Síntesis y estudio comparativo de nuevos receptores de aniones que actúan mediante enlace de hidrógeno, halógeno o calcógeno

Abstract

The main objective of this PhD thesis is the synthesis and study of new receptors that act through unconventionals non-covalents interactions in the anion recognition. To reach this objective we have chosen the 1,4-naphthoquinone, 3-iodo-1,4-naphthoquinone, thiophene, selenophene or tellurofene as anion recognition binding sites. The binding mode of the anion receptors has been studied by nuclear magnetic resonance experiments (1H , 77Se y 125Te NMR) and computational calculations. In addition, anion sensing capabilities have been studied by ultraviolet-visible absorption (UV Vis) and fluorescence emission spectroscopies. In Chapter 1 have been described the synthesis and study of four anion receptors based on two units of 1,4-naphthoquinone or 3-iodo-1,4-naphthoquinone linked to a benzene or pyridine as central spacer by an ester bond (6-9). Receptors 6-9 form complexes with stoichiometry receptor:anion 2:1 with SO42- in acetonitrile. The non covalents interactions involved are: four hydrogen bonds C (sp2) Holefinic···A- differents or four halogen bonds C (sp2) I···A- with the oxygen atoms of the anion. The experiments performed showed that the halogen bond favors the recognition of the SO42-. The recognition of this anion nake eye observed due to the apparition of a strong emission band, therefore, receptors 6-9 are highly selective fluorescent molecular sensors of the SO42- anion. On the other hand, the chemical structure of the 6-9 receptors is modified in the presence of the F-, H2PO4-, HP2O73-, CH3CO2- and C6H5CO2- anions, causing a color change from colorless to orange, therefore, receptors 6-9 act as good colorimetric chemodosimeters of the mentioned anions. In Chapter 2 have been described the synthesis and study of two receptors analogous to studied in Chapter 1, but in which the 1,4-naphthoquinone unit is linked to the central spacer by an amide bond (11 and 12). Receptors 11 and 12 form complexes with the F-, H2PO4-, HP2O73-, CH3CO2- and C6H5CO2- anions through a combination of hydrogen bonds with the following hidrogen atoms: H of the amide group, H olefinific of the 1,4-naphthoquinone unit and the H aromatic at position 3 of the benzene ring used as central spacer. This recognition cause a change color from colorless to orange in a solution of the receptors 11 and 12 in tetrahydrofuran, therefore, the receptors 11 and 12 act a good colorimetric molecular sensors of the anions mentioned above. Finally, in Chapter 3 have been described the synthesis and the anion binding studies of a family of anion receptors based on thiophene, selenophene and tellurofene heterocycles (16-28) as dadors-groups of a new type of non-covalent interaction: the chalcogen bond. Receptors 16-28 forms complex with Cl- and Br- anions in tetrahydrofuran through a combination of hydrogen- and chalcogen-bond interactions. In the receptors that contain the tellurofene heterocycle, the chalcogen bond always dominates the recognition process, however, if the receptors are based in the thiophene or selenophene heterocycles, the incorporation of a perfluorobenzene ring that activates the atom of S or Se is necessary so that chalcogen bond is involved in the recognition process. This shows the great capacity for anion recognition of the Te atom compared to the S and Se atoms.