Molybdenum complexes chemical reactivity

Chemical leach tests on the bulk settled dust samples showed that the dusts are quite chemically reactive. Leach solutions have high alkali-nities, due to the rapid partial dissolution of calcium hydroxide from concrete particles. Indoor dust samples produced higher pH levels (11.8-12.4) and alkalinities (—600 mg CaCOa) than outdoor dusts (pH 8.2-10.4 alkalinity —30mgL CaCOa), indicating that outdoor dust samples had reacted with rainfall or other water prior to collection. Thurston et al (2002) found that the leachate pH of the dusts decreased with decreasing particle size. Some metals or metalloids in the dusts (aluminum, chromium, antimony, molybdenum, barium, copper, zinc, cobalt, nickel) are readily leached by deionized water many of these form oxyanion species or carbonate complexes that are most mobile at the alkaline pH s generated by the leachates. 

Chemical systems of relevance to the molybdenum and tungsten enzymes include synthetic pterins, a-phosphorylated ketones (as precursor models), and a variety of molybdenum and tungsten oxido, sulfido, and 1,2-enedithiolate complexes. These compounds have been used to (1) confirm the identity of MPT derivatives (2) define steps in MPT biosynthesis (3) calibrate spectroscopic observations (4) give precise geometries and reactivities that can be used as input for theoretical studies and (5) provide options for mechanistic consideration. 

The unusual structure of 1 and known reactivity of Mo(dedtc)2(CO)2 compounds with a variety of small molecules (7, 12) in addition to hydrazine suggest that further chemical and structural studies of these and related Mo (II) complexes may provide additional insight concerning the binding of small molecules by low valent molybdenum compounds. 

The chemical form of phosphorus in the water column available for uptake by biota is important. The biologically available phosphorus is usually taken to be soluble reactive phosphorus (orthophosphate) , i.e. which, upon acidification of a water sample, reacts with added molybdate to yield molybdophosphoric acid, which is then reduced with SnCl2 to the intensely-coloured molybdenum blue complex and is determined spectrophotometrically (Imax = 882 nm). Reduction in inputs of phosphate, for example from point sources or by creating water meadows and buffer strips to contain diffuse runoff, has obviously been one of the major approaches to stemming eutrophication trends and... 

Chemical leach tests of the <50 p.m size fraction of dust samples collected around Owens Lake, using water (Reheis etal, 2001, and our unpublished data) and SLFs (our unpubhshed data), show that the dusts are sufficiently aUcahne and reactive to shift the pH of water and SLF to values near 10.5 and 9.5, respectively. Arsenic, chromium, vanadium, molybdenum, hthium, zinc, and other trace metals or metalloids are readily solubilized from the dusts. The trace metals or metalloids leached in the greatest quantities are those that form oxyanion species or abundant carbonate complexes in solution, and that are therefore mobilized most effectively under the alkaline conditions generated by the alkaline dusts. 

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