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91.
Fernando C. Macedo Jr. 《Tetrahedron letters》2004,45(1):53-55
A novel metabolite from Aspergillus terreus, named terreinol, was isolated and its biosynthetic origin was determined by NMR based on the incorporation of [1-13C]-d-glucose. The labeling pattern indicated a predominant polyketide biosynthetic origin for this metabolite. 相似文献
92.
Bond AD Derossi S Jensen F Larsen FB McKenzie CJ Nelson J 《Inorganic chemistry》2005,44(17):5987-5989
Treatment of cryptand L(1) with Cu(II) generates a H3O2(-)-bridged dicopper(II) cryptate, 2, where the guest anion has responded to steric constraint by a significant shortening of the O-O distance to 2.325(9) A; computational optimization at the B3LYP/6-31(d) level suggests that the bridging O-H...O H-bond is bent (approximately 157 degrees) but that the barrier to interchange of the bridging H atom is low (<4 kJ mol(-1)). This cryptate, rather than the [Cu2L(1)muCN]3+ species recently claimed to derive from cleavage of the C-C bond of the solvent, is the product of acetonitrile recrystallization of the initially formed reaction product, 1. 相似文献
93.
Improved preparative electrochromatography column design 总被引:2,自引:0,他引:2
Improved chromatography column fittings were developed for the efficient and reliable application of an electric field to a preparative chromatography column (a process termed electrochromatography). The improved fittings contained electrodes in close proximity to the column packing media and allowed uniform electric fields to be applied. Membranes in the fittings prevented mixing of the electrode and the column eluent buffers. The membranes prevented gases and electrolytic products generated in the electrode chamber from entering the column eluent buffer. An electrode buffer solution was pumped through the electrode chamber to a large external container. The circulation of buffer through the electrode chamber removed the gases and electrolytic products and ensured a uniform electric field by helping to maintain a constant buffer composition. The membranes prevented macromolecules being separated on the column from coming in contact with the electrodes. 相似文献
94.
The chlorine of 8-chloroquinoline undergoes a metathetical reaction with methylamine or ethylamine in aqueous solution under pressure in the presence of cuprous chloride, to give 8-methylaminoquinoline and 8-ethylaminoquinoline. The preparation of 8-aminoquinoline from 8-chloroauinoline is confirmed. 相似文献
95.
Small-angle neutron scattering from micelles of alkylpolyoxyethylene sulfate: Effect of chain length
Small-angle neutron scattering (SANS) data have been obtained for (i) a series of solutions of C
m
H2m+1(OCH2–CH2)2SO4Na, for m=18, 16, and 14; (ii) an approximately 0.07M solution of C14H29(OCH2–CH2)2SO4Na to which different amounts of NaCl were added; and (iii) a series of solutions of variable concentration of C12H25(OCH2–CH2)SO4Na. The increase of the number of carbon atoms of the hydrocarbon chain produces a noticeable increase of the aggregation number of the micelles, while the salt tolerance decreases with increasing m. All the data can be described in terms of a monodispersed, charged, hard-spheres model interacting via a screened Coulombic potential, except the run at highest salt concentration, for which an ellipsoid model gives better results. 相似文献
96.
V L Bond C M Bowman L C Davison P F Roush R D McGrew D G Williams 《Journal of chemical information and computer sciences》1979,19(4):231-234
An improved interactive system for searching substructure and biological activity data has been developed. Features of the system include a two-level substructure search (fragment screen and atom by atom) and an expanded biological activity data base. The system operates on a file of about 150 000 compounds. 相似文献
97.
D. W. Johnson Jr. P. K. Gallagher M. F. Yan H. Schreiber 《Journal of solid state chemistry》1979,30(3)
Measurement of the divalent iron content in acid dissolved MnZn ferrites, fired in controlled atmospheres at various temperatures and quenched, allows calculation of cation vacancy contents. Addition of Ti4+ to these ferrites resulted in the introduction of vacancies at the rate of about 0 to 0.3 per Ti4+ depending on heat treatment conditions. Data are presented whereby the vacancy content with Ti4+ can be calculated based on the oxygen content of the undoped ferrite as available in the literature. Ti4+ stabilizes the hexagonal hematite-like structure and the phase boundary is presented as a function of Ti4+ and temperature. The vacancy contents at the phase boundary in Ti4+-doped ferrite as a function of temperature are in agreement with those calculated from the literature for undoped MnZn ferrites. Finally, the total oxygen content of coexisting spinel and hexagonal phases is presented. 相似文献
98.
Rudzevich Y Vysotsky MO Bohmer V Brody MS Rebek Jr J Broda F Thondorf I 《Organic & biomolecular chemistry》2004,2(21):3080-3084
The dimerization of tetratolyl- and tetratosyl-urea derivatives 1 and 2, derived from a tetrapentoxy calix[4]arene in the cone conformation and of the corresponding tetra-urea derivatives 3 and 4, in which the cone conformation is rigidified by the two crown-3 tethers, have been studied. All six possible equimolar mixtures were examined by 1H NMR using CDCl3 and CD2Cl2 as solvents. While no heterodimers are found for the combinations 1/3 and 2/4 in either solvent, all remaining combinations lead to the (exclusive) formation of heterodimers in CD2Cl2. In CDCl3 heterodimers are only observed for the combinations of 3 with 2 or 4. These results are discussed in terms of entropic and enthalpic contributions and compared with MD-simulations in a box of chloroform solvent molecules. 相似文献
99.
Karl A. Gschneidner Jr. O. D. McMasters 《Monatshefte für Chemie / Chemical Monthly》1971,102(5):1499-1515
Zusammenfassung Das systematische Verhalten (sowie dessen Fehlen) der Seltenerdmetall-Blei-Legierungen wird untersucht. Es wurden 12 verschiedene Verbindungsstöchiometrien beobachtet. Fast alle dreiwertigen Lanthanidenelemente bilden die PhasenR
5Pb3,R
5Pb4 undRPb3. Von den anderen möglichen Stöchiometrien kommen, mit Ausnahme vonRPb2, nur von einigen Lanthaniden Verbindungen vor. Die bekannten kristallographischen Daten werden durchbesprochen und die Existenz und Nichtexistenz einiger Phasen auf Grund kristallchemischer Theorien diskutiert. Das Schmelzverhalten derR-reichen Eutektika und der PhasenR
5Pb3,RPb2 undRPb3 wird dargestellt. Die bekannten Informationen über diese Legierungen werden auf der Basis der relativen Volumskontraktionen und des 4f-Beitrags zur Bindung überprüft und die Ergebnisse zu Voraussagen über die relativen Stabilitäten der VerbindungenR
5Pb3,RPb2 undRPb3 verwertet.
Mit 8 Abbildungen
Herrn Prof. Dr.H. Nowotny gewidmet.
Die Arbeiten wurden im Ames-Laboratorium der US-Atomenergie-kommission durchgeführt (Beitrag Nr. 2972). 相似文献
Systematics of the rare earth-lead alloys
The systematic behavior (and also the lack of it) in the rare earth-lead alloys is examined. Twelve different compound stoichiometries have been observed. Nearly all of the trivalent lanthanide elements form theR 5Pb3,R 5Pb4, andRPb3 phases. For the other stoichiometries, except for possiblyRPb2, compounds exist for only a limited number of the lanthanide elements. The known crystallographic data are reviewed, and the existence and nonexistence of some of the phases are discussed on the basis of crystal chemistry theories. The melting behaviors of theR-rich eutectic and theR 5Pb3,RPb2 andRPb3 phases are presented. The known information on these alloys is examined on the basis of the relative volume contractions and the 4f contribution to the bonding, and the results are used to predict the relative stabilities of theR 5Pb3,RPb2, andRPb3 compounds.
Mit 8 Abbildungen
Herrn Prof. Dr.H. Nowotny gewidmet.
Die Arbeiten wurden im Ames-Laboratorium der US-Atomenergie-kommission durchgeführt (Beitrag Nr. 2972). 相似文献
100.
T. Hondoh H. Anzai A. Goto S. Mae A. Higashi C. C. Langway Jr. 《Journal of inclusion phenomena and macrocyclic chemistry》1990,8(1-2):17-24
We have carried out X-ray diffraction studies on single crystals of natural air-hydrate in deep ice cores recovered at Dye-3 Greenland. Integrated intensities for 470 diffracting planes were measured by an automated four-circle diffractometer. The space group determined is cubicFd3m and the lattice constant is 17.21(3) Å. These results indicate that the crystallographic structure is the Stackelberg's structure II, in contrast to the previously anticipated structure. This finding agrees with the recent results on the synthetic air-hydrate by Davidsonet al. It was also found by difference Fourier synthesis for guest molecules that electron density in a 16-hedral cage has multiple maxima displaced from the center of the cage while that in the 12-hedron was approximately spherical.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena. 相似文献