Novel approaches for the development of chromo fluorogenic chemosensors for detection of cu(ii) and biothiols

Resumen

Abstract This PhD thesis entitled "Novel approaches for the development of chromo-fluorogenic chemosensors for detection of Cu(II) and biothiols" is devoted to the synthesis, characterization and coordination behaviour of new chromo-fluorogenic probes for the recognition and detection of Cu(II) cations and biothiols (glutathione, cysteine and homocysteine). These new probes, which selectively detect Cu(II) cation through colour and/or emission changes, are constructed using a paradigm in which the binding units are included into the signalling unit structure. Besides, some of the Cu(II) complexes of these new probes are used for the chromo-fluorogenic detection of biothiols using displacement reactions. The first chapter of this PhD thesis gives an overview about the conceptual framework in which are located the studies presented in this thesis, which combine concepts related with supramolecular chemistry, optical sensors and molecular probes. In the second chapter, the general objectives of this PhD thesis are presented. The third chapter is devoted to the synthesis and characterization of 4-(4,5-diphenyl-1H-imidazole-2-yl)-N,N-dimethylaniline, a chromo-fluorogenic probe for selective Cu(II) detection in aqueous environment. Water-acetonitrile 1:1 (v/v) solutions of this probe presented a marked absorption band at ca. 320 nm that is selectively red-shifted (to 490 nm reflected in a colour change from colourless to reddish-brown) upon addition of Cu(II) cation. This shift was ascribed to the formation of a non-emissive 1:1 stoichiometry complex in which Cu(II) coordinated with the nitrogen atoms of the imidazole ring. Besides, this Cu(II) complex was used for the selective and sensitive detection of glutathione, which induced the disappearance of the 490 nm absorption with a marked colour change from reddish-brown to colourless. Also a marked emission at 455 nm was observed after glutathione addition. These optical changes were ascribed to a glutathione-induced demetallation process which generated the free probe. In addition, the Cu(II) complex detected glutathione with a remarkable limit of detection as low as 2.0 ¿M. The fourth chapter presented an imidazole-based probe functionalized with two thiophene subunits for the selective detection of Cu(II) cation and biothiols. Water-acetonitrile 9:1 (v/v) solutions of the free probe showed an absorption band at 320 and a marked emission at 475 nm. Of all the cations tested, only Cu(II) induced an emission quenching with a significant colour change from colourless to deep blue (appearance of a new absorption band centred at 555 nm). These remarkable optical changes were ascribed to the formation of 1:1 stoichiometry complexes in which the metal cation coordinated with the nitrogen atoms of the imidazole heterocycle. Besides, the optical response of the Cu(II) complex was tested in the presence of selected amino acids. Of all the amino acids tested, only glutathione, cysteine and homocysteine induced a marked bleaching of the complex solution with a remarkable growing of an emission band centred at 475 nm. These optical changes were ascribed to a demetallation process induced by the coordination of biothiols with Cu(II). Furthermore, viability assays indicated the non-toxicity of the probe for HeLa cells. Also, the probe was successfully employed to detect Cu(II) in HeLa cells using confocal microscopy. The fifth chapter presented the synthesis and characterization of three probes containing N,N-diphenylanilino (as a donor group) and different ¿-spacers (benzene and thiophene) connected with aldehyde moieties. Absorption spectra of the three probes in acetonitrile showed an intense absorption band in the UV-visible region (360-420 nm range) which can be attributed to an intramolecular charge-transfer transition as consequence of the presence of N,N-diphenylanilino electron donor moiety directly linked to (hetero)aromatic bridges functionalized with the aldehyde electron.