Abstract
Combining elastic incoherent neutron scattering experiments at different resolutions with molecular dynamics simulations, we report the observation of a protein-like dynamical transition in linear chains of Poly(N-isopropylacrylamide). We identify the onset of the transition at a temperature $T_d$ of about 225~K. Thanks to a novel global fit procedure, we find quantitative agreement between measured and calculated polymer mean-squared displacements at all temperatures and time resolutions. Our results confirm the generality of the dynamical transition in macromolecular systems in aqueous environments, independently of the internal polymer topology.
Highlights
Along-debated phenomenon in thephysical community is the occurrence of a dynamical transition in proteins, either globular or intrinsically disordered, which has been widely investigated by means of neutron scattering experiments [1]
We conclude that there is no difference between cross-linked and linear chains, highlighting the fact that the dynamical transition does not depend on the details of the internal macromolecular architecture, to what was observed for biological systems
In this work we reported evidence of a low-temperature dynamical transition in linear PNIPAM polymer chains by means of elastic incoherent neutron scattering (EINS) measurements at resolutions covering more than two decades in time
Summary
Along-debated phenomenon in the (bio)physical community is the occurrence of a dynamical transition in proteins, either globular or intrinsically disordered, which has been widely investigated by means of neutron scattering experiments [1]. It is legitimate to ask whether the polymeric architecture has any influence on the occurrence of such a transition by examining the case of PNIPAM linear (non-cross-linked) polymer chains This polymer is mostly exploited for its thermoresponsive properties [21,22,23]: Above room temperature, PNIPAM chains undergo a reversible coil-to-globule transition with increasing temperature T , which makes them suitable to mimic protein folding and to investigate protein cold denaturation [24]. Our results show the occurrence of a dynamical transition at Td ∼ 225 K, a value very similar to that observed in proteins such as myoglobin and lysozyme [1,2,3] This result implies a wide generality of the phenomenon, independently of the structural details of the investigated complex macromolecular system
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