Average number of hydrogen bonds

FIG. 13 Average number of hydrogen bonds (for definition see text) as a function of p in five simulations at different levels of hydration in a Vycor pore. Full hues show the number of water-water bonds, long-dashed hnes show the number of bonds between water molecules and Vycor, and short-dashed lines denote the sum of the two. From top to bottom, the frames correspond to a water content of about 96, 74, 55, 37, and 19% of the maximum possible (corresponding to 2600, 2000,1500, 1000, and 500 water molecules in a cylindrical cavity of about 4nm diameter and 7.13 nm length). (From Ref. 24.)... 

Table 6.8 shows the average number of hydrogen bonds formed between the phospholipid and water molecules. With an increase in cholesterol content, a slight increase in the total number of H-bonds between DPPC and water can be seen, while the number of H-bond bridges decreased. 

Tab. 6.8 Average number of hydrogen bonds per DPPC or cholesterol oxygen, formed with water molecules reported from several simulations. Data for DPPC and DPPC-cholesterol are taken from ref. 73 and data for DMPC-cholesterol sulfate are from ref. 75. Data for DMPC-cholesterol are taken from ref. 71 and data for pure DM PC are taken from ref. 74 and 106.

Although the average number of hydrogen bonds of each water molecule is notably reduced, it is possible to draw the conclusion that the hydrogen bond network persists partially also in the supercritical state, in qualitative agreement with the interpretation of new neutron diffraction experiments [61] and also with the measurements of the proton NMR chemical shifts [62]. 

Table 11-3. Hydrogen bonds of the 15-mer poly(vinyl alcohol) hydroxyl groups. The first line for each system gives the average number of hydrogen bonds of a given type at any time point, the second line gives in parentheses their average life times (ps)a. The table is taken from Muller-Plathe [78]...

Fig. 8 Total average number of hydrogen bonds (a) and the corresponding total hydrogen bonding energy (b) between the carbonyl oxygen of cocaine benzoyl ester and the oxyan-ion hole in the simulated the prereactive BChE-cocaine complex (ES), transition states, intermediates, and product for BChE-catalyzed hydrolysis of (-)-cocaine [115]...

Furthermore, the explicit-water simulations do include the CDS terms to the extent that dispersion and hydrogen bonding are well represented by the force field. Finally, by virtue of the solvent being explicitly part of the system, it is possible to derive many useful non-entropy-based properties "" (radial distribution functions, average numbers of hydrogen bonds, size and stability of the first solvation shell, time-dependent correlation functions, etc.). Since many of these properties are experimentally observable, it is often possible to identify and correct at least some deficiencies in the simulation. Simulation is thus an extremely powerful tool for studying solvation, especially when focused on the response of the solvent to the solute. 

Figure 5. Panel a density profiles of water (solid line) and of nitrobenzene (dotted line) at 7= 300K. The liquid/liquid interface is near Z = OA, and there is also a water liquid/vapor interface near Z = -30 A. Panel b Average number of hydrogen bonds per water molecule (solid line, left vertical axis) and the fraction Pjj of unbroken hydrogen bonds (dotted line).

Figure 5.2 shows the thermal average, < T>, of the average number of hydrogen bond partnerships involving water molecules within the desolvation domain for each residue. Three dehydration hot spots are apparent, comprising residues 171-181, 236-246, and 270-289, respectively. The location of these hot spots corresponds to the three major dehydron clusters shown in Fig. 5.3. 

Fig. 5.2 Thermal average of the average number of hydrogen bond partnerships, T, for water molecules located within the desolvation domain of each residue in the DNA-binding domain of p53. If no water is found in the desolvation domain (buried residue), the bulk water value T =4 is adopted. Reprinted with permission from [19] copyright 2007 American Chemical Society...

Table 1.7 The average number of hydrogen bonds per water molecule at ambient pressures according to various approaches...

We can define the average number of hydrogen bonds made by a molecule as... 

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