Chemical EngineeringChementator Briefs
Biomethane Last month, NextChem, a subsidiary of Maire Tecnimont S.p.A.…

Comment Processing & Handling

A more-sensitive way to differentiate chiral compounds

By Gerald Ondrey |

Circular dichroism (CD) is the established method for distinguishing between enantiomers — the optical isomers of molecules that are mirror images of each other. In this approach, circularly polarized light is passed through the sample and is absorbed differently by the enantiomers. Although CD is widely used in analytical chemistry, in biochemical research, and in the pharmaceutical and food industries, the signals are very weak: the light absorption of two enantiomers differs by just under 0.1%. There are various strategies for amplifying the signals, but these are only suitable if the sample is available in the gas phase. Most studies in chemistry and biochemistry, however, are carried out in liquid solutions.

Now, Swiss researchers from the Paul Scherrer Institute (PSI; Villigen; www.psi.ch), EPF Lausanne (www.epfl.ch) and the University of Geneva (www.unige.ch) have demonstrated a new method, which was reported in a recent issue of Nature Photonics. The new method exploits so-called helical dichroism (HD), which relies on the shape (helical) of the radiation’s wavefront, rather than its polarization.

At the Swiss Light Source (SLS) at PSI, the researchers were able, for the first time, to show that enantiomers can also be distinguished from each other using helical X-ray light. At the cSAXS beamline of SLS, they demonstrated this on a sample of the chiral metal complex iron-tris-bipyridine in powdered form (diagram). The signal they obtained was several orders of magnitude stronger than what can be achieved with CD. HD can also be used in liquid solutions and thus fulfills the prerequisite for applications in chemical analysis. The ability to distinguish enantiomers is also an important tool when separating them.

The researchers were able to create light with the desired properties with spiral-zone plates, diffractive X-ray lenses through which the X-rays pass before hitting the sample. “With the spiral zone plates, we were able, in a very elegant way, to give our X-ray light the desired shape and thus an orbital angular momentum. The beams we create in this way are also referred to as optical vortices,” says PSI researcher Benedikt Rösner, who designed and fabricated the spiral zone plates for this experiment.

Related Content
Pipes, Tubes and Fittings
A portable pipe beveling tool prepares pipe for welding The Wart Millhog Portable Pipe Beveler (photo) is a right-angle I.D.…
Achieving Balance in Combustion
New hardware combined with monitoring technologies can help optimize combustion now and in the carbon-conscious future Combustion has long been…

Chemical Engineering publishes FREE eletters that bring our original content to our readers in an easily accessible email format about once a week.
Subscribe Now
GMP In The Cosmetic Industry
Solve turbomachinery problems: Miba Tilting Pad Bearings
Six Steps to Designing a Storage Vessel That Really Works
SICK Solutions for Cleaner Industries - Powerful Transitions
Gain a Digital Line of Sight Across the Whole Lifecycle of the Plant with a Digital Twin

View More