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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 Chaitali Sheth California State University, Long Beach
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
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
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
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
X-ray Crystallographic Structures Fe(NO)2(1-MeIm)2 [Fe(NO)2(Im)]4
[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.
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.
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
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
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
EPR • This signal was further resolved to a well-split, nine-line spectrum yielding a structure of Fe(NO)2(1-MeIm)2+.
Synthesis • Synthesize iron dinitrosyl complexes with 5,6-dimethylbenzimidazole (Me2BzIm) and 4-methylimidazole (4-MeIm) with similar reaction conditions
Fe(NO)2(L)2 Reactions • Reaction Scheme
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
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
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
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
Acknowledgements Dr. Lijuan Li Dr. Ximeng Wang Howard Hughes Medical Institute