Determining Molecular Chirality with Femtosecond Lasers

一个分子是手性的，有左旋和右旋两种类型，如果一种类型不能旋转，所以它叠加在另一种类型上。这些分子具有非常相似的化学和物理性质，例如具有相同的红外(IR)和核磁共振(核磁共振)光谱。然而，左旋手性分子和右旋手性分子与生物系统的味道、气味和相互作用往往截然不同。大多数药物都是手性化合物，通常只有一种是活性物质，而另一种可能是有毒的。这一点在20世纪50年代和60年代得到了戏剧性的证明，当时给孕妇服用沙利度胺来治疗晨吐，但导致了可怕的出生缺陷。造成这些灾难性后果的原因是，生命的分子是同型手性的，例如，几乎所有的氨基酸都是左旋的，而糖是右旋的。生物手性存在的原因以及它是否是生命的先决条件仍然是一个激烈辩论的主题。因此，手性对于药物的发展和对生命本身的理解具有巨大的影响。然而，目前用于识别不同类型的手性分子的方法并不是非常敏感，并且主要依赖于光的吸收的微小差异，这取决于光是左圆偏振还是右圆偏振。在这个项目中，将研究一种新的概念方法，该方法基于手性分子光电离发射的电子的角分布的不对称性。这一现象比目前的技术大几个数量级，可以对化学样品中的手性进行高度灵敏的测量。我们实验室目前正在开发一种原型仪器，它使用飞秒激光脉冲来电离分子。该装置将用于基础研究和应用，如探测分子马达结构的超快变化和测量痕量手性化合物的利手性。

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.