In Liquid Water: When Is a Hydrogen Bond Not a Hydrogen Bond?

by Dr Richard Henchman (The University of Manchester)

Wednesday 31 Aug 2016, 14:00 → 15:00 Europe/Stockholm

FB54

Hydrogen bonding is central to understanding water's structure and dynamics. However, in contrast to the sophisticated experimental and computational techniques widely used to study water, most measures of hydrogen bonds are quite crude. My interest in this area was driven by the question of how many hydrogen-bond arrangements in liquid water [1], which is an important contribution to water's entropy. My nearest-acceptor definition of a hydrogen bond [2] was driven by the problematic nature of traditional hydrogen bond definitions for solutions [3] and the failure of the traditional tetrahedral model to account for the entropy loss of hydrophobic hydration [4]. My definition assumed the presence of transition states separating stable hydrogen-bond states. It overcome a number of limitations of traditional definitions but still faced a number of objections. More thorough analyses of the stability of hydrogen bonds revealed a strong heterogeneity in hydrogen-bond stability and the factors contributing to it [5,6]. This work further clarifies the two-state nature of water whereby a predominantly tetrahedral component with linear hydrogen bonds is continually disrupted by a mixed-coordinatation component with delocalized free hydrogens. 1. RH Henchman, J. Chem. Phys., 2007, 126, 064504. 2. RH Henchman and SJ Irudayam, J. Phys. Chem. B, 2010, 114, 16792-16810. 3. SJ Irudayam, RD Plumb and RH Henchman, Faraday Discuss., 2010, 145, 467-485. 4. SJ Irudayam and RH Henchman, J. Phys.: Condens. Matter, 2010, 22, 284108. 5. RH Henchman and SJ Cockram, Faraday Discuss., 2013, 167, 529-550. 6. RH Henchman, J. Phys.: Condens. Matter, 2016, 28, 384001.