pH-Responsive Coating of Silver Nanoparticles with Poly(2-(N,N-dimethylamino)ethyl methacrylate): The Role of Polymer Size and Degree of Protonation

Abstract

Metrics & MoreArticle Recommendations * sı Supporting Information ABSTRACT: "Smart" nanomaterials composed of inorganic nanoparticles (NPs) and synthetic polymers represent an exciting and rapidly growing interdisciplinary area of materials science and engineering. Specifically, the coating of NPs with "smart" polymers capable of responding to applied external stimuli makes them promising for various biomedical applications, including drug delivery, tissue engineering, and medical diagnostics. In this work, we present an atomistic molecular dynamics (MD) simulation study of a silver NP (AgNP) grafted with a single-chain poly(2-(N,Ndimethylamino)ethyl methacrylate) (PDMAEMA). PDMAEMA possesses ionizable side-chain groups −N(CH 3 ) 2 , which can be converted into charged moieties upon solution acidification so that this makes the whole macromolecule to be pH responsive.We examined the pH-responsive adsorption of PDMAEMA onto the AgNP as a function of the polymer chain length (220−660 units) and the degree of protonation α.We found out that, in the neutral state at α = 0, the PDMAEMA chain was collapsed and adsorbed onto the AgNP due to the weak non-covalent interactions through the neutral dimethylamino moieties. Partial protonation of these side groups at α = 0.3−0.7 triggers ionic interactions, which drive the unfolding of the polymer chain toward an aqueous solution due to the electrostatic Coulombic repulsion between the generated charges. In the charged state at α = 1, the complete ionization of PDMAEMA side groups increases its solubility that leads to the substantial decrease in the polymer−NP interactions, followed by desorption of the polymer from the inorganic core. Thus, the gradual changes in the protonation degree of PDMAEMA fine-tune a balance of hydrophilic versus hydrophobic NP−polymer interactions and govern the shape, size, and water-protecting efficiency of the polymeric shell. Finally, our MD simulations demonstrated that such pH-adaptive behavior of PDMAEMA makes it promising for the development of a wide range of new generations of "intelligent" polymer coatings for metal NPs.

pH-Controllable Coating of Silver Nanoparticles with PMMA-b-PDMAEMA Oligomers: A Molecular Dynamics Simulation Study

“…The neighboring contact of PMMA 20 - b -PDMAEMA 20 macromolecules with the AgNP surface was established if its distance to the outermost Ag atoms was less than a cutoff distance of 0.42 nm. This cutoff criterion corresponds to the first minimum on radial distribution function (RDF) curves calculated between Ag and the primary anchoring moieties of PDMAEMA …”

“…A primary role of methacrylic polymers in the synthesis of MNPs is the formation of the tight polymeric shell, which protects an inorganic metal core from the water environment. , The use of pH-responsive polymers offers some new opportunities of pH-controllable adjusting the thickness and density of the polymeric coating. , …”

“…The average diameter of such a nanoparticle core equals 3.9 nm, as shown in Figure a. Initial coordinates of AgNPs were taken from our recent MD studies of polymer-protected AgNPs. ,, …”

“…An AgNP core model was composed of neutral Ag atoms with zero partial charges. , The repulsion and dispersion terms of nonbonded interactions between a pair of Ag atoms were computed by using the classical Lennard-Jones (LJ) 12–6 pairwise potential energy function. The parameters of the LJ potentials for Ag–Ag were taken from our recent studies. ,,,,, For mixed nonbonded interactions between Ag and PMMA- b -PDMAEMA and water atoms, the Lorentz–Berthelot combination rules were used …”

“…Recently, we developed the new MD model and FF parameters for PDMAEMA based on the united-atom GROMOS G53a6 FF. , The G53a6 FF treats the CH, CH 2 , and CH 3 moieties as a single interacting site. The G53a6 FF has also revealed a good performance for modeling the physicochemical properties of other structurally similar polymers. ,,,− Self-association behavior and tacticity effects on the conformational structure of PMMA have been studied using the G45a3 and G53a6 FFs. − In addition, the united-atom approximation has recently recommended itself well for studying the swelling behavior of PDMAEMA brushes modeled by using the united-atom G54a7 version of the GROMOS FF .…”