Hydrogen-bonded solids

FIGURE 12.37 Tertiary interactions in yeast phenylalanine tRNA. The molecnle is presented in the conventional cloverleaf secondary strnctnre generated by intrastrand hydrogen bonding. Solid lines connect bases that are hydrogen-bonded when this cloverleaf pattern is folded into the characteristic tRNA tertiary strnctnre (see also Figure 12.36). 

Molecular solids have their lattices composed of molecules held in place by London forces, dipole-dipole forces, and hydrogen bonding. Solid methane and water are example of molecular solids. 

Barium titanate is one example of a ferroelectric material. Other oxides with the perovskite structure are also ferroelectric (e.g., lead titanate and lithium niobate). One important set of such compounds, used in many transducer applications, is the mixed oxides PZT (PbZri-Ji/Ds). These, like barium titanate, have small ions in Oe cages which are easily displaced. Other ferroelectric solids include hydrogen-bonded solids, such as KH2PO4 and Rochelle salt (NaKC4H406.4H20), salts with anions which possess dipole moments, such as NaNOz, and copolymers of poly vinylidene fluoride. It has even been proposed that ferroelectric mechanisms are involved in some biological processes such as brain memory and voltagedependent ion channels concerned with impulse conduction in nerve and muscle cells. 

The most common solid form of water is known as ice Ih (hexagonal ice), with the molecular structure as shown in Figure 2.1 from Durrant and Durrant (1962). In ice each water molecule (shown as a circle) is hydrogen bonded (solid lines) to four others in essentially tetrahedral angles (Lonsdale, 1958). A description of... 

Cyclohexane-1,3-dione is an interesting, but problematic, /J-diketone. Calculational, (cited) spectroscopic and calorimetric studies131 show that it exists as the hydroxyenone 56a in die intermolecularly hydrogen-bonded solid and is most stable as the diketone 56b in the gas. From the experimentally measured enthalpy of formation of this dione at —335.6 1.6 kJ mol-1, we find that reaction 52... 

In the case of intercalates we have seen how the inclusion of guests swells the layers, such that the materials respond dynamically to the intercalation process. We now turn to a different approach in which a crystal engineering based design strategy has created rigid, well-defined materials based on ionic hydrogen-bonded solids in which polar guanidinium disulfonate layers - (C(NH2)3+)2... 

The excess of AH of sublimation above that of a non-hydrogen-bonded solid can be attributed to hydrogen bonds. 

Note that the ability of the H DQ MAS technique to determine accurately the distances in hydrogen bonded solids can also provide an independent distance constraint for the refinement of the structure from X-ray diffraction data [25]. This is somewhat analogous to the use of NOE constraints measured by solution NMR for protein structure determination and promises to be a widely applicable approach once techniques based on H DQ MAS are routinely available. 

Fig. 2.18 Graph set assignments for the binary level of a-glycine. As in Fig. 2.17, different types of hydrogen bonds (solid lines) are distinguished by labelling with lower case bold letters carbon and hydrogen atoms are shown as open circles, oxygen atoms as solid circles, and nitrogen atoms as shaded circles. (From Bernstein and Davis 1999, with permission.)...

Kaliaperumal, R., Sears, R. E. J., Ni, Q. W., and Furst, J. E., Proton chemical shifts in some hydrogen bonded solids and a correlation with bond lengths, J. Chem. Phys. 91,7387-7391 (1989). 

STRUCTURE-PROPERTY RELATIONS FOR HYDROGEN-BONDED SOLIDS... 

Dalai, N., Klymachyov, A. and Bussmann-Holder, A. (1998). Coexistence of order-disorder and displacive features at the phase transitions in hydrogen-bonded solids squaric acid and its analogs. Phys. Rev. Lett. 81, 5924-5927. 

C.N. Tam, P. Bour, J. Eckert F.R. Trouw (1997). J. Phys. Chem. A, 101, 5877-5884. Inelastic neutron scattering study of hydrogen-bonded solid formamide. 

Fig. 51. Variations of the conformational energy for association II of HONCHO H2O. a) Rotation of H2O around the axes, b) Rotation around the 97 axis (i.e. around the hydrogen bond), c) Rotation around the axis (non-linearity of the hydrogen bond). Solid line SCF results dashed line model. From Ref. 69>...

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