Chemistry Reference
In-Depth Information
Fig. 6 The typical disorder of CX
3
peripheral groups about the pseudo threefold axis (
left
) and the
typical pedal motion disorder about the central double bond in E-stilbene kind of molecules (
right
)
observations, especially because of the larger amplitudes of motions in these
samples. In addition, proteins are often damaged by the incident radiation and
cryo-protection is vital. As a consequence, the low temperature is a must for protein
crystallographers [
32
], because it is relevant for the structure solution, not only for
the refinement. However, cryo-crystallographic studies are not without
disadvantages. For example, the crystal quality might be damaged by the cooling,
in particular flash cooling. Moreover, some debate is open on the actual biological
relevance of structures determined at 100 K, but intended to answer questions about
phenomena occurring at 300 K [
55
].
2
In macromolecular crystallography, another
debate is ongoing concerning the improvements when using helium as cryogenic
agent [
56
] and therefore measuring the data at temperatures well below 80 K.
2
More generally, one may ask whether a (macro)molecule frozen in the solid state can really be
representative of the structure in solution, where the molecule is in fact active.
