Assessing the dispersive and electrostatic components of the selenium-aromatic interaction energy by DFT.

Selenium has been increasingly recognized as an important element in biological systems, which participates in numerous biochemical processes in organisms, notably in enzyme reactions. Selenium can substitute sulfur of cysteine and methionine to form their selenium analogues, selenocysteine (Sec) and selenomethionine (SeM). The nature of amino acid pockets in proteins is dependent on their composition and thus different non-covalent forces determine the interactions between selenium of Sec or SeM and other functional groups, resulting in specific biophysical behavior. The discrimination of selenium toward sulfur has been reported. In order to elucidate the difference between the nature of S-π and Se-π interactions, we performed extensive DFT calculations of dispersive and electrostatic contributions of Se-π interactions in substituted benzenes/hydrogen selenide (H2Se) complexes. The results are compared with our earlier reported S-π calculations, as well as with available experimental data. Our results show a larger contribution of dispersive interactions in Se-π systems than in S-π ones, which mainly originate from the attraction between Se and substituent groups. We found that selenium exhibits a strong interaction with aromatic systems and may thus play a significant role in stabilizing protein folds and protein-inhibitor complexes. Our findings can also provide molecular insights for understanding enzymatic specificity discrimination between single selenium versus a sulfur atom, notwithstanding their very similar chemical properties.