A detailed structural characterization of organo-clays is a key in understanding their properties. In this work, mono-, di-, tri-, and tetra-butylammonium (nBA; n = 1–4) cations intercalated in the layered clay mineral montmorillonite (Mnt) have been studied for the first time by combining a theoretical approach based on density functional theory (DFT) and infrared spectroscopy. The DFT calculations revealed the detailed structure and position of nBA cations in the interlayer space. A relation between the basal spacing (d001 parameter) and the cation size and structure was found, and explained with respect to the structure, composition, and size of the organic cations. Hydrogen bonds between -NHx/-CH3/-CH2 groups of the nBA cations and oxygen atoms of the basal planes of the Mnt layers were found to be an important factor for the arrangement and energetic stabilization of cations in the interlayer space. The N-H-O hydrogen bonds are stronger than C-H-O hydrogen bonds and the stabilization decreases with decreased number of bands. Analysis of DFT-calculated vibrational modes helped in understanding a problematic region of the experimental infrared spectra (4000–3000 cm-1), in which assignment of all vibrational modes unambiguously was not possible because of a significant overlap of broad bands.

Safety issues for the use of products containing nanoparticles need to be considered, since these nanoparticles may break through human skin to damage cells. In this paper, applied mathematical techniques are used to model the penetration of a spherical gold nanoparticle into an assumed circular hole in a lipid bilayer. The 6–12 Lennard-Jones potential is employed, and the total molecular interaction energy is obtained using the continuous approximation. Nanoparticles of three different radii, namely, 10, 15 and 20 Å, are studied, which are initiated at rest, confined to the axis of the hole. A similar behaviour for these three cases is observed. The critical hole radii at which these nanoparticles enter the bilayer are 12.65, 17.62 and 22.60 Å, respectively. Further, once the hole radii become larger than 20.79, 23.14 and 27.02 Å, respectively, the gold nanoparticles tend to remain at the mid-plane of the bilayer, and do not pass through the bilayer.