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Synthetic Modeling of Nitric Oxide (No) and Nitroxyl (Hno) Reactivity at Copper Sites

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Synthetic Modeling of Nitric Oxide (No) and Nitroxyl (Hno) Reactivity at Copper Sites SYNTHETIC MODELING OF NITRIC OXIDE (NO) AND NITROXYL (HNO) REACTIVITY AT COPPER SITES A Dissertation submitted to the Faculty of the Graduate School of Arts and Sciences of Georgetown University in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry By Kamille D. Williams, M.S. Washington, DC May 25, 2016 Copyright 2016 by Kamille D. Williams All Rights Reserved ii SYNTHETIC MODELING OF NITRIC OXIDE (NO) AND NITROXYL (HNO) REACTIVITY AT COPPER SITES Kamille D. Williams, M.S. Thesis Advisor: Timothy H. Warren, Ph.D. ABSTRACT The N-O functionality is ubiquitous endogenously. The wide range of oxidation states of the nitrogen atom, (+5 to -3), is attributed to the various biologically relevant congeners containing the NO functionality. The simplest form of the N-O moiety is nitric oxide (NO), a stable free radical, which plays an important role in several biological processes such as neurotransmission, immune function, and oxidative stress. The one electron reduced form of nitric oxide is nitroxyl (HNO). Nitroxyl functionality is similar to but distinct from nitric oxide and some report the endogenous formation of NO via nitric oxide synthase (NOS) actually produces a nitric oxide precursor, presumably HNO. The actual production of nitric oxide requires co-factor copper-zinc superoxide dismutase (CuZnSOD), which has been shown to react with HNO to produce NO at a 4 -1 -1 - rate of k = 9 × 10 M s in the same manner as superoxide dismutases convert O2 to O2. This work seeks to study the interaction between copper and nitroxyl and the formation of a copper-nitroxyl ([Cu](HNO) complex via computational studies and utilization of analogous nitrosobenzene (PhNO). Three binding modes (κ1-N, κ1-O, and η2-ON) were identified for both copper β-diketiminate nitroxyl ([Cu](HNO)) and nitrosobenzene ([Cu](PhNO) complexes. The two viable binding modes (κ1-N and η2-ON) were relatively close in energy and are in exchange at room temperature. The binding of nitrosobenzene to copper results in changes to the copper oxidation state as suggested by x-ray crystallography, cyclic voltammetry, and x-ray absorption iii studies. All of these studies suggest copper-nitrosobenzene complexes may be best classified as copper(II) compounds bound to nitrosobenzene where the ON bond order is 1.5. The β-diketiminate copper nitrosobenzene complexes can be synthesized via (a) the addition of nitrosobenzene to corresponding copper(I) acetonitriles (b) the double deprotonation of N- phenylhydroxylamine by copper(II) hydroxides and (c) via the disproportionation of N- phenylhydroxylamine via corresponding copper(I) acetonitriles. This work proposes a mechanism for the disproportionation of N-phenylhydroxylamine and investigates the requisite copper(II) nitroxide intermediates. The mechanistic insights and isolated intermediates put forth in this work will add potential inferences for larger related systems and can give insights into how to effect these biological NO processesing. iv ACKNOWLEDGEMENTS The research and writing of this thesis is dedicated to everyone who helped along the way. There are a few individuals, however, that I must thank especially. First to God. I am most thankful for the strength and resources you give me, for the wisdom to slam a few doors for my own sanity, and the fresh air that wafts in through the windows you had already opened. Thank you. To my Warren Group labmates. You all have taught me about Chemistry, life, and surviving the difficult times that comprise graduate school, and I could not be more grateful. To the old batch: Yosra Badiei, Marie Melzer, Matt Varonka, Stefan Wiese, Ray Gephart, Allan Cardenas, Joanne Aguila, Dan Seidenberg, Sarah Fried, Nick Sapiezynski, Grace Jang, and Shiyu Zhang, and to the new: Allison McQuilken, Subrata Kundu, T. Kaum Salvador, Gus Bakhoda, Mehdi Raghibi, Sima Sakhaei, Val Hosseininasab, Christine Iseley, and Evan Gardner thank you from the bottom of my heart and up. To the undergraduates who have worked with me: Michelle White, Evan Green, Jenn Oliva, Sophia Chung, Alex Gee, and Paola Santos, my work couldn’t have been as good as it was without you. To my friends whose existence in world makes it a better place. To my crew who were with me before I began my PhD journey, Lydia Patrick, Danielle Rosario-Mullen, Christopher Calfee, Melissa Buchanan, and Osei Gyamfi. I am so grateful for our friendship, our deep conversations regarding life and the pursuit happiness, and the amazing adventures that are our life’s bread. To my Georgetown inner set, Stephanee Synnott and Sayon Kumalah Robinson, your friendship, understanding, and empathy continue to be invaluable to me. Thank you all. v To my family, for your support and bent ears. This thesis and degree could not have been possible without you. Thanks mom for being that mom whose support, love, and friendship were NEVER in doubt and for giving me my dramatic flair and zest for life. Thanks Grams (aka Grumma) for being an inspiration and sharing your stories and insight on the world. And most certainly to my husband, Seth Zucker. Seth, I swear I don’t know how you do it, but thank you for loving me as you do, for understanding my unfinished sentences, and bearing with my cat-like tendencies. No backsies. To everyone who has served on my committee, Bahram Moasser, Rodrigo Maillard, Sarah Stoll, Christian Wolf, and Toshiko Ichiye, thank you for all your guidance, your tough questions, and support thoughout my Georgetown career. A special thank you to my thesis defense committee Sarah Stoll, Christian Wolf and Toshiko Ichiye for making time in their schedule for the defense and for your helpful feedback. And, truly saving the best for last, to Timothy H. Warren. There are times I truly believe that we are where we’re supposed to be, and I wouldn’t be very far without Tim. I wouldn’t have my condo in DC, my PhD degree, and my current life aspirations if it not for him. There is no aspect of my world that he hasn’t improved and I’m thankful. I can only hope that I have had one tenth of an impact on you as you have had on me. Thank you for your support, mentorship, friendship, inspiration, enthusiasm, patience, and all around sheer awesomeness. Many thanks and with so much love, Kamille D. Williams vi TABLE OF CONTENTS Chapter 1 Reactivity of Nitroso Compounds at Copper ............................................ 1 1.1 Introduction ................................................................................................................ 1 1.2. Nitric oxide (NO) ...................................................................................................... 6 1.2.1. Physiological aspects of NO ............................................................................ 6 1.2.2. Formation of NO .............................................................................................. 7 1.2.3. Conversion of NO to organic and redox derivatives ....................................... 8 1.2.4. Metal – nitrosyl (NO) complexes .................................................................... 9 1.2.4.a. NO binding to transition metals .............................................................. 9 1.2.4.b. Copper – NO model complexes ............................................................ 10 1.3. Nitroxyl (HNO) ....................................................................................................... 12 1.3.1. Physiological aspects of HNO ....................................................................... 12 1.3.2. Formation of HNO ......................................................................................... 14 1.3.3. Metal – nitrosyl (HNO) complexes ................................................................ 15 1.3.3.a. HNO binding to transition metals ......................................................... 15 1.3.3.b. Copper – HNO model complexes ......................................................... 17 1.4. Hydroxylamines (H2NOH) ..................................................................................... 19 1.4.1. Physiological aspects of H2NOH ................................................................... 19 1.4.2. Formation of H2NOH ..................................................................................... 19 1.4.3. Conversion of H2NOH to other NO congeners .............................................. 20 1.4.4. Metal – hydroxylamine (H2NOH) complexes ............................................... 20 1.4.4.a. R2NOH binding to transition metals ..................................................... 20 vii 1.4.4.b. Copper – R2NOH interactions .............................................................. 23 1.5. C-Nitroso compounds (RNO) .................................................................................. 23 1.5.1. Physiological aspects of RNO ....................................................................... 23 1.5.2. Formation of RNO ........................................................................................ 25 1.5.3. Conversion of RNO to other NO congeners .................................................. 25 1.5.4. Metal – C-nitroso (RNO) complexes ............................................................. 26 1.5.4.a. RNO binding to transition metals ......................................................... 26 1.5.4.b. Copper – RNO metal complexes .......................................................... 28 • 1.6. Nitroxides (R2NO ) ................................................................................................
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