Investigation of Reactive Radical Intermediates for the Development of X-ray Photonanochemistry

University Of California-Davis, Davis CA

Investigators

Abstract

One of the most important molecules in our life is DNA, which can be broken into pieces in water after exposure to powerful, invisible X-ray radiation. Although X-ray-induced damage to DNA can cause harmful effects to our health, it can also be used beneficially in a number of applications including radiation therapy for cancer treatment. The rate of such damage is found to be accelerated by the presence of tiny metal particles, such as gold particles whose dimensions are on the order of a small fraction of the diameter of a human hair. However, the cause for acceleration in the speed of DNA damage is not fully understood. With the support from the Macromolecular, Supramolecular and Nanochemistry Program of the NSF Division of Chemistry, Professor Guo at the University of California at Davis aims to develop a novel approach to achieve a better fundamental understanding of this important and complex chemical process. The outcome of this research can potentially help scientists tailor these important reactions for applications ranging from disease treatment to catalytic cleavage of synthetic polymers. This interdisciplinary project at the interface of chemistry, biology, and materials science provides valuable research training opportunities and improves competitiveness of students including underrepresented minority students. The X-ray induced DNA strand breaking process in water is generally believed to start with the generation of reactive oxygen species (ROS) by X-rays. The ROS then react with DNA to form reactive DNA intermediates, which subsequently leads to the breaking of the DNA strands. While it was discovered recently that this process can be accelerated in the presence of gold nanoparticles, the mechanism for such catalytic process is not understood. In order to decipher these important and complex reactions, Professor Guo's group develops a novel approach to generate and monitor the reactive intermediates. The approach features nanoreactors irradiated by an X-ray beam. The nanoreactors containing catalyst assemblies are designed and synthesized to control the chemical environment, and the timing of X-ray irradiation, the size of the X-ray beam, and the position of the catalyst assemblies in the nanoreactors are controlled so that the conversion of reactive intermediates to broken DNA strands can be spatially and temporally separated from the production of ROS. Such separation simplifies the interpretation process and allows the identification of the intermediates and measurement of their lifetime, leading to the elucidation of the reaction mechanisms. The anticipated outcome of this project is the development of a novel technique that is useful not only for elucidating X-ray induced chemical reactions (such as DNA strand breakage) but also for controlling chemical reactions that can be used to harvest or detect X-rays through the conversion of X-ray energy to chemical energy. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.