This award by the Inorganic, Bioinorganic, and Organometallic Chemistry Program supports Professor David Tyler at the University of Oregon to investigate the fundamental, underlying principles of radical cage effects with the overall goal of better understanding radical reactivity. The research will focus on four aspects of cage effects. In one study, the still-confusing role of the solvent will be explored using a new model based on the microviscosity of the solvent. Another study will focus on what effect the wavelength of light has on the cage effect in photogenerated radical cage pairs. Preliminary results show a trend opposite to that predicted by theory, and a new principle of dynamics may be uncovered in these experiments. A third investigation will seek confirmation for the existence of secondary (solvent separated) cage pairs. Secondary cage pairs have been hypothesized to explain the effect of radical rotation on radical-radical recombination reactions but secondary cage pairs have not been unequivocally identified. Finally, as part of a study to explore how solvents specifically interact with solute molecules, a fourth study will explore how H-bonding to an H2 ligand in a metal-H2 complex can affect the reactivity of the H2 ligand. The results of these four investigations will give researchers an in-depth understanding of cage effects and how they impact radical reactivity. Although the studies involve organometallic radicals, the fundamental principles uncovered will apply to radicals of all types, whether organic, inorganic, or biochemical. Graduate students involved with this project participate in internship programs. These innovative programs prepare Ph.D. students for successful careers in industry or in academics by placing them in regional companies or in colleges for a one-term internship experience. Companies and colleges are enthusiastic about the program because they have the opportunity to work with interns who have an up-to-date knowledge of chemistry, instrumentation, laboratory techniques, computer skills, and the scientific literature. The research program also fosters closer collaborative ties with local companies and colleges. This has led to professors at regional colleges taking sabbatical leaves in Professor Tyler's lab and to outside students using the instrumentation in the University of Oregon Chemistry Department. Underrepresented groups will have a strong presence in the graduate and undergraduate student audience that participates in the research.
This project studied a phenomenon that occurs when chemical bonds break during a reaction that occurs in solution. The phenomenon is known as the "cage effect." When chemical bonds break, in order for the reaction to continue, it is important for the two parts of the molecule that are produced by breaking the bond to move away from each other. If they don’t move away from each other then the bond will simply reform and there is no net reaction. It is not easy for the particles to move away from each other because the solvent molecules surrounding the particles act as a "cage," which tends to keep the molecules close to each other. Chemists have known about the "cage effect" for decades, but we have only a rudimentary knowledge about the factors that determine the efficiency of "cage escape." It is important to know about the efficiency of "cage escape" because the rates of many important reactions are governed by the "cage escape" efficiency. For example, the manufacture of plastics is governed by "cage escape" efficiencies. Likewise, the degradation of pollutants in our lakes and streams is governed by "cage escape" efficiencies. Despite the major impacts that "cage effects" have on chemical reactivity, at the time we started this research it was surprising that no quantitative predictive knowledge of the "cage effect" was available. The research funded by this grant was designed to redress this situation. Thus, we showed that the mass of the particles in the solvent cage was an important factor in determining their ability to escape the solvent cage. (The more massive the particle, the more likely it was to escape the solvent cage.) Likewise, the size of the particles was important. (For a given mass, the bigger the particle the less likely it was to escape the cage.) The shape of the particle was also important: slender, rod-like particles could escape the cage more easily than more roundish particles. Of course, we quantified these results by expressing them as a mathematical equation relating cage escape probability to size, mass, and shape. In our most practical application of this work, we were able to apply the results described above to the degradation of plastics. Specifically, we showed that "cage effects" are a primary factor in controlling the decomposition rate of plastics. Importantly, we obtained a mathematical equation that can be used to predict the lifetime of plastics when they are exposed to sunlight. It is our intention to use this equation to design plastics that degrade after their useful lifetime, thereby preventing the build-up of waste plastics in the environment. Support from the NSF also enabled my graduate students and me to work on several goals related to the broader impacts of scientific research. Thus, five years ago, four colleagues and I developed a course on the "Chemistry of Sustainability" that we teach to 200 non-science majors every spring term. The course has several themes, including sustainability and green chemistry, as well as the theme that chemists are problem solvers. These themes give me the opportunity to present lectures on the green aspects of modern chemical production (catalysis, use of "earth-abundant" metals as catalysts, energy efficiency, and process design for fewer pollutants). My co-teachers and I discuss the value of doing fundamental research (for example, my NSF-supported research) and how the information learned in these studies may someday be used to improve production efforts. My research group and I worked with 23 undergraduates and 2 high school students over the past five years on the NSF-supported project. Of these 25 students, 14 were women and 2 were African-American. In doing so, this research project contributed to the NSF goal of helping to develop a globally competitive STEM workforce and to increasing the participation of women and under-represented minorities in STEM.
