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41.
The use of capillary electrophoresis (CE) as an alternative to existing methods of quantitation of carbon monoxide (CO) in hemoglobin from postmortem blood samples is presented. The isolation of heme (the portion of the hemoglobin molecule in which CO binding takes place) from hemoglobin is described. Reduced (containing no gas molecules) heme and CO-heme isolated from hemoglobin standards were successfully separated using CE. Heme and CO-heme were also isolated from blood samples of accident victims and analyzed using CE. A quantifiable difference in the CO-heme signals from blood samples containing fatal and nonfatal levels of CO was observed. 相似文献
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43.
Calculations are presented to illustrate the dependence of capillary adsorption upon the interactions present in model pores. The sequence of phase transitions at zero temperature is determined for a Lennard-Jones lattice gas in a pore consisting of 4 × 4 × sites. The dependence of the specific filling sequence upon the comparative strength of the gas-pore wall and the gas-gas interaction well-depths is determined. Grand canonical Monte Carlo simulations of sorption at finite temperature in the continuum version of the same model pore are also reported. Both the theory and the simulations were performed with variable gas-solid and gas-gas energy well-depths. At a temperature of 90 K, the gas-solid heterogeneity associated with atoms adsorbed in the corners, on the walls and in the interior pore volume gives rise to sequential adsorption similar to that observed in the lattice gas calculation at 0 K. A gradual approach to non-wetting behavior is observed as the gas-solid well-depth decreases. Values of the gas-solid well-depth needed to produce pore filling at saturation (i.e., pore-wetting) are discussed. 相似文献
44.
Mass spectral characterization of low-level impurities in drug substances and formulations may be challenging when using a validated HPLC method developed for optimal chromatographic performance. In many cases, either the mobile phase contains non-volatile additives that are deleterious to the operation of the mass spectrometer, or some of the related substances fail to ionize effectively under electrospray ionization or atmospheric pressure chemical ionization conditions. This paper describes a way to capture these low-level compounds from an analytical HPLC column using a small trapping column. Mixture components are retained on the trapping column by means of reducing the solvent strength of the eluent. Subsequent elution of trapped compounds using mobile phases more amenable to mass spectral analysis yields improved detection and characterization of low-level compounds of interest. Possible applications of peak trapping and elution include: (1) analysis of compounds separated using a mobile phase containing high concentrations of non-volatile additives, (2) analysis of organic acids separated using a low-pH mobile phase (containing trifluoroacetic acid), and (3) improving the detection limit of a low-level compound of interest through multiple collections. The peak trapping apparatus and optimization experiments are described. 相似文献
45.
AdamJ. Rucklidge GeorgeE. Morris AlexandraM.Z. Slawin DavidJ. Cole‐Hamilton 《Helvetica chimica acta》2006,89(8):1783-1800
Palladium complexes of [1,2‐phenylenebis(methylene)]bis[di(tert‐butyl)phosphine] ( 1 ) catalyze the methoxycarbonylation of vinyl acetate (= ethenyl acetate) in the presence of methanesulfonic acid (Scheme 1). High selectivities to ester products can be obtained if free phosphine ligand is in excess over the amount of added acid (Table 1). Selectivities to methyl 2‐acetoxypropanoate, a precursor to lactate esters, can be as high as 3.6 : 1 at low temperature and pressure (Table 2). Replacing tBu by iPr groups leads to less‐active catalysts and lower selectivities to the branched product. Replacing the phenylene moiety by a naphthalenediyl moiety also gives lower activity, but with similar selectivity to the phenylene‐based analogues. Linear hydrocarbon‐chain linkers as the backbone instead of the phenylenebis(methylene) linker leads to poor catalysis, except for a propane‐1,3‐diyl linker, which gives good rates but poor branched selectivity (Table 5). The effect of different reaction conditions on the catalysis is discussed. The syntheses of the new xylene‐based diphosphines 2 – 5 with one to four iPr groups replacing the tBu groups at the P‐atoms of 1 and of the ligands 6 and 7 based on 1,2‐ and 2,3‐dimethylnaphthalene are also described (Schemes 2 and 3). 相似文献
46.
Protein tyrosine kinase Csk-catalyzed phosphorylation of Src containing unnatural tyrosine analogues
Using expressed protein ligation, five unnatural tyrosine analogues (amino-phenylalanine, homotyrosine, 2-methyl-tyrosine, (alphaS,betaR)-beta-methyl-tyrosine, and 2,6-difluoro-tyrosine) were incorporated into Src in place of the natural tail tyrosine residue. These semisynthetic substrates were evaluated as Csk substrates or allosteric activators. It appears that the tyrosine phenol hydroxyl is unlikely to be contributing significantly to Src's ground-state binding affinity for Csk. It has been observed that stabilizing tyrosine conformers can further optimize Src's already high substrate efficiency. These latter findings contrast similar studies with synthetic peptide substrates and highlight the value of investigation of protein kinase substrate selectivity with protein substrates. 相似文献
47.
The performance of commercial and enzymatically modified size-exclusion (SE) gels in electrochromatography was compared for preparative protein separations. Dextran and agarose-based SE gels were subjected to enzymatic digestion under mild conditions. This treatment partially hydrolyzed the gel matrix modifying its pore size distribution. Enzymatic treatment of agarose-based SE gels was found to increase the resolution of the separation. Successful separation of preparative amounts of the A and B forms of beta-lactoglobulin (difference in electrophoretic mobility of 8.5%) was achieved with a high degree of purity using agarose-based SE gels. The four major whey proteins, beta-lactoglobulin, alpha-lactalbumin, BSA and immunoglobulins, were purified from an acid whey preparation. The degree of retention of a protein in electrochromatography followed their free-solution electrophoretic mobility (mu) when the protein was able to enter the gel pores and the ratio of diffusion/mu when the protein was excluded. 相似文献
48.
49.
G.H.A. Cole 《物理学进展》2013,62(31):225-251
50.
G. H. A. Cole 《Contemporary Physics》2013,54(6):585-600
Each planet in the Solar System is represented as a mechanically spherical cold body, possibly in rotation. It is seen that, on this basis, the properties of the planets can be understood within the already established principles of the physics of matter under high pressures. Internal structures of the planets can be deduced which are consistent with observed data, although no unique detailed structural model can be isolated at this stage. 相似文献