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Design of Photocage Ligands for Light-Activated Changes in Coordination of D-Block

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Design of Photocage Ligands for Light-Activated Changes in Coordination of D-Block Design of Photocage Ligands for Light-Activated Changes in Coordination of d-block Transition Metals by Katie L. Ciesienski Department of Chemistry Duke University Date:_______________________ Approved: ___________________________ Katherine J. Franz Ph.D, Supervisor ___________________________ Alvin L. Crumbliss, Ph.D. ___________________________ Michael C. Fitzgerald, Ph.D. ___________________________ Jiyong Hong, Ph.D. Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry in the Graduate School of Duke University 2010 ABSTRACT Design of Photocage Ligands for Light-Activated Changes in Coordination of d-block Transition Metals by Katie L. Ciesienski Department of Chemistry Duke University Date:_______________________ Approved: ___________________________ Katherine J. Franz, Ph.D., Supervisor ___________________________ Alvin L. Crumbliss, Ph.D. ___________________________ Michael C. Fitzgerald, Ph.D. ___________________________ Jiyong Hong, Ph.D. An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry in the Graduate School of Duke University 2010 Copyright by Katie L. Ciesienski 2010 Abstract The concept of light-activated “caged” metal ions was first introduced for Ca 2+ . These high affinity coordination complexes are activated by UV light to release calcium ions intracellularly and have found widespread use in understanding the many roles of calcium in biological processes. There is an unmet need for photocaging ligands for biologically relevant transition metal ions. Described here are the first examples of uncaging biologically important d-block metal ions using photoactive ligands. New nitrogen-donor ligands that contain a photoactive nitrophenyl group within the backbone have been prepared and evaluated for their metal binding affinity. Exposure of buffered aqueous solutions of apo-cage or metal-bound cage to UV light induces cleavage of the ligand backbone reducing the denticity of the ligands. Characterization of several caging compounds reveals that quantum efficiency and metal binding affinity can be tuned by modifications to the parent structure. The change in reactivity of caged vs. uncaged metal for promoting hydroxyl radical formation was demonstrated using the in vitro deoxyribose assay. The function of several of these compounds in vivo pre- and post-photolysis has been validated using MCF-7 cells. This strategy of caging transition metals ions is promising for applications where light can trigger the release of metal ions intracellularly to study metal trafficking and distribution, as well as, selectively impose oxidative stress and/or metal toxicity on malignant cells causing their demise. iv Dedication I dedicate my dissertation to my mom and dad for all their love and support. v Contents Abstract .........................................................................................................................................iv List of Tables.............................................................................................................................. xiii List of Figures .............................................................................................................................xiv List of Schemes......................................................................................................................... xvii Acknowledgements ...................................................................................................................xix 1. Keys for Unlocking Photolabile Metal Cages...................................................................1 1.1 Locked Metal Cages ....................................................................................................2 1.2 Unlockable Metal Cages .............................................................................................4 1.2.1 Unlockable Metal Cages Type 1: Photoactive Ligand........................................5 1.2.1.1 Calcium Cages ................................................................................................6 1.2.1.2 d-Block Metal Cages.....................................................................................11 1.2.1.3 Copper Cages................................................................................................11 1.2.1.4 Zinc Cages .....................................................................................................16 1.2.1.5 Iron Cages ......................................................................................................19 1.2.1.6 Platinum Cages.............................................................................................22 1.2.1.7 Ruthenium and Rhodium Cages................................................................27 1.2.2 Unlockable Metal Cages Type 2: Photoactive Metal........................................28 1.2.2.1 Ruthenium Cages .........................................................................................29 1.2.2.2 NO Cages.......................................................................................................30 1.2.2.3 CO Cages .......................................................................................................32 1.3 Summary and Outlook .............................................................................................33 vi 2. A Photolabile Ligand for Light-Activated Release of Caged Copper.........................36 2.1 Background and Significance...................................................................................36 2.2 Materials and Methods .............................................................................................39 2.2.1 Materials and Instrumentation............................................................................39 2.2.2 Synthesis.................................................................................................................40 2.2.2.1 Pyridine-2-carboxylic acid {1-(2-nitro-phenyl)-2-[(pyridine-2-ylmethyl)- carbamoyl]-ethyl}-amide (H 2cage) ..............................................................................40 2.2.2.2 [Cu(OH 2)(cage)] ............................................................................................42 2.2.3 Deoxyribose Assay................................................................................................42 2.2.4 Quantum Yield ......................................................................................................44 2.2.5 Potentiometric and Spectrophotometric Titrations..........................................44 2.2.6 Competition Study of Nitrilotriacetic Acid (NTA) vs. H 2cage for Cu 2+ .........46 2.2.7 X-Ray Data Collection and Structure Solution Refinement ............................46 2.3 Results .........................................................................................................................48 2.3.1 [Cu(OH 2)(cage)] pK a and log β Determination.................................................48 2.3.2 Crystal Structure of [Cu(OH 2)(cage)] .................................................................56 2.3.3 Photolysis of [Cu(OH 2)(cage)] .............................................................................62 2.3.4 Quantum Yield ......................................................................................................66 2.3.5 Effects of [Cu(OH 2)(cage)] in the Deoxyribose Assay......................................66 2.4 Discussion...................................................................................................................69 2.4.1 Stability of [Cu(OH 2)(cage)].................................................................................69 2.4.2 Crystal Structure of [Cu(OH 2)(cage)] .................................................................69 vii 2.4.3 Efficiency of Photolysis ........................................................................................70 2.4.4 Hydroxyl Radical Formation...............................................................................70 2.5 Summary and Conclusions ......................................................................................72 3. A Caged Platinum(II) Complex that Increases Cytotoxicity upon Light Activation 73 3.1 Background and Significance...................................................................................73 3.2 Materials and Methods .............................................................................................77 3.2.1 Materials and Instrumentation............................................................................77 3.2.2 Synthesis.................................................................................................................78 3.2.2.1 [Pt(cage)]........................................................................................................78 3.2.3 X-Ray Data Collection and Structure Solution Refinement ............................78 3.2.4 Characterization of Photoproducts.....................................................................79 3.2.5 Quantum Yield ......................................................................................................80 3.2.6 Cell Culture............................................................................................................82 3.2.7 Cytotoxicity Assay ................................................................................................82
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