PEE-PEO Block Copolymer Exchange Rate Between Mixed Micelles is Detergent and Temperature Activated

Published

March 10, 2017

Author(s)

Allen B. Schantz, Patrick O. Saboe, Ian T. Sines, Hee-Young Lee, Kyle J. M. Bishop, Janna K. Maranas, Paul Butler, Manish Kumar

Abstract

We examine the kinetics of polymer chain exchange between mixed polymer-detergent micelles, a system relevant to the synthesis of protein-containing biomimetic membranes. Although chain exchange between polymer aggregates in water occurs too slowly to observe, the presence of detergent, a key ingredient for stabilizing and reconstituting membrane proteins, allowed us to determine chain exchange for stabilizing and reconstituting membrane proteins, allowed us to determine chain exchange rate constants using time-resolved small-angle neutron scattering (TR-SANS). We chose to examine a membrane-protein-relevant, vesicle-forming, ultra-short polymer, Poly(ethyl ethylene)₂₀-Poly(ethylene oxide)₁₈ (PEE₂₀PEO₁₈). PEE₂₀-PEO₁₈ was solubilized in mixed micelles with the non-ionic detergent octyl-β-D-glucoside (OG), which is compatible with many membrane proteins. Cryo-TEM and SANS are used to determine complete solubilization of the polymer into micelles. We provide the first direct evidence that detergents activate block copolymer chain exchange, and determine kinetic parameters at two detergents activate block copolymer chain exchange, and determine kinetic parameters at two detergent concentrations above the CMS (critical micellar concentration) of OG. We find that chain exchange increases two orders of magnitude when temperature increases from 35 to 55 °C, and that even a 1 mg/mL increases in OG concentration leads to a noticeable increase in exchange rate. Using the Arrhenius equation, we determine that at detergent concentrations slightly above the CMC, the activation energy for chain exchange is 2-3 times higher for PEE₂₀PEO₁₈ than for lipids, and that the activation barrier decreases with increasing OG concentration. Based on these results, we postulate that OG associates with polymer chains in solution, reducing the activation barrier to chain escape. These finding explain the need for high detergent concentration and/or temperature to synthesize polymer/protein membranes.

Citation

Macromolecules

Volume

50

Issue

6

Pub Type

Journals

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Keywords

polymer, membrane, kinetics

Citation

Schantz, A. , Saboe, P. , Sines, I. , Lee, H. , Bishop, K. , Maranas, J. , Butler, P. and Kumar, M. (2017), PEE-PEO Block Copolymer Exchange Rate Between Mixed Micelles is Detergent and Temperature Activated, Macromolecules, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=920049 (Accessed March 13, 2025)