Feb 11 2016
The phenomenon of X-ray diffraction by crystals was discovered more than a century ago, and since then it has been a preferred technique for structure determination. It has established its presence in structural research in the fields of biology, and material science. However, many materials whose structures are unknown, do not easily crystallize as three-dimensional structures.
Crystallization modifies the properties of a material; for example, the function of a protein that is crystallized may be different from that in its natural state. Enclosing structures, including carbon nanotubes in a crystal lattice, can modify their behavior. Acta Crystallographica Section A’s March issue will feature an innovative method developed by Jüstel, Friesecke and James to study these types of structures, utilizing twisted X-rays [Acta Cryst. (2016)]. The researchers show that in order to obtain diffraction data from symmetric, non-crystalline structures, including helices, the symmetry of incident radiation has to match with the symmetry of the structure of interest.
The twisted waves with helical structures produce exciting resonance effects, and this implies that this could be a promising method to determine structures. If the twisted X-rays are sent to a helical structure, and the waves, detector and the structure are axially aligned, then the radiation displays discrete, sharp peaks, since the incident wavelength and the degree of twist are different. Structure determination from the diffraction model works similar to that of crystals. The authors used computer simulations to demonstrate the structure accuracy discovered by twisted X-rays is comparable to that produced by conventional X-ray techniques.
Surprisingly, the new method can be used to determine important structures in the field of biology, and a number of structures in nanoscience: the parts of many viruses, actin, buckyballs and many fullerenes, and graphene, carbon nanotubes, and several two-dimensional structures including those of black phosphorus and the dichalcogenides.
The only thing left to do is to design a machine for twisting the X-rays.
Source: http://www.iucr.org/iucr