Polymer-matrix stabilized metal nanoparticles: Synthesis, characterizations and insight into molecular interactions between metal ions, atoms and polymer moieties

Abstract

Handling nanoparticles on a mesoscale order enhances the functionality of nanoparticles for high-end technological applications such as photonics, catalysis, biomedical applications, etc. In this context, polymer-metal hybrids have shown very popularity among material scientists in recent years where a suitable polymer matrix can be effectively used to stabilize nanoparticles through different mechanisms. The current paper deals with the synthesis of different types of hybrid particles of gold (Au), silver (Ag) and iron (Fe) using micron size carboxylic group functionalized Poly(N-isopropyl acrylamide) (PNIPAM) stimuli-responsive cross-linked microgels as micro-reactor in an in-situ approach. Transmission electron microscope (TEM) directly confirms the successful loading of metal nanoparticles within microgels and all the hybrid microgels have a narrow size distribution. Dynamic light scattering (DLS) measurement in the solution state shows that the swollen size of microgel-metal hybrid is comparatively smaller than that of pure microgels. UV-VIS spectroscopy strongly reveals the presence of plasmon peaks at 520 and 405 nm in case of gold and silver microgel hybrids respectively. In case of microgel-iron hybrids, the particles nicely respond to the applied magnetic field exerted by an external magnet and the effect is also reversible when the magnet is removed. Finally, to understand the type of molecular interaction that is responsible in holding the nanoparticles within the polymer matrices of microgels, we have carried out molecular docking between different metal ions (Au3+, Ag+, Fe2+) and atoms of gold, silver and iron (Au0, Ag0, Fe0) with the functional moieties (NIPAM monomer and carboxylate ion, COO−) of the polymer. Molecular docking studies with different types of interaction potentials (Van der Waals, hydrophobic, solvation, torsional and electrostatic) suggest that the electrostatic attraction dominates over all other potentials between positive metal ions and negative carboxylate ion (COO−) giving rise to the net binding energy of −9.28, −5.7, −1.46 kcal/mol for Fe2+, Au3+, and Ag+ respectively.