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Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

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Water-Polymer Coupling Induces a Dynamical Transition in Microgels.

Letizia Tavagnacco¹, Ester Chiessi², Marco Zanatta³

¹CNR-ISC and Department of Physics , Sapienza University of Rome , Piazzale A. Moro 2 , 00185 Rome , Italy.

The Journal of Physical Chemistry Letters

|February 9, 2019

Summary

The protein dynamical transition, observed in poly-N-isopropylacrylamide (PNIPAM) microgels, originates from water-macromolecule hydrogen bonding. This crucial coupling drives the transition, impacting various hydrated systems beyond biological functions.

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Area of Science:

Polymer science
Physical chemistry
Biophysics

Background:

The protein dynamical transition is a long-debated phenomenon.
This transition has recently been observed in nonbiological macromolecules like poly-N-isopropylacrylamide (PNIPAM) microgels.

Purpose of the Study:

To elucidate the molecular origin of the dynamical transition in PNIPAM microgels.
To investigate the role of water-macromolecule interactions in this phenomenon.

Main Methods:

Atomistic molecular dynamics simulations were employed.
Comparison of PNIPAM-water dynamics with bulk water was performed.

Main Results:

Below the dynamical transition temperature (T_d), PNIPAM dynamics are governed by methyl group rotations.
Water dynamics are dominated by hydrogen bonding.
PNIPAM-water hydrogen bonding was identified as the primary cause of the transition.

Conclusions:

The dynamical transition in PNIPAM microgels is critically dependent on water-macromolecule coupling.
This finding is relevant to a broad range of hydrated systems, irrespective of biological function.