| 1. |
- Tenn, William J., III, et al.
(author)
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Oxy-Functionalization of Nucleophilic Rhenium(I) Metal Carbon Bonds Catalyzed by Selenium(IV)
- 2009
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 131:7, s. 2466-2468
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Journal article (peer-reviewed)abstract
- We report that SeO(2) catalyzes the facile oxy-functionalization of (CO)(5)Re(I)-Me(delta-) with IO(4)(-) to generate methanol. Mechanistic studies and DFT calculations reveal that catalysis involves methyl group transfer from Re to the electrophilic Se center followed by oxidation and subsequent reductive functionalization of the resulting CH(3)Se(VI) species. Furthermore, (CO)(3)Re(I)(Bpy)-R (R = ethyl, n-propyl, and aryl) complexes show analogous transfer to SeO(2) to generate the primary alcohols. This represents a new strategy for the oxy-functionalization of M-R(delta-) polarized bonds.
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| 2. |
- Whitmore, T.J., et al.
(author)
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Arsenic contamination of lake sediments in Florida: evidence of herbicide mobility from watershed soils
- 2008
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In: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 40:3, s. 869-884
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Journal article (peer-reviewed)abstract
- Organic arsenical herbicides, which include monosodium methylarsonate (MSMA), have been applied to golf courses and lawns throughout Florida, USA, since the 1950s. These products convert rapidly to inorganic forms of arsenic (As) in soils and are mobilized readily. Leachates have been known to contaminate groundwater and surface waters, although past studies have not examined whether use of these products has led to significant As accumulation in lake sediments. We used paleolimnological methods to document the depositional history and inventories of total As in sediments and porewaters of Little Lake Jackson in Florida, which is adjacent to three golf courses. Six sediment cores, four of which were Pb-210 dated, showed porewater total As concentrations as high as 435 mu g l(-1), and dry-sediment total As concentrations as high as 148 mg kg(-1). Approximately 537 kg of total As is present in > 19,000 metric tons of sediment (dry mass), and an additional 18 kg of As is dissolved in 10.8 x 10(4) m(3) of porewaters. Total As content in surface sediments (mean = 47.3 mg kg(-1)) exceeds the consensus-based sedimentary concentration for probable toxicity effects in freshwater benthic fauna. Surface and subsurface waters flow to the lake from topographically higher areas to the west, where golf courses and residential areas are located. Total As concentrations were elevated highly in monitoring wells and in a stream that flows between the golf courses and lake, but As was below detection limits in wells that were located at the distal perimeter of the golf courses. Subsurface and surface waters exit the lake towards topographically lower areas to the east. Nearly all As in sediments remains bound in the solid phase, indicating that As sedimentary profiles largely reflect depositional history. Sedimentary As concentrations are correlated strongly with aluminum and iron, which suggests that As was scavenged from lake waters during the past. Sedimentary As concentrations increased until the 1980s, then declined somewhat to the present time. Dissolved As was scavenged efficiently from the water column when hypolimnetic waters were oxygenated persistently, but after eutrophication led to a seasonally anoxic hypolimnion in the 1980s, apparently less As was co-precipitated, and more was lost to hydrological outflow. Arsenic accumulation in sediments might be common in areas where As derived from organic arsenical herbicide applications is directed by shallow water tables towards adjacent lakes.
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| 3. |
- Ahlquist, Mårten, et al.
(author)
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Product Protection, the Key to Developing High Performance Methane Selective Oxidation Catalysts
- 2009
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 131:47, s. 17110-17115
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Journal article (peer-reviewed)abstract
- Selective, direct conversion of methane to methanol might seem an impossible task since the C-H bond energy of methane is 105 kcal mol(-1) compared to the C-H bond energy for methanol of 94. We show here that the Catalytica catalyst is successful because the methanol is protected as methyl bisulfate, which is substantially less reactive than methanol toward the catalyst. This analysis suggests a limiting performance for systems that operate by this type of protection that is well above the Catalytica system.
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| 4. |
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