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Synthesis and Characterization of Iron Dinitrosyl Complexes with Ligands that Mimic Histidine

Synthesis and Characterization of Iron Dinitrosyl Complexes with Ligands that Mimic Histidine. Chaitali Sheth California State University, Long Beach. Nitric Oxide. Active molecule in biological systems

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Synthesis and Characterization of Iron Dinitrosyl Complexes with Ligands that Mimic Histidine

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  1. Synthesis and Characterization of Iron Dinitrosyl Complexes with Ligands that Mimic Histidine Chaitali Sheth California State University, Long Beach

  2. Nitric Oxide • Active molecule in biological systems • Plays a vital role in giving men erections, lowering blood pressure, arming the immune system, and preventing premature birth and memory loss • Forms complexes with transition metals, such as Fe

  3. Dinitrosyl Iron Complexes • Non-heme iron dinitrosyl complexes store and release NO • Rhodococcus Sp contains a light-sensitive nitrile hydratase, which stores NO at its non-heme iron center • NO is released upon irradiation of the enzyme • It is difficult to isolate and characterize such enzymes

  4. Objectives • Synthesize iron dinitrosyl complexes using dinitrosyl dicarbonyl iron, Fe(NO)2(CO)2, with ligands that mimic biologically active compounds Histidine • Characterize the compounds with FT-IR, UV-Vis, Electron Paramagnetic Resonance (EPR), Nuclear Magnetic Resonance (NMR), and electrochemical techniques • Study the NO releasing kinetics of the compounds • Such compounds can be incorporated in potential drugs for medicinal use

  5. Previous Studies • Reactions of Fe(NO)2(CO)2 with 1-methylimidazole (1-MeIm) and imidazole (Im) have been carried out • Reaction conditions: • Temperature: 25°C • Solvents: ether and methylene chloride • Environment: N2 purged 1-MeIm Im

  6. X-ray Crystallographic Structures Fe(NO)2(1-MeIm)2 [Fe(NO)2(Im)]4

  7. [Fe(NO)2(Im)]4 • IR frequencies of nitrosyls in Fe(NO)2(CO)2 (1810 and 1767 cm-1) shifted upon the addition of Im (1796 and 1726 cm-1), suggesting the role of Im as a σ-donor.

  8. Cyclic Voltammetry • Cyclic voltammetry of the complex at a Pt electrode in THF and 0.1 M Tetrabutylammonium perchlorate showed a reversible one-electron reduction at E1/2 = -0.875 V with a scan rate of 0.1 V/s.

  9. EPR • EPR spectra of the complex were recorded at 170K in THF. The hyperfine, nine-line structure was a result of the coupling of two equivalent 14N nuclei from the nitrosyl and one 14N from the imidazole ligand. g = 2.035 Preliminary EPR Simulation EPR in THF

  10. UV-Vis Spectroscopy • The UV-Vis spectrum in THF showed three peaks at 759 (from d-d transition), 519 (metal-ligand charge transfer, MLCT), and 342 nm (from imidazole ligand). Probable MLCT

  11. Fe(NO)2(1-MeIm)2 • Fe(NO)2(1-MeIm)2 has been characterized by FT-IR and EPR spectroscopy. • IR frequencies of nitrosyls in Fe(NO)2(CO)2 (1810 and 1767 cm-1) shifted upon the addition of 1-MeIm (1673 and 1616 cm-1), suggesting the role of 1-MeIm as a σ-donor. • Fe(NO)2(CO)2 gave a broad peak with g = 2.0275 at 298 K. The addition of 1-MeIm gave a signal at g = 2.0151 at 240 K

  12. EPR • This signal was further resolved to a well-split, nine-line spectrum yielding a structure of Fe(NO)2(1-MeIm)2+.

  13. Synthesis • Synthesize iron dinitrosyl complexes with 5,6-dimethylbenzimidazole (Me2BzIm) and 4-methylimidazole (4-MeIm) with similar reaction conditions

  14. Fe(NO)2(L)2 Reactions • Reaction Scheme

  15. Characterization • FT-IR: To prove the carbonyl substitution by ligands • UV-Vis: To study the electronic behavior • NMR: To decipher the structure in the absence of a crystal structure • EPR: To examine the biological non-heme relevance • Cyclic Voltammetry: To study the redox behavior • NO Releasing Kinetics: By photolysis of products

  16. Cyclic Voltammetry • Can be used to study the binding mechanism of Fe to the ligands • React constant number of moles of Fe(NO)2(CO)2 with varying moles of the ligands http://nanonet.rice.edu/research/CVtutorial2/sld011.htm

  17. Recrystallization • Use a soluble solvent to dissolve the product • Filter through gravity filtration • Collect filtrate in a vial and add a few drops of a non-soluble solvent • Place the vial at considerably low temperature • Vapor diffusion techniques may be used

  18. Conclusions • From the preliminary data, it is established that the reaction of dinitrosyl dicarbonyl iron with ligands containing the imidazole moiety gives Fe(NO)2(L)2 or [Fe(NO)2(L)]4 type complexes • These complexes are easy to characterize to study their electronic and binding behavior • NO releasing kinetics can be easily studied from these complexes

  19. Acknowledgements Dr. Lijuan Li Dr. Ximeng Wang Howard Hughes Medical Institute

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