Abstract Atmospheric pressure ionization (API) mass spectrometry is a novel form of mass spectrometry in which the ionization process is carried out in a reaction chamber external to the mass analyzer region. The mass analyzer serves as a device to detect positive or negative ions present in the reaction chamber, which is maintained at atmospheric pressure. 相似文献
Uniformly sized microparticles of poly(d,l-lactic-co-glycolic) (PLGA) acid, with controllable median diameters within the size range 40–140 μm, were successfully prepared by membrane emulsification of an oil phase injected into an aqueous phase, followed by solvent removal. Initially, simple particles were produced as an oil in water emulsion, where dichloromethane (DCM) and PLGA were the oil phase and water with stabiliser was the continuous phase. The oil was injected into the aqueous phase through an array type microporous membrane, which has very regular pores equally spaced apart, and two different pore sizes were used: 20 and 40 μm in diameter. Shear was provided at the membrane surface, causing the drops to detach, by a simple paddle stirrer rotating above the membrane. Further tests involved the production of a primary water in oil emulsion, using a mechanical homogeniser, which was then subsequently injected into a water phase through the microporous membrane to form a water in oil in water emulsion. These tests used a water-soluble model drug (blue dextran) and encapsulation efficiencies of up to 100% were obtained for concentrations of 15% PLGA dissolved in the DCM and injected through a 40 μm membrane.
Solidification of the PLGA particles was followed by removal of the DCM through the surrounding aqueous continuous phase. Different PLGA concentrations, particle size and osmotic pressures were considered in order to find their effect on encapsulation efficiency. Osmotic pressure was varied by changing the salt concentration in the external aqueous phase whilst maintaining a constant internal aqueous phase salt concentration. Osmotic pressure was found to be a significant factor on the resulting particle structure, for the tests conducted at lower PLGA concentrations (10% and 5% PLGA). The PLGA concentration and particle size distribution influence the time to complete the solidification stage and a slow solidification, formed by stirring gently overnight, provided the most monosized particles and highest encapsulation efficiency. 相似文献
The Mössbauer determined cation distributions of FeV2O4, FeCr2O4, FeMn2O4, Fe3O4, FeCo2O4, CoV2O4, CoCr2O4, CoMn2O4, CoFe2O4 and Co3O4 are compared with the quantitative d-orbital stablization energies of McClure and of Dunitz and Orgel. They are also compared with the qualitative ligand field stabilization energies of Cotton. These theories do not account for observation in the cases of FeMn2O4, FeCo2O4 and CoFe2O4. 相似文献
Clusters of galaxies are excellent probes of cosmic structure and evolution. X-ray studies of clusters provide some of their
key parameters, viz., temperature of the hot intra-cluster gas, its metallicity, X-ray luminosity and surface brightness giving
mass distribution and mass-flow rate in the case of cooling flows. X-ray measurements for a large sample of clusters have
lead to estimates of the total gravitating mass in them, which can be compared to the virial masses derived from dynamical
considerations and gravitational lensing in some of them. X-ray derived total masses are consistent with masses obtained from
the other methods after the effects due to the presence of cooling flows are taken into account in the analyses. Estimated
virial masses, lack of evolution in X-ray properties, and detection of several very hot clusters at high redshifts indicate
a Universe with a low value (≤ 0.3) for the Ω parameter. 相似文献
Max Dehn is famous for his contributions to group theory and topology, but almost half of his publications are on the foundations
of geometry. In this article I hope to show that Dehn's interest in geometry was not misplaced, and that his contributions
to it are also remarkable. First, let us survey Dehn's main contributions to geometry, in chronological order. 相似文献
Mass spectra of trimethylsilyl (TMS) derivatives of long chain dicarboxylic acids, hydroxy acids, cyano acids, and terminal diols, dithiols and diamines have been examined. A number of fragmentation pathways involving rearrangement of partial or intact TMS groups between the termini or remote points in the chain have been determined, using deuterium and carbon-13 labeling, and high resolution mass spectrometry. Knowledge of the occurrence of functional group migrations of this type is essential to the correct interpretation of mass spectra of TMS derivatives, which are now in wide use in mass spectrometry and gas chromatography. These data in addition provide further evidence for the general ability of remote functional groups to interact, by winding or coiling of long chains. A number of interesting doubly-charged ions are reported, in which the charges are reported, in which the charges are located at opposite ends of long chains, and for which no singly-charged counterparts are observed. 相似文献
Unequal affinity between lipids has been hypothesized to be a mechanism for the formation of microdomains/rafts in membranes. Our studies focus upon the interaction of cholesterol with polyunsaturated fatty acid (PUFA)-containing phospholipids. They support the proposal that steric incompatibility of the rigid steroid moiety for highly disordered PUFA chains, in particular docosahexaenoic acid (DHA), provides a sensitive trigger for lateral segregation of lipids into PUFA-rich/sterol-poor and PUFA-poor/sterol-rich regions. Solid state 2H NMR and x-ray diffraction (XRD) demonstrate that the solubility of cholesterol is reduced in 1-palmitoyl-2-docosahexaenoyl-phosphatidylethanolamine (16-0:22:6PE) bilayers. In mixed membranes of phosphatidylethanolamine (PE) with the lipid raft forming molecules egg sphingomyelin (SM) and cholesterol, diminished affinity of the sterol for 16:0-22:6PE relative to 1-palmitoyl-2-oleoylphosphatidylethanolamine (16:0-18:1PE) is identified by 2H NMR order parameters and detergent extraction. Phase separation of the PUFA-containing phospholipid from SM/cholesterol rafts is the implication, which may be associated with the myriad of health benefits of dietary DHA. 相似文献