Letizia Tavagnacco^1,2, Marco Zanatta³, Elena Buratti⁴, Monica Bertoldo⁴, Ester Chiessi⁵, Markus Appel⁶, Francesca Natali⁷, Andrea Orecchini^8,9, Emanuela Zaccarelli^1,2*

1 CNR Institute of Complex Systems, Uos Sapienza, Piazzale Aldo Moro 2, 00185 Rome, Italy

2 Department of Physics, Sapienza University of Rome, Piazzale Aldo Moro 2, 00185 Rome, Italy

3 Department of Physics, University of Trento, via Sommarive 14, 38123 Trento, Italy

4 Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari 46, 44121 Ferrara, Italy

5 Department of Chemical Science and Technologies, University of Rome Tor Vergata,Via della Ricerca Scientifica I, 00133 Rome, Italy

6 Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042 GRENOBLE Cedex 9, France

7 CNR-IOM, Operative Group Grenoble (OGG), Institut Laue Langevin, F-38042 Grenoble, France

8 Dipartimento di Fisica e Geologia, Università di Perugia, Via Alessandro Pascoli, 06123 Perugia, Italy

9 CNR-IOM c/o Dipartimento di Fisica e Geologia, Università di Perugia, Via Alessandro Pascoli, 06123 Perugia, Italy

* Corresponding authors emails: emanuela.zaccarelli@cnr.it

DOI10.24435/materialscloud:6n-zd [version v1]

Publication date: Jun 24, 2024

How to cite this record

Letizia Tavagnacco, Marco Zanatta, Elena Buratti, Monica Bertoldo, Ester Chiessi, Markus Appel, Francesca Natali, Andrea Orecchini, Emanuela Zaccarelli, Water slowing down drives the occurrence of the low temperature dynamical transition in microgels, Materials Cloud Archive 2024.96 (2024), https://doi.org/10.24435/materialscloud:6n-zd

Description

The protein dynamical transition marks an increase in atomic mobility and the onset of anharmonic motions at a critical temperature, which is considered relevant for protein functionality. This phenomenon is ubiquitous, regardless of protein composition, structure and biological function and typically occurs at large protein content, to avoid water crystallization. Recently, a dynamical transition has also been reported in non-biological macromolecules, such as poly(N-isopropyl acrylamide) (PNIPAM) microgels, bearing many similarities to proteins. While the generality of this phenomenon is well-established, the role of water in the transition remains a subject of debate. In this study, we use atomistic molecular dynamics simulations and elastic incoherent neutron scattering (EINS) experiments with selective deuteration to investigate the microscopic origin of the dynamical transition and distinguish water and PNIPAM roles. While a standard analysis of EINS experiments would suggest that the dynamical transition occurs in PNIPAM and water at a similar temperature, simulations reveal a different perspective, also qualitatively supported by experiments. From room temperature down to about 180 K, PNIPAM exhibits only modest changes of dynamics, while water, being mainly hydration water under the probed extreme confinement, significantly slows down and undergoes a mode-coupling transition from diffusive to activated. Our findings therefore challenge the traditional view of the dynamical transition, demonstrating that it occurs in proximity of the water mode-coupling transition, shedding light on the intricate interplay between polymer and water dynamics.

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Keywords

microgels water dynamical transition