Low-energy electron induced processes in radiation damage: relationship to astrochemistry, radiobiology and radiotherapy

二次电子是物质中高能辐射产生的最丰富的种类；大多数能量低于20ev。这种低能电子（LEEs）在一系列领域发挥着关键作用，包括天体化学、光化学和放射治疗。为了理解和/或控制这种现象，需要在分子和生物分子材料内部和界面处发生的lee诱导过程的数据。在接下来的五年里，我们的目标是在两个不同的科学领域研究LEE相关的现象：i) LEE引起的DNA和DNA复合物（DNAC，由潜在的或临床可用的放射增敏剂或化疗药物与DNA结合而形成）的损伤；我们将描述DNA和DNAC中LEE相互作用的基本机制，这些相互作用的目标越来越复杂（例如，DNA亚基膜、寡核苷酸、质粒DNA等），在逐渐接近细胞中遇到的实验条件下。这将通过在超高真空（UHV）或大气压下在这些薄膜中共同吸附O2、H2O、氨基酸及其混合物来实现。因此，本研究旨在更好地了解lee诱导的DNA和DNAC与细胞分子密切接触的过程。为了实现这一目标，我们将继续开发最先进的双分子薄膜技术和新的LEE源。由于DNA是放疗的靶点，这项工作将有助于确定新的模式和分子药物，以改善单独放疗或联合化疗的癌症治疗。以前对lee诱导的辐射对生物分子的这些基本方面的研究得到了CIHR的支持，但目前CIHR的资助更适合于这些工作的临床应用。（ii）天体化学：分子冰的辐射处理，就像在空间环境中发现的那样，对于解释天文数据和合成复杂分子具有相当大的意义。因此，这些冰中LEEs引发的化学反应可能与宇宙和紫外线照射下生命起源前分子的形成有关。我们将继续研究在特高压下形成的薄膜冰的lee驱动化学。它们将包含H2O、NH3、CO2、CO和CH4等分子的混合物，这些分子在星际介质中凝结在尘埃颗粒上，存在于彗星和行星冰中。基于我们最近在lee辐照冰中鉴定甘氨酸的工作，我们将尝试研究其他氨基酸、小肽、DNA碱基和相关分子的形成。在这两个领域，我们将专注于确定主导产品产量的基本物理机制，包括瞬态阴离子形成。本研究旨在促进lee -分子相互作用领域的最高水平的研究质量，激发学术兴趣，并提供一个激励的培训环境。

Secondary electrons are the most abundant species produced by high-energy radiation in matter; most have energies below 20 eV. Such low-energy electrons (LEEs) play key roles in a range of fields, including astrochemistry, photochemistry and radiation therapy. To understand and/or control of such phenomena, data is needed on LEE-induced processes occuring within, and at the interfaces of, molecular and biomolecular materials. Our objective during the next five years is to study LEE related phenomena in two distinct scientifically significant areas: i) LEE induced damage to DNA and DNA complexes (DNAC, formed by binding potential or clinically-available radiosensitizers or chemotherapeutic agents to DNA): We will characterize the fundamental mechanisms of LEE interactions in DNA and DNAC in targets of increasing complexity (e.g., films of DNA subunits, oligonucleotides, plasmid DNA, etc.,) under experimental conditions that progressively approach those encountered in cells. This will be done by coadsorbing in these films O2, H2O, amino acids and mixtures thereof, under ultrahigh vacuum (UHV) or at atmospheric pressure. Thus, this research seeks an improved understanding of LEE-induced processes in DNA and DNAC in close contact with cellular molecules. To achieve this goal, we will continue to develop state-of-the-art bimolecular thin-film technology and new LEE sources. Since DNA is the target in radiotherapy, this work will help identify new modalities and molecular agents to improve cancer treatment with radiotherapy alone or combined with chemotherapy. Previous research on these fundamental aspects of LEE-induced radiation damage to biomolecules was supported by the CIHR, but presently CIHR funding is more appropriately requested only for the clinical applications of such work. ii) Astrochemistry: radiation processing of molecular ices, like to those found in space environments is of considerable current interest for the interpretation of astronomical data and the synthesis of complex molecules. The chemistry initiated by LEEs in such ices may thus relates to the formation of pre-biotic molecules by cosmic and UV irradiation and the origins of life. We will continue our studies into LEE-driven chemistry on thin-film ices formed in UHV. These will contain mixtures of molecules such as H2O, NH3, CO2, CO and CH4 that condense upon dust grains in the interstellar medium and are present in comets and planetary ices. Building on our recent work on the identification of glycine in LEE-irradiated ices, we will attempt to investigate the formation of other amino acids, small peptides, DNA bases and related molecules. In both areas, we will focus on the identification of basic physical mechanisms that dominate product yields, including transient anion formation. This research is intended to promote the highest levels of research quality in the field of LEE-molecule interactions, spur academic interest and provide a stimulating training environment.