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151.
Young Jin Ham Hana Yu Nam Doo Kim Jung-Mi Hah Khalid B. Selim Hwan Geun Choi Taebo Sim 《Tetrahedron》2012,68(7):1918-1925
A Rh-catalyzed diastereoselective reductive cyclization, mediated by hydrogen, of optically active 1,6-enynes using chiral BINAP was successfully applied to the total synthesis of four stereoisomers of the proposed structure of lucentamycin A. In order to synthesize two of these four stereoisomers, we successfully constructed chiral proline derivatives bearing cis-carbon substituents at C2 and C3 positions based on Krische’s methodology, which has very rarely been reported. Anti-proliferative activities on HCT-116 cell line and NMR data of these four stereoisomers were compared with those of naturally occurring lucentamycine A. The results show that the proposed structure of lucentamycin A needs revision. 相似文献
152.
Two new noncentrosymmetric (NCS) polar oxides, BaMgTe(2)O(7) and BaZnTe(2)O(7), have been synthesized and characterized, with their crystal structures determined by single crystal X-ray diffraction. The iso-structural materials exhibit structures consisting of layers of corner-shared MgO(5) or ZnO(5), Te(6+)O(6), and Te(4+)O(4) polyhedra that are separated by Ba(2+) cations. The Te(4+) cation is found in a highly asymmetric and polar coordination environment attributable to its stereoactive lone-pair. The alignment of the individual TeO(4) polar polyhedra results in macroscopic polarity for BaMgTe(2)O(7) and BaZnTe(2)O(7). Powder second-harmonic generation (SHG) measurements revealed a moderate SHG efficiency of approximately 5 × KDP (or 200 × α-SiO(2)) for both materials. Piezoelectric charge constants of 70 and 57 pm/V, and pyroelectric coefficients of -18 and -10 μC·m(-2)·K(-1) were obtained for BaMgTe(2)O(7) and BaZnTe(2)O(7), respectively. Although the materials are polar, frequency dependent polarization measurements indicated that the materials are not ferroelectric, that is, the observed macroscopic polarization cannot be reversed. Infrared, UV-vis diffuse spectroscopy, and thermal properties were also measured. Crystal data: BaMgTe(2)O(7), orthorhombic, space group Ama2 (No. 40), a = 5.558(2) ?, b = 15.215(6) ?, c = 7.307(3) ?, V = 617.9(4) ?(3), and Z = 4; BaZnTe(2)O(7), orthorhombic, space group Ama2 (No. 40), a = 5.5498(4) ?, b = 15.3161(11) ?, c = 7.3098(5) ?, V = 621.34(8) ?(3), and Z = 4. 相似文献
153.
The extrapolation of small-cluster exact-diagonalisation calculations and the Monte-Carlo method is used to study the spin-one-half Falicov–Kimball model extended by the spin-dependent Coulomb interaction (J) between the localized f and itinerant d electrons as well as the on-site Coulomb interaction (U ff ) between the localized f electrons. It is shown that in the symmetric case the ground-state phase diagram of the model has an extremely simple structure that consists of only two phases, and namely, the charge-density-wave (CDW) phase and the spin-density-wave (SDW) phase. The nonzero temperature studies showed that these phases persist also at finite temperatures. The critical temperature T c for a transition from the low-temperature ordered phases to the high-temperature disordered phase is calculated numerically for various values of J and U ff . 相似文献
154.
Hana Baili 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2013,19(6):601-616
We wish to compute in discrete real time the best estimate for the composition of the total active power recorded at a customer's house, without any intrusion. A new solution for online characterization of the electric load is proposed. The solution is based on issues from the applied stochastic analysis of Markov processes. We specifically suggest that optimal filtering of a hybrid stochastic differential system covers entirely the detection and separation subproblems underlying the main problem. 相似文献
155.
Hana Dejmkova Candan Dag Jiri Barek Jiri Zima 《Central European Journal of Chemistry》2012,10(4):1310-1317
New methods for the determination of metoclopramide, antiemetic and gastroprokinetic pharmaceutical, were developed, using
differential pulse voltammetry (DPV) and flow injection analysis (FIA) with amperometric detection on a boron-doped diamond
film electrode. Electrode pretreatment necessary to ensure the stable results was investigated and it was found, that while
DPV requires frequent electrode cleaning, FIA with a sufficiently high flow rate can maintain a stable signal with no signs
of electrode passivation. The calculated quantification limits of the DPV and FIA with amperometric detection were 0.13 μmol
L−1 and 0.015 mmol L−1, respectively. The applicability of the new methods was verified by the determination of metoclopramide in a pharmaceutical
preparation. FIA with amperometic detection proved to be sensitive, accurate and, due to the resistance of the electrode to
the passivation, also simple to handle.
相似文献
156.
Milan Meloun Zuzana Ferenčíková Hana Málková Tomáš Pekárek 《Central European Journal of Chemistry》2012,10(2):338-353
Risedronate inhibits bone resorption in diseases like osteoporosis, Paget’s disease, tumor bone diseases or the malfunction
of phosphocalcium metabolism. The acid-base properties of risedronate in an aqueous solution have been studied in a pH range
from 2 to 12 and can be described in terms of four dissociation steps: pK
a,2, pK
a,4, pK
a,5 (related to the dissociation of POH groups) and pK
a,3 related to the dissociation of protonated amino group NH3
+. The mixed dissociation constants were determined at different ionic strengths I = 0.02 to 0.20 mol dm−3 KCl and of 25°C and 37°C using pH-spectrophotometric and pH-potentiometric titration methods. Determination of group parameters L
0, H
T might lead to false estimates of common parameters
p
K
a;therefore, the computational strategy employed is important. A comparison between the two programs ESAB and HYPERQUAD demonstrated
that the ESAB program provides a better fit of potentiometric titration curve. The thermodynamic dissociation constants pK
aT were estimated by a nonlinear regression of (pK
a, I) data and a Debye-Hückel equation at 25°C and 37°C, pK
a,2T = 2.37(1) and 2.44(1), pK
a,3T = 6.29(3) and 6.26(1), pK
a,4T = 7.48(1) and 7.46(2) and pK
a,5T = 9.31(7) and 8.70(3) at 25°C and 37°C using pH-spectroscopic data and pK
a,2T = 2.48(3) and 2.43(1), pK
a,3T= 6.12(2) and 6.10(2), pK
a,4T = 7.25(2) and 7.23(1) and pK
a,5T = 12.04(5) and 11.81(2) at 25°C and 37°C. The ascertained estimates of three dissociation constants pK
a,3, pK
a,4, pK
a,5 are in agreement with the predicted values obtained using PALLAS
相似文献
157.
Edmund K. Burke Jakub Mareček Andrew J. Parkes Hana Rudová 《Annals of Operations Research》2012,194(1):71-87
A branch-and-cut procedure for the Udine Course Timetabling problem is described. Simple compact integer linear programming
formulations of the problem employ only binary variables. In contrast, we give a formulation with fewer variables by using
a mix of binary and general integer variables. This formulation has an exponential number of constraints, which are added
only upon violation. The number of constraints is exponential. However, this is only with respect to the upper bound on the
general integer variables, which is the number of periods per day in the Udine Course Timetabling problem. 相似文献
158.
159.
1H and 13C NMR spectroscopies were applied to investigate phase separation in solutions of poly(N-isopropylmethacrylamide) (PIPMAm) in D2O/ethanol (EtOH) mixtures induced by solvent composition (cononsolvency) and temperature. Effects of EtOH content in D2O/EtOH mixtures and temperature on the appearance and extent of the phase separation were characterized. Differences in mesoglobules formed during the phase separation induced by cononsolvency and temperature were found. For temperature-induced phase separation, 13C spin-spin relaxation times showed that besides the free EtOH expelled from the PIPMAm mesoglobules, there are also EtOH molecules bound in these mesoglobules. On the other hand, virtually no bound EtOH molecules were detected for mesoglobules formed as a consequence of the cononsolvency. For PIPMAm random copolymers containing negatively charged methacrylate units the phase separation induced by solvent composition was not observed. 相似文献
160.
Flow‐through detector with renewable working material based on glassy carbon or copper microparticles was used for flow injection determination of tyrosine by direct oxidation and phenylalanine via the complexation reaction with copper ions, respectively. Copper‐based detector allows the determination of electrochemically inactive amino acid, but the detection conditions are limited and fabrication and handling of the detector are more demanding. Low working potential, applied for the detection on copper microparticles, makes the determination very selective. Moreover, low baseline noise compensates lower sensitivity of copper‐based detector, enabling to reach quantification limit 4.7×10?6 mol L?1, in comparison with quantification limit 1.6×10?6 mol L?1 obtained for tyrosine on carbon‐based detector. 相似文献