Copper predominance speciation

The stability and solubility constants derived at 25 °C for zero ionic strength have been used to create a predominance speciation diagram for copper(II). The diagram is illustrated in Figure 11.86. The diagram is based on the assumption that the dominant solid crystalline phase is spertiniite, Cu(OH)2(s). It also shows... 

Chemical models for the speciation of Cu in freshwater (Millero, 1975) predict that free Cu (aq) is less than 1% of the total dissolved Cu and that Cu(C03)i and CuCO are equally important for the average river water. Leckie and Davis (1979) showed that the CuCO complex is the most important one near the neutral pH. At pH values above 8, the dihydroxo-Copper(ll) complex predominates. The chemical form of Cu is critical to the behavior of the element in geochemical and biological processes (Leckie and Davis, 1979). Cupric Cu forms strong complexes with many organic compounds. 

The most definitive assessment of the metal composition of metalloproteins comes from the application of element-specific detection methods. CE-ICP-MS provides information not only about the type and quantity of individual metals bound to the proteins but also about the isotopes of each element as well [11,12]. Elemental speciation has become increasingly important to the areas of toxicology and environmental chemistry. Such analytical capability also opens up important possibilities for trace element metabolism studies. Figure 1 depicts the separation of rabbit liver metallothionein containing zinc, copper, and cadmium (the predominant metal) using CE-ICP-MS with a high-sensitivity, direct injection nebulizer (DIN) interface. UV detection (200 nm) was used to monitor the efficiency of the CE separation of the protein isoforms (MT-1 and MT-2), whereas ICP-MS detection made it possible to detect and quantify specific zinc, copper (not shown), and cadmium isotopes associated with the individual isoform peaks. 

These findings have important implications for methane oxidation in natural samples. First, they suggest that the pMMO is the predominant enzyme system for methane oxidation in natural populations and thus provide more impetus for understanding this enzyme system. Second, the response of natural populations to changes in methane concentrations will most likely depend on a complex set of parameters, of which available copper concentration may be the key. It is now important to study how methanotrophs utilize copper and how they respond to changes in copper and methane concentrations and to copper speciation, in order to predict how natural populations will respond to environmental perturbations. 

The general trend for spring is that the majority of metals are found in the lower molecular weight fractions and therefore can be considered to be soluble. Calcium was found for the most part in the lowest molecular weight fraction, whereas the major trace metals were found predominately in the 1-lOK fraction. ASV measurements for copper, cadmium, and lead showed no detectable free or labile metal. These results, combined with the molecular size distribution of metals in proportion to organics, indicate that metal speciation in the upper Mississippi and Minnesota Rivers is dominated by organometallic interactions. 

Although concentrations in soils did not exceed the geochemical background, zinc turned out to be more mobile than copper. Mobile (fraction 1) and exchangeable (fraction 2) fractions of both metals corresponded very well with each other, reflecting first of all soil texture and the clay content. However, while fractions 4 and 2 were the main fractions of copper in most soils, the predominant concentrations of zinc were found in fractions 7 and 6, in sandy soils in fractions 6 and 2. Detailed results of metal speciation are presented in Tables 6.4-6.6 (on the following pages). 

Figure 11.86 Predominance diagram for the speciation of the copper(ll) ion at 25°C. The behaviour in the region of -log [H+]> 12 should be treated with caution due to changes...

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