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排序方式: 共有148条查询结果,搜索用时 31 毫秒
1.
2.
TDDFT calculations confirm a controversial proposal by DiMagno and co-workers that ruffling distortions, by themselves, do not bring about sizable red shifts in the electronic absorption spectra of "simple" nontransition-metal porphyrins. We now report that the same also holds for saddling distortions. The situation is more complex for transition metal porphyrins. For example, ruffling does bring about strong red shifts in the electronic spectra of nickel porphyrins because of a specific metal(d)-porphyrin(pi) orbital interaction. 相似文献
3.
Gerhard Buchbauer Waltraud Pernold Dorothea Rassl Brigitte Blach 《Monatshefte für Chemie / Chemical Monthly》1981,112(4):517-527
The synthesis of some new potentially, nitrogenefree spasmolytics is described. Formally the benzene nucleus in some mandelic acid esters, known by their mild spasmolytic activity, is substituted for the isocamphane bicyclus by a) SeO2 oxidation of 1-(3,3-Dimethyl-2-exo-norbornyl)-ethanone (5) to the corresponding ketoaldehyde6, b) oxidation of6 to the isocamphane analogous mandelic acid4 and c) esterification of derivatives of4 with isoamylalcohol and benzylalcohol. Attemps to dehydrate the methylester7 to camphenylideneacetic acid methylester (12) by various methods failed, probably because of the ring strain.
Teil der Diplomarbeit vonB. Blach, Universität Wien 1981. 相似文献
4.
The enthalpy of oxidation of SrFe1-xCoxO3-d with x=0.33 and 0.67 has been determined by adiabatic calorimetry; average values for x=0.33 and 0.67 are -67±11 and -49.5±9 kJ (mol O2)-1. These data and the previously reported value for SrFeO3-d suggest that the enthalpy of oxidation for pure (perovskite-type) SrCoO3-d is close to zero. Earlier reported composition - partial pressure data for SrFe0.67Co0.33O3-d are reproduced when preferential oxidation of iron is assumed for low partial pressures of oxygen.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
A chiral supramolecular assembly encapsulates the two cationic ruthenium sandwich complexes [CpRu(eta(6)-C(6)H(6))](+) and [CpRu(p-cymene)](+). The host-guest complexes K(11)[CpRu(eta(6)-C(6)H(6)) subset Ga(4)L(6)] (2) and K(11)[CpRu(p-cymene) subset Ga(4)L(6)] (3) were characterized by one- and two-dimensional NMR techniques as well as by electrospray mass spectrometry. Encapsulation of the prochiral complex [CpRu(p-cymene)](+) by the chiral host renders enantiotopic protons diastereotopic as evidenced by (1)H NMR spectroscopy. 相似文献
6.
Hege Rebecka Johansen Christian Thorstensen Tyge Greibrokk Georg Becher 《Journal of separation science》1993,16(3):148-152
On-line coupled supercritical fluid extraction and gas chromatography (SFE-GC) has been utilized for the determination of PCBs and other organochlorine compounds in human milk and blood serum. The procedure involved preconcentration of the sample on C18-silica sorbent in an extraction cell: after precipitation of the proteins up to 20 ml of human milk was concentrated on 0.5 g of sorbent. Serum (up to 5 ml) was applied to the C18 material without pretreatment. Basic alumina was utilized as a selective adsorbent for lipids in the on-line SFE-GC system. The method was used to analyze milk and serum spiked with 0.5 and 10 ng of Aroclor 1260 and the results compared with those obtained by liquid–liquid extraction of serum. 相似文献
7.
Fiedler D Leung DH Bergman RG Raymond KN 《Journal of the American Chemical Society》2004,126(12):3674-3675
A supramolecular metal-ligand assembly encapsulates a variety of cationic half-sandwich ruthenium complexes. Due to the chirality of both host and guest, chiral recognition is observed with diastereomeric excesses up to 70%. The chiral cavity can be used to carry out a dynamic resolution of the rapidly equilibrating enantiomers of the chiral organometallic guest. 相似文献
8.
Johan Sjöblom Hege Ebeltoft Alf Bjørseth Stig E. Friberg Chris Brancewicz 《Journal of Dispersion Science and Technology》2013,34(1):21-34
Hydrolysis and condensation of monomolecular alkyloxysilane films by the Langmuir technique is presented. Octadecyltrimethoxysilane formed monolayers on aqueous subphases with different properties depending on the bulk pH. At pH 1 a solid condensed film was directly formed with a molecular area of 23 Å2 and a surface pressure/surface area variation similar to that on non-ionized stearic acid. At pH 5.6 and 11 several phase transitions were observed during the compression of the monolayer with a final collapse at a molecular area of 20 Å2. Relaxation measurements confirmed the stability of the films for longer than 12 hours at different surface pressures below a critical value. 相似文献
9.
10.
Niko Kivel Dorothea Schumann Ines Günther-Leopold 《Analytical and bioanalytical chemistry》2013,405(9):2965-2972
In many scientific fields, the half-life of radionuclides plays an important role. The accurate knowledge of this parameter has direct impact on, e.g., age determination of archeological artifacts and of the elemental synthesis in the universe. In order to derive the half-life of a long-lived radionuclide, the activity and the absolute number of atoms have to be analyzed. Whereas conventional radiation measurement methods are typically applied for activity determinations, the latter can be determined with high accuracy by mass spectrometric techniques. Over the past years, the half-lives of several radionuclides have been specified by means of multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) complementary to the earlier reported values mainly derived by accelerator mass spectrometry. The present paper discusses all critical aspects (amount of material, radiochemical sample preparation, interference correction, isotope dilution mass spectrometry, calculation of measurement uncertainty) for a precise analysis of the number of atoms by MC-ICP-MS exemplified for the recently published half-life determination of $^{60}$ Fe (Rugel et al, Phys Rev Lett 103:072502, 2009). 相似文献