Factors that affect the stability of metal-ligand interactions

FACTORS THAT AFFECT THE STABILITY OF METAL-LIGAND INTERACTIONS 

On taking a sample from the organism, changes occur in pH, ionic charge, ionic composition, temperature, and enzyme activity. Furthermore in response to this trauma a number of biochemical reactions are triggered. 

In order to reduce the effect of some of these changes, it is essential that samples are either processed soon after collection or stored at temperatures below -20°C. A temperature of -130°C may be required in order to maintain the integrity of cell membranes. However, it has recently been shown that some urinary enzymes rapidly lose activity when stored at low temperatures (Matteucci et al., 1991). It is therefore essential when studying the chemical forms of an element in a given sample to examine the effect of storage on the distribution of the chemical species. 

According to Vallee and Coleman (1964) the association between metals and proteins can be divided into two groups namely metalloproteins and metal-protein complexes. In metalloproteins the metal forms an integral part of the protein structure, and it is present in stoichiometric amounts. Furthermore, the metal is not lost during the purification step. The transition metals have a tendency to form this type of association. These complexes have high thermodynamic stability and are relatively inert. On the other hand, in metal-protein 

Both the thermodynamic stability and the reactivity of a complex are influenced by the changes in experimental conditions such as pH, ionic strength, temperature, and redox potential. 

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