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61.
Applications of solid-phase microextraction (SPME) in the measurement of very hydrophobic organic compounds (VHOCs) are limited, partly due to the difficulty of calibrating SPME fibers for VHOCs. This study used a static SPME strategy with a large sample volume (1.6 L) and a five-point calibration procedure to determine the distribution coefficients for a large suite of polychlorinated biphenyls (PCBs) and chlorinated pesticides between a polydimethylsiloxane (PDMS) phase (100 microm thickness) coated on a glass fiber and seawater. An extraction time of 12 days was deemed adequate for equilibrium calibration from kinetic experiments. Two groups of randomly selected fibers divided into three batches (up to nine fibers in each batch) were processed separately with two gas chromatography-mass spectrometry (GC-MS) systems. Matrix effects arising from losses of the analytes to glass container walls and stirring bars were corrected. Relative standard deviations within the same batch were generally smaller than those for the entire group. Furthermore, KfVf (Kf and Vf are the distribution coefficient of an analyte between the polymer-coated fiber and aqueous phase and the fiber volume, respectively) values determined with two GC-MS systems were statistically different. These results indicate the calibrated KfVf values were less affected by the random selection of SPME fibers than by other experimental conditions, and therefore average KfVf values may be used for the same type of commercially available SPME fibers. The relative accuracy of our calibration method was similar to that of a previous study [P. Mayer. W.H.J. Vaes, J.L.M. Hermens, Anal. Chem. 72 (2000) 459] employing different coating thickness and calibration procedure. The present study also obtained a bell-shaped relationship between log Kf and log Kow (octanol-water partition coefficient) for PCB congeners with the maximum log Kf corresponding to log Kow approximately 6.5. This bell-shaped relationship was attributed mainly to steric effects arising from the interplay between the PDMS thickness and molecular sizes of the target analytes. 相似文献
62.
Lay E Song YH Chiu YC Lin YM Chi Y Carty AJ Peng SM Lee GH 《Inorganic chemistry》2005,44(20):7226-7233
Volatile low-melting CuII metal complexes Cu[OC(CF3)2CH2C(Me)=NMe]2 (4) and Cu[OC(CF3)2CH2CHMeNHMe]2 (5) were synthesized and characterized by spectroscopic methods. A single-crystal X-ray diffraction study on complex 4 shows the anticipated N2O2 square-planar geometry with the imino alcoholate ligand arranged in the all-trans orientation. In contrast, a highly distorted N2O2 geometry with a dihedral angle of 33 degrees was observed for complex 5, suggesting that the fully saturated amino alcoholate ligand produces a much greater steric congestion around the metal ion. Metal CVD experiments were conducted, showing that both complexes, 4 and 5, are capable of depositing copper metal at temperatures of 275-300 degrees C using an inert argon carrier gas mixed with low concentrations (2-8%) of O2. The best copper thin film showed a purity of approximately 96 at. % and a resistivity of 2.11 microOmega cm versus that of the bulk standard (1.7 microOmega cm), as revealed by XPS and four-point probe analyses, respectively. We speculate that the low concentration of O2 promotes partial ligand oxidation, thus releasing the reduced copper on the substrate and affording the high-purity copper deposit. 相似文献
63.
Dudley E Lemiere F Van Dongen W Langridge JI El-Sharkawi S Games DE Esmans EL Newton RP 《Rapid communications in mass spectrometry : RCM》2003,17(11):1132-1136
Modified nucleosides in the urine have been postulated to be diagnostic indices of disease, particularly of cancer. The urine of a patient with terminal head and neck cancer has been found to contain a modified nucleoside with a protonated molecule of m/z 228. By means of high-performance liquid chromatography/ion trap mass spectrometry (HPLC/ITMS) and capillary liquid chromatography/triple quadruple mass spectrometry (CapLC/TQMS) we have identified the compound as 5'-deoxycytidine. This is the first report of 5'-deoxycytidine in man: in addition to the elucidation of its structure, its possible origins and the potential significance of its occurrence are discussed. 相似文献
64.
Dudley E Tuytten R Bond A Lemière F Brenton AG Esmans EL Newton RP 《Rapid communications in mass spectrometry : RCM》2005,19(21):3075-3085
Many nucleosides and their modified forms have been studied by mass spectrometry elaborating the detailed fragmentation pathways under MS2 and MS(n) conditions. Although the C-nucleoside pseudouridine has been fragmented and studied briefly, usually amongst many other nucleosides, it has not been investigated to the same extent as other nucleosides. In this report a number of different mass spectrometric techniques are applied to obtain a fuller picture of pseudouridine fragmentation. At the same time this study is used to compare different tandem mass spectrometric techniques, including a novel methodology utilising a quadrupole time-of-flight (Q-ToF) instrument for MS(n) analysis comparable with that available with an ion trap mass spectrometer. 相似文献
65.
Burgdorf T Löscher S Liebisch P Van der Linden E Galander M Lendzian F Meyer-Klaucke W Albracht SP Friedrich B Dau H Haumann M 《Journal of the American Chemical Society》2005,127(2):576-592
Structure and oxidation state of the Ni-Fe cofactor of the NAD-reducing soluble hydrogenase (SH) from Ralstonia eutropha were studied employing X-ray absorption spectroscopy (XAS) at the Ni K-edge, EPR, and FTIR spectroscopy. The SH comprises a nonstandard (CN)Ni-Fe(CN)(3)(CO) site; its hydrogen-cleavage reaction is resistant against inhibition by dioxygen and carbon monoxide. Simulations of the XANES and EXAFS regions of XAS spectra revealed that, in the oxidized SH, the Ni(II) is six-coordinated ((CN)O(3)S(2)); only two of the four conserved cysteines, which bind the Ni in standard Ni-Fe hydrogenases, provide thiol ligands to the Ni. Upon the exceptionally rapid reductive activation of the SH by NADH, an oxygen species is detached from the Ni; hydrogen may subsequently bind to the vacant coordination site. Prolonged reducing conditions cause the two thiols that are remote from the Ni in the native SH to become direct Ni ligands, creating a standardlike Ni(II)(CysS)(4) site, which could be further reduced to form the Ni-C (Ni(III)-H(-)) state. The Ni-C state does not seem to be involved in hydrogen cleavage. Two site-directed mutants (HoxH-I64A, HoxH-L118F) revealed structural changes at their Ni sites and were employed to further dissect the role of the extra CN ligand at the Ni. It is proposed that the predominant coordination by (CN),O ligands stabilizes the Ni(II) oxidation state throughout the catalytic cycle and is a prerequisite for the rapid activation of the SH in the presence of oxygen. 相似文献
66.
67.
The crosslinking of poly(vinyl alcohol) (PVA) with glutaraldehyde at 80 °C was characterized by viscosity and pulse field gradient (PFG) nuclear magnetic resonance (NMR) techniques. NMR signified an initial dormant period of approximately 6 hr, in which the self‐diffusion coefficient of PVA was found to be constant and independent of time. During the next 7 hr (the “primary” gel period), this induction period was succeeded by a fast decay of the self‐diffusion coefficient of rate (9.13 ± 0.45) × 10−5 sec−1 followed by a slower decay rate of (3.22 ± 0.30) × 10−5 sec−1 (the “secondary” gel period). The viscosity of the solution showed the same time behavior, i.e. an initial dormant period (∼ 6 hrs), followed by a fast increase of the viscosity for the next 7 –8 hr. During the “secondary” gel regime, the viscosity became too large to be reliably determined. However, within the time regime where both techniques produced reliable data, they gave identical information regarding the kinetics of the gel process, suggesting that PFG NMR enables in situ monitoring of gelation within porous materials (for instance sandstone). Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
68.
69.
Open- and closed-loop aberration correction by use of a quadrature interferometric wave-front sensor
Baker KL Stappaerts EA Wilks SC Young PE Gavel DT Tucker JW Silva DA Olivier SS 《Optics letters》2004,29(1):47-49
Experimental results are presented for an adaptive optics system based on a quadrature Twyman-Green interferometric wave-front sensor. The system uses a circularly polarized reference beam to form two interferograms with a pi/2 phase shift. The experiments conducted used Kolmogorov phase screens to simulate atmospheric phase distortions. Strehl ratio improvements by a factor of 8, to an absolute value of 0.45, are demonstrated. 相似文献
70.
Sotelo E 《Molecular diversity》2004,8(2):159-163
Arrays of polysubstituted pyridazinones were prepared through three- or four-component transformations starting from the readily accessible ene-adducts 2. 相似文献