Energetics and structure of Langmuir monolayers of palmitic acid: a DFT study

Abstract

Langmuir monolayers are monomolecular wide films composed of amphiphilic molecules with a bi-dimensional structure typically formed at the air–water interface.

Langmuir-Blodgett monolayers holding a wound healing active compound and its effect in cell culture. A model for the study of surface mediated drug delivery systems

“…The negative values imply that both structures are possible in the formation of stable monolayers. Moreover, since the difference in formation energy is only 0.09 eV, which is in the order of the precision of the calculations [39], both structures coexist, as it is expected in the fluidic Langmuir monolayer, which has characteristics of bidimensional liquid [19].…”

“…The calculations were made with Vanderbilt ultrasoft pseudopotentials and Perdew Burke Ernzerhof (PBE) simplified generalized gradient approximation [38] exchange-correlation functional, using a plane wave cut-off of 750 eV at the Γ-point, with a convergence threshold for the total energy set to 0.0001 eV. Surfactant-surfactant interactions greatly influence the physicochemical properties of Langmuir monolayers; therefore, the dihydrogen (intermolecular van der Walls) interactions critically contribute to the packing energy, and to the monolayer formation [39]. As consequence, the DFT-D2 [40,41] approach was implemented in the calculations to include this type of forces.…”

“…As consequence, the DFT-D2 [40,41] approach was implemented in the calculations to include this type of forces. The crystallographic structures of PA Langmuir monolayers were created based on the optimized structures of Toledano et al [39] and conserving the area per molecule found experimentally here. Each unit cell contains two PA molecules with approximately 1.4 a/b ratio, which has been related to the herringbone (HB) structure [42].…”

“…The computational simulations of pure surfactant clusters and bidimensional liquid composites in Langmuir films using ab initio quantum chemistry methods is a challenging task, due to the complexity of the interactions present in the Langmuir monolayers, and to the large number of atoms that contains their long amphiphilic chains [39]. Here we reported the results of the theoretical studies using DFT to describe the structures underlying both, PA and PA-MT monolayers.…”

Theoretical Description of Mixed Film Formation at the Air/Water Interface: Carboxylic Acids–Fatty Amines

“…Fewer theoretical papers have been devoted to the behavior simulation of individual surfactants and their mixtures during film formation. , Previously, we developed an approach to describe 2D clusterization of pure nonionic surfactants (carboxylic acids, , amines, etc.) at the air/water interface in the framework of quantum chemical modeling (PM3).…”