Insights into the miscibility of polymethyl methacrylate (PMMA) and nile blue oxazone (NBO) flurophores: tacticity and chain length aspects

Abstract

Polymethyl methacrylate (PMMA) based florescent nanoparticles are noteworthy carriers that may be explored for the delivery of numerous anti-cancer and anti-viral drugs. Particularly, the PMMA-nile blue oxazone (NBO) carriers are one of the most frequently used fluorescent probes. Despite various PMMA-based cargos being explored for drug delivery, the spatial arrangement of the methyl and ester groups on the PMMA chains with respect to the encapsulated agent remains a largely unexplored area.In the present work Molecular dynamics simulation and docking studies were carried out to explore the effect of chain length of PMMA and its tacticity on its miscibility with NBO dye molecules. Energetic behavior of the modeled chains was assessed using COMPASS force field. Total potential energy of the chains increased as their length increased. The total potential Intermolecular energy of the isotactic chains was higher as compared to their syndiotactic counterparts, for all the chain lengths considered unlike the intramolecular energy, which was higher for syndiotactic chains. Flory huggins interaction parameter (χ) was calculated for polymer chains of varying lengths and tacticities, with respect to NBO. Interaction parameter increased with increase in the chain length of the polymer chains, which indicated superior interaction with smaller chains. Syndiotactic chains showed strongest interactions with the dye molecule for all the chain lengths of the polymer, whereas isotactic chains exhibited the weakest interactions. Binding energy analysis validated the patterns obtained from flory huggins theory and also established that the polymer chains had higher propensities to self- assemble within themselves, as compared to interactions with NBO molecules. Analysis of the radius of gyration of the polymer chains in the PMMA- NBO complexes, at the end of dynamics run, exhibited that the syndiotactic chains formed smallest coiled structures while the isotactic chains formed the largest coiled structures. Flexibility of the polymer chains was calculated by determining the ratio of the radius of gyration at beginning and at the end of simulation run. Here, isotactic chains were found to have maximum flexibility, followed by atactic and syndiotactic chains. These results were more coherent when the calculations were performed on larger systems, differing in the relative number of PMMA chains and NBO molecules.