Aluminum complexes speciation

A novel study on the speciation of aluminum in solution has been reported by Bertsch et al. [35], Fluoro, oxalato, and citrate aluminum complexes were identified as distinct peaks together with free AI(IIl). Post-column reaction/UV detection was used. These studies were used in kinetic, ion-exchange, and toxicological investigations. 

Analysis of ms spectta confu ined the potentiometrically obtained speciation. In addition the complex Allmlx)," was identified. Al-mfx chelates are very stable and may increase aluminum solubility. 

Al(III) is an example of an aquatic ion that forms a series of hydrated and protonated species. These include AlOrf Al(OH)J, Al(OH)3, and other forms in addition to AP. (For simplicity, we omit the H2O molecules that complete the structures of these complexes.) Most of these species are amphoteric (able to act as an acid or a base). Thus the speciation of Al(III) and many other aquatic ions is sensitive to pH. In this case, an aggregate variable springs from the conservation of mass condition. In the case of dissolved aluminum, the total dissolved aluminum is given by... 

Delhi soils by studying its speciation in the soil profile and to assess if there was any spatial variability. Soils representing the Aravali Ridge and the alluvial floodplains of river Yamuna were collected as a single, undisturbed core up to a depth of lm and the profile differentiated into four layers- 0-17 cm, 17-37 cm, 37-57 cm, and 57-86 cm. Pseudo total Aluminum and Iron in the soils were speciated into the operationally defined species (weakly exchangeable, organic matter complexes, amorphous oxides and hydroxides, and crystalline or free oxides) by widely recommended selective extraction procedures. Both A1 and Fe in these soils are bound predominantly as Fe oxides and silicates and have only very low percentages in the easily mobilizable pools. 

Dayde S, Filella M, Berthon G. 1990. Aluminum speciation studies in biological fluids. Part 3. Quantitative investigation of aluminum-phosphate complexes and assessment of their potential significance in vivo. J Inorg Biochem 38 241-259. 

Desroches, S., Dayde, S., and Brethon, G. Aluminum speciation studies in biological fluids. Part 6. Quantitative investigation of aluminum(III)-tartrate complex equilibria and their potential implications for aluminum metabolism and toxicity. J. Inorg. Biochem., 81, 301-312, 2000. 

One of the outstanding chemical problems associated with aluminum biology is the characterization of its speciation, i.e., its distribution among different complexes, and their structures, stability constants, and rates of formation. As is often the case, it is the complexes formed with small ligands that present most experimental difficulties. 

Many stability constant measurements have been made and an indication of how misleading the analysis using them can be is provided by Findlow et al. (46) These authors aimed to calculate the speciation of aluminum in human and bovine milk using two sets of stability constants for AP -citrate. Calculations with one set of constants indicated —80% of the AP+ was bound into neutral complexes, but the second set of constants, considered to be more accurate than the first, showed that less than 10% of the AP was in the form of neutral complexes. 

For polynuclear complexes of aluminum, Al-NMR spectroscopy has been used extensively to characterize the structure of the complexes as well as the speciation of the aqueous fluids. The characteristics of NMR spectroscopy—nucleus specific, quantitative intensities, and sensitivity to only short-range structure—combined with the high natural abundance of K make this a powerful technique at millimolar concentrations. However, the quadrupolar nature of the K nucleus (spin number I = 5/2) introduces some complications in spectral interpretation that are worth mentioning here. 

Jordan PA, Clay den NJ, Heath SL, Moore GR, Powell AK, Tapparo A (1996) Defining speciation profiles of Al complexed with small organic ligands the Al -heidi system. Coord Chem Rev 149 281-309 Karlsson M (1998) Structure studies of aluminum(III) complexes in solids, in solutions, and at the solid/water interface. PhD thesis. University of Umea... 

Within the context of toxicological and clinical importance, speciation studies have been focused on relatively few elements, mainly aluminum, antimony, arsenic, chromium, iodine, lead, mercury, platinum, selenium and tin. However, coupled HPLC-ICP-MS has most often been used for speciation of arsenic, selenium, iodine and, to a lesser extent, mercury. The primary species of these elements include different oxidation states, alkylated metal and/or metalloid compounds, selenoamino acids and selenopeptides.In addition, applications in smdies on the pharmacokinetics of metal-based drugs (mainly platinum complexes) and metalloproteins should be included. " In the following sections, the advances in speciation smdies of individual elements are reviewed. 

The fluoride ion chemisorbs on clays and oxides by ligand exchange of surface OH", a reaction favored at low pH and on oxide and silicate minerals of low crystallinity. Fluoride, a hard base, has a particular affinity for a hard acid. Soluble AP -fluoride cationic and anionic complexes are quite stable, and can dominate the speciation of dissolved aluminum in low-humus soils. The mobility of A1 can be increased by the presence of F soluble complex formation with A1 may explain the rather high solubility and mobility of F in acid soils. 

We have shown above that dissolution rates of multiple oxides can be related to the abundance and speciation of hydrogen and hydroxyl radicals at different metal centers at the surface. Since dissolution of most complex oxides is nonstoichiometric, the identity of these centers varies as a function of time and experimental conditions. The selective removal of some cations from the solid surface creates a reacted layer that is depleted in those elements that dissolve rapidly (i.e, modifying cations during basalt dissolution or sodium, calcium, and aluminum in the case of feldspars). As steady-state dissolution is controlled by the dismantling of these altered layers, it is critical to know their chemical characteristics and to identify the main mechanisms that control their formation. Two important findings obtained via microbeam techniques will be presented here. 

For the formation of hydroxyl and proton complexes, the story is different. Aluminum, for example, may exist in solution dominantly as various hydroxy-complexes such as Al(OH)2 andAl(OH)2+. Obviously, then, the charge on much of the aluminum in solution is less than +3. But the OH- contribution to the charge balance is determined from the p, which reflects only the free OH-, not the complexed OH-. In acid solutions, free OH- are completely insignificant, but the complexed OH- is not. In very alkaline solutions, the story is similar, but it is the role of H+ which becomes important. It is this factor which causes the difference between stoichiometric and speciated charge balances. 

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