Bioavailability metal complexes

Free, ionic species of metals are at their highest concentrations at lower pH, so metals tend to be more bioavailable under these conditions.121128 At acidic pH, more protons are available to saturate metal-binding sites.99 For example, metals are less likely to form insoluble precipitates with phosphates when the pH of the system is lowered because much of the phosphate has been protonated. Under basic conditions, metal ions can replace protons to form other species, such as hydroxo-metal complexes. Some of the hydroxo-metal complexes are soluble, such as those formed with cadmium, nickel, and zinc, whereas those formed with chromium and iron are insoluble. 

White, V. and Knowles, C., Effect of metal complexation on the bioavailability of nitrilotriacetic acid to Chelatobacter heintzii ATCC 29600, Arch Microbiol, 173 (5), 373-382, 2000. 

In addition, dissolved organic carbon (DOC) is also an important soil solution solute affecting speciation and bioavailability of many trace elements in soil solution. Many trace elements and heavy metals complex with dissolved organic carbon. This is especially important in arid and semi-arid environments since high soil pH increases the solubility of organic molecules and accordingly increases concentrations of dissolved organic carbon in soil solution. 

Once mineral-bound aluminum is recovered from ores, it forms metal complexes or chelates. Examples of the different forms of aluminum include aluminum oxide, aluminum chlorhydrate, aluminum hydroxide, aluminum chloride, aluminum lactate, aluminum phosphate, and aluminum nitrate. The metal itself is also used. With the exception of aluminum phosphide, the anionic component does not appear to influence toxicity, although it does appear to influence bioavailability. Aluminum phosphide, which is used as a pesticide, is more dangerous than the other forms however, this is because of the evolution of phosphine gas (a potent respiratory tract and systemic toxin) rather than to the exposure to aluminum. 

Bioavailable metals and metalloid species are either adsorbed or incorporated into the structure of proteins, lipids, nucleic acids, amino acids, sugars, vitamins and hormones to form complexes of varying degrees of thermodynamic stability and reactivity. These complexes could be classified as either metal-proteins or metalloproteins on the basis of their stability during isolation and purification (Vallee and Coleman, 1964). Whereas metal-proteins are relatively labile and the metal is easily lost during dialysis, metalloproteins are stable and inert. 

As(V), and Hg(II) versus MMHg (monomethyl-Hg)], solubility [e.g., Fe(II) versus Fe(III) and Mn(II) versus Mn(IV)], the difference in volatility [Hg(0) versus Hg(II)], and bioavailability (e.g., labile-bound metal complex/strongly bound metal complex). It is therefore a challenge to identify and quantify the major species of elements such as Cr, Fe, Mn, As, and Fig in aquatic systems. Table 7.1 gives an overview of the levels of common trace metals in various aquatic systems. 

Element uptake from soil and transfer into the edible parts of plants have been addressed in several other studies. Soil-to-plant transfer factors in fruit and vegetables grown in various agricultural conditions have been determined for, for example, Pt [100], T1 [101], and various other metal contaminants [102], In a study on stable isotopes of fission product elements (Ce, Cs, Sr), an in vitro enzy-molysis method has been applied to investigate the solubilization of the analytes from fodder in a simulated ruminant digestion [103], The effect of inhibitors of fission product solubility was also considered and essential elements were determined simultaneously to evaluate potential nutrition problems for the animals from the use of such inhibitors. Selective leaching of individual classes of metal complexes with different ligands and sequential enzymolysis have been recently applied to estimate the potential bioavailability to humans of Cd and Pb in cocoa powder and related products [104]. 

Slaveykova VI, Wilkinson KJ. 2005. Predicting the bioavailability of metals and metal complexes critical review of the biotic ligand model. Environ Chem 2 9-24. 

Often overlooked in the evaluation of the effects of diet upon mineral availability is the role that food processing plays in the formation of or breaking of ligand-metal complexes. Several individual or unit processing steps are needed to produce a soy concentrate, a bread or a spray-dried egg white. Some or all steps may have a bearing upon final mineral bioavailability. Soy concentrate from company A is not produced in precisely the same manner as from company B. In fact, lot to lot variation for the same product may be quite variable, particularly in mineral content. 

TCs are well documented to bind various metal ions, including alkaline earth metals, Al(ni) and transition metals VO(II), Cr(III), Mn(II), Fe(II/III), Co(II), Ni(II), Cu(II) and Zn(II) . TC can form 2 1 TC-metal complexes with transition metal ions in non-aqueous solution, in which the metal is bound at the 2-amido and 3-enolate chelating sites . TCs are present in plasma mainly in the Ca(II)-bound form or Mg(n)-bound form to a lesser extent, when they are not bound to proteins such as serum albumin. Thus, the bioavailability of TCs should be dependent upon the physical and biochemical properties of their metal complexes instead of their metal-free form. 

Many aspects of the redox chemistry, acid-base chemistry, and metal complexation chemistry of DOM are manifestations of the H/C and O/C ratios of the DOM. When a complete elemental composition is available, it is even possible to estimate quite well the relative proportions of aliphatic carbon, aromatic carbon, and other forms of carbon in DOM (Perdue, 1984, 1998 Wilson et al., 1987). From a biological and ecological perspective, the structural and compositional information that can be derived from a complete elemental analysis have been shown to relate directly to the bioavailability of DOM to bacterial assemblages in river water (Sun et al., 1997 Vallino et al., 1996 Hunt et al., 2000). 

The term bioavailability is often used in an absolute sense when a particular form of a nutrient is either available or not available to an organism. In the case of trace-metal complexes, which... 

Complexation is one of several ways to favorably enhance the physicochemical properties of pharmaceutical compounds. It may loosely be defined as the reversible association of a substrate and ligand to form a new species. Although the classification of complexes is somewhat arbitrary, the differentiation is usually based on the types of interactions and species involved, e.g., metal complexes, molecular complexes, inclusion complexes, and ion-exchange compounds. Cyclodextrins (CDs) are classic examples of compounds that form inclusion complexes. These complexes are formed when a guest molecule is partially or fully included inside a host molecule e.g., CD with no covalent bonding. When inclusion complexes are formed, the physicochemical parameters of the guest molecule are disguised or altered and improvements in the molecule s solubility, stability, taste, safety, bioavailability, etc., are commonly seen. 

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