The role of organic complexation

Rue, E. L., and K. W. Bruland. 1997. The role of organic complexation on ambient iron chemistry in the equatorial Pacific Ocean and the response of a mesoscale iron addition experiment. Limnology and Oceanography 42 901—910. 

Sicree A. A. and Barnes H. L. (1996) Upper Mississippi Valley district ore fluid model the role of organic complexes. Ore Geol. Rev. II, 105-131. 

There is an abundant research on the interactions of HIOCs and metals with biological interphases, in which organic chemicals and metals are treated independently. However, few studies have considered the role of combinations of HIOCs with metals. There is a particular lack of mechanistic approaches. With regard to the metals, the FIAM has been very successful, but it remains to be shown under which conditions additional interactions, such as partitioning of hydrophobic complexes and uptake of specific complexes, are important for metal uptake and toxic effects. In particular, the role of hydrophobic complexes with both natural and pollutant compounds in natural waters has not yet been fully elucidated, since neither their abundance nor their behaviour at biological interphases are known in detail. 

Sometimes 3(d — n ) and k ) states are said to be derived from delocalized orbitals and d—d) state from localized orbitals. The shift of the chelate emission from that of the free ligand increases in the sequence Rh(III) < Ir(III) < Ru(II) and reflects increasing cf-orbital participation in the emission orbital. The decrease in the chelate emission lifetime from the free ligand values also reflect the contamination of the molecular orbitals with d-character. The role of metal complexes as quenchers of excited states of it-electrons in organic compounds can be rationalized from such considerations. Emission from Cr8+ is the basis of one of the most important solid state laser system, the Ruby laser (Figure 10.14). 

However, dissolution studies indicate that quartz does dissolve, albeit slowly, in vitro (Jurinski and Rimstidt, 2001) this suggests that organic species or some other ligand not considered in these calculations may be helping to complex aqueous silica and therefore driving the dissolution. Further work is needed to evaluate the potential role of organic complexes with silica in vivo. 

A detailed kinetic study on the disproportionation of (49b) in neutral aqueous solutions has been performed recently in relation to the mechanisms of oxidative DNA cleavage promoted by this complex.208 Such Crv oxo complexes are among the few known types of metal complexes that cause oxidative DNA cleavage in the absence of reactive oxygen species.209 The interactions of (49b) or [CrO(salen)]+ with DNA have been studied in detail and several possible mechanisms of these reactions have been proposed (reviewed in 2000-2003).11,13,210 Several mechanistic studies on the reactions of [CrO(salen)]+ and related complexes with organic reductants have been performed in relation to the roles of these complexes in Crm-salen-catalyzed oxo-transfer reactions (Section 4.6.5.8.4).211-215... 

Correlations between concentrations of dissolved metals (iron and/or aluminum) and of either DOM or organic acids in infiltrating waters suggest that DOM, or some component of DOM, facilitates metal solubilization and translocation in soils (14). The role of DOM in metal mobilization is also supported by the occurrence of organically complexed metals in soil solutions (3, 15, 16). Precipitation and transformations of soil minerals can be inhibited by DOM, which tends to stabilize metastable phases [such as amorphous aluminum hydroxide and pseudoboehmite (17), ferrihydrite (18), and octacal-cium phosphate (19)] and to prevent formation of more crystalline phases. 

Zutic, V., and W. Stumm. 1982. On the role of surface complexation in weathering reactions. Dissolution kinetics of hydrous alumina in the presence of organic ligands, p. 613-621. In H. van Olphen and F. Verniale (ed.) Int. Clay Conf. 1981. Developments in sedimen-tology, Vol. 35. Elsevier, New York. 

Organic gels were prepared by polycondensation of resorcinol with formaldehyde in water as a solvent. Three series of carbon samples were prepared one without addition of metal the two others containing nickel and palladium (about 1% weight) respectively. The incorporation of metal was achieved by dissolution of a metal salt nickel acetate (tetrahydrate) and palladium acetate were used. As resorcinol plays the role of nickel complexant, nickel is easily soluble in resorcinol-formaldehyde aqueous solutions. On the contrary, significant amounts of palladium cannot be dissolved without using an additional complexant. Diethylenetrinitrilopentaacetic acid (DTPA) was then added to the solution. No sodium carbonate as polymerisation catalyst was used. In this work, the pH was adjusted to a chosen value by the use of sodium hydroxide (aqueous solution) and measured by a pH-meter. 

Another set of features added to SOLMINEQ.88 is the ability to include additional anions and cations in the user defined data set at run time. Up to 14 complexes of each can be included if their equilibrium constants are known. The addition of two user defined anions is particularly useful in the study of the role of organic ligands because SOLMINEQ.88 incorporates thermochemical data for aqueous species of only acetate, oxalate and succinate. These are the dominate organic ligands in sedimentary basins, but others may be important in these and other systems (20). In addition, up to five user defined minerals can be included with the necessary information to calculate both low and high temperature saturation indices. 

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