Molybdate complexes

Polarimetric analysis of sorbitol and mannitol in the presence of each other and of sugars is possible because of their enhanced optical rotation when molybdate complexes are formed and the higher rotation of the mannitol molybdate complex under conditions of low acidity (194). The concentration of a pure solution of sorbitol may be determined by means of the refractometer (195). Mass spectra of trimethylsilyl ethers of sugar alcohols provide unambiguous identification of tetritols, pentitols, and hexitols and permit determination of molecular weight (196). 

From strongly addic solutions benzoin-a-oxime precipitates molybdate and tungstate ions quantitatively chromate, vanadate, niobate, tantalate, and palladium) II) are partially predpitated. The molybdate complex is best ignited at 500-525 °C to Mo03 before weighing alternatively, the predpitate may be dissolved in ammonia solution and the molybdenum predpitated as lead molybdate, in which form it is conveniently weighed. 

Co-extraction of Mo and Cu is potentially a problem with certain feed solutions,14 and again selectivities are very dependent on the nature of modifiers present in formulated reagents.142 The Mo species extracted have not been fully characterized, but may include a neutral dioxo complex, [Mo02L2], which can be assumed to have an N2022 donor set similar to that in the Cu11 complex, and molybdate complexes solvated by neutral phenolic oxime ligands such as [M0O4112 LI l].143 Formation of solvated forms of molybdic acid is supported by evidence that extraction is favorable at very low pH values and that the complexes are readily stripped by aqueous ammonia to produce ammonium molybdate,144... 

Peroxide titanate complexes, 25 98 Peroxide value, 20 827 in soap making, 22 736 Peroxidic compounds, 25 42 Peroxoborates, names, CAS numbers, and IUPAC names of, 18 398t Peroxocarbonates, 28 401 Peroxo compounds, 28 392-393, 397 Peroxodisulfate ion, 28 408 Peroxodisulfates, 28 392, 408-410 Peroxodisulfate salts, 28 418 uses for, 28 408-409 Peroxodisulfuric acid, 28 407 408 Peroxohydrate(s), 24 40 28 411—415 of melamine, 28 415 stabilization of, 28 413 Peroxo molybdate complexes, 2 7 22 Peroxomonophosphate ion, 28 403 Peroxomonophosphoric acid, 28 403 Peroxomonosulfates, 28 406 407... 

Figure 1. Characteristic EPR signals of Fe(II)Fe(III) sites in semimethemerythrinj (a), semimethemerythrinQ (b), reduced uteroferrin (c), reduced uteroferrin-molybdate complex (d), reduced bovine spleen purple acid phosphatase (e), reduced component A of methane monooxygenase (f). (Reproduced with permission from ref. 26. Copyright 1987 Elsevier.)...

Oxyanions also affect the coordination chemistry of the metal center (84). Molybdate and tungstate are tightly bound noncompetitive inhibitors (Ki s of ca. 4 (iM) (85). These anions bind to the reduced form of the enzyme, changing the rhombic EPR spectrum of the native enzyme to axial (Figure 1) and affecting the NMR shifts observed (84,85). Comparisons of the ENDOR spectra of reduced uterofenin and its molybdate complex show that molybdate binding causes the loss of iH features which are also lost when the reduced enzyme is placed in deuterated solvent (86). These observations suggest that molybdate displaces a bound water upon complexation. 

Hexacyanoferrates were immobilized on Au covered with SAM of 3,3 -thiodipropionic acid [86]. It has been found from voltammetric studies that the surface coverage of hexacyanoferrate is close to one monolayer and such an electrode exhibits very good surface redox behavior. Cheng et al. [87] have described the formation of an extremely thin multilayer film of polybasic lanthanide heteropolytungstate-molybdate complex and cationic polymer of quaternary poly(4-vinylpyridine), partially complexed with osmium bis(2,2 -bipyridine) on a gold electrode precoated with a cysteamine SAM. Consequently, adsorption of inorganic species might also be related to the properties of SAMs. This problem will be discussed in detail in a separate section later. 

Ga2(W04)3 is identified in the Ga203-W03 phase diagram. Several gallium tungstates and some polytungstate and molybdate complexes have recently been characterized.561,562... 

The silicic acid concentrations were analyzed at different times by withdrawing 1 ml. from the solution after a high speed centrifugation of the suspended particulates. The colorimetric determination of oligomeric silicic acid by means of the blue ammonium molybdate complex, as described by Stegemann and Fitzek (16), was used for the quantitative measurements. 

Molybdenum oxide - alumina systems have been studied in detail (4-8). Several authors have pointed out that a molybdate surface layer is formed, due to an interaction between molybdenum oxide and the alumina support (9-11). Richardson (12) studied the structural form of cobalt in several oxidic cobalt-molybdenum-alumina catalysts. The presence of an active cobalt-molybdate complex was concluded from magnetic susceptibility measurements. Moreover cobalt aluminate and cobalt oxide were found. Only the active cobalt molybdate complex would contribute to the activity and be characterized by octahedrally coordinated cobalt. Lipsch and Schuit (10) studied a commercial oxidic hydrodesulfurization catalyst, containing 12 wt% M0O3 and 4 wt% CoO. They concluded that a cobalt aluminate phase was present and could not find indications for an active cobalt molybdate complex. Recent magnetic susceptibility studies of the same type of catalyst (13) confirmed the conclusion of Lipsch and Schuit. 

The absolute configuration of the side chain of isoharringtonine has been deduced (174) to be 2R,35(299) by comparing the CD spectra of its molybdate complexes with those of piscidic acid (300) of known absolute configuration. 

Molybdate diluting solution. Dissolve 0.5 g of Na2C03 and 0.5 g of Na2B407 in 100 ml of 0.39 M nitric acid. Add 100 ml of molybdate complexing solution and dilute to 500 ml with 0.126 M HN03. This solution can be used until a scale of hydrated molybdenum oxide develops on the container walls (several days to a week). Then a fresh solution should be prepared. The scale can be removed with ammonium hydroxide solution. 

The original catalysts reported for the metathesis of acyclic alkenes were related to alkene polymerization systems. Banks and Bailey reported in 1964 that the heterogeneous cobalt molybdate complexes would promote the metathesis reaction. Since that time a wide variety of catalysts that use Mo, W and Re as Ae active metal in combination with a variety of supports, promoters and activation conditions have been reported. These heterogeneous catalysts are the systems of choice for most industrial fine chemical applications. 

Riley, 1962 Oscarson et al 1980 Strickland and Parson, 1968). This method is based on the spectrophotometric measurement of the blue As(V) and P(V) molybdate complexes. Phosphate is measured in one sample after reducing As(V) to As(III), which does not form the color complex. In a second sample, both P(V) and As(V) are measured and the As(V) concentration determined by subtracting the P(V) concentration. A third sample is oxidized to convert As(III) to As(V), and the As(lll) concentration obtained by subtracting As(V) and P(V). 

Apart from some Weakley-type complexes (Table 22), there has been little systematic investigation of lanthanide-molybdate complexes. Multinuclear NMR studies of solutions of the well-established dodecamolybdates [MIVMo12042]8- (M = Ce, U), with a range of di- and trivalent transition-metal and lanthanide cations, show the formation of complexes incorporating two metal cations. In most cases these complexes are labile on the NMR timescale.368-370... 

The ability of zinc ions to block copper absorption, possibly by formation of- intestinal metallothionein that strongly binds copper, has led to its use in pharmacological doses in the management of Wilson s disease/ Similarly molybdate ion can form insoluble copper-molybdate complexes in the intestine that limit copper absorption. The detrimental effects of organic phosphate (phytic acid) in limiting zinc absorption are aggravated by excess dietary calcium, probably by formation of a highly insoluble Ca-Zn-phytate complex. The subject of these and other interactions has been reviewed, ... 

Combi cassette. The ColorLock Gold assay kit is based on malachite green-molybdate colorimetric assay, and the yellow reagent turns green in the presence of phosphate. The stabilizer stabilizes acid-labile substrates and the molybdate complex to maintain signal stability. 

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