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41.
Attila R. Imre W. Alexander Van Hook Bong Ho Chang Young Chan Bae 《Monatshefte für Chemie / Chemical Monthly》2003,134(12):1529-1539
Summary. Upper critical solution temperatures (UCSTs) for liquid–liquid demixing in a set of mixtures of linear alkanes (pentane (N
1=5) to pentacontane (N
1=50)) with an oligostyrene (1241amu, N
2=12) are reported. We find strong correlation between the Hildebrand solubility parameters of the alkanes and the UCST. Correlations are developed which enable predictions concerning the miscibility of mixtures of compounds with longer chains. 相似文献
42.
Grasso D Grasso G Guantieri V Impellizzeri G La Rosa C Milardi D Micera G Osz K Pappalardo G Rizzarelli E Sanna D Sóvágó I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(2):537-547
An abnormal interaction between copper and the prion protein is believed to play a pivotal role in the pathogenesis of prion diseases. Copper binding has been mainly attributed to the N-terminal domain of the prion protein, but this hypothesis has recently been challenged in some papers which suggest that the C-terminal domain might also compete for metal anchoring. In particular, the segment corresponding to the helix II region of the prion protein, namely PrP180-193, has been shown both to bind copper and to exhibit a copper-enhanced cytotoxicity, as well as to interact with artificial membranes. The present work is aimed at extending these results by choosing the most representative model of this domain and by determining its copper affinity. With this aim, the different role played by the electrostatic properties of the C- and N-termini of PrP180-193 (VNITIKQHTVTTTT) in determining its conformational behaviour, copper coordination and ability to perturb model membranes was investigated. Owing to the low solubility of PrP180-193, its copper affinity was evaluated by using the shorter PrPAc184-188NH2 (IKQHT) analogue as a model. ESI-MS, ESR, UV/Vis, and CD measurements were carried out on the copper(II)/PrPAc184-188NH2 and copper(II)/PrP180-193NH2 systems, and showed that PrPAc184-188NH2 is a reliable model for the metal interaction with the helix II domain. The affinity of copper(II) for the helix II fragment is higher than that for the octarepeat and PrP106-126 peptides. Finally, the different ability of PrP180-193 analogues to perturb the DPPC model membrane was assessed by DSC measurements. The possible biological consequences of these findings are also discussed briefly. 相似文献
43.
M. Liang H. Ohm B. De Sutter K. Sistemich B. Fazekas G. Molnär 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(2):223-224
The half-lives of low-lying levels of the neutron-rich isotopes102Mo and104Mo have been measured at the fission product separator Josef with the ß-- triple coincidence technique. Values of t1/2= 126(4)ps and 0.72(4)ns have been obtained for the 21
+ levels at 296 keV and 192 keV in102Mo and104Mo, respectively. Deformation parameters of ßq=0.28(1) and 0.31(1), respectively, are deduced, which are smaller than those of the isotones of Sr and Zr. The interacting boson model accounts well for the trend of 2+ energies in the Mo isotopes but slightly overpredicts the B(E2) values at saturation. A smooth dependence of 21
+ vs. E 21
+ is found for the A 100 region in agreement with the hydrodynamical model.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday 相似文献
44.
The effect of diffusion on radiation-initiated graft polymerization has been studied with emphasis on the single- and two-penetrant cases. When the physical properties of the penetrants are similar, the two-penetrant problem can be reduced to the single-penetrant problem by redefining the characteristic parameters of the system. The diffusion-free graft polymerization rate is assumed to be proportional to the v power of the monomer concentration C, in which the proportionality constant a = kpR/k, where kp and kt are the propagation and termination rate constants, respectively, and Ri is the initiation rate. The values of v, w, and z depend on the particular reaction system. The results of our earlier work were generalized by allowing a non-Fickian diffusion rate, obtained from an extension of the Fujita free-volume theory, which predicts an essentially exponential dependence on the monomer concentration of the diffusion coefficient, D = D0 [exp(δC/M)], where M is the saturation concentration. It was shown that a reaction system is characterized by the three dimensionless parameters v, δ, and A = (L/2)[aM(v?1)/D0]1/2, where L is the polymer film thickness. Graft polymerization tends to become diffusion controlled as A increases. Larger values of δ and v cause a reaction system to behave closer to the diffusion-free regime. The transition from diffusion-free to diffusion-controlled reaction involves changes in the dependence of the reaction rate on film thickness, initiation rate, and monomer concentration. Although the diffusion-free rate is w order in initiation rate, v order in monomer, and independent of film thickness, the diffusion-controlled rate is w/2 order in initiator rate and inverse first-order in film thickness. The dependence of the diffusion-controlled rate on monomer is dependent in a complex manner on the diffusional characteristics of the reaction system. 相似文献
45.
In aqueous solutions (with or without salts) containing carboxylic acids, water can be bound with anhydrous sodium sulphate at a molar ratio of [Na2SO4]/[H2O] ? 0.9. This is used prior to gas chromatography of aliphatic and aromatic di- and poly-carboxylic acids (oxalic to mellitic acid) in aqueous matrices (solutions, suspensions). Such acids are extracted quantitatively into diethyl ether within 8–10 min, which is much faster than conventional methods. Esterification is done with diazomethane. 相似文献
46.
Expedient and Diastereodivergent Assembly of Terpenoid Decalin Subunits having Quaternary Stereocenters through Organocatalytic Robinson Annulation of Nazarov Reagent
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Barbara Berkes Kristóf Ozsváth Laura Molnár Tamás Gáti Tamás Holczbauer György Kardos Tibor Soós 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(50):18101-18106
We report an expedient approach to highly functionalized cis‐ and trans‐decalines that could function as key structural subunits toward the synthesis of various classes of terpenoids. Key to the strategy is an organocatalyzed Robinson annulation reaction of the Nazarov reagent that affords chiral enone building blocks with high enantioselectivities. The quaternary carbon stereogenic center can direct the subsequent reactions and allow the rapid and diastereoconvergent assembly of complex decalines with contiguous stereocenters. 相似文献
47.
Truong Son Pham Katalin Gönczi György Kardos Krisztina Süle László Hegedűs Mihály Kállay Miklós Kubinyi Pál Szabó Imre Petneházy László Tőke Zsuzsa Jászay 《Tetrahedron: Asymmetry》2013,24(24):1605-1614
Several cinchona based squaramide catalysts were applied to the asymmetric Michael addition of α-nitroethylphosphonates to acrylic acid aryl esters, resulting in high yields and enantioselectivities. The absolute configuration of one of the quaternary α-nitrophosphonate adducts was deduced from its experimental and calculated CD spectra. The adducts were reduced to their cyclic aminophosphonates by catalytic hydrogenation. 相似文献
48.
In several real networks large heterogeneity of links is present either in intensity or in the nature of relationships. Therefore, recent studies in network science indicate that more detailed topological information are available if weighted or multi-layer aspect is applied. In the age of globalization air transportation is a representative example of huge complex infrastructure systems, which has been analyzed from different points of view. In this paper a novel approach is applied to study the airport network as a weighted multiplex taking into account the fact that the rules and fashion of domestic and international flights differ. Restricting study to only topological features and their correlations in the system (disregarding traffic) one can see reasons why simple network approximation is not adequate. 相似文献
49.
50.
László Töke Gyorgy Clementis Imre Petneházy Zsuzsa M. Jászay Peter Tömpe 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract During the formation of oxaphospholenes the phosphorus in the reagent gets oxidized and the double bond in the enones gets reduced. 相似文献