Molecular Interactions between Orinoco Belt Resins

This paper describes the characterization of structural, energetic, and electric properties of the molecular complexes between Orinoco belt resins through the application of computational molecular mechanics (MM), semi-empirical parametrization (PM6), and density functional theory (DFT) (PW91 and HCTH) in conjunction with the double numeric and polarized (DNP) basis set. The resin sources for the studied molecules are Orinoco belt vacuum residues (Carabobo, Hamaca, Merey, Merey-Mesa, and Zuata). Molecular structures of these compounds were proposed from analysis of experimental characterization. The study of molecular interactions has shown that these resins are able to form stable van der Waals complexes, where their computed stability has a large dependence upon the applied theory level. A qualitative description of the formation of these complexes could be obtained with these methodologies. In particular, MM overestimates resin interaction energies when compared to PM6 and DFT (PW91 and HCTH) results. However, the HCTH/DNP approach leads to interaction energy values for resin-resin complexes that lie in the range from -2.39 to -7.09 kcal/mol, in better agreement with literature reports and chemical expectations than PW91/DNP interaction energy values. The stability of these complexes and the strength of the resin self-association can be rationalized considering their chemical nature and the induced electric properties (dipole moment and polarizabilities) by molecular interactions. Additionally, inclusion of dispersion in the DFT calculations of the resin molecular complexes improves the energetic pattern of the studied molecules significantly.