Water dimer structure hydrogen bond

While crystal structures of rubredoxins have been known since 1970 (for a full review on rubredoxins in the crystalline state, see Ref. (15)), only recently have both crystal and solution structures of Dx been reported (16, 17) (Fig. 3). The protein can be described as a 2-fold symmetric dimer, firmly hydrogen-bonded and folded as an incomplete /3-barrel with the two iron centers placed on opposite poles of the molecule, 16 A apart. Superimposition of Dx and Rd structures reveal that while some structural features are shared between these two proteins, significant differences in the metal environment and water structure exist. They can account for the spectroscopic differences described earlier. 

FIG. 3 The vapor phase water dimer structure. Polar covalent bonds are shown as solid lines and the hydrogen bond as a dashed line (adapted from Ludwig, 2001). 

Water forms a hydrogen-bonded dimer, the structure of which has been determined by microwave spectroscopy, as shown in Fig. 16.3.1(b). The experimental value of the binding energy of this dimeric system is 22.6 kJ mol-1. 

Figure 10 gives the results for the water dimer. The optimized water dimer structure also compared well with recent gas-phase experimental data on the gas water dimer by Dyke (1984) r00 = 2.98A and tilt angle = 123°. The energy obtained in forming the hydrogen bond is given in Table 2. 

Fig. 3. Stereoview of the inclusion complex between a hydrogen-bonded dimer of host 3 with water and methylene chloride as guests. The crystal structure of this compound contains two additional species, a disordered CH Clj and fractional water (donated by S ). Both lie outside the complex between the bound water and an adjacent host unit (taken from Ref.28>)...

Fig. 8. Stereoscopic illustration of the inclusion compound of host 5 (folded conformation) with acetic acid and 2 mol of water. Host-host and host-water hydrogen bonding interactions stabilize the structure. The solvation layers consist of cyclic carboxy dimers of acetic acid surrounded by water species (crystal data a = 7.857, b = 11.379,c = 13.831 A,a = 92.50,/i = 101.21, y = 101.12°, space group Pi taken from Ref. 351)...

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