Chiral Molecules in Intense Laser Fields

Abstract

Chiral molecules play a prominent role in diverse fields such as biochemistry, physics, biology and most importantly pharmaceutical industry. Chiral molecules are non-superimposable mirror images of each other. Every species in nature shows specific chiral properties in chemical structures as well as macroscopic anatomy. Humans left and right hand are an example of chirality, you cannot superimpose them no matter how you rotate them. The left and right handed molecules are known as enantiomers. They have the same number of atoms but they are arranged differently. Additionally, chiral molecules have identical physical and chemical properties, yet the two enantiomers interact differently with chiral light or with another chiral molecule. Chiral molecules do not exist equally in nature, some of these molecules exist only in one form of the two enantiomers such as sugars, amino acid, enzymes and DNA. This plays an important role in pharmaceutical industry because diff erent enantiomers of a chiral drug will have different e ffects on our cells. These enantiomers can often exhibit diff erent metabolism rate, potency, or toxicity. For example, the S-enantiomer citalopram which is used to treat depression is 30 times stronger than the R-enantiomer. Therefore, techniques for detecting and quantifying chirality are very important tools for drug development. The interaction of light with matter gives us the insight to understand enantiomer structure and the ability to distinguish them. Advances in laser technology have enabled the study of molecular interactions with light, specifi cally, intense light pulses. Due to the importance of chiral diff erentiation, several techniques have been developed. However, these techniques have their limitations, for example, the drawback of the circular dichroism method is that the measurement is done in liquid samples and has poor sensitivity. Thus, this led to the development of the photoelectron technique to avoid solvent e ects. Furthermore, in the case of the Coulomb explosion method, it cannot be done with large molecules because it is hard to detect all the fragments. Finally, the high harmonic generation method by Cireasa et al (2015); is complicated and consists of three steps as described in section (1.2.5). Therefore, in this thesis, we used a new simple technique to detect chirality. Molecular photoionization enables chiral discrimination via mass spectrometry depending on elliptical polarized light. This thesis demonstrates the ability of photoionization mass spectrometry to discriminate enantiomers using elliptically polarized light. The rst chapter describes existing techniques to characterize chiral molecules and the most used technique to study chirality as well as a description of strong eld ionization with the emphasis on the process of photoionization which results in chiral discrimination. The second chapter of this thesis describes the experimental methods and strong eld double ionization technique capable of distinguishing chirality. The third chapter contains the results and discussion. The last chapter presents the future work and conclusion.