Adsorption of explosive molecules on human hair surfaces

The molecular mechanics (MM) and density functional theory (DFT) methods were used to study the role of hair structure on the adsorption of various explosive molecules (TATP, TNT, NG, EGDN, and RDX). The present study is limited to adsorption of explosives onto the hairs outer surface while possible diffusion into deeper layers in the hair is neglected. The adsorption properties of the hair surface are estimated from changes in the Gibbs free energy. The calculations suggest that the molecular adsorption of all explosives examined is due mainly to interaction between the molecule and the lipid layer that covers the hair surface. The binding of explosive molecules to the lipid layer consists of interplay between dispersive and Coulomb interactions as well as the distortion of the lipid layer induced by the molecular adsorption. The relative importance of these effects depends on the chemical nature, the size, and the shape of the adsorbed molecule. Several possible adsorption positions, along the lipid molecules, were found for all adsorbates examined. The theoretical prediction that explosive molecules adsorption is mainly due to the interaction with the lipid layer was examined and partially proved experimentally. Moreover, comparison of the calculated results with available experimental data allowed us to obtain the temperature-dependent sticking probability of the various explosives to the hair surface.