Cooperative rearranging regions in water at biological and inorganic interfaces

CIC nanoGUNE Seminars

Giancarlo Franzese, Universitat de Barcelona, Barcelona, Spain
nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
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Cooperative rearranging regions in water at biological and inorganic interfaces We study, by simulations and analytic approach, the behaviour of water at the interface with proteins or in hydrophobic nanoconfinement. For water molecules adsorbed on the protein surface, we calculate the temperature dependence of the relaxation time of the dynamics of the hydrogen bond (HB) network, finding two dynamic crossovers, (i) at approximately 252 K and (ii) at approximately 181 K. We show how the two crossovers relate to the presence of two specific heat maxima. The first is caused by fluctuations in the HB formation, and the second, at a lower temperature, is due to the cooperative reordering of the HB network [1]. For water between hydrophobic walls, at nanoscopic separation, we study how the diffusion constant parallel to the walls depends on the microscopic structure of water. At low temperature, water diffusion can be associated with the number of defects in the hydrogen bond network [2]. However, the number of defects solely does not account for the peculiar diffusion of water, with maxima and minima along isotherms. We calculate a relation that quantitatively reproduces the behavior of diffusivity, focusing on the high-temperature regime. We clarify how the interplay between breaking of hydrogen bonds and cooperative rearranging regions of 1-nm size gives rise to the diffusion extrema in nanoconfined water and offers a possible explanation for the ultrafast transport of water in nanochannels with size smaller than 1 nm [3]. We finally find a dramatic decrease of compressibility, thermal expansion coefficient, and specific heat for water confined in disordered nanochannels [4]. References 1) M. G. Mazza, K. Stokely, S. E. Pagnotta, F. Bruni, H. E. Stanley, and G. Franzese, Proc. Natl. Acad. Sci. USA 108, 19873 (2011). 2) F. de los Santos, and G. Franzese, J. Phys. Chem. B 115, 14311 (2011). 3) F. de los Santos, and G. Franzese, Phys. Rev. E 85, 010602(R) (2012). 4) E. G. Strekalova, M. G. Mazza, H. E. Stanley, G. Franzese, Phys. Rev. Lett. 106, 145701 (2011).