Theoretical Studies of Metal Ion Selectivity. 3. A Theoretical Design of the Most Specific Combinations of Functional Groups Representing Amino Acid Side Chains for the Selected Metal Ions (Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, and Hg²⁺)

Theoretical efforts to devise the most selective combinations of amino acid (AA) side chains (i.e., metal-binding sites) for six studied metal ionsCo2+, Ni2+, Cu2+, Zn2+, Cd2+, and Hg2+have been accomplished in this work. Utilizing the results of the preceding two articles of the series, the complexation energies of these ions have been calculated for each combination of simple functional groups representing AA side chains in four coordination geometries (linear, tetrahedral, square planar, and octahedral) according to the approximate formula derived recently. To eliminate the errors of 5−15 kcal mol-1 inherent in approximate calculations, 10 potential candidates for the most specific site for each ion have been subject to a rigorous quantum chemical investigation. It resulted in the calculations of their complexation energies in 50 different sites and the final assignment of three or four most specific sites for each of them. As the calculated results were obtained by the “gas-phase model chemistry”, a part of discussion is devoted to the accuracy and limitations of the above predictions.