Molecular dynamics studies of polyethylene oxide and polyethylene glycol: Hydrodynamic radius and shape anisotropy

¹ National Institutes of Health
² University of Maryland

^* To whom correspondence should be addressed. E-mail: pastorr{at}nhlbi.nih.gov.

Submitted on March 7, 2008
Revised on April 8, 2008
Accepted on 8 April 2008

	Abstract

A revision (C35r) to the CHARMM ether force field is shown to reproduce experimentally observed conformational populations of dimethoxyethane (DME). Molecular dynamics (MD) simulations of 9, 18, 27, and 36-mers of polyethylene oxide (PEO) and 27-mers of polyethylene glycol (PEG) in water based on C35r yield a persistence length = 3.7 Å, in quantitative agreement with experimentally obtained values of 3.7 Å for PEO and 3.8 Å for PEG; agreement with experimental values for hydrodynamic radii of comparably sized PEG is also excellent. The exponent relating the radius of gyration and molecular weight (R_h M_w) of PEO from the simulations equals 0.515 ± 0.023, consistent with experimental observations that low molecular weight PEG behaves as an ideal chain. The shape anisotropy of hydrated PEO is 2.59:1.44:1.00. The dimension of the middle length for each of the polymers nearly equals the hydrodynamic radius R_h obtained from diffusion measurements in solution. This explains the correspondence of R_h and R_p, the pore radius of membrane channels: a polymer such as PEG diffuses with its long axis parallel to the membrane channel, and passes through the channel without substantial distortion.

Key Words: Kirkwood-Riseman equation, diffusion constant, membrane pores, persistence length