Understanding the Chemistry of Lead at a Molecular Level: The Pb(II) 6s6p Lone Pair Can Be Bisdirected in Proteins

Pb(2+) complexes can attain several different topologies, depending of the shape of the Pb 6s6p lone pair. In this paper, we study structures with a bisdirected Pb lone pair with quantum mechanics (DFT) and QM/MM calculations. We study small symmetric Pb(2+) models to see what factors are needed to get a bisdirected lone pair. Two important mechanisms have been found: First, the repulsion of the lone pair of Pb(2+) with other lone pairs in the equatorial plane leads to a bisdirected structure. Second, a bisdirected lone pair can also arise due to interactions with double bonds, lone pairs, or hydrogen atoms. Moreover, we have analyzed Pb(2+) sites in proteins and to see if a bisdirected lone pair can exist in an asymmetrical environment. Several instances of bisdirected lone pairs were discovered.