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211.
212.
Moe MK Anderssen T Strøm MB Jensen E 《Rapid communications in mass spectrometry : RCM》2004,18(18):2121-2130
We report a novel method allowing the complete structural characterization of intact species of the phospholipid classes phosphatidylcholine and phosphatidylethanolamine by utilizing negative electrospray ionization quadrupole tandem mass spectrometry (MS/MS). Information on the molecular weight of the intact phospholipid species, the class to which it belongs, the molecular mass of the fatty acid substituents and their regioisomerism, is easily revealed by MS/MS. Throughout our investigations the R2COO- ions were more abundant than the R1COO- ions, and this observation is used for regioisomeric assignment of the two fatty acids. However, for phospholipid species containing an unsaturated fatty acid, information on the position of the double bond is not achieved in this way. By converting the olefinic sites to their 1,2-dihydroxylated derivatives, information on the position of the hydroxyl groups (and hence of the double bond) is obtained by performing a second MS/MS experiment. Thus, a complete structural characterization of intact phosphatidylcholine and phosphatidylethanolamine species is obtained by performing these two MS/MS experiments. In order to ensure structural distinction of isobaric species, a number of phosphatidylethanolamine and phosphatidylcholine species were synthesized from lyso-phosphatidylcholine and analyzed by the present method. The applicability of the method to real samples is also demonstrated by the complete structural elucidation of the two phosphatidylcholine species 16:0/18:1Delta9 and 16:0/18:1Delta11 from egg yolk. 相似文献
213.
Einar Hille 《Annali di Matematica Pura ed Applicata》1961,55(1):133-148
Summary The properties of solutions of finite systems are analyzed and it is shown by examples how these properties may be distorted
and ultimately lost in passing from finite to infinite systems.
To Enrico Bompiani on his Scientific Jubilee
This research was supported in part by United States Army through its Office of Ordnance Research under Grant DA-ORD-12. —
Most of the results have been presented to various organisations such as Section A of the American Association for the Advancement
of Science and mathematics colloquia at the universities of Leningrad, Moscow, and Toronto. 相似文献
214.
The ionisation potentials for a series of thiazolo[3,2-a]pyridinium-3-oxides are reduced by about 1.7 to 1.8eV on introduction of an 8-OH group. The gaseous species from the former compounds are ascribed a mesoion, structure while the hydroxy-derivatives are rearranged to non charged molecules. 相似文献
215.
Finite element approximations for the Dirichlet problem associated to a second-order elliptic differential equation are studied. The purpose of this paper is to discuss domain embedding preconditioners for discrete systems. The essential boundary condition on the interior interface is removed by introducing Lagrange multipliers. The associated discrete system, with a saddle point structure, is preconditioned by a block diagonal preconditioner. The main contribution of this paper is to propose a new operator, constructed from the -inner product, for the block of the preconditioner corresponding to the multipliers.
216.
Balchen M Gjelstad A Rasmussen KE Pedersen-Bjergaard S 《Journal of chromatography. A》2007,1152(1-2):220-225
Electrokinetic cross membrane extraction of acidic drugs was demonstrated for the first time. The acidic drugs were extracted from an alkaline aqueous donor solution (300 microl), through a thin supported liquid membrane of 1-heptanol sustained in the pores of the wall of a porous hollow fiber, and into an aqueous alkaline acceptor solution (30 microl) present inside the lumen of the hollow fiber by the application of a d.c. electrical potential. The negative electrode was placed in the donor solution, and the positive electrode was placed in the acceptor solution. Optimal extractions were accomplished with 1-heptanol as the supported liquid membrane, with 50 V as the driving force, and with pH 12.0 in both the donor and acceptor solutions, respectively (NaOH). Equilibrium extraction conditions were obtained after 5 min of operation with the whole assembly agitated at 1200 rpm. Eleven different acidic drugs were extracted with recovery values between 8 and 100%, and initial data supported that electrokinetic cross membrane extraction provided repeatable data and linear response between original donor concentration and final acceptor concentration of the acidic model compounds. 相似文献
217.
Zatula AS Andersson PU Ryding MJ Uggerud E 《Physical chemistry chemical physics : PCCP》2011,13(29):13287-13294
Bisulfate water clusters, HSO(4)(-)(H(2)O)(n), have been studied both experimentally by a quadrupole time-of-flight mass spectrometer and by quantum chemical calculations. For the cluster distributions studied, there are some possible "magic number" peaks, although the increase in abundance compared to their neighbours is small. Experiments with size-selected clusters with n = 0-25, reacting with D(2)O at a center-of-mass energy of 0.1 eV, were performed, and it was observed that the rate of hydrogen/deuterium exchange is lower for the smallest clusters (n < 8) than for the larger (n > 11), with a transition taking place in the range n = 8-11. We propose that the protonic defect of the bisulfate ion remains rather stationary unless the degree of hydration reaches a given level. In addition, it was observed that H/D scrambling becomes close to statistically randomized for the larger clusters. Insight into this size dependency was obtained by B3LYP/6-311++G(2d,2p) calculations for HSO(4)(-)(H(2)O)(n) with n = 0-10. In agreement with experimental observations, these calculations suggest pronounced effectiveness of a 'see-saw mechanism' for pendular proton transfer with increasing HSO(4)(-)(H(2)O)(n) cluster size. 相似文献