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51.
The crystal and molecular structure of 1,2,3-trithia-[3]-ferrocenophane has been determined from three-dimensional X-ray data collected by counter techniques. The molecule consists of two nearly parallel, eclipsed cyclopentadienyl rings linked by an S3 bridge. The material crystallizes in the monoclinic space groupP21/c with unit cell parametersa = 9·628(3),b = 9·347(4),c= 11·408(4) Å, = 96·70(3) °. The structure was solved by standard techniques and the least-squares refinement converged to a conventionalR factor of 9·6 %.We wish to thank A. Davison for the gift of the crystals and the U.S. Atomic Energy Commission for financial support. 相似文献
52.
The X-ray crystal structure of glechomafuran (1,10,4,5-diepoxy-7,8-furanogermacrane), a natural product obtained from seeds ofSmyrnium olusatrum L., has been determined in order to establish the correct relative configuration of the molecule. Crystals are monoclinic, space groupP21 witha=6.785(4),b=12.325(9),c=16.390(6) Å,=97.89(4)°, and four molecules in the unit cell. The two epoxides are found to be ,-attached, and the associated methyl groups are positionedsyn to each other. The furan ring is essentially flat, and shows no evidence of any double bond delocalization. 相似文献
53.
Toribio L del Nozal MJ Bernal YL Alonso C Jiménez JJ 《Journal of separation science》2008,31(8):1307-1313
The semipreparative chiral separation of lansoprazole and two related compounds (pantoprazole and rabeprazole) using supercritical fluid chromatography (SFC) is presented in this work. Different loads were evaluated in order to obtain high enantiomeric purities and production rates. The volumes injected were 1, 2 and 4 mL. The concentrations of the racemic mixtures were 3 and 6 g/L for lansoprazole and 1.5 g/L for pantoprazole and rabeprazole. In all the cases, the recoveries, for a purity higher than 99.9%, were better for the second eluted enantiomer than for the first one. This fact conditioned the production rate of the first eluted enantiomer that, considering a fixed purity, was always lower than that obtained for the other one. In the case of lansoprazole it was possible to obtain 0.025 and 0.090 mg/min of the first and second eluted enantiomer, respectively, with an enantiomeric purity of 99.9%. For rabeprazole enantiomers 0.037 and 0.062 mg/min, and in the case of pantoprazole the results were better (0.062 and 0.122 mg/min) due to the higher resolution. 相似文献
54.
Nozal MA Bernal JL Martín MA Bernal J Alvaro A Martín R Higes M 《Journal of chromatography. A》2008,1190(1-2):224-231
In this work a new liquid chromatography with diode array detection and electrospray ionization mass spectrometry (LC-DAD-ESI-MS) method has been developed for the determination of fumagillin residues in honey. This procedure involves a solid-phase extraction on polymeric cartridges for the isolation of fumagillin from diluted honey. Chromatographic separation of fumagillin was performed in isocratic mode, on a C(18) column (150 mm x 4.60mm i.d., 5 microm), the mobile phase consisted of a mixture of ammonium formate 20mM in water and acetonitrile (61/39, v/v), at 35 degrees C and the flow rate was set at 1.0 mL/min. Average analyte recoveries, influenced by the botanical origin were from 88 to 96% in replica sets of fortified honey samples. The detection limits of the LC-DAD-ESI-MS method were between 24 and 1 microg/kg for clear honeys (rosemary) and between 45 and 4 microg/kg for dark honeys (heather). The developed method has been applied to the analysis of fumagillin residues in honey samples collected from veterinary treated beehives, infected by Nosema ceranae and fed with the technical product at different doses. 相似文献
55.
In the crystalline state, the OH- anion is shown to be capable of acting as a base or as an acid with respect to waters of crystallization to which it is linked by hydrogen bonds. We examined the OH- anion in three crystalline samples and studied its behavior using quantum mechanics. Four quantum mechanical approximations were employed (HF, B3LYP, SVWN, and MP2) to obtain the relative stability of isomers of the H3O2- molecule in the three crystals considered. In one crystal state (LICQIX), the H3O2- anion corresponds to a geometry in which OH- acts as an acid, but not so as a free molecule. The free anion H3O2- has two qualitatively different structures. In one structure, the hydrogen bond is long, while in the other structure, the hydrogen bond is shorter and the hydrogen atom lies at an equal distance between donor and acceptor oxygen atoms. 相似文献
56.
Roots of Iostephane heterophylla (Cav.) Benth ex Hemsl are used mainly in Mexican traditional medicine to heal skin problems. The development of a column high-performance liquid chromatography (LC)-UV detector method for the determination of xanthorrhizol, the major and active component of the roots of I. heterophylla, is described in this paper. The content of this compound was quantitatively determined employing a Symmetry C18 5 microm particle size column with the isocratic mobile phase acetonitrile-water (85 + 15). The flow rate was 1.0 mL/min, and UV detection was at 230 nm. The limits of detection and quantitation were 0.2 and 0.5 microg/mL, respectively. Quantities of xanthorrhizol measured by this method ranged between 1.8 to 10.94 mg/g of root of the plant in 11 different samples of I. heterophylla. Xanthorrhizol was not detected in a sample of I. madrensis, so xanthorrhizol could be used as a marker compound of I. heterophylla. The LC method described here was shown to be reliable, reproducible, and accurate. 相似文献
57.
Mukhopadhyay U Grunert CM Kusz J Reiman S Gütlich P Bernal I 《Chemical communications (Cambridge, England)》2007,(14):1444-1446
The compound [Cu(N,N'app)Cl](2)[Fe(CN)(6)].xH(2)O, with N,N'app being bis(N,N'-3-aminopropylpiperazine), was prepared and its structure determined by single crystal X-ray analysis, confirming a ratio of two copper complexes to one iron complex; (57)Fe M?ssbauer spectra showed three quadrupole doublets typical of iron(iii) low spin species which call for the presence of a superstructure. 相似文献
58.
Toribio L del Nozal MJ Bernal JL Alonso C Jiménez JJ 《Journal of chromatography. A》2007,1144(2):255-261
The chiral resolution of four antifungal compounds, three imidazoles (miconazole, econazole and sulconazole) and one triazole (itraconazole) using supercritical fluid chromatography on the amylose-based chiral stationary phase Chiralpak AD, is presented in this work. The influence of pressure, type and percentage of organic modifier and temperature on retention times and resolution was studied. The enantiomeric separation of the three imidazoles was achieved with resolutions higher than two and analysis times lower than 10 min, obtaining the best results using methanol as modifier. However, the analysis time of the triazole was higher than 80 min due to the existence of a high number of functional groups that were able to interact with the chiral stationary phase. In this case, the resolution of the four stereoisomers was achieved only partially with mixtures of ethanol and 2-propanol as modifier. The isoenantioselective temperatures were obtained from the study of the influence of the temperature, they were above the range of temperatures assayed, except for sulconazole using 2-propanol. 相似文献
59.
Conservative methods for the Toda lattice equations 总被引:1,自引:0,他引:1
We are concerned with the numerical integration of the Todalattice equations by using different conservative methods. Numericalexperiments suggest that the global error for isospectral schemesdecreases exponentially with time but it is almost constantfor either symplectic or more general integrators. We providea theoretical explanation for these experimental findings. 相似文献
60.
M. I. Bernal‐Uruchurtu M. T. C. Martins‐Costa C. Millot M. F. Ruiz‐Lpez 《Journal of computational chemistry》2000,21(7):572-581
Hydrogen bonding is not well described by available semiempirical theories. This is an important restriction because hydrogen bonds represent a key feature in many chemical and biochemical processes, besides being responsible for the singular properties of water. In this study, we describe a possible solution to this problem. The basic idea is to replace the nonphysical gaussian correction functions (GCF) appearing in the core–core repulsion terms of most MNDO‐based semiempirical methods by a simple function exhibiting the correct physical behavior in the whole range of intermolecular separation distances. The parameterized interaction function (PIF) is the sum of atom‐pair contributions, each one having five adjustable parameters. In this work, the approach is used to study water–water interactions. The parameters are optimized to reproduce a reference ab initio intermolecular energy surface for the water–water dimer obtained at the MP2/aug‐cc‐pVQZ level. OO, OH, and HH parameters are reported for the PM3 method. The results of PM3‐PIF calculations remarkably improve qualitatively and quantitatively those obtained at the standard PM3 level, both for water–dimer properties and for water clusters up to the hexamer. For example, the root‐mean‐square deviation of the PM3‐PIF interaction energies, with respect to ab initio values obtained using 700 points of the water dimer surface, is only 0.47 kcal/mol. This value is much smaller than that obtained using the standard PM3 method (4.2 kcal/mol). The PM3‐PIF water dimer energy minimum (−5.0 kcal/mol) is also much closer to ab initio data (−5.0±0.01 kcal/mol) than PM3 (−3.50 kcal/mol). The method is therefore promising for the development of new semiempirical approaches as well as for application of combined quantum mechanics and molecular mechanics techniques to investigate chemical processes in water. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 572–581, 2000 相似文献