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A Possible Model for Nickel Superoxide Dismutase

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A Possible Model for Nickel Superoxide Dismutase SYNTHESIS AND CHARACTERIZATION OF NICKEL IMINE/AMINE COMPLEXES; A POSSIBLE MODEL FOR NICKEL SUPEROXIDE DISMUTASE A Thesis by Tom Muinde Mwania Bachelor of Science, Wichita State University, 2008 Submitted to the Department of Chemistry and the faculty of the Graduate School of Wichita State University in partial fulfillment of the requirement for the degree of Masters of Science May 2012 © Copyright 2012 by Tom Muinde Mwania All Rights Reserved SYNTHESIS AND CHARACTERIZATION OF NICKEL IMINE / AMINE COMPLEXES; A POSSIBLE MODEL FOR NICKEL SUPEROXIDE DISMUTASE The following faculty members have examined the final copy of this thesis for form and content, and recommended that it be accepted in partial fulfillment of the requirement for the degree of Master of Science with a major in Chemistry. _______________________________________ David M. Eichhorn, Committee Chair _______________________________________ D. Paul Rillema, Committee Member _______________________________________ William C. Groutas, Committee Member _______________________________________ George Bousfield, Committee Member iii DEDICATION For my family and friends, for all of their support iv ACKNOWLEDGEMENTS It would not have been possible to write this thesis without the help and support of Dr. David M. Eichhorn, principal supervisor, whom am really grateful for his patience with me, not to mention his advice and unsurpassed knowledge in chemistry and crystallography, his guidance and direction has really made an impact in my academic and research work. Also I would like to thank the rest of my committee members: Dr. Rillema, Dr. Groutas, and Dr. Bousfield, for their support and cooperation to make this possible. I would like to acknowledge the faculty and staff of the Wichita State University Chemistry Department for academic, technical and financial support. I would like to thank my lab and class colleagues both past and present: Anh Tran, Eric Oweggi, Nilmini, Nguyen, Lava, John, Wade and Megan. Finally, I would like to thank two of the most important people in my life i.e. my mum and my wife Kitra Mwania for their encouragement and patience during my graduate studies, and also my brothers and other family members, who have also been giving me their unequivocal support. v ABSTRACT Superoxide dismutases are ubiquitous enzymes that efficiently catalyze the disproportionation of superoxide radical anions to protect biological molecules from oxidative damage. Several SODs have been identified having different metals at their active sites. These include Mn SOD, Fe SOD, Cu/Zn SOD and, most recently, Ni SOD. The catalytic center of Ni SOD resides in the N-terminal active-site loop, where a Ni(II) is coordinated by the amine N of His-1, the amide N of Cys-2, and two thiolate S atoms of Cys-2 and Cys-6. In the oxidized form, Ni(III) adds the imidazole N of His-1 as an axial ligand. For the past decade, we have been developing methodology using 2, 2’-dithiodibenzaldehyde (DTDB) for the synthesis of metal complexes with mixed N/S coordination. We are reporting on the application of this methodology to the synthesis of model complexes for the active site of NiSOD, in which we II have successfully synthesized and characterized three Ni N2S2 complexes of imine/amine N t donors: Ni(NNS)SPh (1), Ni(NNS)SPhNO2 (2) and Ni(NNS)S Bu (3). These may be used as a model for reduced NiSOD, with future plans of comparing to complexes with amide/amine N donors, thus establishing the role of the amide. vi TABLE OF CONTENTS Chapter Page 1. INTRODUCTION……………………………………………………………………1 1.1 Superoxide Dismutases …………………………………………………………..1 1.1.1 Structure ……………………………………………………………...2 1.1.2 Redox Properties ……………………………………………………..3 1.1.3 Catalytic Mechanism …………………………………………………4 1.2 NiSOD Model Complexes ……………………………………………………….7 1.2.1 Computational Modeling ……………………………………………..7 1.2.2 Synthetic Models ……………………………………………………...9 1.2.3 Peptide Models …………………………………………………........16 1.3 Past DTDB work of relevance …………………………………………………...18 2. SYNTHESIS AND CHARACTERIZATION OF OTHER METAL COMPLEXE 2.1 Introduction ……………………………………………………………………….21 2.2 Ni(NNS)(SR) Complexes ………………………………………………………....22 2.2.1 Synthesis ………………………………………………………………22 2.2.2 Structural Characterization ……………………………………………23 2.2.3 Electronic Spectroscopy ………………………………………………28 2.2.4 Electrochemistry ……………………………………………………..29 2.3 Attempt to synthesize other nickel complexes…………………………..................31 2.3.1 Complexes with pendant N donor………………………………………31 2.4 Complexes with a propyl bridge…..……………………………………………......33 2.5 Complexes with other metal………..……………………………………………….34 2.6 Experimental ………………………………………………………………………..35 vii TABLES OF CONTENTS (continued) Chapter Page 2.6.1 General Experimental …………………………………………………35 2.6.1 Synthesis of Ni(NNS)SPh (1) …………………………………………37 2.6.1 Synthesis of Ni(NNS)SPhNO2 (2)……………………………………..37 2.6.1 Synthesis of Ni(NNS)StBu (3)…………………………………………38 2.6.1 Synthesis of Ni(NNS)’Cl ………………...……………………………38 2.6.1 Synthesis of Ni(NNS)’StBu ……………………………………………39 2.6.1 Synthesis of Co(deaeba)Cl3 (4) ………………………………………...39 2.6.1 Synthesis of Ni(NNS)SC2H4NH2 ……………………………………...40 2.6.1 Synthesis of Ni(NNS)SC2H4N(CH3)2 ………………………………….40 2.6.1 Synthesis of Ni(NNS)SEt ………………………………………………40 2.6.1 Synthesis of Ni(NNS)’SPh ……………………………………………..41 2.6.1 Synthesis of Ni(NNS)’SPhNO2 ………………………………………...41 3 CONCLUSION ………………………………………………………………………..42 REFERENCES ………………………………………………………….......................43 APPENDICES …………………………………………………………………………49 A. Crystallography Data Parameters …………………………………………..50 viii LIST OF TABLES Table Page 1.2.2.1 Electronic absorption spectral properties & oxidation potentials of complexes 2 – 6 reported in MeCN at 298 K ……………………………………………………11 1.2.3.1 The electrochemical values for compounds illustrated in Figure 1.2.3.1 ……………17 2.2.2.1 Selected bond length in (Å) & angles (°) for Ni(NNS)(SR) …………………………26 2.2.2.2 Shows bond distance (Å) for NiSOD & NiN2S2 model complexes ………………….27 2.2.3.1 Electronic absorption spectral properties in MeCN at 298 K ………………………...28 2.2.4.1 Oxidation & reduction potentials of compound 1 – 3 in MeCN at 298 K w/o Pyrazole……………………………………………………………………………….29 2.2.4.2 Oxidation & reduction potentials of compounds 1 – 3, in MeCN at 298 K w Pyrazole ………………………………………………………………………………29 2.6.1 Shows atomic bond distances between N1 – S1 & Co – N2 …………………………...34 ix LIST OF FIGURES Figure Page 1.1.1.1 Truncated structures of NiSODred & NiSODox ………………………………………..3 1.1.3.1 Proposed catalytic cycle for superoxide degradation in NiSOD. Ni3+ oxidation state is found in the unbound His-imidazole ring complex (structure I and II)……….5 1.1.3.2 NiSOD catalytic mechanism as proposed by Getzoff …………………………………6 1.2.1.1 Energy minimization of oxidized (NiIII(SOD-on)) and reduced ((NiII(SOD-off)) NiSOD computational models were performed by DFT methods …………………….8 1.2.2.1 Active site of Ni-SODred (left), Ni-SODox (middle), and Ni-SOD synthetic model systems, {Ni(nmp)(SR)}- (right). Bottom: R groups {RSH = HSC6H4-P-Cl (2), HStBu (3), o-benzoylaminobenzene thiol (4), N-(2-mercaptoethyl)benzamide (5), and N-acetyl –L-cysteine methyl ester (6) …………………………………………….9 t 1.2.2.2 ORTEP diagrams of Ni(nmp)(SC6H4-P-Cl)(2) and Ni(nmp)(S Bu) (3) as determined by Harrop ………………………………………………………………...10 1.2.2.3 ORTEP diagrams of the anion of (Et4N){Ni(nmp)(S-o-babt)} (4), (Et4N){Ni(nmp)(S-meb)} (5) …………………………………………………………10 1.2.2.4 Redox equilibrium between 1 (X-ray structure with 50% thermal ellipsoid &H atoms omitted) and 3* (optimized structure; Im = Imidazole)……………………………….......................................................................12 1.2.2.5 X-band EPR spectrum of 3 obtained after the addition of 2.5 equiv of Imidazole in electrogenerated 2, recorded in CH2Cl2 (0.1 M Bu4NPF6) at 100 K………………….........................................................................................................13 Ph,Me Ph,Me 1.2.2.6 X-ray crystal structure of Tp NiS2CNPh2(left), Tp NiS2CNEt2 (center), Ph,Me and Tp NiS2COEt (right) ………………………………………………………….13 1.2.2.7 Chemdraw of Masuda Ni(II) complex ………………………………………………...15 1.2.2.8 Ni(BEAAM) as determined by Shearer & Zhao ………………………………………15 x LIST OF FIGURES (continued) Figure Page 1.2.3.1 NiIII/II(SODM1-Im-X) X = Me, H, DNP, & TOS ………………………………………16 2.2.2.1 50% thermal ellipsoid ORTEP drawing of {Ni(NNS)SPh} (1), {Ni(NNS)SPhNO2} (2) and {Ni(NNS)StBu} (3) showing thermal ellipsoid for all non-hydrogen atoms (H-atoms omitted for clarity)………………………………………………………..24-25 2.2.4.1 Cyclic voltammogram of 1.8 mM compound 2 {Ni(NNS)SPhNO2} solution in CH3CN in 0.1 M tetrabutyl ammonium perchlorate at vitreous platinum electrode (3 mm diameter) ………………………………………………………….30 2.3.1.1 50% thermal ellipsoid ORTEP drawing of {Ni(NNS)Cl} (5)………………………….32 2.4.1 ESI-MS spectrum of {Ni(NNS)’StBu} ………………………………………………..33 2.5.1 ORTEP showing 50% thermal ellipsoid of {Co(deaba)Cl3} (4) ……………………...35 xi LIST OF SCHEMES Scheme Page 1.3.1 DTDB synthesis schematic ……………………………………………………………18 1.3.2 Synthesized compounds in our lab related to my research ……………………………19 2.2.1.1 Schematic formation of {Ni(NNS)SPh} (1), {Ni(NNS)SPhNO2} (2), t and {Ni(NNS)S Bu} (3) ……………………………………………………………..23 2.3.1.1 Schematic formation of compound (Ni(SNS))2 …………………………………….31 xii LIST OF ABBREVIATIONS Asp Aspartic Acid CH2Cl2 Dichloromethane Cys Cysteine deaeba 2- (2-Dimethylamino-ethyl)-benzo[d]isothiazol-2-ium tetraphenylborate DFT Density Functional Theory TD-DFT Time Dependent Density Functional Theory dmap N,N-dimethyldiaminopropane dmen N,N-dimethylethylenediamine
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