Anions as Triggers in Controlled Release Protocols from Mesoporous Silica Nanoparticles Functionalized with Macrocyclic Copper(II) Complexes

Three different mesoporous silica nano-sized materials (SC1, SC2, and SC3), loaded with [Ru(bipy)(3)](2+) dye (bipy= bipyridine) and functionalized on the external surface with three macrocyclic copper(II) complexes (C1, C2, and C3), were synthesized and characterized. When SC1, SC2, and SC3 were suspended in water, the entrapped [Ru(bipy)(3)](2+) dye was free to diffuse from the inner pores to the solution. However, addition of anions induced certain degrees of pore blockage, with subsequent dye release inhibition. Small monovalent and divalent anions were unable to induce complete pore blockage, whereas bulky and highly charged anions induced marked reductions in [Ru(bipy)(3)](2+) delivery. The best [Ru(bipy)(3)](2+) delivery inhibitors were ATP and hexametaphosphate anions. Inhibition was ascribed to the interaction of the anions with the grafted Cu-II complexes on the surface of the SC1, SC2, and SC3 supports. The hexametaphosphate anion was selected to prepare two capped materials (SC1-mPh and SC3-mPh). Studies of the [Ru(bipy)(3)](2+) dye release from solids SC1-mPh and SC3-mPh alone and in the presence of a collection of selected anions (HS-, F-, Br-, Cl-, I-, CN-, HPO42-, AcO-, citrate, NO32-, HCO3-, SO42-, and S2O82-), amino acids (alanine and histidine), thiol-containing biomolecules (cysteine, methylcysteine, homocysteine, and glutathione (GSH)), and oxidants (H2O2) were performed. None of the chemicals tested, except hydrogen sulphide, was able to induce remarkable cargo delivery in both solids. The observed dye release was ascribed to a demetalation reaction of the C1 and C3 complexes induced by the hydrogen sulphide anion.