Theoretical-computational comparative study of the persistent organic pollutants 2,3,7,8-tetrachloro dibenzo-p-dioxin (tcdd) and 2,3,7,8-tetrachloro dibenzo furan (tcdf)adsorption, detection and permeability

Abstract

In today's world, the great pollution puzzle is undoubtedly the greatest challenge facing the world's population. The reduction of pollutant emissions, the elimination of pollution already generated and the study of the interaction of these pollutants with living beings are the three fundamental pillars in research related to the problem of pollution. In this sense, the role of computational modelling of these types of systems ranges from the study of their biological activity to the search for an effective detection method and sustainable treatment. With advances in materials science, there are now different substrates that can be used in the treatment of different pollutants, either as a base for detectors or acting more actively as filters or adsorbents. In addition to activated carbon, which is widely used for this purpose, there are different carbon allotropes, such as fullerenes, nanotubes or graphene and graphite sheets, with great potential for the detection and adsorption of toxic compounds. Graphene sheets are of great interest, mainly due to their versatility, standing out in molecular detection, so they can be important in the treatment of pollutants. Materials such as white graphene, structurally analogous to graphene but consisting of borazine (boron-nitrogen) rings, or hybrid boron-nitrogen-carbon (h-BNC) structures, could also have a high potential in this field. In particular, they could be used as substrates in molecular detection techniques based on linear optical response, such as SERS (Surface Enhanced Raman Spectroscopy), or non-linear, such as SEHRS (Surface Enhanced HyperRaman Spectroscopy), given the similarities between the electronic properties of these materials and graphene. The latter is already used as a substrate in SERS, a technique known as GERS (graphene enhanced Raman spectroscopy). However, it is worth mentioning that the greater the knowledge of the mechanism of action of these substances in biological systems, the more efficient will be the design of new materials for their detection and elimination, achieving, from a theoretical point of view, a complete view of the problem. Information on the uptake and diffusion of toxic molecules into cell membranes is still uncertain. Several observations indicate that, although present in many organs and tissues, the most toxic pollutants accumulate mainly in fatty tissues due to their hydrophobic character. In this way, cell membranes behave as storage reservoirs for contaminants, becoming an internal source of chronic exposure to contaminants. The complexity of these biological membranes, together with the lack of experimental data, makes the mechanism of cellular uptake and distribution of contaminants within them the great unknown to elucidate their toxicokinetics. For a molecular description of the uptake process, as well as the changes induced in the membranes due to the molecules absorbed into the medium, the intermolecular interactions between the contaminants and the membranes must be known in detail. The combination of quantum calculations and molecular dynamics techniques allows the study of this type of large systems. This thesis proposes a complete theoretical study that encompasses the interaction of these new materials with the main chemical agents within the persistent organic compounds (POPs), which are of general interest to society, together with the study of their behaviour in biological systems. The combination of both lines would give a complete vision of the action, detection and treatment of these substances and a global perspective within the same problem.