Biomedical subjects

Neil C Sturchio

Publications and source records attributed to Neil C Sturchio.

11 recordsLinked to original sources

PubMed2006

Hydration and distribution of ions at the mica-water interface.

Molecular-scale structures of mica surfaces in electrolyte solutions reveal how ion and interfacial hydration control cation adsorption. Key differences are obtained for Rb+and Sr2+ using resonant anomalous x-ray reflectivity: Rb+ adsorbs in a partially hydrated state and incompletely compensates the surface charge, but Sr2+ adsorbs in both fully and partially hydrated states while achieving full charge compensation. These differences are driven by balancing the energy cost of disrupting ion and interface hydration with the electrostatic attraction between the cation and charged surface.

Journal Article↗

PubMed2005

Perchlorate isotope forensics.

Perchlorate has been detected recently in a variety of soils, waters, plants, and food products at levels that may be detrimental to human health. These discoveries have generated considerable interest in perchlorate source identification. In this study, comprehensive stable isotope analyses (37Cl/35Cl and 18O/17O/16O) of perchlorate from known synthetic and natural sources reveal systematic differences in isotopic characteristics that are related to the formation mechanisms. In addition, isotopic analyses of perchlorate extracted from groundwater and surface water demonstrate the feasibility of identifying perchlorate sources in contaminated environments on the basis of this technique. Both natural and synthetic sources of perchlorate have been identified in water samples from some perchlorate occurrences in the United States by the isotopic method.

Journal Article↗

PubMed2005

Polybrominated diphenyl ethers in the sediments of the Great Lakes. 3. Lakes Ontario and Erie.

Sediment cores were taken in 2002 in Lakes Ontario and Erie at four locations. A total of 48 sediment samples were characterized, dated using 210Pb, and analyzed for 10 congeners of polybrominated diphenyl ethers (PBDEs) including BDE209 as well as 39 congeners of polychlorinated biphenyls (PCBs). The surficial concentrations of nine tri- through hepta-BDE congeners (sigma9PBDE) are 4.85 and 6.33 ng g(-1), at sampling sites ON40 and ON30 in Lake Ontario, and 1.83 and 1.95 ng g(-1) at ER37 and ER09 in Lake Erie, respectively, based on dry sediment weight. The surficial BDE209 concentrations are 242 and 211 ng g(-1) at ON40 and ON30 and 50 and 55 ng g(-1) at ER37 and ER09. The sigma(9-) PBDEs fluxes to the sediment around 2002 are 147 and 195 pg cm(-2) year(-1) at ON40 and ON30 and 136 and 314 pg cm(-2) year(-1) at ER37 and ER09, respectively. The fluxes of BDE209 are 6.5 and 7.3 ng cm(-2) year(-1) at ON30 and ON40 and 3.7 and 8.9 ng cm(-2) year(-1) at ER37 and ER09, respectively. Dramatic increases in PBDE concentrations and fluxes upward toward the sediment surface and the present time are evident at both locations in Lake Ontario, while PCBs concentrations peak in the middle of sediment cores around the dated time of 1970s and 1960s. For both locations of Lake Erie, the increasing trends of both PBDEs and PCBs from the bottom to the surficial segments were distorted by sediment mixing. BDE209 is the most abundant congener among PBDEs in the sediments, constituting about 96 and 91% of the total PBDEs on mass basis in Lakes Ontario and Erie, respectively.

Environmental Monitoring↗

PubMed2005

Polybrominated diphenyl ethers in the sediments of the Great Lakes. 2. Lakes Michigan and Huron.

Sediment cores were taken in 2002 in Lakes Michigan and Huron at six locations. A total of 75 samples were characterized, dated using 210Pb, and analyzed for 10 congeners of polybromodiphenyl ether (PBDE) including BDE209, as well as 39 congeners of polychlorinated biphenyls (PCBs). The concentrations of nine tri- through hepta-BDE congeners (Sigma9PBDE) in the surficial sediments range from 1.7 to 4 ng g(-1) for Lake Michigan and from 1.0 to 1.9 ng g(-1) for Lake Huron, on the basis of the dry sediment weight. The Sigma9PBDEs fluxes to the sediment around the year 2002 are from 36 to 109 pg cm(-2) yr(-1) in Lake Michigan and from 30 to 73 pg cm(-2) yr(-1) in Lake Huron, with spatial variations in both lakes. The flux of BDE209 ranges from 0.64 to 2.04 ng cm(-2) yr(-1) and from 0.67 to 1.41 ng cm(-2) yr(-1) in Lake Michigan and Lake Huron, respectively. Dramatic increases in PBDE concentrations and fluxes upward toward the sediment surface and the present time are evident at all locations. The inventory of PBDEs in both lakes appears to be dependent upon latitude and the proximity to populated areas, implying that north-bound air plumes from urban areas are the major sources of PBDEs found in the lake sediments at locations away from the shores. Heavier congeners are more abundant in the sediments than in air and fish samples in the region. BDE209 is about 96% and 91% of the total PBDEs on a mass basis in Lake Michigan and Lake Huron, respectively; both are higher than the 89% found in Lake Superior, although a t test shows that the value for Lake Huron is not statistically different from that for Lake Superior at the 95% confidence level.

Environmental Monitoring↗

PubMed2005

Probing outer-sphere adsorption of aqueous metal complexes at the oxide-water interface with resonant anomalous x-ray reflectivity.

Resonant anomalous x-ray reflectivity near the Pt L(III) edge simultaneously revealed the geometric and spectroscopic structures of Pt(NH(3))(4)(2+) ions adsorbed at the quartz(100)-water interface. The derived Pt geometric subprofile shows two discrete "outer-sphere" adsorbed layers, and the interface-specific x-ray absorption edge profile exhibits a significant white-line enhancement compared to the bulk-solution species.

Journal Article↗

PubMed2005

Nano-SIMS analysis of Mg, Sr, Ba and U in natural calcium carbonate.

Concentrations of minor (Mg and Sr) and trace (Ba and U) elements in four natural calcium carbonate samples were first analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after chemical dissolution and calibrated against a standard dolomite. Their homogeneities were checked by in situ laser ablation (LA) ICP-MS with 10-20 spots. The carbonate samples were measured by using a high lateral resolution secondary ion mass spectrometer (Nano-SIMS NS50). A approximately 4 nA O- primary beam was used to sputter a 5-6-microm diameter crater on the sample surface, and secondary positive ions were extracted for mass analysis using an accelerating voltage of 8 kV and a Mattauch-Herzog geometry. A multi-collector system was adjusted to detect 26Mg+, 43Ca+, 88Sr+, 138Ba+, 238U16O+ and 238U16O2+ ions at the same time. A resolving power of 2500-5000 at 10% peak height was attained by an entrance slit set at 40 microm, and each exit slit at 50 microm with adequate flat-topped peaks. The observed 26Mg/43Ca, 88Sr/43Ca, 138Ba/43Ca and 238U16O2/43Ca ratios agreed well with those measured by LA-ICP-MS. Foraminifera shells were analyzed at 5-6 microm scale by Nano-SIMS. There was a large variation of the Mg/Ca ratios, up to +/- 38%, even in a single fragment of the shell, suggesting that although the ratios provide a useful paleoceanographic proxy at bulk scale, they may reflect a more complex pattern at < 10 microm scale.

Barium↗

PubMed2004

Interaction of uranyl with calcite in the presence of EDTA.

Adsorption of uranyl at the surface of calcite was investigated by using batch sorption experiments and synchrotron X-ray standing wave (XSW) measurements. Aqueous solutions containing 236U(VI) (4.5 x 10(-7) to 1.0 x 10(-4) M) and EDTA (5.0 x 10(-7) to 1.1 x 10(-4) M) were reacted for 90 s to 60 min with freshly cleaved calcite (104) surfaces and calcite powders. Surface exchange coefficients, sorption kinetics, and influence of powder surface area/solution volume (SA/V) ratio were investigated by alpha-counting of 236U. Powder sorption results at SA/V = 870 cm2/mL fit a Freundlich isotherm [log [U]surface (in monolayers) = log K + n log [U]aq (in moles/L)], where K = 1.9+/-0.5 and n = 0.9+/-0.1, consistent with uptake of U(VI) by a specific surface reaction where the availability of sorption sites is nonlimiting in the U concentration range measured. Measured U(VI) coverages along this isotherm, based on the calcite (104) surface Ca site density, ranged from 0.04% to 5.4% of a monolayer. Steady state surface coverages were obtained within 90 s. Sorption of U(VI) on calcite (104) single-crystal cleavage surfaces using identical solutions yielded higher coverages, because of increased step density induced by dissolution at the relatively low SA/V ratio (approximately 1) of these measurements. The crystallographic location of the sorbed U(VI) was examined with the synchrotron XSW technique. Measurements were performed at the Advanced Photon Source on fresh calcite (104) cleavage surfaces reacted for 90 s with U(VI) solutions. Coherent fractions for sorbed U ranged from 0.14 to 0.62, and the mean value of the U coherent position was 0.84+/-0.02. This position was independent of dissolved U(VI) concentration and corresponds to a distance between the U atom and the calcite (104) plane of 2.55+/-0.06 A. These results are consistent with U(VI) adsorption atthe calcite surface as an inner-sphere uranyl-carbonate surface complex bonded with the outer oxygen atom(s) of a single surface carbonate group. Steric considerations allow this observed U(VI) surface complex to occur both at step sites ((441)_ and (481)_) and on terrace areas adjacent to Ca vacancies.

Adsorption↗

PubMed2004

Invariant chlorine isotopic signatures during microbial PCB reductive dechlorination.

In order to develop more robust insight into the natural attenuation of polychlorinated biphenyls (PCBs), the chlorine isotopic composition of residual 2,3,4,5-tetrachlorobiphenyl (2,3,4,5-CB) was monitored as it underwent microbial reductive dechlorination to 2,3,5-trichlorobiphenyl (2,3,5-CB) in laboratory cultures. Reverse-phase high performance liquid chromatography (HPLC) was employed to isolate the former compound from the experimental matrix for delta37Cl measurement. No detectable isotopic fractionation was observed over the 90 day incubation with sterile control, standard, and inoculated samples all exhibiting delta37Cl values with a range of approximately 0.5 per thousand. These results show that this type of biological activity can be discriminated from other transformations by the absence of a measurable isotope effect during microbial reductive dechlorination. The utility of HPLC isolation for compound-specific delta37Cl analyses of environmentally relevant species is also demonstrated.

Bacteria↗

PubMed2003

Chlorine isotope fractionation during microbial reduction of perchlorate.

Perchlorate contamination of surface water and groundwater is an emerging public health problem that has adversely affected the drinking water supplies of millions of people in the western United States. Microbial reduction has shown promise as a cost-effective means for in situ bioremediation of perchlorate-contaminated water. Measurements of stable isotope ratios of light elements (H, C, N, O, S, Cl) can often be used to distinguish biodegradation of organic and inorganic molecules from abiotic loss mechanisms such as adsorption, dispersion, or volatilization because of the relatively large kinetic isotope effects accompanying biodegradation. We quantified chlorine isotope fractionation during perchlorate biodegradation by a common perchlorate-reducing bacterium, Dechlorosoma suillum, initially isolated from a perchlorate-contaminated groundwater source in southern California. The values of the chlorine isotopic fractionation factor alpha derived from two microcosm experiments were alpha = 0.9834 +/- 0.0001 (R2 = 0.9999) and alpha = 0.9871 +/- 0.0008 (R2 = 0.9832). These alpha values indicate that the rate of the 35ClO4 reduction is approximately 1.3-1.7% faster than that of the 37ClO4 reduction. This relatively large kinetic isotope effect indicates that chlorine isotope analysis provides a sensitive technique by which to document in situ bioremediation of perchlorate in groundwater.

Chlorine↗

PubMed2002

A chlorine isotope effect for enzyme-catalyzed chlorination.

Several chlorinated organic compounds (COCs) that have been detected in a wide range of human, animal, and environmental samples may be derived from natural or anthropogenic sources. To determine whether the Cl isotope ratios of these compounds could be used to differentiate sources, we investigated the chlorine isotope effect for enzyme-catalyzed chlorination. Two aromatic substrates, 1,3,5-trimethylbenzene (TMB) and 3,5-dimethylphenol (DMP), were treated with a chloroperoxidase isolated from the fungus Caldariomyces fumago. A kinetic isotope effect (KIE) (in terms of k35/k37) was calculated to be 1.012 for TMB and 1.011 for DMP. A similar reaction, but not catalyzed, with hypochlorite yielded a much smaller KIE. These results indicate that a substantial KIE exists for this process. Furthermore, natural COCs synthesized by this enzymatic pathway may have Cl isotope ratios that will be easily distinguished from anthropogenic COCs.

Chloride Peroxidase↗

PubMed2002

Stable chlorine intramolecular kinetic isotope effects from the abiotic dehydrochlorination of DDT.

INTENTION, GOAL, SCOPE, BACKGROUND: Identifying different sources and following reaction pathways of chlorinated organic contaminants in the environment can be challenging, especially when only their concentrations are available. Compound-specific stable chlorine measurements of some contaminants have recently been shown to provide additional information and an increased understanding of their biogeochemistry. These studies, however, have been generally limited to volatile molecules. OBJECTIVE: Here, the stable chlorine isotope ratios of the semi-volatile pesticide, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) were investigated. Specifically, the intramolecular stable chlorine isotopic compositions of DDT and the kinetic isotope effect (KIE) for the abiotic dehydrochlorination of DDT to 2,2-bis(p-chlorophenyl)-1,1-dichloroethene (DDE) were determined. METHODS: Selective chemical oxidation of DDT to dichlorobenzophenone (DCBP) and analysis of each compound was used to calculate the stable chlorine isotope ratios of the alkyl and aromatic chlorines in DDT. To determine the KIE for dehydrochlorination, DDT was reacted in a basic solution to yield DDE at 52 degrees C, 60 degrees C, and 72 degrees C for 3, 5, and 5 days, respectively. RESULTS AND DISCUSSION: Significant intramolecular stable chlorine isotopic differences were observed in one sample of DDT where the alkyl and aromatic delta 37Cl values were -5.76 +/- 0.45 and -2.21 +/- 0.24%@1000, respectively. Dehydrochlorination of DDT to DDE in basic solutions at 52, 60, and 70 degrees C resulted in a substantial intramolecular KIE where the alkyl chlorines of DDE shifted by approximately 3%@1000 relative to the alkyl chlorines in DDT. However, no temperature dependence was observed. The KIE, calculated by an iterative program, was 1.009. CONCLUSIONS: Intramolecular differences in the stable chlorine isotope ratios were observed in DDT and this is the first such finding. Dehydrochlorination of DDT yields a measurable and distinct intramolecular stable chlorine KIE. RECOMMENDATION AND OUTLOOK: The results of this study demonstrate the existence of significant intramolecular differences in chlorinated organic compounds. Many other chlorinated semi-volatile and volatile organic contaminants are synthesized from multiple sources of chlorine, and we recommend that similar studies be performed on many such molecules in order to attain a clear understanding of their intramolecular chlorine isotopic differences. The existence of a measurable KIE for the dehydrochlorination of DDT to DDE shows the potential strength of using isotopic measurements to investigate the biogeochemistry of these important compounds. For example, the isotopically depleted aqueous chloride produced by dehydrochlorination of DDT to DDE may be a useful tracer of these reactions in freshwater environments.

Chlorine↗