Water, Properties of

Geiger, Alfons; Paschek, Dietmar

doi:10.1002/9780470048672.wecb627

Cited by 9 publications

(13 citation statements)

References 126 publications

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“…Trace amounts of nonacceptors (NA) and quadruple acceptors (QA) are also detected, with bent and octahedral coordinations. All such species are not new, having been seen in numerous computer simulations 18,[23][24][25][26]30,51,[56][57][58][59][60][61][62][63]65 and X-ray crystal structures of hydrated solutes. 86,87 but the difference here is that these SA and TA structures are substantial and almost equal to each other.…”

Section: Topological Hydrogen Bond Denition and Water Structurementioning

confidence: 99%

“…Thirdly, HB cut-offs may well bring about artificial short-lived non-tetrahedral structure but this does not imply that all non-tetrahedral structure is a consequence of this problem. Fourthly, non-tetrahedral water has been shown to be the very means to facilitate water's rapid dynamics; [21][22][23][24][25][26][27][28][29][30][31] if only tetrahedral water were present, then multiple molecules would have to interconvert simultaneously in order to preserve tetrahedrality, 16,32,33 an unlikely event. Fifthly, neutron diffraction shows that the structure of supercritical water is better described as trigonal rather than tetrahedral before breaking down entirely at higher pressure, 34,35 so it is unlikely that trigonal structure entirely disappears at more ambient conditions.…”

Section: Introductionmentioning

confidence: 99%

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Water's non-tetrahedral side

Henchman

Cockram

2013

Faraday Discuss.

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The case for liquid water having non-tetrahedral as well as tetrahedral coordination is put forward. Given the dependence of structure on the hydrogen bond definition, a recent conceptual breakthrough has been the topological hydrogen bond definition which overcomes the shortcomings of traditional cut-off-based hydrogen bond definitions. It identifies the hydrogen bonds in water's first coordination shell using assumed transition states as boundaries instead of fixed cut-offs. Here, the topological definition is applied to liquid water to characterise the distances, angles and energies of the hydrogen bonds for the different types of coordinations found. These coordinations include bent, trigonal, tetrahedral, trigonal bipyramidal, and octahedral structures, as well as bifurcated hydrogens, bifurcated oxygens and cyclic dimers, and larger polygons. All species are shown to have properties consistent with their classification, justifying their assignments, and supporting the structure of water as a continuous, single phase mixture. However, a detailed analysis to assess the existence of the assumed transition states reveals the remarkable finding that hydrogen bond switching via a bifurcated hydrogen under certain circumstances is a barrierless process. The likelihood of a switch depends on both the acceptor numbers and on the proximity of a donor to its acceptor. Specifically, a donor in an acceptor's outermost subshell switches uphill to an acceptor of the same or higher coordination to the starting acceptor, downhill to an acceptor of lower coordination by two or more, or sits bifurcated between two acceptors if the new acceptor has a coordination lower by only one. Which it is depends intimately on the donor molecule's oscillations and on other hydrogen bond switches that control the nearby acceptors' coordinations. Finally, a search is conducted for long-range structure in water in terms of asymmetry in the distribution of the donor-acceptor bias but none is found.

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Section: Topological Hydrogen Bond Denition and Water Structurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Water's non-tetrahedral side

Henchman

Cockram

2013

Faraday Discuss.

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“…The defects provide lower-energy pathways for reorientational motions and thus "catalyze" the restructuring of the infinitely connected network. [55] Such a process seems to be unlikely for the system under investigation. In DMSO a single water molecule forms two strong H bonds to the S=O groups.…”

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confidence: 98%

Structure and Dynamics of Water Confined in Dimethyl Sulfoxide

Wulf

Ludwig

2006

ChemPhysChem

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We study the structure and dynamics of hydrogen-bonded complexes of H2O/D2O and dimethyl sulfoxide (DMSO) by infrared spectroscopy, NMR spectroscopy and ab initio calculations. We find that single water molecules occur in two configurations. For one half of the water monomers both OH/OD groups form strong hydrogen bonds to DMSO molecules, whereas for the other half only one of the two OH/OD groups is hydrogen-bonded to a solvent molecule. The H-bond strength between water and DMSO is in the order of that in bulk water. NMR deuteron relaxation rates and calculated deuteron quadrupole coupling constants yield rotational correlation times of water. The molecular reorientation of water monomers in DMSO is two-and-a-half times slower than in bulk water. This result can be explained by local structure behavior.

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“…To characterize the symmetry of the local water environment, we consider the tetrahedron formed by the four nearest neighbor molecules around a central water molecule 40. As shown in Figure 5 a, the temperature dependence of P ( M T ) indicates a bimodal distribution at high temperatures, suggesting the presence of two major local structural forms,19, 41, 42 graphically illustrated in Figure 1. With decreasing temperature only the highly ordered structures prevail.…”

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confidence: 99%

Pressure and Salt Effects in Simulated Water: Two Sides of the Same Coin?

et al. 2007

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Water is certainly the most important liquid for life on earth. Moreover, it is also perhaps the liquid with the most puzzling physical properties. One of waters best known anomalies is the decrease of density upon cooling below 4 8C at atmospheric pressure. Other anomalous properties include the sharp increase of specific heat and compressibility upon cooling and supercooling. In addition to these thermodynamic features, the kinetic properties are also unusual, as the increase of diffusivity and decrease of viscosity upon compression indicate. [1,2] Adding solutes considerably broadens the spectrum of observed effects. For this reason the structure and dynamics of water in the vicinity of solutes have been studied for decades. The structure-making (kosmotrope) and structure-breaking (chaotrope) influence of ions on the hydration water has been understood as emerging from a balance between the water-water and ion-water interactions, which varies considerably with the charge density on the solute surface. [3][4][5][6][7][8][9] Lebermann and Soper used neutron diffraction to compare the effects of applied pressure and high salt concentrations on the hydrogen-bonding network of water. They found that the ions induce a change in structure equivalent to the application of high pressures, and that the size of the effect is ion-specific.[10] Similar effects have been reported by Botti et al., [11,12] who studied the solvation shells of H + and OH À ions in water. Mancinelli et al. could show that the structural perturbation due to monovalent ions (in aqueous solutions of NaCl and KCl) exists outside the first hydration shell of the ions.[13] Their study emphasized longer-ranged ion-induced perturbation and related shrinkages of the second and third coordination shells of water molecules, while the first hydration shell is largely unchanged. The O-O pair correlation function of water was modified by the ions in a manner closely analogous to what happens in pure water under pressure. In contrast, recent molecular dynamics (MD) simulations of aqueous CaCl 2 solutions indicate unequivocally that the changes of the water structure caused by the presence of ions in solution cannot be emulated as a pressure effect owing to the local nature of such a structure perturbation. [14] Growing evidence is emerging that the anomalous behavior of water and aqueous solutions is closely related to the existence of at least two major distinct local structural forms of water. [15,16] At low temperatures and at low to moderate pressures, water approaches a low-density liquid (LDL) state, which exhibits an almost perfectly interconnected random tetrahedral network. In the LDL state water has an average of four nearest neighbors, similar to the situation in ice I h (see Figure 1 a). Close to the low-density structure the mobility of water strongly slows down. [17][18][19][20][21][22] MD simulations suggest that defects in the random tetrahedral hydrogen-bonding network show fivefold water coordination. [18,22] With increasing pressure, these d...

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Water, Properties of

Cited by 9 publications

References 126 publications

Water's non-tetrahedral side

Water's non-tetrahedral side

Structure and Dynamics of Water Confined in Dimethyl Sulfoxide

Pressure and Salt Effects in Simulated Water: Two Sides of the Same Coin?

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