Theoretical study of solvent effects on the coil-globule transition

Abstract

The coil-globule transition of a polymer in a solvent has been studied using Monte Carlo simulations of a single chain subject to intramolecular interactions as well as a solvent-mediated effective potential. This solvation potential was calculated using several different theoretical approaches for two simple polymer/solvent models, each employing hard-sphere chains and hard-sphere solvent particles as well as attractive square-well potentials between some interaction sites. For each model, collapse is driven by variation in a parameter which changes the energy mismatch between monomers and solvent particles. The solvation potentials were calculated using two fundamentally different methodologies, each designed to predict the conformational behavior of polymers in solution: (1) the polymer reference interaction site model (PRISM) theory and (2) a many-body solvation potential (MBSP) based on scaled particle theory introduced by Grayce [J. Chem. Phys. 106, 5171 (1997)]. For the PRISM calculations, two well-studied solvation monomer-monomer pair potentials were employed, each distinguished by the closure relation used in its derivation: (i) a hypernetted-chain (HNC)-type potential and (ii) a Percus-Yevick (PY)-type potential. The theoretical predictions were each compared to results obtained from explicit-solvent discontinuous molecular dynamics simulations on the same polymer/solvent model systems [J. Chem. Phys. 125, 194904 (2006)]. In each case, the variation in the coil-globule transition properties with solvent density is mostly qualitatively correct, though the quantitative agreement between the theory and prediction is typically poor. The HNC-type potential yields results that are more qualitatively consistent with simulation. The conformational behavior of the polymer upon collapse predicted by the MBSP approach is quantitatively correct for low and moderate solvent densities but is increasingly less accurate for higher densities. At high solvent densities, the PRISM-HNC and MBSP approaches tend to overestimate, while the PRISM-PY approach underestimates the tendency of the solvent to drive polymer collapse.

Conformation of a flexible polymer in explicit solvent: Accurate solvation potentials for Lennard-Jones chains

“…21,22 Solvent induced polymer chain collapse and/or precipitation can be a) taylormp@hiram.edu realized in these simple chain-in-solvent systems by varying the solvent-polymer interaction potential. [23][24][25][26][27][28][29] A rigorous statistical mechanical treatment of the coupling between the local structure of a polymer and its immediate environment is a difficult many-body problem. 12,30 This problem is often avoided when studying a polymer chain in dilute solution by treating the solvent implicitly as a continuum whose average effects are accounted for by an effective polymer site-site interaction potential.…”

“…9 However, more recent work by Polson et al suggests that Grayce's approach breaks down for longer chains and at high solvent density. 28 In general, such multi-body potentials are difficult to work with, and thus, this exact approach does not necessarily simplify the problem. By introducing the approximation of pairwise additivity for the exact n-body solvation potential, we can significantly simplify the chain-in-solvent problem, reducing it to a single n-mer chain self-interacting via a set of (at most) n(n − 1)/2 effective site-site potentials.…”

Magnetic‐induced coil‐globule transition for polyelectrolytes

“…The coil‐globule transition can be influenced or induced by various factors,1–11 such as confinement, chain stiffness, hydrogen bond, and hydrodynamic interactions. Excellent studies on theories, experiments, and simulations can be found everywhere 12, 13. Additionally, there are two classical polymer physics books14, 15 where more details can be found.…”

Conformation of a flexible chain in explicit solvent: Exact solvation potentials for short Lennard-Jones chains

“…In both the SW and LJ systems, one can drive chain collapse in a dense, low temperature solvent environment by simply reducing the attractive part of the chain-solvent interaction (leaving the solvent-solvent and intramolecular chain-chain interactions unchanged). 17,[23][24][25][26][27][28] This change reduces the solvating power of the solvent and allows for a continuous tuning of solvent conditions from good to poor.…”

“…14 However, Polson et al have recently shown that Grayce's approximate many-body approach fails for longer chains at high solvent density. 28 We have recently investigated the validity of the pair decomposition approximation for both short HS and SW chains in monomeric HS and SW solvent, respectively. 17 Our "numerically exact" results show that while a single two-site solvation potential is unable to capture the complete effects of solvent, a set of two-site solvation potentials can exactly map the chain-in-solvent problem onto that of an isolated chain.…”