Determining Molecular Chirality with Femtosecond Lasers

Lead Research Organisation: Queen's University of Belfast
Department Name: Sch of Mathematics and Physics

Abstract

A molecule is chiral, having left and right handed types, if one type cannot be rotated so that it is superposed on the other. These molecules have very similar chemical and physical properties such as having the same infrared(IR) and nuclear magnetic resonance (NMR) spectra. However, left and right handed chiral molecules often taste, smell and interact with biological systems very differently. Most drugs are chiral compounds and often only one type is the active agent while the other can be poisonous. This was dramatically demonstrated in the 1950s and 1960s when thalidomide was given to pregnant woman to cure morning sickness but resulted in terrible birth defects. The reason for these catastrophic consequences is that the molecules of life are homochiral, for instance nearly all amino acids are left-handed while sugars are right-handed. The reasons for the existence of biological homochirality and if it is a pre-requisite for life remain a subject of intense debate.

Chirality therefore has massive implications for the development of drugs and understanding life itself. However, present methods for identifying the different types of a chiral molecule are not very sensitive and mainly rely on the small differences in light absorption depending on whether the light is left or right circularly polarized. For this project a new conceptual approach based on asymmetry in the angular distribution of electrons emitted from photoionization of chiral molecules will be investigated. This phenomenon is several orders of greater in magnitude than current techniques and could provide a highly sensitive measurements of chirality in chemical samples. A prototype instrument is currently in development in our lab which uses femtosecond laser pulses to ionise the molecules. This device will be used for both fundamental studies and applications, such as to probe ultrafast changes in the structure of molecular motors and measuring the handedness of trace amounts of chiral compounds.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509541/1 01/10/2016 30/09/2021
1786238 Studentship EP/N509541/1 23/09/2016 31/03/2020 Caoimhe Maria Bond
 
Description We have shown that PECD can be used to determine the enantiomer differences in pharmaceutical drugs. A new smaller version of the equipment use to measure this PECD effect is currently in the initial testing stage , this device is more compact and as such is more commercially viable. In collaboration with CELIA in Bordeaux a new phenomenon based on PECD has been discovered called PEELD (Photoelectron Elliptical Dichroism), whereby the relationship between ellipticity and the asymmetry in the electron emission is not necessarily linear and is unique to each molecule so can act as a "fingerprint" to identify the molecule.
Exploitation Route New device in testing stage which may become commercially viable. The ability to measure PECD in pharmaceuticals may prove interesting to pharmaceutical companies for use in research and development processes. As chiral molecules, such as limonene, are also found in food produce this research could also be used in food development.
Sectors Agriculture, Food and Drink,Chemicals,Pharmaceuticals and Medical Biotechnology

 
Description We are beginning to show the usefulness of the PECD (PhotoElectron Circular Dichroism) effect and the ability of the equipment designed at QUB in determining the enantiomeric excess of pharmaceutically interesting molecules. We are also in discussions with a local engineering company about making the device available for industry. This impact is currently being developed and the results are unpublished so full information cannot be given, but we hope to publish before the end of the year.
First Year Of Impact 2018
Sector Chemicals,Pharmaceuticals and Medical Biotechnology