排序方式: 共有24条查询结果,搜索用时 15 毫秒
1.
K. A. Zaklika Thomas Kissel Arthur L. Thayer Paul A. Burns A. Paul Schaap 《Photochemistry and photobiology》1979,30(1):35-44
Abstract— The chemiluminescence from the cleavage of a number of 1,6-diaryl-2,5,7,8-tetraoxabicyclo[4.2.0]octanes 1 has been examined. The ease of oxidation of (object) the aryl moiety strongly influences both the stability and chemiluminescence efficiency of these 1,2-dioxetanes. When Ar is difficult to oxidize, 1 is comparable in stability to simple. alkyl-substituted 1,2-dioxe-tanes and affords triplet excited states in moderate yield. Both biradical and concerted cleavage mechanisms have been suggested to explain this behavior. However, when Ar is a readily oxidized group, 1 is substantially destahilized and gives excited singlet states in high yield. In this instance 1 is analogous to a number of bioluminescent systems. Cleavage mechanisms involving intramolecular electron transfer are proposed to account for this observation. In certain cases thermolysis of 1 occurs by both types of mechanism in competition, and the electron transfer mechanism may be selectively catalyzed by polar, protic media. 相似文献
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Abstract In vivo 31 P-NMR spectroscopy was applied to the investigation of the time course of metabolic response of MCA mammary carcinoma in the C,H mouse subjected to a subcurative treatment with photodynamic therapy. Eleven animals were injected with 12.5 mg kg_1 Photofrin II and after 24 h were photoactivated with 25 J cm−2 of light between 630 ± 5 nm. In vivo NMR spectroscopy was performed 1-4, 24 and 72 h after treatment. The ratio of (J-ATP intensity to inorganic phosphate (Pi) intensity changed over the time course of the study. At the 1-4 and 24 h time points the ratio of fi-ATP to Pi decreased from control values. At 72 h there was a significant increase in the ratio above the post treatment values to levels equal to or exceeding that of control pretreatment ratios. 相似文献
3.
The refractive index correction to the radiative rate constant in fluorescence lifetime measurements
R.A. Lampert S.R. Meech J. Metcalfe D. Phillips A.P. Schaap 《Chemical physics letters》1983,94(2):137-140
The dependence of fluorescence decay times upon the refractive index of the solvent has been measured in two types of system: (a) in a single solvent at different temperatures, (b) in different solvents. The results are consistent with an n2 dependence of the radiative rate constant, as has been predicted theoretically. 相似文献
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Gerard Van Koten Cees A. Schaap Johann T.B.H. Jastrzebski Jan G. Noltes 《Journal of organometallic chemistry》1980,186(3):427-445
The synthesis and structural characterization by 1H NMR and 197Au Mössbauer spectroscopy as well as by chiral labelling of the built-in ligands of three different types of arylgold(I) compounds is described.197Au Mössbauer data revealed that the benzyl- and arylgold(I) triphenylphosphine complexes which bear potential coordinating substituents at an ortho position still contain linearly coordinated AuI with 2c-2e gold(I)carbon bonds. The observation of isochronous NME resonances in (S)-2-Me2NCH(Me)C6H4AuPPh3 confirms that no additional intramolecular AuN coordination occurs in solution. Preliminary results of an X-ray diffraction study of 2,6-(MeO)2C6H3AuPPh3 are reported (R = 0.040, PAuC1 angle 172.6°. Unsymmetrical AuC1C2 and AuC1C6 angles of 126.4 and 117.4°, respectively).Pure, uncomplexed arylgold(I) compounds have been isolated from the reaction of diarylgoldlithium compounds (arylaurates) with trimethyltin bromide. (S)-2-Me2NCHMeC6H4Au has a dimeric structure which most likely consists of two monomeric units associated by intermolecular AuN coordination thus forming a ten-membered chelate ring. The structure of insoluble 2-Me2NCH2C6H4Au and 2-Me2NC6H4Au are less clear. The former compound probably has a structure similar to (S)-2-Me2NCHMeC6H4Au (IS/QS values for two-coordinate AuI centers). However, the strongly deviating IS and QS values of 2-Me2NC6H4Au indicate that a polynuclear structure for this compound similar to that proposed for 2-Me2NC6H4Cu cannot be excluded (a polymeric structure containing 2-Me2NC6H4 groups which span three Au atoms by 3c-2e Au2C bonds and AuN coordination).The mixed Au/Cu cluster (2-Me2NCH2C6H4)4Au2Cu2 is accessible via the reaction of (2-Me2NCH2C6H4)4Au2Li2 with CuI. Molecular weight and 1H NMR studies point to a tetranuclear structure in solution, while mass spectrometry shows fragment ions with m/e corresponding to (2-Me2NCH2C6H4)3Au2Cu2+, (2-Me2NCH2C6H4)3Cu2Au+, (2-Me2NCH2C6H4)2CuAu2+ and of (2-Me2NCH2C6H4)2Au+. 相似文献
6.
Silvio Dutz M.E. Hayden Allison Schaap Boris Stoeber Urs O. Häfeli 《Journal of magnetism and magnetic materials》2012
Magnetic microspheres (MMS) are useful tools for a variety of medical and pharmaceutical applications. Typically, commercially manufactured MMS exhibit broad size distributions. This polydispersity is problematic for many applications. Since the direct synthesis of monodisperse MMS is often fraught with technical challenges, there is considerable interest in and need associated with the development of techniques for size-dependent fractionation of MMS. In this study we demonstrated continuous size-dependent fractionation of sub-micron scale particles driven by secondary (Dean effect) flows in curved microfluidic channels. Our goal was to demonstrate that such techniques can be applied to MMS containing superparamagnetic nanoparticles. To achieve this goal, we developed and tested a microfluidic chip for continuous MMS fractionation. Our data address two key areas. First, the densities of MMS are typically in the range 1.5–2.5 g/cm3, and thus they tend be non-neutrally buoyant. Our data demonstrate that efficient size-dependent fractionation of MMS entrained in water (density 1 g/cm3) is possible and is not significantly influenced by the density mismatch. In this context we show that a mixture comprising two different monodisperse MMS components can be separated into its constituent parts with 100% and 88% success for the larger and smaller particles, respectively. Similarly, we show that a suspension of polydisperse MMS can be separated into streams containing particles with different mean diameters. Second, our data demonstrate that efficient size-dependent fractionation of MMS is not impeded by magnetic interactions between particles, even under application of homogeneous magnetic fields as large as 35 kA/m. The chip is thus suitable for the separation of different particle fractions in a continuous process and the size fractions can be chosen simply by adjusting the flow velocity of the carrier fluid. These facts open the door to size dependent fractionation of MMS. 相似文献
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Nitrogen and sulfur-substituted dioxetanes exhibit dramatically lower activation energies for decomposition compared to the corresponding oxygen-bearing dioxetane. A mechanism involving intramolecular electron-transfer processes is proposed for the cleavage of these unstable dioxetanes. 相似文献
8.
A. Paul Schaap Luigi Lopez Stuart D. Anderson Steven D. Gagnon 《Tetrahedron letters》1982,23(52):5493-5496
Electron-transfer photooxygenation of 1,1,2,2-tetraphenylcyclopropane with 9,10-dicyanoanthracene in oxygen-saturated acetonitrile yields 1,1,3,3-tetraphenyl-2-propen-1-o1 after reduction of the intermediate hydroperoxide. The rate of reaction is significantly increased by the addition of biphenyl as a cosensitizer. 相似文献
9.
G. Favrel J. Katz O. P. A. H. Schaap und L. van Itallie 《Fresenius' Journal of Analytical Chemistry》1925,66(7):303-304
Ohne Zusammenfassung 相似文献
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