Silica and silica organically modified nanoparticles: Water dynamics in complex systems

Four silica-based porous nanosystems were synthesized with different organic substitutes and the molecular dynamics of water in these constrained environment was investigated. The nanosystems were silica and three organic modified silica nanoparticles (NP) with diameters in the range 80-300 nm with different porous dimensions, surface areas, and surface properties (e.g. hydrophilicity/hydrophobicity). Molecular dynamics was studied by pulsed field gradient NMR and by proton spin-lattice relaxation in a broad range of Larmor frequencies. A coherent analysis of the diffusion coefficients and spin-lattice relaxation data is presented taking into account a relaxation model associated to water molecular dynamics in close contact with NP surfaces. From our results it was possible to access the details of the water molecular movements in the nanosystems and to single out two water populations presenting distinct molecular dynamics. Characteristic distances for water rotations mediated by translational diffusion were estimated in consistency with the NP's dimensions and pores sizes obtained by TEM and BET experimental techniques. This knowledge has both fundamental and practical relevance since these NP have applications in nanomedicine, not only in therapy but also in diagnostic procedures and more recently in theranostic. (C) 2015 Elsevier Inc. All rights reserved.