NMR studies of copper speciation in the bovine rumen environment

Abstract

Dietary copper supplements containing complexed copper have been asserted to be more bioavailable than `inorganic' supplements. Since bioavailability is intimately related to the particular metal ion species that exist in any given environment, studies of solution speciation can be used to examine this assertion. In a previous study, our computer modeling of copper speciation in bovine saliva indicated that when a lysine-complexed copper supplement is used, the complex will not persist. In the present study, these conclusions are supplemented and extended using 1H NMR experiments. Lysine and the copper(II)–lysine system are characterized, and chemical shifts of the individual species obtained. Chemical shift values for the copper(II)–lysine–bovine saliva system can then be predicted. Results show good agreement with experimental values. The scope of the computer modeling is then expanded to include the major low molar mass ligands present in the rumen. Implications of the results are discussed. The validity of this rumen model is further evaluated by NMR investigations on biological samples. The study provides further evidence that complexes such as copper(II)–lysine would disintegrate in the gastrointestinal tract, and are unlikely to be absorbed intact.