Neutron diffraction studies white

Fig. 10.5 In the vapour state, formic acid exists as both (a) a monomer and (b) a dimer, the structures of which have been determined by electron diffraction, (c) In the solid state, a more complex assembly is formed as revealed in a neutron diffraction study of deuterated formic acid, DCO2D the figure shows part of the packing diagram for the unit cell. [A. Albinati et al. (1978) Acta Crystallogr., Sect. B, vol. 34, p. 2188.] Distances are in pm. Colour code C, grey O, red H, white D, yellow.

Kundrot and Richards (1987, 1988) described the solvation shell in the hen egg white lysozyme crystal, in connection with a study of the compressibility of protein and solvent. Mason et al. (1984) carried out a neutron diffraction analysis of triclinic lysozyme at 1.4 A resolution, with 239 water molecules included in the refinement. 

Figure 6 Neutron studies of CjsCsfNHj), (from top to bottom x= 1.90, 1.54, 1.25, 0.94, 0.74, 0.42, 0.20, 0.0). (A) Rotational tunnelling spectra and (B) neutron diffraction patterns recorded simultaneously at 4.2 K as a function of x. (Data recorded with IRIS at ISIS). Reproduced with permission from Cariile CJ, Jamie IM, Lockhart G and White JW (1992) Two-dimensional caesium-ammonia solid solutions in C28Cs(NH))x. Molecular Physics 76 173-200.

Some of the powerful biophysical techniques of structure determination can be and have been applied to fluid phase bilayers. Wiener and White published a series of papers in the early 1990s on a method to combine neutron and X-ray diffraction data to arrive at one of the most detailed pictures of a fluid phase bilayer determined by experiments thus far. Unfortunately, the degree of hydration of this system was much lower than what is biologically interesting and what is used in most simulations. Recently the structure of a fully hydrated DPPC bilayer was determined from X-ray methods. This study will provide a stringent test of simulations of DPPC. It provides accurate values for the area per lipid (62.9 1.3 A), bilayer form factors which can be obtained from electron density profiles, volume per lipid, and water stochiometry. 

---