ExxonMobil (Canada)

The fern Pteris vittata accumulates unusually high levels of arsenic. Using X-ray absorption spectroscopy (XAS) and XAS imaging, we reveal the distribution of arsenic species in vivo. Arsenate is transported through the vascular tissue from the roots to the fronds (leaves), where it is reduced to arsenite and stored at high concentrations. Arsenic-thiolate species surrounding veins may be intermediates in this reduction. In gametophytes, arsenite is compartmentalized within the cell vacuole. Arsenic is excluded from cell walls, rhizoids, and reproductive areas. This study provides important insights into arsenic hyperaccumulation, which may prove useful for phytoremediating arsenic-contaminated sites, and demonstrates the strengths of XAS imaging for distinguishing highly localized species.

Crystalline orientation and phase transition acceleration induced by shear are demonstrated to occur in different edible fats using synchrotron X-ray diffraction. Cocoa butter, milk fat, stripped milk fat, and palm oil were crystallized statically and under shear (90 s-1 and 1400 s-1) from the melt (50 °C) to 18 °C at a constant rate of 3 °C min-1. The 2D diffraction patterns clearly showed crystallite orientation imposed by the flow in the different phases. A dramatic reduction in phase transition times was also evident. These effects of shear on crystallizing fats are of great importance for the industrial processes carried out in chocolate, dairy, margarine, and shortening production, since temperature and shear treatments are the tools for tailoring the desired crystalline structures.

Abstract Diagenesis significantly impacts mudstone lithofacies. Processes operating to control diagenetic pathways in mudstones are poorly known compared to analogous processes occurring in other sedimentary rocks. Selected organic-carbon-rich mudstones, from the Kimmeridge Clay and Monterey Formations, have been investigated to determine how varying starting compositions influence diagenesis. The sampled Kimmeridge Clay Formation mudstones are organized into thin homogenous beds, composed mainly of siliciclastic detritus, with some constituents derived from water-column production (e.g., coccoliths, S-depleted type-II kerogen, as much as 52.6% total organic carbon [TOC]) and others from diagenesis (e.g., pyrite, carbonate, and kaolinite). The sampled Monterey Formation mudstones are organized into thin beds that exhibit pelleted wavy lamination, and are predominantly composed of production-derived components including diatoms, coccoliths, and foraminifera, in addition to type-IIS kerogen (as much as 16.5% TOC), and apatite and silica cements. During early burial of the studied Kimmeridge Clay Formation mudstones, the availability of detrital Fe(III) and reactive clay minerals caused carbonate- and silicate-buffering reactions to operate effectively and the pore waters to be Fe(II) rich. These conditions led to pyrite, iron-poor carbonates, and kaolinite cements precipitating, preserved organic carbon being S-depleted, and sweet hydrocarbons being generated. In contrast, during the diagenesis of the sampled Monterey Formation mudstones, sulfide oxidation, coupled with opal dissolution and the reduced availability of both Fe(III) and reactive siliciclastic detritus, meant that the pore waters were poorly buffered and locally acidic. These conditions resulted in local carbonate dissolution, apatite and silica cements precipitation, natural kerogen sulfurization, and sour hydrocarbons generation. Differences in mud composition at deposition significantly influence subsequent diagenesis. These differences impact their source rock attributes and mechanical properties.

Many sulfide-oxidizing organisms, including the photosynthetic sulfur bacteria, store sulfur in "sulfur globules" that are readily detected microscopically. The chemical form of sulfur in these globules is currently the focus of a debate, because they have been described as "liquid" by some observers, although no known allotrope of sulfur is liquid at physiological temperatures. In the present work we have used sulfur K-edge X-ray absorption spectroscopy to identify and quantify the chemical forms of sulfur in a variety of bacterial cells, including photosynthetic sulfur bacteria. We have also taken advantage of X-ray fluorescence self-absorption to derive estimates of the size and density of the sulfur globules in photosynthetic bacteria. We find that the form of sulfur that most resembles the globule sulfur is simply solid S(8), rather than more exotic forms previously proposed.

Time-resolved synchrotron X-ray diffraction techniques were used to study the effect of cooling rates and temperature on the crystallization dynamics and polymorphism of anhydrous milk fat (AMF) and milk fat triacylglycerols (MFTs). The crystallization of AMF at fast cooling rates and low final temperatures proceeded through the metastable phase α and resulted in the formation of a mixture of phases β‘ and β. Slow cooling rates and high final temperatures resulted in the formation of phase β‘ only, with no formation of phase α nor phase β. Moreover, in the absence of polar lipids, MFTs had a decreased tendency to form the α and β phases. The formation of the β phase was largely dependent on the initial amount of α phase formed. At high cooling rates and low crystallization temperatures, polar lipids may have initiated the crystallization process together with a high melting fraction of milk fat in the α phase. In time, this metastable phase transformed to the β phase. When no α phase was initially formed (high temperatures and/or slow cooling rates), no β phase was formed either. Small-angle X-ray diffraction could be used to monitor compositional variation of crystals over time, and demonstrated that minor polar lipids present in the milk fat delayed the onset of crystallization and reduced the rate of crystal growth.

Fish is a major dietary source of potentially neurotoxic methylmercury compounds for humans. It is also a rich source of essential selenium. We have used in situ mercury L(III)-edge and selenium K-edge X-ray absorption spectroscopy to chemically characterize the methylmercury and selenium in both fresh fish and fish digested with simulated gastric fluid. For the mercury, we confirm our earlier finding [ Harris et al. ( 2003 ) Science 301 , 1203 ] that the methylmercury is coordinated by a single thiolate donor, which resembles cysteine, and for the selenium, we find a mixture of organic forms that resemble selenomethionine and an aliphatic selenenyl sulfide such as Cys-S-Se-Cys. We find that local chemical environments of mercury and selenium do not change upon digestion of the fish with simulated gastric fluid. We discuss the toxicological implications for humans consuming fish.

Allium herbs, such as Chinese chive, garlic, and onion, share a common sulfur biochemistry that occurs on cell breakage. Sulfoxide precursors are converted enzymatically to sulfenic acid intermediates and thence to a variety of pungent and in some cases noxious sulfur species that probably act to deter herbivores. Very similar biochemistry has been proposed to occur in shiitake mushrooms. Prior to the present work, our understanding of the sulfur biochemistry of these plants and fungi has been derived largely from conventional analysis procedures. We have used in situ sulfur K-edge X-ray absorption spectroscopy in intact and disrupted allium plants and shiitake mushroom. The expected changes in sulfur forms following cell breakage are indeed observed for the alliums, but no significant changes occur for the fungus. Thus, any changes involving the sulfur-containing compounds of shiitake mushroom following cell breakage occur to a far smaller extent than those involving allium plants, presumably reflecting the need in shiitake for action by multiple enzymes, namely a gamma-glutamyl transpeptidase and a C-S lyase. The shiitake C-S lyase occurs in far lower concentrations than the corresponding enzyme in garlic. Furthermore, cleavage of the flavorant precursor by the shiitake C-S lyase is reported to cease before cleavage of the precursor has been completed, presumably due to a product or suicide inhibition mechanism.

Abstract Canada’s largest bitumen resource is contained within the McMurray Formation, a complex deepening-upward fluvial-estuarine succession typified by abrupt facies changes, inclined stratal geometries, and high-relief unconformities. Within this succession, fluvial-estuarine point-bar reservoirs represent a significant fraction of the resource that can be developed through surface mining and in-situ thermal recovery processes such as steam-assisted gravity drainage (SAGD). At Syncrude Canada Ltd.’s Mildred Lakemine, closely spaced core-hole data are tied to high-wall exposures of a point-bar succession that is 55m (180 ft) thick and occupies an area of at least 15 km 2(6 mi 2). Data are integrated using two 3-D visualization tools: light detection and ranging (LIDAR), a laser technology that produces high-resolution digital terrain models of the outcrop, and LogVu3D, an application that displays large sets of geophysical logs in a 3-D volume. The point-bar model developed here describes sand body dimensions, stratal stacking patterns, lithofacies distributions, and mudstone heterogeneity at a variety of scales. A conceptual model of steam chamber growth in a heterogeneous point bar is presented that has implications for steam chamber definition, resource assessment, reservoir modeling, and development well planning.

We report on the discovery of a new solid phase in cocoa butter, the main structural component of chocolate. We also report on novel effects of shear on the phase behavior of this material. These findings are both of fundamental and industrial interest, since the properties of solid fat networks are determined by their microstructure and polymorphic crystalline state.

OBJECTIVES: To update mortality for 34 560 employees from diverse operating segments of a Canadian petroleum company; and to investigate potential relations with occupational factors. METHODS: Employees from 1964-83 were linked to the Canadian mortality data base to provide 11 years additional follow up. There were 6760 deaths and 750 683 person-years of follow up compared with 3909 and 428 190, respectively, in the earlier study. Analyses used standardised mortality ratios (SMRs) to compare worker cause specific mortality with the Canadian general population. Duration of employment and latency analyses were performed for causes previously found to be increased in this and other petroleum cohorts, as well as any findings of interest. RESULTS: For the period 1964-94, employees experienced significantly low overall mortality (SMR=0.86 men, SMR=0.80 women). Kidney cancer, which has been increased in some studies of petroleum workers, was not increased. Acute non-lymphocytic leukaemia in exposed operating segments was consistent with the expected or only slightly, non-significantly increased. The most notable finding was increased deaths from mesothelioma among refinery and petrochemical workers (SMR 8.68; 95% confidence interval (95% CI) 5.51 to 13.03), most of whom were long term employees in jobs with presumed exposure to asbestos (mechanical and pipefitters). Deaths from multiple myeloma among marketing and distribution workers, which were previously increased, remained increased (SMR 2.08; 95% CI 0.95 to 3.95) in the update period 1984-94; however, there was no clear pattern by duration of employment or latency. Aortic aneurysms, which also were previously significantly increased among marketing and distribution workers approached the expected in the update period (SMR 1.18; 95% CI 0. 65-1.98). Analyses by duration of employment showed suggestive trends for aortic aneurysms, but earlier studies of this cohort have not found a relation between aortic aneurysms and exposure to hydrocarbons. CONCLUSION: The additional 2851 deaths and 322 493 person-years of follow up strengthened the assessment of mortality patterns relative to occupational factors. With the exception of mesothelioma, no clear work related increases in disease were identified.

ABSTRACT Radiometric dating of fault gouges has become a useful tool for regional tectonics studies and for exploring and understanding fault and earthquake processes. Methods to define the absolute age of faults achieved a solid scientific foundation almost 25 years ago when the development and application of illite age analysis for investigating sedimentary burial and thermal histories found a new potential application – defining the age of fold-and-thrust development. Since then, the methods have benefitted from further development and incorporation of the 40 Ar/ 39 Ar micro-encapsulation method and quantitative clay mineral evaluation to distinguish polytypes ( Wildfire ). These refinements to the methods have improved their application in fold-and-thrust terrains and have opened up applications in normal and strike-slip fault environments. Another important development is the use of absolute dating methods in retrograde clay gouges in which clays in a fault develop from igneous or metamorphic wall rocks that contain no clays. In addition, the method has also been shown to be useful at dating folds in fold-and-thrust belts. We think the method is now an established part of the geological toolkit, look forward to future fault structural and tectonic studies that incorporate fault ages and hope that researchers continue to probe and discover ways that the method can assist fault process studies, including earthquake fault studies.

The nature of polyolefin branch−block copolymers produced using mixed-metallocene catalysts has been further characterized in an attempt to relate polymer microstructure to properties. These copolymers were synthesized by incorporating vinyl-terminated, crystallizable macromonomers into amorphous backbones. It was shown that polymer properties depended strongly on the fine details of the polymerization procedure (sequential or ex-situ vs simultaneous or in-situ). Here we present rheological, chromatographic, and thermal data along with polymerization kinetic model simulations to interpret the observed property differences between ex-situ and in-situ produced polymers.

The metal sites of selenate reductase from Thauera selenatis have been characterized by Mo, Se, and Fe K-edge X-ray absorption spectroscopy. The Mo site of the oxidized enzyme has 3 to 4 sulfur ligands at 2.33 A from two molybdopterin cofactors, one Mo=O group at 1.68 A and one Mo-O with an intermediate bond length of 1.81 A. The reduced enzyme has a des-oxo active site, again with about four Mo-S ligands (at 2.32 A) and possibly one oxygen ligand at 2.22 A. The enzyme was found to contain Se in a reduced form (probably organic) although the sequence does not indicate the presence of selenocysteine. The Se is coordinated to both a metal (probably Fe) and a lighter scatterer such as carbon.

Abstract This paper documents some of the key findings on the data required and methods used to detect and correct issues with drilling control systems such as auto drillers, top drive active torsional damping systems, and heave compensation systems. It has been found that the rig control systems and how they are tuned can have a significant impact on drilling dynamics. Issues related to drilling dynamics have varied widely among rigs, even among those that are in the same field and that have the same equipment and specifications. The standard answer has been that drilling is different on the ‘other side of the road, river, or anticline', or that one rig crew is better than the other. While there are significant differences in the drilling environment and between crews, recognition of the effects of the control systems employed can explain many of these differences and expand the tools and techniques available to improve drilling performance and reduce dysfunctions. Once the fundamental elements of a control system are understood, the performance limiters identified can often be applied to other rigs in the fleet with different systems via effective documentation of the changes made and their results. Opportunities abound for improvement in oilfield drilling control systems, their basic design, and documentation on how they should be tuned and best used. There are also opportunities in crew training catered to different audiences: Drilling Engineers, Rig Supervisors, Drillers, Directional Drillers, and Rig Electricians. Lastly, there is often a knowledge and communication gap between the software/control/user experience and engineers designing the control systems. Since rig control systems are not usually identified as the source of drilling dysfunction, requests for software or interface redesign have not often been initiated in the past. Not surprisingly, the best progress has been made when four way work groups were formed with all key stakeholders involved: the operator's drill team, internal technical experts, rig contractor and crew, and OEM control systems experts. Investing the time and personnel in this process and establishing group trust has helped prevent gaps in understanding of overall system performance. It also allows each stakeholder to contribute their expertise, raise concerns, and get buy in from their extended teams. This process takes commitment from all parties to change the way work is done, but the performance improvements are immediate and can be clearly seen. Challenges for the future are to continue to upgrade rig site manuals, arrange for more crew training, upgrade the control system design, and to incorporate the control system response as part of the topside boundary condition for future drilling dynamics models.

The molybdenum site of the Arginine 160 --> Glutamine clinical mutant of the physiologically vital enzyme sulfite oxidase has been investigated by a combination of X-ray absorption spectroscopy and density functional theory calculations. We conclude that the mutant enzyme has a six-coordinate pseudo-octahedral active site with coordination of Glutamine Oepsilon to molybdenum. This contrasts with the wild-type enzyme which is five-coordinate with approximately square-based pyramidal geometry. This difference in the structure of the molybdenum site explains many of the properties of the mutant enzyme which have previously been reported.

Problems associated with accurately quantifying dinitrogen (N2) fixation in field-grown annual legumes have impeded progress in selecting superior strains of rhizobia, legume cultivars, and agronomic conditions that reduce dependence on fertilizer and soil N. Although 15N isotope dilution is not without its limitations, if the basic assumptions of the procedure are accepted and experimentally evaluated, it provides the most reproducible and precise estimate of percent N2 fixed and N2 fixation in field-grown annual legumes. It determines rates of N2 fixation integrated over the entire period of plant growth while simultaneously indicating the three possible N sources (atmosphere, soil, and fertilizer) which, under the plant's genetic control, contribute to its yield and permit the plant to attain its genetic yield potential. A major drawback of isotope dilution to the present date is that it is a totally destructive analytical technique.

The Khor Al Adaid embayment of southern Qatar represents a unique shallow-water mixed siliciclastic‑carbonate coastal depositional system that developed in a hyper-arid climatic setting over the past 6000 years. The embayment, which was formed during the Flandrian transgression as a result of flooding across a partially fault-controlled incised fluvial drainage, is supplied by quartz-rich sands delivered by wind-blown dunes migrating southward across the surface of Qatar. These offshore-migrating eolian-derived sediments are being redistributed by tidal currents in an otherwise low-energy coastal zone, where in situ formation of carbonate mud and a low-diversity skeletal assemblage is ongoing within salinity-restricted environments. Three depositional sectors are delineated: 1) an energetic, linear, fault-controlled Entrance Channel into which the eolian dunes spill directly; 2) a relatively deep (up to 20 m) Outer Lagoon, interpreted to represent a flooded karst-collapse structure; and 3) a sprawling, low-energy, shallow (<2 m) Inner Lagoon occupying low-lying areas between deflated eolian dunes. Physical oceanographic modeling, integrating multi-seasonal current meter and tidal gage measurements, demonstrates tidal current flow velocities are relatively high in both the Entrance Channel and at the constricted entrance to the Inner Lagoon. Associated flow expansion into less confined areas results in deposition of the eolian-derived sands as flood-tidal deltas, one in the Outer, and two in the Inner Lagoon. A weakly-developed ebb-tidal delta occurs where the Entrance Channel debouches into the Arabian Gulf. Flood-tide dominance is also apparent in Entrance Channel deposits, where sand accumulates in seaward-terminating “ebb barbs” along the margins of the flood-dominant thalweg. Such flood-tide dominance of the thalweg is unusual and likely reflects the absence of river discharge. Evidence of significant inverse estuarine circulation (seaward flow of a brine along the embayment floor) is mostly absent in spite of the landward increase of salinity, where concentrations reach more than double normal seawater salinity in the Inner Lagoon. Modeling results show that seaward-flowing brines formed in the Inner Lagoon are trapped in the relatively deep Outer Lagoon, and that mixing by tidal currents in the energetic Entrance Channel precludes the formation of vertical density gradients there. Because siliciclastic mud is essentially absent, and most of the sediment forming the deltas consists of sand, upper intertidal deltaic deposits that would normally consist of mud are absent, resulting in the flood-tide deltas having a pronounced lobate geometry similar to that of fluvial deltas formed predominantly of sand. Away from tidal deltas, low-energy lagoons are floored by carbonate mud of local production, with minor gypsum precipitating in the Inner Lagoon. Wind-generated waves only locally influence sedimentation, forming complex nearshore bars along some lagoonal shorelines. The overall landward increase in salinity is accompanied by a decrease in the diversity of benthic fauna and their skeletal remains. A fairly diverse faunal assemblage is observed in the Entrance Channel near the Arabian Gulf, including colonial corals, whereas the inner lagoon assemblage is dominated gastropods belonging to Pirenella cingulata. The remnants of large eolian dunes are preserved in the low-energy setting of the Inner Lagoon, segmenting the waterbody, and locally increasing restriction. The sedimentology of the arid-zone coastal Khor Al Adaid embayment may serve as an analogue for environmental settings that were perhaps more commonplace in arid zones of flooded continents during greenhouse times.

A five-stage strategy is suggested for conducting an exposure assessment of mixtures that may contain numerous chemical components. The stages are: (1) determination of mixture composition and variability, (2) selection of component groups within the mixture and documentation of criteria used for this selection, (3) compilation of relevant property data for each group, (4) assessment of environmental fate of each group, and (5) assessment of environmental and human exposure to each group and to the mixture as a whole. A subsequent step is the assessment of environmental and/or human risk associated with the individual and aggregate exposure to each group. The approach is illustrated by application to gasoline, which is treated as 24 component groups or hydrocarbon blocks. Focusing on stages 2-4, the illustration shows that the groups display widely different environmental fates as a result of their different physicochemical properties, degradation half-lives, and mode-of-entry into the environment. As a result, the relative proportions of groups in each environmental medium (such as air and water) differ greatly from that of the original mixture. It is thus important to treat gasoline and similar mixtures as a number of component groups instead of as a single substance. A generic procedure is suggested in which the model is run for unit emissions of each component group to air, water, and soil. These results are compiled into matrices that can then be conveniently scaled to actual emission rates without rerunning the model. Methods for determining subsequent exposure and risk are also briefly outlined.

Valuable information on the active sites of molybdenum enzymes has been provided by Mo(V) electron paramagnetic resonance (EPR) spectroscopy. In recent years, multiple resonance techniques have been extensively used to examine details of the active-site structure, but basic continuous-wave (CW) EPR has not been re-evaluated in several decades. Here, we present a re-examination of the CW EPR spectroscopy of the sulfite oxidase low-pH chloride species and provide evidence for direct coordination of molybdenum by chloride.

The redox chemistry of the molybdenum site of the C207S mutant of recombinant human sulfite oxidase has been studied via potentiometric titrations employing both electron paramagnetic resonance (EPR) spectroscopy and X-ray absorption spectroscopy (XAS) as probes of the active site structure. In earlier EXAFS studies, oxidized Cys207Ser enzyme has been shown to possess a novel tri-oxo active site, in which Ser207 does not appear to be a ligand to Mo [George, G. N.; Garrett, R. M.; Prince, R. C.; Rajagopalan, K. V. J. Am. Chem. Soc. 1996, 118, 8588−8592]. Redox titrations show that the active site is modified under reducing conditions to a mono-oxo Mo(IV) species, probably with Ser207 ligated to the metal. The Mo(IV) species can be reoxidized to a mono-oxo Mo(V) species still coordinated to Ser207, which in turn can be further reoxidized to yield the initial tri-oxo Mo(VI) structure with loss of Ser207 ligation.