Abstract
In this thesis we have developed different controlled release devices using hybrid materials and their use as molecular gate.
It is developed, first, a method of controlled release of vitamin B2 or riboflavin (soluble vitamin needed for the metabolism of carbohydrates, fats and especially in the metabolism of proteins involved in oxygen transport) through the use of 'nanoscopic molecular gates’ prepared by anchoring of polyamines groups, which act as' molecular gate 'at the outer surface of the pores of mesoporous solids. The pH and the presence of certain anions will control the opening/closure state of the gate alowing the release of the vitamin that is encapsulated inside the pores. At acidic pH, amino groups at the surface are protonated and positively charged and, therefore, it has electrostatic repulsion, so the 'gate' remains closed. At neutral pH, due to the absence of electrostatic repulsion, so the 'gate' remains opened, resulting in the release of the vitamin.
Second, we describe the development, synthesis, characterization and operation of a mesoporous material loaded with a dye and functionalized with a disaccharide that acts as 'molecular nanoscopic gate', which is opened in the presence of an intestinal enzyme. The solid consists of a mesoporous material, MCM-41 loaded with a dye, [Ru(bipy)3]2+ and functionalized with an alkoxysilane derived from lactose disaccharide. Due to steric hindrance showed by the sugar, the pores are blocked. The presence of ß-D-galactosidase in the solution, enables the hydrolysis of O-glycosidic-bond linking the monosaccharides of lactose, being able to ‘open’ the pores and so allowing the release of the dye.
Third, we describe the synthesis of a nanodevice, which consists of MCM-41 mesoporous silica nanoparticles, functionalized on the outside of the pores with a starch derivative. The material is loaded inside first with a dye, [Ru(bipy)3]2+, necessary for monitoring the device. Then it is loaded with a cytotoxic, doxorubicin, capable of killing cancer cells. Preliminary controlled release studies show the ‘non’ release of dye or citotoxic in water at pH 7.5, and the almost total release in the presence of an aqueous solution at pH 7.5 with amylase (able to hydrolyse the glycosidic a1 ? 4 bond, linking glucose molecules present in the starch). Due to the presence of amylase in the lysosomes of cells, the nanodevice is used to study the controlled release of the dye or the cytotoxic, in intracellular enviroment. HeLa tumoral cells and LLC-PK1 nontumoral cells were used for feasibility testing of the solid loaded with the dye, which indicate the 'non' toxicity of the material. Internalization in HeLa cells via endocytosis is confirmed by confocal microscopy. The endocytic process targets the nanoparticles to lysosomes where the anchored starch is degraded by the lysosomal enzymes. Hydrolysis of the polysaccharide in the material loaded with the cytotoxic is confirmed by the significant cell death observed by confocal microscopy, as the cytotoxic is released inside the cells.
Finally, polyesters including azo groups are synthesized, characterized, grafted onto nano-silica mesoporous support and used as ‘nanoscopic molecular gates’. Due to the presence of the bulky polyesters functionalized with azo groups the release of cargo occluded inside the pores is blocked. The presence of esterases, able to hydrolyze polyesters, allowed the release of de entrapped cargo. HeLa tumoraland MCF-7 tumoral cells are used for feasibility testing, indicating the 'non' material toxicity. Internalization via endocytosis and cargo release, thanks to the esterases present in the lysosomes, in HeLa cells are confirmed by confocal microscopy.