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101.
O. T. Farmer III K. B. Olsen M. L. Thomas S. J. Garofoli 《Journal of Radioanalytical and Nuclear Chemistry》2008,276(2):489-492
A method for the separation and determination of total and isotopic uranium and plutonium by ICP/MS was developed for IAEA samples on cellulose-based media. Preparation of the IAEA samples involved a series of redox chemistries and separations using TRU® resin (Eichrom). The sample introduction system, an APEX nebulizer (Elemental Scientific, Inc.), provided enhanced nebulization for a several-fold increase in sensitivity and reduction in background. Application of mass bias (ALPHA) correction factors greatly improved the precision of the data. By combining the enhancements of chemical separation, instrumentation and data processing, detection levels for uranium and plutonium approached high attogram levels. 相似文献
102.
Melanins are ubiquitous catecholic pigments, formed in organelles called melanosomes within melanocytes, the function of which is to protect skin against harmful effects of UV radiation. Melanosomes within melanoma cells are characteristically abnormal, with fragmented melanin and disrupted membranes. We hypothesize that the disruption of melanosomal melanin might be an early event in the etiology and progression of melanoma, leading to increased oxidative stress and mutation. In this report, we examine the effect of a combination of UV treatment and metal ion exposure on melanosomes within melanocytes, as well as their ability to act as pro-oxidants in ex situ experiments, and assay the effects of this treatment on viability and cell cycle progression. UVB exposure causes morphologic changes of the cells and bleaching of melanosomes in normal melanocytes, both significantly enhanced in Cu(II) and Cd(II)-treated cells, as observed by microscopy. The promoted bleaching by Cu(II) is due to its ability to redox cycle under oxidative conditions, generating reactive oxygen species; verified by the observed enhancement of hydroxyl radical generation when isolated melanosomes were treated with both Cu(II) ions and UVB, as assayed by DNA clipping. Single-dose UVB/Cu treatment does not greatly affect cell viability or cell cycle progression in heavily pigmented cells, but did so in an amelanotic early stage melanoma cell line. 相似文献
103.
Tompkins EM Jones DJ Lamb JH Marsden DA Farmer PB Brown K 《Rapid communications in mass spectrometry : RCM》2008,22(1):19-28
A method has been developed for the simultaneous detection and quantitation of five different 2-hydroxyethyl-DNA (HE-DNA) adducts that could be formed as a result of exposure to ethylene oxide (EO). In addition to the major N7-HE-guanine (N7-HEG) adducts this assay can also measure the less prevalent but potentially more biologically significant N1-HE-2'-deoxyadenosine (N1-HEdA), O(6)-HE-2'-deoxyguanosine (O(6)-HEdG), N(6)-HE-2'-deoxyadenosine (N(6)-HEdA) and N3-HE-2'-deoxyuridine adducts (N3-HEdU). The method involves the isolation of HE adducts from the unmodified nucleosides by either neutral thermal hydrolysis or enzymatic digestion, followed by high-performance liquid chromatographic (HPLC) purification, before detection and quantification by liquid chromatography tandem mass spectrometry (LC/MS/MS) using selective reaction monitoring (SRM). The limits of detection were in the range 0.5-25 fmol for each individual adduct, making this one of the most sensitive assays available for the detection of N7-HEG. To illustrate the possible applications of the assay, it has been employed in the measurement of endogenous/background and EO-induced HE adducts in a variety of DNA samples. 相似文献
104.
Cizdziel JV Ketterer ME Farmer D Faller SH Hodge VF 《Analytical and bioanalytical chemistry》2008,390(2):521-530
Sector field inductively coupled plasma mass spectrometry (SF-ICPMS) has been used with analysis of solution samples and laser
ablation (LA) of electrodeposited alpha sources to characterize plutonium activities and atom ratios prevalent in the western
USA. A large set of surface soils and attic dusts were previously collected from many locations in the states of Nevada, Utah,
Arizona, and Colorado; specific samples were analyzed herein to characterize the relative contributions of stratospheric fallout
vs. Nevada Test Site (NTS) plutonium. This study illustrates two different ICPMS-based analytical strategies that are successful
in fingerprinting Pu in environmental soils and dusts. Two specific datasets have been generated: (1) soils are leached with
HNO3-HCl, converted into electrodeposited alpha sources, counted by alpha spectrometry, then re-analyzed using laser ablation
SF-ICPMS; (2) samples are completely dissolved by treatment with HNO3-HF-H3BO3, Pu fractions are prepared by extraction chromatography, and analyzed by SF-ICPMS. Optimal laser ablation and ICPMS conditions
were determined for the re-analysis of archived alpha spectrometry “planchette” sources. The best ablation results were obtained
using a large spot size (200 μm), a defocused beam, full repetition rate (20 Hz) and scan rate (200 μm s−1); LA-ICPMS data were collected with a rapid electrostatic sector scanning experiment. Less than 10% of the electroplated
surface area is consumed in the LA-ICPMS analysis, which would allow for multiple re-analyses. Excellent agreement was found
between 239+240Pu activities determined by LA-ICPMS vs. activity results obtained by alpha spectrometry for the same samples ten years earlier.
LA-ICPMS atom ratios for 240Pu/239Pu and 241Pu/239Pu range from 0.038–0.132 and 0.00034–0.00168, respectively, and plot along a two-component mixing line (241Pu/239Pu = 0.013 [240Pu/239Pu] – 0.0001; r
2 = 0.971) with NTS and global fallout end-members. A rapid total dissolution procedure, followed by extraction chromatography
and SF-ICPMS solution Pu analysis, generates excellent agreement with certified 239+240Pu activities for standard reference materials NIST 4350b, NIST 4353, NIST 4357, and IAEA 385. 239+240Pu activities and atom ratios determined by total dissolution reveal isotopic information in agreement with the LA-ICPMS dataset
regarding the ubiquitous mixing of NTS and stratospheric fallout Pu sources in the regional environment. For several specific
samples, the total dissolution method reveals that Pu is incompletely recovered by simpler HNO3-HCl leaching procedures, since some of the Pu originating from the NTS is contained in refractory siliceous particles. 相似文献
105.
Ru‐Yi Zhu Marcus E. Farmer Yan‐Qiao Chen Prof. Jin‐Quan Yu 《Angewandte Chemie (International ed. in English)》2016,55(36):10578-10599
Achieving selective C?H activation at a single and strategic site in the presence of multiple C?H bonds can provide a powerful and generally useful retrosynthetic disconnection. In this context, a directing group serves as a compass to guide the transition metal to C?H bonds by using distance and geometry as powerful recognition parameters to distinguish between proximal and distal C?H bonds. However, the installation and removal of directing groups is a practical drawback. To improve the utility of this approach, one can seek solutions in three directions: 1) Simplifying the directing group, 2) using common functional groups or protecting groups as directing groups, and 3) attaching the directing group to substrates via a transient covalent bond to render the directing group catalytic. This Review describes the rational development of an extremely simple and yet broadly applicable directing group for PdII, RhIII, and RuII catalysts, namely the N‐methoxy amide (CONHOMe) moiety. Through collective efforts in the community, a wide range of C?H activation transformations using this type of simple directing group have been developed. 相似文献
106.
Gen-Cheng Li Peng Wang Marcus E. Farmer Prof. Dr. Jin-Quan Yu 《Angewandte Chemie (International ed. in English)》2017,56(24):6874-6877
The meta-C−H arylation of free phenylacetic acid was realized using 2-carbomethoxynorbornene (NBE-CO2Me) as a transient mediator. Both the modified norbornene and the mono-protected 3-amino-2-hydroxypyridine type ligand are crucial for this auxiliary-free meta-C−H arylation reaction. A series of phenylacetic acids, including mandelic acid and phenylglycine, react smoothly with various aryl iodides to provide the meta-arylated products in high yields. 相似文献
107.
Grata E Boccard J Glauser G Carrupt PA Farmer EE Wolfender JL Rudaz S 《Journal of separation science》2007,30(14):2268-2278
To study the stress-induced effects caused by wounding under a new perspective, a metabolomic strategy based on HPLC-MS has been devised for the model plant Arabidopsis thaliana. To detect induced metabolites and precisely localise these compounds among the numerous constitutive metabolites, HPLC-MS analyses were performed in a two-step strategy. In a first step, rapid direct TOF-MS measurements of the crude leaf extract were performed with a ballistic gradient on a short LC-column. The HPLC-MS data were investigated by multivariate analysis as total mass spectra (TMS). Principal components analysis (PCA) and hierarchical cluster analysis (HCA) on principal coordinates were combined for data treatment. PCA and HCA demonstrated a clear clustering of plant specimens selecting the highest discriminating ions given by the complete data analysis, leading to the specific detection of discrete-induced ions (m/z values). Furthermore, pool constitution with plants of homogeneous behaviour was achieved for confirmatory analysis. In this second step, long high-resolution LC profilings on an UPLC-TOF-MS system were used on pooled samples. This allowed to precisely localise the putative biological marker induced by wounding and by specific extraction of accurate m/z values detected in the screening procedure with the TMS spectra. 相似文献
108.
A. Farmer R. Rye G. Landis C. Bern C. Kester I. Ridley 《Isotopes in environmental and health studies》2013,49(3):169-177
We evaluated the potential use of stable isotopes to establish linkages between the wintering grounds and the breeding grounds of the Pectoral Sandpiper (Calidris melanotos), the White-rumped Sandpiper (Calidris fuscicollis), the Baird's Sandpiper (Calidris bairdii), and other Neotropical migratory shorebird species (e.g., Tringa spp.). These species molt their flight feathers on the wintering grounds and hence their flight feathers carry chemical signatures that are characteristic of their winter habitat. The objective of our pilot study was to assess the feasibility of identifying the winter origin of individual birds by: (1) collecting shorebird flight feathers from several widely separated Argentine sites and analyzing these for a suite of stable isotopes; and (2) analyzing the deuterium and 18O isotope data that were available from precipitation measurement stations in Argentina. Isotopic ratios (δ13C, δ15N and δ34S) of flight feathers were significantly different among three widely separated sites in Argentina during January 2001. In terms of relative importance in separating the sites, δ34S was most important, followed by δ15N, and then δ13C. In the complete discriminant analysis, the classification function correctly predicted group membership in 85% of the cases (jackknifed classification matrix). In a stepwise analysis δ13C was dropped from the solution, and site membership was correctly predicted in 92% of cases (jackknifed matrix). Analysis of precipitation data showed that both δD and δ18O were significantly related to both latitude and longitude on a countrywide scale (p < 0.001). Other variables, month, altitude, explained little additional variation in these isotope ratios. Several issues were identified that will likely constrain the degree of accuracy one can expect in predicting the geographic origin of birds from Argentina. There was unexplained variation in isotope ratios within and among the different wing feathers from individual birds. Such variation may indicate that birds are not faithful to a local site during their winter stay in Argentina. There was significant interannual variation in the δD and δ18O of precipitation. Hence, specific locations may not have a constant signature for some isotopes. Moreover, the fractionation that occurs in wetlands due to evaporation significantly skews local δD and δ18O values, which may undermine the strong large-scale gradients seen in the precipitation data. We are continuing the research with universities in Argentina with a focus on expanding the breadth of feather collection and attempting to resolve the identified issues. 相似文献
109.
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