Abstract

In this paper, we have extended our studies concerning aluminum (III) and aminoacid chain interactions. We focus on the sulfur containing aminoacid chains of Cysteine (Cys) and Methionine (Met) and analyze the interactions with the toxic aluminum (III) and the non-toxic magnesium (II) cations. We start with the simplest model representing the aminoacid and complete it adding methyl groups to model more accurately the aminoacid chain. We compare the results obtained for both cation complexes. Mg (II) was found to bind to all of the neutral ligands in this study with binding energies of 79, 97, 109, and 120 kcal/mol for SH$_2$, HSCH$_3$, CH$_{3}$SCH$_{3}$, and CH$_{3}$SCH$_{2}$CH$_{3}$, respectively while Al (III) bound only to the largest of these ligands (binding energy: 383 kcal/mol) and then in a bidentate form with a bond to both S and the terminal C. The binding to the anionic ligands was much stronger; binding energies of 351 and 360 kcal/mol are predicted for Mg(II) binding to SH$^-$ and SCH$_3^-$, respectively; for Al(III) those values are 702 and 741 kcal/mol. We also study the differences between these complexes and the complexes formed between these metal cations and the acid and acid derivative aminoacid chains studied in earlier works.