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物种；大多数能量低于20 eV。这种低能电子(LEE)在包括天体化学、光化学和放射治疗在内的一系列领域中发挥着关键作用。为了理解和/或控制这种现象，需要关于分子和生物分子材料内部和界面上发生的李氏诱导过程的数据。我们在未来五年的目标是在两个不同的具有重要科学意义的领域研究Lee相关现象：*i)Lee对DNA和DNA复合体的损伤(DNAC，由结合潜力或临床上可用的放射增敏剂或化疗药物与DNA形成)：我们将在逐渐接近细胞中遇到的实验条件下，表征DNA和DNAC中日益复杂的靶点(例如DNA亚基、寡核苷酸、质粒DNA等的膜)中Lee相互作用的基本机制。这将通过在超高真空(UHV)或大气压下，在这些薄膜中共吸附O2、H2O、氨基酸及其混合物来实现。因此，这项研究试图更好地理解与细胞分子密切接触的DNA和DNAC中Lee诱导的过程。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李氏光源。由于DNA是放射治疗的靶点，这项工作将有助于确定新的模式和分子制剂，以改善单独放射治疗或联合化疗的癌症治疗。先前关于LEE辐射对生物分子损伤的这些基本方面的研究得到了CIHR的支持，但目前CIHR更合适的是将资金仅用于此类工作的临床应用。*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，在天文数据的解释和复杂分子的合成方面具有相当大的当前兴趣。因此，在这类冰中由Lees引发的化学可能与宇宙和紫外线辐射形成的生物前分子以及生命的起源有关。我们将继续研究在超高真空中形成的薄膜冰上的李驱动化学。它们将包含H2O、NH3、CO2、CO和CH4等分子的混合物，这些分子凝聚在星际介质中的尘埃颗粒上，并存在于彗星和行星冰中。在我们最近对Lee辐射冰块中甘氨酸的鉴定工作的基础上，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，我们将专注于鉴定主导产品产量的基本物理机制，包括瞬时阴离子形成。这项研究旨在促进李-分子相互作用领域的最高水平的研究质量，激发学术兴趣，并提供一个激动人心的培训环境。

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.*****