Structure-dissolution relationships of phosphate and bioactive glasses by liquid, solid-state and paramagnetic NMR: structural role and coordination environment of cobalt in phosphate glasses & the role of cations on the mechanism of hydrolysis

Abstract

The doctoral thesis comprises a study of the relationships between structure and dissolution behaviour of phosphate and bioactive glasses by employing analytical techniques such as electron paramagnetic resonance (EPR), liquid NMR, solid-state MAS NMR and paramagnetic NMR spectroscopy, among others. The understanding of the corrosion processes of phosphate glasses is important for their technological applications, e.g. drug delivery, antibacterials and tissue engineering. In the present work, the NMR findings provided insights about the role of cations on the mechanism of hydrolysis of phosphate glasses. The incorporation of cobalt into glasses is a new approach to overcome the vascularization limitation in tissue engineering by stimulating the production of blood vessels. These glasses are also interesting as semiconductors, optical devices and solid-state lasers, among others. This work shows that structural (i.e. thermal) properties of cobalt phosphate glasses with constant basicity are dictated by the coordination number of Co2+ sites. The second part of the study on cobalt phosphate glasses is in publication process under the title: "Co2+ as an internal paramagnetic 31P NMR probe for structural analysis of cobalt-phosphate glasses in the solid-state and leachate solutions". This work presents a new approach to investigate the mechanism of dissolution of phosphate glasses based on the paramagnetic effects. Accordingly, features such as the spin-orbit (SO) coupling, zero-field splitting (ZFS) and symmetry of Co2+ sites are correlated to the paramagnetic shift, paramagnetic relaxation enhancement (PRE) and broadening effects on the spectra. That allows the assessment of the distribution of Co2+ ions in the glass network. Additionally, it enables monitoring structural dynamics of phosphate complexes in solution, including conformational changes, upon ligand binding recognition under different conditions, i.e. buffer aqueous solutions (Tris, EDTA)