Scientists have been able to demonstrate, for the first time ever, the ability to quickly and reliably identify the chirality of different molecules present in the same mixture
[Translation by Dr. Nachmani Moshe]
Scientists were able to demonstrate, for the first time ever, the ability to quickly and reliably identify the chirality of different molecules present in the same mixture.
The research, led by chemists from the University of Nottingham and the University of Amsterdam, published in the prestigious scientific journal Nature Communications, will be able to offer an innovative method for determining whether a molecule exists in a chiral form (Chirality) one or the opposite. The breakthrough could be important for the development of effective molecules for use in a wide range of fields and industries - from the development of safer medicines and disease diagnostics to the development of pesticides that are less toxic to humans and the environment.
Many of the molecules exist in forms that are virtually identical, except for the fact that they are exact mirror images of each other, like our two palms. In biological systems, molecules with only one type of chirality usually appear, although the scientific community still does not fully understand why this is what happened in nature. For example, although both configurations of amino acids (the building blocks of life itself) can be prepared in the laboratory, in nature they occur in only one configuration.
The chirality of these biomolecules also significantly affects the way they react with other molecules, for example, with chiral drugs. Today, more than half of the drugs produced in the commercial market are active in only one of their two possible configurations. The lead researcher explains: "This is true for molecules such as sugars and also for much larger macromolecules, for example DNA. People are well aware of the double helix structure of DNA, but most of them are not aware that the helices always twist in the same direction and not in the other possible direction. The chemistry of life is picky about chirality. It's like having only one type of glove of the two types (right hand and left hand). Just as it would be difficult for you to shake another human's left hand with your right hand, the same is true for molecules that react with each other. If you refer to a molecule with left chirality, it will have priority in its reaction with a molecule with left or right chirality".
Chirality is important because it may affect the properties and function of apparently identical molecules, effects that can be recognized in the human body. A classic example is the chirality of pairs of molecules that emit completely different aromas. The limonene scent molecule - which is used as a citrus fruit fragrance and as a fat delivery agent in a wide variety of household cleaning products - is well known for its ability to smell like either oranges or lemons, depending on the chirality of the individual molecule. In the field of pharmacy, chirality can be critical in view of the fact that one form can produce a positive result and the other lead to negative side effects, as in the well-known case of the drug thalidomide given to pregnant women in the sixties.
An existing method for distinguishing between opposite chiral forms, called circular dichroism, involves exposing the molecules to a circularly polarized light beam and measuring the difference in light absorption by the different molecules. However, the size of the different effects is low - only fractions of a single percent - so this method struggles to reach the level of sensitivity of a human nose. The research demonstrates a new and fast method that can be used for the detection of chiral molecules, a method that produces more tangible results with a higher level of accuracy. The new method - Mass-Selected PhotoElectron Circular Dichroism (MS-PECD) - utilizes circularly polarized light produced by a laser to ionize the molecules by removing an electron from their content. By tracking the direction in which the electron that detaches from the molecule moves - either in the direction of the front of the laser beam or in the direction opposite to the beam - it is possible to differentiate between the different chirality of the molecules while obtaining a level of accuracy of tenths of a percent, a level many times greater than the levels obtained by existing methods.
The method also incorporates mass spectroscopy during which a small electrical voltage is applied to the negatively charged electron and the positively charged ion, a voltage that causes them to move away from each other in opposite directions. In this way, the researchers are able to simultaneously locate both the electron and the positive ion derived from it, when if they arrive at the detectors at the same time, it is likely that they came from the same molecule. The mass of the ion can be measured and matched to its corresponding electron. By combining these two methods, it is possible to determine both the chirality of the molecules and their relative amount in a given mixture.
Another advantage of the new method lies in the fact that within its framework it is possible to use gaseous samples and not high concentrations of the substance in the solution. The method could be important for the development of effective molecules for use in a wide range of fields and industries - starting with the development of safer medicines and diagnosing diseases and ending with the development of "green" pesticides that are less toxic to humans and the environment. Chiral molecules are also emitted from several types of plants and trees when these are found in stressful conditions and thus the detectors capable of measuring their concentrations in air samples can be used to monitor the ecological changes occurring in our environment. In the field of the food industry, the new method will allow companies to adjust more efficiently the concentrations of odorants and flavors added to the food and drinks we consume.
