Surface charging behavior of nanoparticles by considering site distribution and density, dielectric constant and pH changes – a Monte Carlo approach

Abstract

Monte Carlo simulations are used to describe the charging behavior of metal oxide nanoparticles thus enabling a novel and original approach to predict nanoparticle reactivity and the possible interactions with biological and environmental molecules. The charging behavior of spherical nanoparticles is investigated by adjusting the pH of the media and the influence of surface site distribution, density and dielectric constant as well as the acid/base properties of the surface sites and ΔpKa(0) values (difference between two successive deprotonation constants) is systematically studied using a grand canonical Monte Carlo method. A primitive Coulomb model is applied to describe the interaction energies between the explicit discrete sites. Homogeneous/heterogeneous surfaces and patches with homogeneous and heterogeneous distributions are considered in order to reproduce possible site distributions of metal oxide nanoparticles. Two models are used. In the 1-pKa(0) model (one deprotonation step) the results indicate that the deprotonation process is controlled by inter-site distances which are defined by site distributions and densities. It is shown that the homogeneous surface is the most efficient site distribution to obtain high ionization degrees. In the 2-pKa(0) model (two deprotonation steps), the ΔpKa(0) value is found to control the surface charge properties with regard to pH changes. By considering the variation of the total nanoparticle surface charge as a function of pH our results help in the distinction between the zero charge and the isoelectric point and interpretation of experimental NP titration curves.

Modelling the interaction processes between nanoparticles and biomacromolecules of variable hydrophobicity: Monte Carlo simulations

“…37 Adsorption processes on nanoparticles or surfaces involving DNA-like chains are commonly studied by computer simulations. 46 Conformational phase diagrams, provided by Guo et al 47 for the adsorption of different mixtures of proteins on small nanoparticles by molecular simulations, confirm the structural change of proteins by enhancing the β-sheets attributed to their geometry and flexibility. 38 Moreover, the abrupt transitions between adsorbed and desorbed states, occurring when the interactions between chains and particles are not strong enough to overcome the chain entropic penalty, can be associated with a first-order-like transition between both states.…”

Plasma polymerized nanoparticles effectively deliver dual siRNA and drug therapy in vivo

“…Chemical characterization of PPNs was consistent with our previous reports on PP-derived materials 33 , 34 , confirming incorporation of elemental carbon and nitrogen into the nanoclusters followed by surface restructuring due to oxidation (Figure S1 a) and the presence of amine and carboxyl functional moieties (Figure S1 b). These surface functional groups improve surface hydrophilicity 35 , 36 , significantly increase surface reactivity and can be readily protonated (or de-protonated) in solution by changing pH 37 , allowing fine tuning of surface charge and stability in solution 27 . The versatile surface properties of PPNs facilitate robust tethering of clinically relevant molecules of various sizes, charge and chemical structures using a simple one-step incubation in aqueous solution 27 .…”

DLS and zeta potential – What they are and what they are not?

“…The practical way to confirm the nature (positive / negative) as well as to determine charge density on NPs is to titrate it with known amounts of ions. A detailed description of such titration technique falls beyond the scope of this article although excellent reference literature is available [122,123].…”