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71.
The method of differences is used to establish that every 2-regular multigraph onv– 10,2 (mod 3) points occurs as the neighbourhood graph of an element in a twofold triple system of orderv, with two exceptions: C2C3and C3C3.Dedicated to Professor Hanfried Lenz on the occasion of his seventieth birthday 相似文献
72.
Shoenfield's unramified version of Cohen's forcing is defined in two stages: one which does not preserve double negation and the other which modifies the former so as to preserve double negation. Here we express the unramified forcing, which preserves double negation, in a single stage. Surprisingly enough, the corresponding definition of forcing for equality acquires a rather simple form. In [2] forcing ∥- is expressed in terms of strong forcing \( \Vdash * \) viap∥-Q iffp \( \Vdash * \) ¬ ¬Q for every formulaQ ofZF set theory and every elementp of a partially ordered set (P, ≦). In its turn,p \( \Vdash * \) Q is defined by the following five clauses: (1) $$p \Vdash * a \in biff(\exists c)(\exists q \geqq p)((c,q) \in b \wedge p \Vdash * a = c)$$ (2) $$\begin{gathered} p \Vdash * a \ne biff(\exists c)(\exists q \geqq p)(((c,q) \in a \wedge p \Vdash * c \notin b) \hfill \\ ((c,q) \in b \wedge p \Vdash * c \notin a)) \hfill \\ \end{gathered} $$ (3) $$p \Vdash * \neg Qiff(\forall q)(q \leqq p \to \neg (q \Vdash * Q))$$ (4) $$p \Vdash * (Q \vee S)iff(p \Vdash * Q) \vee (p \Vdash * S)$$ (5) $$p \Vdash * (\exists x)Q(x)iff(\exists b)(p \Vdash * Q(b))$$ . 相似文献
73.
74.
Silva L Coutinho A Fedorov A Prieto M 《Journal of photochemistry and photobiology. B, Biology》2003,72(1-3):17-26
Nystatin is a polyene antibiotic frequently applied in the treatment of topical fungal infections. In this work, a 7-nitrobenz-2-oxa-1,3-diazole (NBD) hexanoyl amide derivative of nystatin was synthesized and its detailed photophysical characterization is presented. The average conformation of the labelled antibiotic in tetrahydrofuran, ethanol and methanol was determined by intramolecular (tetraene to NBD) fluorescence resonance energy transfer measurements. At variance with the literature [Can. J. Chem. 63 (1985) 77-85], it was concluded that there is no need to invoke a solvent-dependent conformational equilibrium between extended and closed conformers of the antibiotic, because the mean tetraene-to-NBD separating distance was found to remain constant (approximately 18 A) in all the solvents studied. In addition, the large solvent dependence of the fluorescence anisotropy observed for the non-derivatized nystatin, was rationalized on the basis of the prolate ellipsoidal geometry of the molecule. It was concluded that the rod shaped and amphipathic antibiotic remains monomeric in different solvents within the concentration range studied (2-20 microM). 相似文献
75.
Pressure-supported packed capillary electrochromatography (CEC) and packed capillary high-performance liquid chromatography (pHPLC) have been coupled on-line to electrospray ionization-mass spectrometry (ESI-MS) and coordination ion spray-mass spectrometry (CIS-MS). Separation of enantiomers of barbiturates and chlorinated alkyl phenoxypropanoates were performed on a permethylated beta-cyclodextrin stationary phase by pressure-supported CEC. For on-line detection with ESI- and CIS-MS, a modified sheath-liquid interface was used. CIS-MS is a universal, novel ionization technique which improves the selectivity as well as the sensitivity. Charged complexes were formed through the addition of central complexing ions such as silver(I), cobalt(II), copper(II), and lithium(I) to the sheath flow. Advantages of CIS-MS detection compared to the ESI-MS mode are discussed. In the CIS-MS mode, increased sensitivity and high selectivity was attained through different possibilities of complexation. The superiority of pressure-supported CEC compared to pHPLC in the hyphenation with CIS-MS is demonstrated. 相似文献
76.
A Study of the Uptake of Toluidine Blue O by Porphyromonas gingivalis and the Mechanism of Lethal Photosensitization 总被引:2,自引:1,他引:2
Manpreet Bhatti Alexander MacRobert Sajeda Meghji Brian Henderson Michael Wilson 《Photochemistry and photobiology》1998,68(3):370-376
The purpose of the study was to determine the distribution of the photosensitizer toluidine blue O (TBO) within Porphyromonas gingivalis and the possible mechanism(s) involved in the lethal photosensitization of this organism. The distribution of TBO was determined by incubating P. gingivalis with tritiated TBO (3H-TBO) and fractionating the cells into outer membrane (OM), plasma membrane (PM), cytoplasmic proteins, other cytoplasmic constituents and DNA. The percentage of TBO in each of the fractions was found to be, 86.7, 5.4, 1.9, 5.7 and 0.3%, respectively. The involvement of cytotoxic species in the lethal photosensitization induced by light from a helium-neon (HeNe) laser and TBO was investigated by using deuterium oxide (D2O), which prolongs the lifetime of singlet oxygen, and the free radical and singlet oxygen scavenger L-tryptophan. There were 9.0 log10 and 2 log10 reductions in the presence of D2O and H2O (saline solutions), respectively, at a light dose of 0.44 J (energy density = 0.22 J/cm2), suggesting the involvement of singlet oxygen. Decreased kills were attained in the presence of increasing concentrations of L-tryptophan. The effect of lethal photosensitization on whole cell proteins was determined by measuring tryptophan fluorescence, which decreased by 30% using 4.3 J (energy density = 4.3 J/ cm2) of light. Effects on the OM and PM proteins were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. There was evidence of change in the molecular masses of several PM proteins and OM proteins compared to controls. There was evidence of damage to the DNA obtained from irradiated cells. Scanning electron microscopic studies showed that there was coaggre-gation of P. gingivalis cells when sensitized and then exposed to laser light. These results suggest that lethal photosensitization of P. gingivalis may involve changes in OM and/or PM proteins and DNA damage mediated by singlet oxygen. 相似文献
77.
Alexander Aster Christopher Rumble Anna-Bea Bornhof Hsin-Hua Huang Naomi Sakai Tom olomek Stefan Matile Eric Vauthey 《Chemical science》2021,12(13):4908
1,4,5,8-Naphthalenediimides (NDIs) are widely used motifs to design multichromophoric architectures due to their ease of functionalisation, their high oxidative power and the stability of their radical anion. The NDI building block can be incorporated in supramolecular systems by either core or imide functionalization. We report on the charge-transfer dynamics of a series of electron donor–acceptor dyads consisting of a NDI chromophore with one or two donors linked at the axial, imide position. Photo-population of the core-centred π–π* state is followed by ultrafast electron transfer from the electron donor to the NDI. Due to a solvent dependent singlet–triplet equilibrium inherent to the NDI core, both singlet and triplet charge-separated states are populated. We demonstrate that long-lived charge separation in the triplet state can be achieved by controlling the mutual orientation of the donor–acceptor sub-units. By extending this study to a supramolecular NDI-based cage, we also show that the triplet charge-separation yield can be increased by tuning the environment.Ultrafast electron transfer from singlet and triplet excited states in equilibrium results in the population of both singlet and triplet charge-separated states. 相似文献
78.
Rodolphe Clérac Dieter Fenske Ibrahim Issac Alexander Rothenberger 《Journal of Cluster Science》2004,15(2):189-198
Two Fe–Ta containing sulfido complexes were prepared by the reaction of the metal halide salts with bis-trimethylsilylsulfide in the presence of PMe3. The complexes demonstrate that coordination chemistry with iron sulfides can give access to a range of heterometallic complexes. In [Cl(Me3P)Ta(
2-S)2(
3-S)Fe(PMe3)2]2 the two [Cl(Me3P)Ta] units are arranged around one central Fe2(
2-S)2 unit. In [(Me3P)4(MeCN)2FeII]2+[(Me3P)2TaIVFeII
3(
3-S)4Br4]2– a [TaFe3S4]2+ cuboidal arrangement was observed. The complex salt forms a polymeric structure in the solid-state with weak H-bonds between the ions. The [(Me3P)2TaIVFeII
3(
3-S)4Br4]2– ion was characterised by magnetic measurements showing strong antiferromagnetic interactions between the metal centres. 相似文献
79.
Volodkin DV Petrov AI Prevot M Sukhorukov GB 《Langmuir : the ACS journal of surfaces and colloids》2004,20(8):3398-3406
A new approach to fabricate polyelectrolyte microcapsules is based on exploiting porous inorganic microparticles of calcium carbonate. Porous CaCO3 microparticles (4.5-5.0 microns) were synthesized and characterized by scanning electron microscopy and the Brunauer-Emmett-Teller method of nitrogen adsorption/desorption to get a surface area of 8.8 m2/g and an average pore size of 35 nm. These particles were used as templates for polyelectrolyte layer-by-layer assembly of two oppositely charged polyelectrolytes, poly(styrene sulfonate) and poly(allylamine hydrochloride). Calcium carbonate core dissolution resulted in formation ofpolyelectrolyte microcapsules with an internal matrix consisting of a polyelectrolyte complex. Microcapsules with an internal matrix were analyzed by confocal Raman spectroscopy, scanning electron microscopy, force microscopy, and confocal laser-scanning fluorescence microscopy. The structure was found to be dependent on a number of polyelectrolyte adsorption treatments. Capsules have a very high loading capacity for macromolecules, which can be incorporated into the capsules by capturing them from the surrounding medium into the capsules. In this paper, we investigated the loading by dextran and bovine serum albumin as macromolecules. The amount of entrapped macromolecules was determined by two independent methods and found to be up to 15 pg per microcapsule. 相似文献
80.
Structures of New SeII and TeII Complexes Containing 2,2-Dicyanethylene-1,1-dithiolate, 2,2-Dicyanethylene-1,1-thioselenolate, and 2,2-Dicyanethylene-1,1-diselenolate (NBu4)2{Se[S2C?C(CN)2]2} ( I ), (AsPh4)2 · {Te[SSeC?C(CN)2]2} ( II ), and (NBu4)2{Te[Se2C?C(CN)2]2} ( III ) containing the bidentate chelate ligands 2,2-dicyanethylene-1,1-dithiolate i-mnt , 2,2-dicyanethylene-1,1-thioselenolate i-mnts , and 2,2-dicyanethylene-1,1-diselenolate i-mns have been prepared and characterized by X-ray structure analysis. The central units consist of [M(X? X)2E2]2? (M = Se, Te; X? X = ligand; E = lone-pair) with fourfold coordinated SeII and TeII, respectively. The complex anions [Se(i-mnt)2E2]2? as well as [Te(i-mnts)2E2]2? show a trapezoide distortion with d(Se? S) = 2.276(5); 2.287(5); 2.803(5); 2.789(5) Å and d(Te? Se) = 2.611(2); 2.617(3); d(Te? S) = 2.889(5); 2.935(4) Å. In III there are centrosymmetric complex anions [Te(i-mns)2E2]2? with nearly identical Te? Se-bond-lengths: 2.674(3) and 2.692(2) Å. These Te? Se bonds are elongated compared to usual Te? Se bonds. 相似文献