Chain of hydrogen-bonded water molecules

Suhai128 investigated water dimer and an infinite chain of hydrogen-bonded water molecules by means of the DFT and post-Hartree-Fock calculations. For the infinite system, the DFT(BLYP), MP2, and MP4 binding energies were within 0.2 kcal/mol, whereas the corresponding interatomic distances were within 0.04 A. A similar agreement was reported for water dimer. 

In the calculations of the energy of hydration of metal complexes in the inner coordination sphere, one must consider hydrogen bond formation between the first-shell water molecules and those in bulk water, which leads to chains of hydrogen-bonded water molecules. Such hydrogen-bonded chains of ethanol molecules attached to the central metal ion have been found as a result of DFT B3LYP calculations on ethanol adducts to nickel acetylacetonate, where the calculated energy of hydrogen bonds correlated well with experimental data [90]. 

Extended chains of hydrogen-bonded water molecules proposed by Christian von Grotthuss in the early 19th century to explain electrolyte conductance in water. ... 

In ice a chain of hydrogen-bonded water molecules links the hydroxide and the hydrogen ions (Eq. 9-94). By synchronous movement of electron pairs from the OH ion and from each of the water molecules in the... 

The third alternative is proton exchange along hydrogen-bonded water molecules (33-35). In bacteriorhodopsin, for example, a recent structural model at 3.5-A resolution strongly suggests that water molecules form a narrow channel and are involved in proton delivery to the chromophore (36). The remainder of this review will discuss chains of hydrogen-bonded water molecules as potential proton translocators and describe some initial tests of the concept. 

How might this knowledge be applied to proton flux through the F0 subunit The F0 subunit of the E. coli ATP synthase is composed of approximately 10 a-helical c subunits associated with one a subunit and two b subunits (27). It seems reasonable to suggest as a working hypothesis that the c subunits encircle the a subunit. Their a-helices and those of the a subunit would then form complexes within the lipid bilayer with protonconducting characteristics similar to those described in the model system of Lear et al. If the complexes are tetramers of associated a-helices, chains of hydrogen-bonded water molecules would be able to translocate protons across the assembled F0 subunit. 

We conclude that a chain of hydrogen-bonded water molecules is able to translocate protons at a rate sufficient for measured ATP synthesis if the proton supply from the bulk phase is adequate. In the physiological pH range, the question of proton supply to a putative proton channel becomes... 

We observe that the solvent is arranged as a one dimensional chain of hydrogen bonded water molecules, whose properties are considerably different than ordinary three dimensional water. For example, this linear water is a better ion solvent than three dimensional water in terms of solvation energy as a function of distance from the ion to the water. In addition, the 25 A long chain of waters tends to translate as a correlated unit, thus leading us to discuss the possibility of water structures in proteins acting as the intermediary for chemical action at a distance, particularly in allosteric effects in enzymes. ... 

The probability P(TP ig) calculated from (96) can be used to assess the quality of reaction coordinates. For a good reaction coordinate, all transition states, i.e., the states x with large probability P(TP x), should correspond to approximately the same value of the reaction coordinate. Hence, the probability E (TP ) should be a sharply peaked function with a maximum at the transition state value of q. For a poor reaction coordinate, on the other hand, P(TP ) is expected to be rather featureless according to (95), as in this case no strong correlation between the value of q x) and the probability P(TP x) exists. Best and Hummer have successfully used this approach to test reaction coordinates for the folding of a simple three-helix bundle protein and the collective dipole flip of ordered one-dimensional chains of hydrogen-bonded water molecules in narrow carbon nanotubes [261]. 

Fig. 23.12. Results of computer studies simulating the hydration of amino acids, (top) self-bridging loops of hydrogen-bonded water molecules around alanine (center) polar bridging chains between polar solute atoms of threonine (bottom) water networks associated with the apolar groups of leucine [847]...

The model proposed does not imply that at a given moment the environment of all water molecules is identical. Indeed, some water molecules may, in addition to being hydrogen bonded to each other, also form hydrogen bonds with the polymer, whereas others may be exclusively hydrogen bonded to each other. At any instant long, essentially linear, chains of H-bonded water molecules exist. Diffusion of such a cluster occurs if some water molecules break H-bonds with the polymer and, simultaneously, others in the same cluster form H-bonds with the polymer, without breakage of H-bonds between water molecules. 

Clathrate hydrates are ice-like materials that belong to the category of inclusion compoimds. They consist of a sohd network of hydrogen bonded water molecules that form cavities encaging various guesf molecules such as methane, carbon dioxide or small hydrocarbon chains. Hydrates have attracted significant industrial and scientific interest as a result of their involvement in a number of important applications [1]. In particular, hydrate formation is a major concern for safety and flow assiuance in gas and oil pipelines, as well as in unit operations where high pressures and moderately low temperature conditions exist, such that hydrate formation is possible. 

Fig. 35.—(a) Stereo view of about a turn of the 3-fold double helix of potassium gellan (41). The two chains are drawn in open and filled bonds for distinction. Both intra- and inter-chain hydrogen bonds stabilize the helix. The vertical line is the helix axis. Octahedrally coordinated potassium ions (crossed circles) and triply hydrogen-bonded water molecules (open circles) located above the ions are integral components of the structure of 41. 

Water Vapor transmission. Table 3 lists water vapor transmission (WVTR) values for selected polymers. Comparison of Tables 1 and 3 shows that often there is a reversal of roles. Those polymers that are good oxygen barriers are often poor waler-vapor barriers and vice versa. This can be rationalized as follows. Barrier polymers often rely on dipole-dipole interactions to reduce chain mobility and, licncc, diffusional movement of pcrmcants. These dipoles can be good sites for hydrogen bonding. Water molecules are attracted to these sites. Polymer molecules without dipole—dipole interactions, such as polyolefins, dissolve very little water and have low. WVTR and permeability values. The low values of S more than compensate for the naturally higher values of D. 

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