Journal of Polymer Science.Polymer Physics》2004,42(9):1640-1655
Multisticker associative polyelectrolytes of acrylamide (≈86 mol %) and sodium 2‐acrylamido‐2‐methylpropanesulfonate (≈12 mol %), hydrophobically modified with N,N‐dihexylacrylamide groups (≈2 mol %), were prepared with a micellar radical polymerization technique. This process led to multiblock polymers in which the length of the hydrophobic blocks could be controlled through variations in the surfactant‐to‐hydrophobe molar ratio, that is, the number of hydrophobes per micelle (NH). The rheological behavior of aqueous solutions of polymers with the same molecular weight and the same composition but with two different hydrophobic block lengths (NH = 7 or 3 monomer units per block) was investigated as a function of the polymer concentration with steady‐flow, creep, and oscillatory experiments. The critical concentration at the onset of the viscosity enhancement decreased as the length of the hydrophobic segments in the polymers increased. Also, an increase in the NH value significantly enhanced the thickening ability of the polymers and affected the structure of the transient network. In the semidilute unentangled regime, the behavior of the polymer with long hydrophobic segments (NH = 7) was studied in detail. The results were well explained by the sticky Rouse theory of associative polymer dynamics. Finally, the viscosity decreased with an increase in the temperature, mainly because of a lowering of the sample relaxation time. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1640–1655, 2004 相似文献
43.
Two planar tetranuclear dysprosium(III) complexes, [Dy(4)(mu(3)-OH)(2)(hmmpH)(2)(hmmp)(2)(Cl)(4)].3MeCN.MeOH (1) and [Dy(4)(mu(3)-OH)(2)(hmmpH)(2)(hmmp)(2)(N(3))(4)].4MeOH (2) {hmmpH(2) = 2-[(2-hydroxyethylimino)methyl]-6-methoxyphenol}, which exhibit an anion-dependent magnetic slow relaxation behavior, have been synthesized by in situ condensation of o-vanillin and 2-aminoethanol. The higher energy barrier observed in 2 could be the result of a more favorable crystal field and/or orientations of single-ion easy axes of magnetization of the Dy(III) ions. 相似文献
44.
Summary In this paper we analize the reversibility of the diffusion property for the solution of certain infinite-dimensional systems of stochastic differential equations. Necessary and sufficient conditions ensuring this reversibility are given. The proofs use the techniques of the stochastic calculus of variations.This work was partly done when the first author was visiting the Centre de Recerca Matemàtica at Barcelona 相似文献
45.
Valeriu Mereacre Denis Prodius Ayuk M. Ako Narpinder Kaur Janusz Lipkowski Charles Simmons Naresh Dalal Ion Geru Christopher E. Anson Annie K. Powell Constantin Turta 《Polyhedron》2008
Reaction of manganese acetate and lanthanide nitrates in the presence of excess of PhCOOH affords highly asymmetric dodecanuclear mixed-metal [Mn10Ln2(OH)(O)8(PhCOOH)(PhCOO)19] (Ln = PrIII (1), NdIII (2)) clusters. The similar reaction, but with only 2 equiv. of PhCOOH resulted in the compounds with higher nuclearity [Mn11Eu4(O)8(OH)8(PhCOO)18(NO3)2(H2O)6]NO3 · 4CH3CN (3). Variable-temperature solid-state magnetic susceptibility of 1 and 2 in the temperature range 1.8–300 K were carried out, and for both complexes antiferromagnetic exchange interactions between the metal centers were observed, giving an estimated S = 17/2 ground state. AC magnetic susceptibility data have revealed out-of-phase signals, which suggest that these complexes exhibit a slow relaxation of magnetization as observed in single-molecule magnets. 相似文献
46.
Jing-Jing Zhu Chao-Feng Zhang Mian Zhang S.W. Annie Bligh Li Yang Zhi-Min Wang Zheng-Tao Wang 《Journal of chromatography. A》2010,1217(33):5384-5388
Six C-glucosyl anthrones were characterized as three pairs of epimers by on-line high performance liquid chromatography–circular dichroism (HPLC–CD) analysis and isolated from the roots of Rumex dentatus by column chromatography. Their structures were elucidated by mass spectrometry, nuclear magnetic spectroscopy and HPLC–CD analysis. They are 10R-C-β-d-glucosyl-10-hydroxyemodin-9-anthrone (rumejaposide E, 1) and 10S-C-β-d-glucosyl-10-hydroxyemodin-9-anthrone (rumejaposide F, 2), 10R-C-β-d-glucosylemodin-9-anthrone (rumejaposide G, 3) and 10S-C-β-d-glucosylemodin-9-anthrone (rumejaposide H, 4), 10S-C-β-d-glucosyl-10-hydroxychrysophanol-9-anthrone (cassialoin, 5) and 10R-C-β-d-glucosyl-10-hydroxychrysophanol-9-anthrone (rumejaposide I, 6). Rumejaposides F–I (2–4 and 6) were new C-glucosyl anthrones. Rumejaposide E (1) and cassialoin (5) were isolated for the first time in Rumex plants. On-line HPLC–UV–CD analysis was a useful tool for structure elucidating epimeric C-glycosides anthrones 3–6 because of the poor stability of the pure isomers (3 and 4) and the minute quantity of 5 and 6 in the mixture. 相似文献
47.
Alpha-glucosidase inhibitors from Millettia conraui 总被引:1,自引:0,他引:1
Tiabou Tchinda A Nahar Khan S Fuendjiep V Ngandeu F Ngono Ngane A Choudhary MI 《Chemical & pharmaceutical bulletin》2007,55(9):1402-1403
A new geranylated isoflavone, 7-O-geranyl-6-methoxypseudobaptigenin (1) was isolated from the stem barks of Millettia conraui, along with known compounds 5-methoxydurmillone (2), conrauinone A (3), beta-amyrine (4), sitosterol (5), 3-O-beta-D-glucopyranosyl sitosterol (6) and n-docosanol (7). Compounds 1 and 4 showed a significant alpha-glucosidase inhibitory activity. The structures of the compounds were determined by analysis of their spectroscopic data. 相似文献
48.
The monitoring of insulin is of great relevance for the management of diabetes, the detection of pancreatic islet-cell malfunction, the definition of hypoglycemia, and the diagnosis of insulinoma. A liposomal immunosensing system for the determination of insulin was developed in this study. The insulin sensor was constructed by the immobilization of anti-insulin antibodies on the inner wall of the microcapillary immunoseparator. Liposomes tagged with anti-insulin and encapsulating a fluorescent dye were used as the detectable label. In the presence of insulin, sandwich immunocomplexes were formed between the immobilized antibodies in the column, the sample of insulin, and the antibody-tagged sulforhodamine B-dye-loaded liposomes. Signals generated by lysing the bound liposomes with 30 mM n-octyl-β-d-glucopyranoside were measured by a fluorescence detector. The detected signal was directly proportional to the amount of insulin in the test sample. The liposomal immunosensing system successfully detected as low as 136 attomole. MeOH (30%) was used for the regeneration of antibody-binding sites in the microcapillary after each measurement, which allowed the immunoseparator to be used for at least 70 repeated assays. The antibody activity in this proposed microcapillary immunoseparator could be well maintained for at least 1 week. The calibration curve for insulin in Tris-buffered saline had a linear dynamic range of 10 pM-10 nM, and the total assay time was less than 30 min. The coefficient of variation for triplicate measurements was <5.00%, which indicated that well-reproducible results can be obtained by this newly developed method. 相似文献
49.
Feltham HL Klöwer F Cameron SA Larsen DS Lan Y Tropiano M Faulkner S Powell AK Brooker S 《Dalton transactions (Cambridge, England : 2003)》2011,40(43):11425-11432
A family of thirteen tetranuclear heterometallic zinc(II)-lanthanide(III) complexes of the hexa-imine macrocycle (L(Pr))(6-), with general formula Zn(II)(3)Ln(III)(L(Pr))(NO(3))(3)·xsolvents (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm or Yb), were prepared in a one-pot synthesis using a 3:1:3:3 reaction of zinc(II) acetate, the appropriate lanthanide(III) nitrate, the dialdehyde 1,4-diformyl-2,3-dihydroxybenzene (H(2)L(1)) and 1,3-diaminopropane. A hexanuclear homometallic zinc(II) macrocyclic complex [Zn(6)(L(Pr))(OAc)(5)(OH)(H(2)O)]·3H(2)O was obtained using a 2:0:1:1 ratio of the same reagents. A control experiment using a 1:0:1:1 ratio failed to generate the lanthanide-free [Zn(3)(L(Pr))] macrocyclic complex. The reaction of H(2)L(1) and zinc(II) acetate in a 1:1 ratio yielded the pentanuclear homometallic complex of the dialdehyde H(2)L(1), [Zn(5)(L(1))(5)(H(2)O)(6)]·3H(2)O. An X-ray crystal structure determination revealed [Zn(3)(II)Pr(III)(L(Pr))(NO(3))(2)(DMF)(3)](NO(3))·0.9DMF has the large ten-coordinate lanthanide(III) ion bound in the central O(6) site with two bidentate nitrate anions completing the O(10) coordination sphere. The three square pyramidal zinc(II) ions are in the outer N(2)O(2) sites with a fifth donor from DMF. Measurement of the magnetic properties of [Zn(II)(3)Dy(III)(L(Pr))(NO(3))(3)(MeOH)(3)]·4H(2)O with a weak external dc field showed that it has a frequency-dependent out-of-phase component of ac susceptibility, indicative of slow relaxation of the magnetization (SMM behaviour). Likewise, the Er and Yb analogues are field-induced SMMs; the latter is only the second example of a Yb-based SMM. The neodymium, ytterbium and erbium complexes are luminescent in the solid phase, but only the ytterbium and neodymium complexes show strong lanthanide-centred luminescence in DMF solution. 相似文献
50.
The Staudinger ligation provides a means to form an amide bond between a phosphinothioester and azide. This reaction holds promise for the ligation of peptides en route to the total chemical synthesis of proteins. (Diphenylphosphino)methanethiol is the most efficacious of known reagents for mediating the Staudinger ligation of peptides, providing high (> 90%) isolated yields for equimolar couplings in which a glycine residue is at the nascent junction. Surprisingly, the yields are lower (< 50%) for non-glycyl couplings due to an aza-Wittig reaction that diverts the reaction toward a phosphonamide byproduct. Here, the partitioning of the reaction toward Staudinger ligation (and away from the aza-Wittig reaction) is shown to increase with increasing electron density on phosphorus. This electron density can be tuned either by installing functional groups on the phenyl substituents of (diphenylphosphino)methanethiol or by changing the polarity of the solvent. Installing p-methoxy groups and using a solvent of low polarity (such as toluene or dioxane) provide especially high (> 80%) isolated yields for the ligation of two non-glycyl residues. These conditions retain the high chemoselectivity of the reaction and do not lead to a substantial change in reaction rate. The traceless Staudinger ligation is now poised to enable the iterative ligation of peptides with little regard for their sequence, as well as the synthesis of amide bonds for other purposes. 相似文献