The chemistry of complexation or chelation as it is commonly known has created a great deal of confusion in the animal feed industry. Terms such as metal amino acid complexes, metal amino acid chelates, metal polysaccharide complexes and metal proteinates abound, yet official definitions remain vague and unhelpful. Richard Murphy at Alltech’s European Bioscience Centre discusses important factors in mineral chelation.
‘Organic Trace Minerals – Enhancing Mineral Bioavailability Through Chelation’
Typically speaking, chelates are prepared by reacting inorganic mineral salts with, for example, enzymatically prepared mixtures of amino acids and small peptides, under controlled conditions. Such amino acid and peptide ligands bind the metal at more than one point ensuring that the metal atom becomes part of a biologically stable ring structure. Many different assertions are made as to the relative merits and suitability’s of amino acids versus peptides in forming mineral chelates, with an even greater number of arguments existing in relation to the so-called bioavailability of such products.
The role of bond strength on OTM stability
Most amino acids and peptides bind metal ions though either nitrogen, oxygen or sulphur atoms. Individual amino acids exhibit a range of stabilities when complexed with mineral and these can be assessed in a variety of databases. It is reasonable to expect that peptides which have a greater number of donor atoms and hence the potential to form a number of chelate rings when binding to a metal ion would have higher stabilities than simple amino acids such as glycine. This is however dependent on the peptide being able to actually form more than one chelate ring. As in the case of amino acids, peptides also exhibit a range of stabilities.
Consider the data in the table below which compares a range of ligands when complexed with copper under the same physiological conditions.
What this indicates is that the size of the bonding group is not the most critical factor influencing bond strength and ultimately stability of a chelate. Claims of superiority based on size clearly have little merit. However, simply increasing the number of amino acids in a ligand may not increase the stability of the metal complex and thus may not necessarily increase the relative proportion of bound mineral. Ultimately, not only does the type of amino acid influence the stability of a given chelate but the position of amino acids in a peptide can also significantly influence how the ligand and mineral interact.
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