Structure and Dynamics of the Hydrogen Bond Network in Water by Computer Simulations

Abstract

We summarize previous results of our hydrogen bond network analysis on pure water and discuss the influence of temperature at constant density in the region of the supercooled liquid. A very weak temperature dependence of the single bond properties is contrasted by marked temperature effects on static and dynamic properties, which are determined by the collective influence of many bonds. Also, the existence of a minimum in the structure factor S (Q) at low wave vectors Q was found for the model liquid, indicating the presence of density fluctuations with correlation lengths of several molecular diameters

The Importance of Tetrahedrally Coordinated Molecules for the Explanation of Liquid Water Properties

“…The average number of nearest neighbors is 2.6. The new clusters resemble structures investigated by Geiger et al [15][16][17] who took snapshots of structural elements from MD simulations. Since cyclic pentamers and hexamers are found to have rather similar thermody-namic stability in the liquid range, higher-coordinated clusters in the 12-to 26-mer range built from five-and six-membered ring structures were considered (the Supporting Information Figure S1); but none of them occurred in the liquid phase.…”

Cooperative molecular motions in water: The liquid-liquid critical point hypothesis

“…Standard liquid theories fail to explain its dynamical and thermodynamic properties, which differ from those of most other liquids [3][4][5][6]. Although the anomalous properties of water are not understood, many workers believe that a central role is played by the possibility for the water molecule to form hydrogen bonds and to create a tetrahedrally coordinated open network in both the solid and the liquid phases [7][8][9][10][11][12][13].…”

Solvent structure and dynamics: How relevant to molecular and quantum pharmacology?

“…Literature on the hydrophobic effect shows, however, that this does not happen, and computer simulations show that only about 25% of the bonds are missing, whereas the remaining 25 % is reinforced and takes part in longer-lived clathrate-like cages [24,25]. We note that this is just what one expects as a result of the reduced orientational and translational mobility of water molecules sitting on hydrophobic groups and missing the "catalytic" action of a fifth bond [26], if the effect described in Figure 2 and illustrated in Figure 4 is operative. If more constraints (e.g., hydrophilic and hydrophobic) are simultaneously imposed by one (or more) solutes, within geometries/topologies compatible with self-consistency of H-bond cages, the same mechanism and its propagation along H-bond pathways may give rise, under appropriate conditions, to puttern-sensitive amphiphilic synergism [ 1,4].…”

“…As Figure 4 strongly suggests [19], H-bond cages are "imprinted" in the nearby solvent by water molecules at solute hydration sites. These cages are characterized by (1) a lifetime which is longer than that of ordinary H-bond pathways and is related to (2) a connectivity larger than ordinary, similar to that of "patches" of four-H-bonded molecules whose population tends to diverge at sufficiently low temperatures [ 16,17,21,26,28]. The longer lifetimes of the imprinted structures are expected to play a dominant role in that part of the interaction between two (or more) solutes, or between parts of one solute, which is mediated by the solvent [Eq.…”

“…Once this was done, "seeing" the percolation of H-bond pathways at room temperature, or the trend towards the onset of a second percolation, along four-H-bonded molecules (at supercooling) was possible and fruitful [16,17,21,26].…”