Water-induced functional Supramolecular Solvents: modeling, characterization and analytical applications

Abstract

The content of this Doctoral Thesis has been structured in four chapters preceded by a general Introduction in which the theoretical and practical aspects related to the synthesis, modeling possibilities and application of supramolecular solvents (SUPRAS) as well as the encapsulation of lipophilic bioactive substances in nanostructured lipid carriers are discussed. Below, the content of each chapter is described: Chapter I: Volatile amphiphile-based supramolecular solvents for reducing phospholipid-based matrix effects in LC-MS/MS The research presented in this chapter has focused on the synthesis and characterization of volatile SUPRAS with restricted access properties for the elimination of matrix effects in the analysis of biological samples by LC-MS/MS. For this purpose, a SUPRAS has been synthetized from hexanol in THF solutions by the addition of water as coacervating agent. The phase diagram for this ternary mixture was constructed, delimiting the SUPRAS region, and its composition was investigated according to the environmental conditions established for the self-assembly of hexanol. The equation predicting the volume of SUPRAS formed as a function of environmental conditions was established. As in the case of other alkanols, hexanol aggregates in the SUPRAS as inverse hexagonal structures in which the alcohol groups surround aqueous cavities while the hydrocarbon chains are dispersed in THF. The ability of the SUPRAS synthesized for the removal of matrix effects in bioanalysis was investigated by the determination of bisphenol A (BPA) in urine. The insitu formation of SUPRAS in this matrix and the removal of proteins and phospholipids were investigated. It was demonstrated that supramolecular extracts can be analyzed directly by LC-MS/MS avoiding matrix effects, which allowed the quantification of BPA via external calibration. BPA was quantitatively extracted in the SUPRAS (recoveries in the 96-107% range). The limit of quantification of the method for BPA was 0.025 ng/mL. The method was applied to the quantification of BPA in urine samples. Chapter II: Supramolecular solvents formed by oligomeric surfactants to reduce surfactant losses in the equilibrium solution The research carried out in this chapter has focused on the synthesis and characterization of SUPRAS obtained from solutions of poly-undecylenic acid (an oligomeric surfactant) in THF or ethanol, using water as coacervating agent. A comparative study of both ternary mixtures has been performed in terms of phase diagrams, the chemical composition of SUPRAS generated from different environmental conditions, the volume of SUPRAS formed and structural characteristics. Different equations have been derived, generated as a function of the composition of the synthetical solution, for predicting the volume and chemical composition of these SUPRAS. The hypothesis of the oligomer being completely incorporated into the SUPRAS was fully demonstrated. This property will make possible the application of this novel SUPRAS to wastewater treatment and to the analysis of pollutants when the use of high volumes of water is required. Chapter III: High thermally stable supramolecular solvents applicable to headspace gas chromatography The research described in this chapter is focused on the synthesis of SUPRAS from solutions of the oligomer poly-undecylenic acid in tetraglyme via the addition of water as coacervating agent. The phase diagram from this ternary mixture was constructed, delimiting the SUPRAS formation region, that was also characterized in terms of chemical composition and physical properties such as thermal stability. The applicability of these SUPRAS in headspace gas chromatography (HS-GC) was investigated by the direct analysis of the extracts obtained from the extraction of residual solvents in pharmaceutical products. The methodology developed allowed the quantitative extraction of the different legislated classes of residual solvents (37 solvents belonging to classes 1, 2A, 2B and 2C) and their determination by HS-GC-MS. The determination of the 2C class solvents by previously described procedures is very complex due to their high boiling points. It was demonstrated that the method can be applied to a wide variety of pharmaceutical products. The method was also validated according to the criteria established in the relevant legislation [ICH Q2 R1]. Chapter IV: Multifunctional supramolecular solvents for the combination of the extraction and encapsulation of lipophilic bioactive components The research described in this chapter has been developed in the ―lnstitut National de la Santé et de la Recherche Médicale Unit 1148" in Paris, during the stay of the PhD student in this center. This research has aimed at the combination of SUPRAS and nanostructured lipid carriers (NLCs) for the effective extraction, stabilization and encapsulation of lipophilic bioactive compounds. For this purpose, SUPRAS previously described by the SAC research group for the extraction of astaxanthin from Haematococcus pluvialis and formed by octanoic acid in ethanol-water have been used. In previous research, the SAC group has demonstrated that these SUPRAS with restricted access properties quantitatively extract astaxanthin and are able to produce oleoresins that show the same composition as those obtained by extraction with supercritical fluids (SFE), but at a much lower cost. The oleoresins thus obtained were used as the liquid lipid fraction to get SUPRAS-NLCs. The synthetized nanoparticles were characterized by several different techniques: DLS, AFM and Cryo-SEM microscopy, indicating that spherical particles with an approximate size of 100 nm were formed. Their antioxidant activity was determined by ORAC and α-TEAC and its ability to inhibit ROS in vitro was assessed by the DHE probe. The results showed that the SUPRAS-NLCs here synthetized exhibit an exceptional stability (at least 6 months at 4ºC) when compared to previous research. This Report also includes a section in which the main conclusions derived from the obtained results are discussed. Finally, appendix A lists the scientific papers published in specialized international journals derived for this Thesis and, appendix B, the contributions made to national and international conferences.