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91.
Fujiki S Iwao Y Kobayashi M Miyagishima A Itai S 《Chemical & pharmaceutical bulletin》2011,59(5):553-558
It has been reported that tablets of clarithromycin (CAM), a 14-membered macrolide antibiotic, are especially stable under low pH conditions such as in gastric fluid, and showed excellent antibacterial efficiency even though CAM molecules themselves are rapidly decomposed. Therefore, we aimed to clarify the stabilization mechanism of CAM tablets under low pH conditions. From the results of stability and dissolution tests, the optimal decomposition rate constant (K(dec)) and dissolution rate constant (K(dis)) at various pH values were calculated by curve-fitting to consecutive reactions. Consequently, log(K(dec)) increased as pH decreased. On the other hand, log(K(dis)) increased as pH decreased from 3.0 to 1.5, but decreased as pH decreased from 1.5 to 1.0. In addition, the disintegration time of commercially available tablets at pH 1.0 and 1.2 was found to be delayed, resulting in a decrease of K(dis). Furthermore, from powder X-ray diffraction, HPLC and elemental analysis, the delay in disintegration time might be attributable to the formation of a transparent gel, formed by the reaction between CAM molecule and hydrochloric acid under low pH conditions, on the surface of CAM tablet. On the basis of these results, this report can be considered the first case where a transparent gel prevents gastric fluid from penetrating the tablet, resulting in reduced decomposition of CAM following oral administrating. 相似文献
92.
Tsupreva VN Titov AA Filippov OA Bilyachenko AN Smol'yakov AF Dolgushin FM Agapkin DV Godovikov IA Epstein LM Shubina ES 《Inorganic chemistry》2011,50(8):3325-3331
Interaction of the copper, {[3,5-(CF(3))(2)Pz]Cu}(3), and silver, {[3,5-(CF(3))(2)Pz]Ag}(3), macrocycles [3,5-(CF(3))(2)Pz = 3,5-bis(trifluoromethyl)pyrazolate] with cyclooctatetraeneiron tricarbonyl, (cot)Fe(CO)(3), was investigated by IR and NMR spectroscopy for the first time. The formation of 1:1 complexes was observed at low temperatures in hexane. The composition of the complexes (1:1) and their thermodynamic characteristics in hexane and dichloromethane were determined. The π-electron system of (cot)Fe(CO)(3) was proven to be the sole site of coordination in solution and in the solid state. However, according to the single-crystal X-ray data, the complex has a different (2:1) composition featuring the sandwich structure. The complexes of ferrocene with copper and silver macrocycles have a columnar structure (X-ray data). 相似文献
93.
Acid-base interaction between transition-metal hydrides: dihydrogen bonding and dihydrogen evolution
94.
Shubina E. S. Krylov A. N. Muratov D. V. Fil'chikov A. A. Epstein L. M. 《Russian Chemical Bulletin》1993,42(11):1919-1920
The interaction of Cp*M(CO)2 (M=Ir or Rh) with CF3COOH in low polar media results in partial protonation of these compounds giving molecular (M...HO) and ionic (MH+...O–) hydrogen-bonded complexes. According to IR spectral data, a decrease in temperature results in a shift of the equilibrium toward the ionic forms. These compounds react with phenol to give molecular complexes only.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2002–2003, November, 1993. 相似文献
95.
96.
Aligning simulation models: A case study and results 总被引:1,自引:0,他引:1
Robert Axtell Robert Axelrod Joshua M. Epstein Michael D. Cohen 《Computational & Mathematical Organization Theory》1996,1(2):123-141
This paper develops the concepts and methods of a process we will call “alignment of computational models” or “docking” for short. Alignment is needed to determine whether two models can produce the same results, which in turn is the basis for critical experiments and for tests of whether one model can subsume another. We illustrate our concepts and methods using as a target a model of cultural transmission built by Axelrod. For comparison we use the Sugarscape model developed by Epstein and Axtell. The two models differ in many ways and, to date, have been employed with quite different aims. The Axelrod model has been used principally for intensive experimentation with parameter variation, and includes only one mechanism. In contrast, the Sugarscape model has been used primarily to generate rich “artificial histories”, scenarios that display stylized facts of interest, such as cultural differentiation driven by many different mechansims including resource availability, migration, trade, and combat. The Sugarscape model was modified so as to reproduce the results of the Axelrod cultural model. Among the questions we address are: what does it mean for two models to be equivalent, how can different standards of equivalence be statistically evaluated, and how do subtle differences in model design affect the results? After attaining a “docking” of the two models, the richer set of mechanisms of the Sugarscape model is used to provide two experiments in sensitivity analysis for the cultural rule of Axelrod's model. Our generally positive experience in this enterprise has suggested that it could be beneficial if alignment and equivalence testing were more widely practiced among computational modelers. 相似文献
97.
We show that the statistics of loop erased random walks above the upper critical dimension, 4, are different between the torus and the full space. The typical length of the path connecting a pair of sites at distance L, which scales as L2 in the full space, changes under the periodic boundary conditions to Ld/2. The results are precise for dimensions ≥5; for the dimension d=4 we prove an upper bound, conjecturally sharp up to subpolyonmial factors. 相似文献
98.
Consider the standard continuous percolation in ℝ4, and choose the parameters so that the induced percolation on a fixed two dimensional linear subspace is critical. Although
two dimensional critical percolation dies, we show that there are exceptional two dimensional linear subspaces, in which percolation
occurs.
Received: 1 April 1997 / Revised version: 20 January 1998 相似文献
99.
The reaction between chlorite ion and thiourea has been studied both in a closed (batch) system and in a flow reactor (CSTR). The principal stoichiometry is given by In batch, the reaction displays an induction period, whose length is proportional to [CS(NH2)2]/[ClO] [H+], followed by the rapid buildup and disappearance of a ClO2 intermediate. At [ClO]/[CS(NH2)2] ratios between 2.5 and 3.5, a second peak in the ClO2 absorbance is observed. In the CSTR, this iodine-free system displays simple and complex periodic oscillation, bistability, aperiodic oscillation, and birhythmicity. 相似文献
100.