Microsolvation of lithium–phosphorus double helix: a DFT study

Abstract

The chemistry of complexes becomes interesting due to their structural diversity in different environments like in aqueous phase, in gas-phase or in the interior of a host. In the last few decades, powerful tools for the determination of gas-phase have been developed. In this context, the microsolvation approach of Li7P7 helix, where the passage from the bare double-strand helix to the hydrated denatured helix, has been addressed through successive attachment of water molecules using density functional theory. The stability of helical structure of the small clusters has been analyzed on the basis of polar bonding interaction between oxygen end of water molecule and Li centers of the Li7P7 helix. The Li7P7 helix is favored when associated with zero to eight water molecules, but the binding of the ninth water molecule brings a drastic change in the structure. Our results suggest that the natural charges on some sites in Li7P7 are large enough to induce partial and eventually total dissociation of water molecules. We shed light on the bonding situation through natural bond orbital, quantum theory of atoms in molecules and energy decomposition analyses which suggest dominant electrostatic interaction between Li centers of Li7P7 and O centers of water molecules (accounting for 60–64% of total bonding attraction). Nevertheless, 31–36% of total attraction is also originated from the orbital interaction. Variation in reactivity on microhydration is also analyzed. In order to check the site selectivity, we have computed conceptual density functional theory-based local reactivity descriptors such as dual descriptor based on the Fukui function, Δf(r), and multiphilic descriptor based on the philicity, Δω(r).