Physico-Chemical Approaches to Investigate Surface Hydroxyls as Determinants of Molecular Initiating Events in Oxide Particle Toxicity

Abstract

The study of molecular recognition patterns is crucial for understanding the interactions between inorganic (nano)particles and biomolecules. In this review we focus on hydroxyls (OH) exposed at the surface of oxide particles (OxPs) which can play a key role in molecular initiating events leading to OxPs toxicity. We discuss here the main analytical methods available to characterize surface OH from a quantitative and qualitative point of view, covering thermogravimetry, titration, ζ potential measurements, and spectroscopic approaches (NMR, XPS). The importance of modelling techniques (MD, DFT) for an atomistic description of the interactions between membranes/proteins and OxPs surfaces is also discussed. From this background, we distilled a new approach methodology (NAM) based on the combination of IR spectroscopy and bioanalytical assays to investigate the molecular interactions of OxPs with biomolecules and membranes. This NAM has been already successfully applied to SiO2 particles to identify the OH patterns responsible for the OxPs’ toxicity and can be conceivably extended to other surface-hydroxylated oxides.

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“…In this context, the zeta potential has been considered a pertinent factor, i.e., since it is known that the surface charge of engineered nano-SiO 2 influences its toxicological profile . In brief, the surface charge development mechanism in metal-oxides is well-known, as follows: due to their amphoteric character, surface silanols (Si–OH) determine the surface charge of nanosilica materials in an aqueous dispersion. , Protonation/deprotonation reactions , occur due to pH alteration, while an equilibrium between the protonated and deprotonated species can be readily achieved following the general reaction described below …”

“…In this context, the zeta potential has been considered a pertinent factor, i.e., since it is known that the surface charge of engineered nano-SiO 2 influences its toxicological profile . In brief, the surface charge development mechanism in metal-oxides is well-known, as follows: due to their amphoteric character, surface silanols (Si–OH) determine the surface charge of nanosilica materials in an aqueous dispersion. , Protonation/deprotonation reactions , occur due to pH alteration, while an equilibrium between the protonated and deprotonated species can be readily achieved following the general reaction described below normalM − O − + H 3 O + ↔ M − normalO normalH + H 2 normalO ↔ normalM − O H 2 + + normalO normalH − …”