Molecular Dynamics Simulations of Star Polymeric Molecules with Diblock Arms, a Comparative Study

Abstract

We have performed all atom explicit solvent molecular dynamics simulations of three different star polymeric systems in water, each star molecule consisting of 16 diblock copolymer arms bound to a small adamantane core. The arms of each system consist of an inner "hydrophobic" block (either polylactide, polyvalerolactone, or polyethylene) and an outer hydrophilic block (polyethylene oxide, PEO). These models exhibit unusual structure very close to the core (clearly an artifact of our model) but which we believe becomes "normal" or bulk-like at relatively short distances from this core. We report on a number of temperature-dependent thermodynamic (structural/energetic) properties as well as kinetic properties. Our observations suggest that under physiological conditions, the hydrophobic regions of these systems may be solid and glassy, with only rare and shallow penetration by water, and that a sharp boundary exists between the hydrophobic cores and either the PEO or water. The PEO in these models is seen to be fully water-solvated at low temperatures but tends to phase separate from water as the temperature is increased, reminiscent of a lower critical solution temperature exhibited by PEO-water mixtures. Water penetration concentration and depth is composition and temperature dependent with greater water penetration for the most ester-rich star polymer.

Role of Hydrophilicity and Length of Diblock Arms for Determining Star Polymer Physical Properties

“…For the adamantane core and the linkage of adamantane to the hydrophobic chain of PVL, OPLS-AA parameters 7 were used but with improved parameters of Price et al 8 for the alkane torsion angle energy expressions. Our previous study carefully reparameterized the charge model and C-C-O-C and O-C-C-O torsions for PEG to be suitable for aqueous solvation studies 4 . These modified OPLS parameters were derived from QM calculations and then validated on Raman spectra for DME.…”

“…In a recent paper, some of us have performed all atom explicit solvent molecular dynamics simulations of three different star polymeric systems in water at physiological temperatures 4 . In this previous star polymer comparison, the diblock arms consisted of an inner "hydrophobic" block which was varied in the three systems to be either polylactide, poly-δ-valerolactone (PVL), or polyethylene, while holding the outer hydrophilic block fixed to the same polyethylene glycol (PEG) polymer that is widely used as an in vivo biomaterial.…”

Conformation of Hydrophobically Modified Thermoresponsive Poly(OEGMA-co-TFEA) across the LCST Revealed by NMR and Molecular Dynamics Studies

“…[46][47][48] Of particular relevance, molecular dynamics (MD) simulations have been applied to the study of the conformation changes of thermo-responsive polymers at different temperatures. [49][50][51][52] Mancini et al 49 have reported MD simulations of conformational transitions of single-chains of thermo-responsive PNIPAAm. The coil-to-globule transition of PNIPAAm consisting with 30 monomer units was observed as the temperature was increased through the LCST.…”

Composition controlled synthesis of PCL–PEG Janus nanoparticles: magnetite nanoparticles prepared from one-pot photo-click reaction

“…To the best of our knowledge, previous investigations on interactions of PCL-PEG have been more focused on PCL-PEG block copolymers and dendritic architectures. [19][20][21][22] Studies of PEG-PCL block copolymers have proven that the ratio of PEG to PCL and complex hydrophobicity have profound effects on the overall shape of the complexes formed, ranging from bicelles and worm-like micelles to spherical micelles. 23,24 As with the role of hydrophobic PCL, atomistic simulations have proved that a slight degradation of PCL will drive a worm-to-sphere transition, as clarified in the simulations below of the PEG-PCL phase diagram, and this will tend to release drug and thus contribute to the enhanced anti-cancer effects of drug-loaded worms.…”