X-ray luminescent nanocomposite LaF3:Tb/Citr@[Ru(bpy)2(nic)2]2+ as a model targeted delivery system for photopharmacology and photodynamic therapy

The study is devoted to the development of the concept of targeted delivery of pharmacological agents. A nanocomposite (NC) – (LaF3:Tb/Citr@RuBiNic), which is formed by luminescent nanoparticles (ScNPs) – LaF3: Tb/Citr and a photosensitive substance – [Ru(bpy)2(nic)2]2+ (where bpy = 2,2′ bipyridine and nic = nicotine (3-[(2S)-1-methylpyrrolidin-2-yl] pyridine) – (RuBiNic), in response to X-ray irradiation, emits quanta of visible light, as a result is released of a pharmacological agent – nicotine from the NC surface. In principle, when implementing the methods of photopharmacology, or photodynamic therapy, it allows controlling the desired physiological or therapeutic effect in a specific place and at the right time with high specificity of influence. To conduct research, LaF3:Tb/Citr nanoparticles were synthesized, and RuBiNic was used as a model photosensitive substance. The size and morphology (TEM), surface (FTIR-spectroscopy), thermogravimetric (TG/DTG/DTA) and X-ray structural analysis were carried out, SSA value and acid-base characteristics of the surface were determined. In the static mode at 25°С, the processes of adsorption immobilization of the RuBiNic complex on the surface of nanoparticles in the medium of an aqueous solution were investigated. Diffuse kinetics models, pseudo-first- and pseudo-second-order kinetics models, Langmuir and Freundlich models were used to quantitatively describe the equilibrium adsorption processes. The kinetics of RuBiNic adsorption is characterized by a mixed-diffusion mechanism. The pseudo-second-order model was also found to have a higher correlation coefficient than the pseudo-first-order model, confirming the chemisorption process. The data of fitting the adsorption isotherm according to the Langmuir adsorption model (r2 = 0.99) indicate chemisorption of RuBiNic on the surface of ScNPs LaF3:Tb/Citr with a maximum adsorption capacity of 7.47 mg⋅g−1. The obtained data are useful for optimizing the conditions of adsorption immobilization of molecules of photosensitive substances on the surface of phosphors based on lanthanum fluoride. The LaF3:Tb/Citr@RuBiNic system shows potential for future applications in photopharmacology and X-ray photodynamic therapy.