BRIGE: Redox Noninnocent Ligands - Application to the Reductive Transformation of Veterinary Pharmaceuticals Containing Carbon-Nitrogen Double Bonds

Temple University, Philadelphia PA

Investigators

Abstract

PI: Zhang, Huichun J. Proposal Number: 1125713 Research Objectives and Approach: Redox noninnocent ligands (RNILs) have been extensively studied by inorganic chemists on the redox-nature of the complexes formed with many transition metals. Yet, little information is available regarding the redox activity of RNILs, particularly as it pertains to the fate and transformation of emerging contaminants. On the other hand, soluble Fe(II) complexes with organic cathechol- and thiol-ligands, considered only as redox ligands in the literature, have been recently recognized for their ability to reduce a number of organic contaminants. Given the ubiquitous presence and fast redox reactivity of Fe(II) complexes in the environment, this lack of understanding of the nature of the ligands (., redox innocent versus noninnocent) will significantly prevent accurate estimation of the fate and transformation of emerging contaminants in reducing environments. For this reason, the proposed study will apply the concept of redox noninnocent ligands to the overall reductive transformation of a group of veterinary pharmaceuticals (VPs) containing carbon-nitrogen double bonds; the role and transformation of both the VPs and RNILs will be investigated from mechanistic perspective. Based on our preliminary results and the literature, we hypothesize that this group of VPs will undergo fast redox reaction with Fe(II) complexes with a number of RNILs including -catecholate, o'diaminophenylene, o-aminophenolate, o-dithiolene, and o-aminothiolate ligands. To test this hypothesis, a series of experiments have been structured (1) to illustrate the redox noninnocent nature of the complexes, (2) to determine the reaction kinetics and mechanism of the selected VPs and structurally related model compounds, and (3) to develop quantitative structural-activity relationships (QSARs) that can be used to predict reductive transformation of other structurally similar contaminants. Methodologically, the study will rely on diverse methods including but not limited to cyclic voltammatry, FTIR, HPLC, LC-MS-MS, NMR, and UV-visible measurements coupled with analytical determinations. Intellectual Merit: This study is one of the first to examine the redox noninnocent behavior of environmentally relevant Fe(II) complexes. Advanced experimental and interpretative methods will be used to generate knowledge that is critical for accurate modeling of environmental fates of an important group of VPs containing carbon-nitrogen double bonds, which are also a common structural moiety for many other emerging contaminants such as human pharmaceutical and personal care products and pesticides. The intellectual merit of this project is based on: 1) fundamental understanding of the redox noninnocent behavior of a number of Fe(II) complexes; 2) mechanistic understanding of the reduction reaction between the complexes and a group of VPs; and 3) development of QSARs that can be used to estimate the fate of other structurally related contaminants beyond VPs. On the basis of this project, the PI will be able to systematically study the role of many other metal(II)-RNIL complexes in the fate and transformation of a variety of emerging contaminants. Broader Impacts: Results of this project can be used by environmental scientists/engineers to develop environmental fate models to accurately predict the fate and transformation of organic contaminants in redox-active environments. Moreover, this project will contribute to training, mentoring and overall development of our graduate, undergraduate and high school students. Underrepresented minority and female students will be particularly encouraged to participate through a variety of activities planned with the pioneering CEET (Chemistry for the Environment - Education and Training) program, the Chapter of the Society of Women Engineers, College?s senior design course, Alliance For Minority Participation program, one-week residential summer program "Women's Engineering Exploration" and Department?s weekly seminars. Results and techniques of this study will be integrated into the environmental curriculum at the Temple University through a combination of lectures, experiments and demonstrations. In addition, findings from this project will be broadly disseminated to over 30 industrial partners at the annual industrial advisory board meetings of the Water and Environmental Technology (WET) Center at the Temple University.