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991.
Croley TR Hughes RJ Koenig BG Metcalfe CD March RE 《Rapid communications in mass spectrometry : RCM》2000,14(13):1087-1093
Environmental analytical chemistry has recently changed focus from analysis of non-polar, persistent contaminants (e.g. polychlorinated biphenyls and dioxins) to more polar and labile compounds that interfere with biological processes. For example, natural and synthetic estrogens and their metabolites have been detected in sewage treatment plant effluents at nanogram/liter concentrations that are similar to those at which both total sex reversal and intersex (containing both testes and ova) is induced in fish exposed to these compounds in laboratory experiments. The development of techniques for the analysis of natural and synthetic estrogens in biological fluids (i.e. serum and urine) has been a priority in the biomedical field. However, the recent recognition that estrogen hormones are contaminants in the environment that may contribute to endocrine disruption has focused attention on the need for highly sensitive and specific techniques that are applicable for trace analysis in complex environmental matrices. Three optimized mass spectrometric protocols have been developed for the determination and quantitation of steroid hormones in environmental matrices using gas chromatography/tandem mass spectrometry (GC/MS/MS), liquid chromatography/mass spectrometry selected ion monitoring, (LC/MS - SIM) and liquid chromatography/tandem mass spectrometry (LC/MS/MS). The advantages and disadvantages of each method are presented. 相似文献
992.
Clark SC Walz JY Ducker WA 《Langmuir : the ACS journal of surfaces and colloids》2004,20(18):7616-7622
We describe the use of evanescent wave scattering to measure the separation between the surface of a solid and a particle that is attached to an atomic force microscope (AFM) cantilever. Termed evanescent wave atomic force microscopy, our approach involves measuring the intensity of the light scattered from an evanescent field formed by the total internal reflection of a laser beam at a solid/fluid interface. In a conventional AFM "colloid probe" measurement, this separation must be inferred from an examination of the surface forces. Direct measurement of this separation with an evanescent wave atomic force microscope (EW-AFM) removes some ambiguity in the surface force measurement and, in addition, allows new types of measurements. For example, the force can be monitored at a constant separation. Our evanescent scattering apparatus is essentially identical to that used in total internal reflection microscopy (TIRM), except that we collect the light that scatters back into the incident medium, because the AFM partly obscures the forward scattered light (i.e., light scattered into the transmitted region). Compared to a conventional TIRM measurement, where the particle moves freely, attaching the particle to the cantilever in an EW-AFM gives much greater control of the particle position. 相似文献
993.
Mathias Zeidler Tilman Lamparter Jon Hughes Elmar Hartmann Anja Remberg Silvia Braslavsky Kurt Schaffner Wolfgang Gartner 《Photochemistry and photobiology》1998,68(6):857-863
Abstract— The phytochrome-encoding gene Cerpu;PHY;2 ( CP2 ) of the moss Ceratodon purpureus was heterologously expressed in Saccharomyces cerevisiae as a polyhistidine-tagged apoprotein and assembled with phytochromobilin (P φ B) and phycocyanobilin (PCB). Nickel-affinity chromatography yielded a protein fraction containing approximately 80% phytochrome. The holoproteins showed photoreversibility with both chromophores. Difference spectra gave maxima at 644/716 nm (red-absorbing phytochrome [Pr ]) far-red-absorbing phytochrome [Pfr ]) for the PCB adduct, and 659/724 nm for the PφB-adduct, the latter in close agreement with values for phytochrome extracted from Ceratodon itself, implying that PφB is the native chromophore in this moss species. Immunoblots stained with the antiphytochrome antibody APC1 showed that the recombinant phytochrome had the same molecular size as phytochrome from Ceratodon extracts. Further, the mobility of recombinant CP2 holophyto-chrome on native size-exclusion chromatography was similar to that of native oat phytochrome, implying that CP2 forms a dimer. Kinetics of absorbance changes during the Pr → Pfr photoconversion of the PCB adduct, monitored between 620 and 740 nm in the microsecond range, revealed the rapid formation of a red-shifted intermediate (I70 o)> decaying with a time constant of - 110 u.s. This is similar to the behavior of phytochromes from higher plants when assembled with the same chromophore. When following the formation of the Pfr state, two major processes were identified (with time constants of 3 and 18 ms) that are followed by slow reactions in the range of 166 ms and 8 s, respectively, albeit with very small amplitudes. 相似文献
994.
Spencer DJ Reynolds AM Holland PL Jazdzewski BA Duboc-Toia C Le Pape L Yokota S Tachi Y Itoh S Tolman WB 《Inorganic chemistry》2002,41(24):6307-6321
A series of Cu(I) and Cu(II) complexes of a variety of beta-diketiminate ligands (L(-)) with a range of substitution patterns were prepared and characterized by spectroscopic, electrochemical, and, in several cases, X-ray crystallographic methods. Specifically, complexes of the general formula [LCuCl](2) were structurally characterized and their magnetic properties assessed through EPR spectroscopy of solutions and, in one instance, by variable-temperature SQUID magnetization measurements on a powder sample. UV-vis spectra indicated reversible dissociation to 3-coordinate monomers LCuCl in solution at temperatures above -55 degrees C. The Cu(I) complexes LCu(MeCN) exhibited reversible Cu(I)/Cu(II) redox couples with E(1/2) values between +300 and +520 mV versus NHE (cyclic voltammetry, MeCN solutions). These complexes were highly reactive with O(2), yielding intermediates that were identified as rare examples of neutral bis(mu-oxo)dicopper complexes on the basis of their EPR silence, diagnostic UV-vis absorption data, and O-isotope-sensitive resonance Raman spectroscopic features. The structural features of the compounds [LCuCl](2) and LCu(MeCN) as well as the proclivity to form bis(mu-oxo)dicopper products upon oxygenation of the Cu(I) complexes are compared to data previously reported for complexes of more sterically hindered beta-diketiminate ligands (Aboelella, N. W.; Lewis, E. A.; Reynolds, A. M.; Brennessel, W. W.; Cramer, C. J.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 10600. Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.; Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 2108. Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 1999, 121, 7270). The observed structural and reactivity differences are rationalized by considering the steric influences of both the substituents on the flanking aromatic rings and those present on the beta-diketiminate backbone. 相似文献
995.
N So D P Chandra I S Alexander V J Webster D W O'Gorman Hughes 《Journal of chromatography. A》1985,337(1):81-90
The use of large doses of methotrexate (MTX), greater than 3 g/m2, for the treatment of some malignant disorders requires careful monitoring of serum concentrations. A simple and sensitive method for the separation of MTX and 7-hydroxymethotrexate (7-OH-MTX) by reversed-phase high-performance liquid chromatography (HPLC) is described. The method involves deproteinizing the serum sample on a Sep-Pak C18 cartridge, followed by separation on a C18 column and detection at 313 nm. The extraction efficiency of free MTX from serum is 70% and the maximum sensitivity is 2.2 X 10(-8) M. A high degree of correlation was obtained between the HPLC method of serum MTX determination and an enzyme multiplied immunoassay technique. The HPLC method separates MTX from its analogues, or drugs which may be administered concomitantly with MTX. Concentrations of MTX and 7-OH-MTX achieved over a 24-h period during high-dose therapy, (500-1000 mg/m2), and over 48 h for very-high-dose methotrexate therapy (8-12 g/m2) are described. A significant observation is the presence of 7-OH-MTX in sera of patients 6 h after commencement of infusion. This method was also utilized for monitoring cerebrospinal fluid MTX concentrations. 相似文献
996.
Summary Metal complexes of 2-mercaptobenzothiazole (5-RC7H3-NS2H) (R=H) and its 5-ethoxy (R=EtO) and 5-ethyl (R=Et) derivatives which are reasonably soluble in common organic solvents are described. The species prepared include M(5-RC7H3NS2)2(pyr)2 (pyr=pyridine; M=Zn, Ni or Co; R=Et or EtO) and [M(5-RC7H3NS2)2]n (M=Zn or Ni; R= Et or EtO; M=Co, R=EtO). Addition of [Me4N]-[5-RC7 H3NS2] to [Ni(5-RC7H3NS2)2]n afforded green, paramagnetic [Me4N][Ni(5-RC7H3NS2)3] (R=H or EtO). Attempts to oxidise [Ni(5-EtOC7H3NS2)2] to nickel(IV) species are described. The formation of Co(5-EtC7H3NS2)3-(pyr)2 and Co(C7H4NS2)3I2, which may contain cobalt(III), is reported. 相似文献
997.
Croce V Cosgrove T Dreiss CA Maitland G Hughes T Karlsson G 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):7984-7990
The effect of adding an alcohol ethoxylate nonionic surfactant (C(18)E(18)) to aqueous solutions of a cationic surfactant, erucyl bis(hydroxyethyl) methylammonium chloride (EHAC,CH(3)(CH(2))(7)(CH)(2)(CH(2))(12)N(+)-(CH(2)CH(2)OH)(2)CH(3)Cl(-)), was studied using small-angle neutron scattering (SANS), steady-state rheology, and cryo-transmission electron microscopy (Cryo-TEM). This cationic surfactant has the ability to self-assemble into giant wormlike micelles in the presence of an electrolyte, such as KCl. In salt-free solutions, the mixture of the two surfactants gave rise to spherical micelles. The scattering curves obtained were fitted with a polydisperse core-shell model combined with a Hayter Penfold potential. The inner and outer radii were found to be dependent on the surfactant ratio. In the presence of KCl, mixed wormlike micelles were formed. However, further addition of C(18)E(18) promoted the breaking of the micellar worms with the appearance of a structure peak in the scattering curves. In addition, it was found that the low shear viscosity is decreased upon addition of the alcohol ethoxylate nonionic surfactant. These findings are in good qualitative agreement with the Cryo-TEM images. The results show that the addition of the nonionic surfactant to the system is a method of controlling the worm length. 相似文献
998.
Hughes D Dailianis A Duncan L Briggs J McKintyre DA Silbernagel K 《Journal of AOAC International》2003,86(2):340-354
A collaborative study was conducted to validate new enrichment methods for the TECRA Listeria Visual Immunoassay (TLVIA). These new methods incorporate a newly formulated medium, TECRA Listeria Enrichrment Broth, which does not contain the highly toxic antifungal agent, cycloheximide. The new procedures will provide an alternative to the enrichment procedures described in AOAC Method 995.22. Three food types (raw ground beef, lettuce, and ice cream) were analyzed in the United States, and 2 food types (cooked turkey and cooked fish fillets) were analyzed in Australasia. Thirty collaborators participated in the study, 16 in Australasia and 14 in the United States. With the exception of one batch of ground beef, comparison of the proportion of positive test portions (p > or = 0.05) showed no significant difference between the TLVIA and the reference method for the 5 foods at 3 inoculation levels. For the one batch of naturally contaminated raw ground beef, the TLVIA gave significantly more confirmed positive results than the reference method. 相似文献
999.
McKee CT Clark SC Walz JY Ducker WA 《Langmuir : the ACS journal of surfaces and colloids》2005,21(13):5783-5789
We describe measurements of the scattering of visible light from an evanescent field by both spherical particles (R = 1-10 mum) that are glued to atomic force microscopy (AFM) cantilevers, and by sharp tips (R < 60 nm) that were incorporated onto the cantilevers during manufacture. The evanescent wave was generated at the interface between a flat plate and an aqueous solution, and an atomic force microscope was used to accurately control the separation, h, between the particle and the flat plate. We find that, for sharp tips, the intensity of scattered light decays exponentially with separation between the tip and the plate all the way down to h approximately 0. The measured decay length of scattered intensity, delta, is the same as the theoretical decay length of the evanescent intensity in the absence of the sharp tip. For borosilicate particles, (R = 1-10 mum), the scattering also decays exponentially with separation at large separations. However, when the separation is less than roughly 3delta, the measured scattering intensity is smaller in magnitude than that which would be predicted by extrapolating the exponential decay observed at large separations. For these particles, the scattering approximately fits the sum of two exponentials. The magnitude of the deviation from exponential at contact was roughly 10-15% for R = 1 mum particles and about 30% for larger particles and is larger for s-polarized light. Preliminary experiments on polystyrene particles shows that the scattering is also smaller than exponential at small separations but that the deviation from exponential is larger for p-polarized light. In evanescent wave AFM (EW-AFM) the scattering-separation can be calibrated for situations where the scattering is not exponential. We discuss possible errors that could be introduced by assuming that exponential decay of scattering continues down to h = 0. 相似文献
1000.
Croce V Cosgrove T Dreiss CA King S Maitland G Hughes T 《Langmuir : the ACS journal of surfaces and colloids》2005,21(15):6762-6768
Flow-SANS experiments were performed on viscoelastic aqueous solutions of erucyl bis(hydroxyethyl) methylammonium chloride in the presence of potassium chloride. This cationic surfactant has the ability to form very long and flexible wormlike micelles upon addition of salt. The effects of the key-parameters-shear rate, temperature, surfactant and salt concentration-on the ability of the micelles to align in the flow-field were investigated. The scattering data were analyzed in terms of an anisotropy factor (Af). It was found that the wormlike micelles aligned in the direction of the applied shear rate and that the anisotropy factor increased with shear rate. In addition, an increase in temperature caused a decrease of the anisotropy factor (Af) due to the formation of shorter worms. Furthermore, the branching of the micelles at high ionic strength caused the anisotropy factor to decrease in comparison with the values obtained from linear wormlike micelles, hence revealing that the formation of 3-way junctions restricts the alignment of the micelles in the shear-flow. Furthermore, the total surfactant concentration was found to affect the shear-induced patterns significantly, and different behaviors were observed depending on the ionic strength. 相似文献