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

Mimic HistidineMimic Histidine

Chaitali ShethChaitali Sheth

California State University, Long BeachCalifornia State University, Long Beach

Nitric OxideNitric Oxide

• Active molecule in biological systemsActive molecule in biological systems• Plays a vital role in giving men erections, Plays a vital role in giving men erections,

lowering blood pressure, arming the immune lowering blood pressure, arming the immune system, and preventing premature birth and system, and preventing premature birth and memory lossmemory loss

• Forms complexes with transition metals, such as Forms complexes with transition metals, such as FeFe

Dinitrosyl Iron ComplexesDinitrosyl Iron Complexes

• Non-heme iron dinitrosyl complexes store and release Non-heme iron dinitrosyl complexes store and release NONO

• Rhodococcus Sp Rhodococcus Sp contains a light-sensitive nitrile contains a light-sensitive nitrile hydratase, which stores NO at its non-heme iron hydratase, which stores NO at its non-heme iron centercenter

• NO is released upon irradiation of the enzymeNO is released upon irradiation of the enzyme• It is difficult to isolate and characterize such enzymesIt is difficult to isolate and characterize such enzymes

ObjectivesObjectives

• Synthesize iron dinitrosyl complexes using dinitrosyl Synthesize iron dinitrosyl complexes using dinitrosyl dicarbonyl iron, Fe(NO)dicarbonyl iron, Fe(NO)22(CO)(CO)22, with ligands that mimic , with ligands that mimic biologically active compoundsbiologically active compounds

Histidine Histidine

• Characterize the compounds with FT-IR, UV-Vis, Electron Characterize the compounds with FT-IR, UV-Vis, Electron Paramagnetic Resonance (EPR), Nuclear Magnetic Paramagnetic Resonance (EPR), Nuclear Magnetic Resonance (NMR), and electrochemical techniquesResonance (NMR), and electrochemical techniques

• Study the NO releasing kinetics of the compoundsStudy the NO releasing kinetics of the compounds• Such compounds can be incorporated in potential Such compounds can be incorporated in potential

drugs for medicinal usedrugs for medicinal use

Previous StudiesPrevious Studies

• Reactions of Fe(NO)Reactions of Fe(NO)22(CO)(CO)22 with 1- with 1-

methylimidazole (1-MeIm) and imidazole (Im) methylimidazole (1-MeIm) and imidazole (Im) have been carried out have been carried out

• Reaction conditions: Reaction conditions: – Temperature: 25Temperature: 25°C°C

– Solvents: ether and methylene chlorideSolvents: ether and methylene chloride

– Environment: NEnvironment: N22 purged purged

ImIm

1-MeIm1-MeIm

X-ray Crystallographic X-ray Crystallographic StructuresStructures

Fe(NO)Fe(NO)22(1-MeIm)(1-MeIm)22

[Fe(NO)[Fe(NO)22(Im)](Im)]44

[Fe(NO)[Fe(NO)22(Im)](Im)]44

• IR frequencies of nitrosyls in Fe(NO)IR frequencies of nitrosyls in Fe(NO)22(CO)(CO)22 (1810 and (1810 and

1767 cm1767 cm-1-1) shifted upon the addition of Im (1796 and ) shifted upon the addition of Im (1796 and 1726 cm1726 cm-1-1), suggesting the role of Im as a σ-donor), suggesting the role of Im as a σ-donor..

Cyclic VoltammetryCyclic Voltammetry

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

EPREPR

• EPR spectra of the complex were recorded at 170K in EPR spectra of the complex were recorded at 170K in THF. The hyperfine, nine-line structure was a result of THF. The hyperfine, nine-line structure was a result of the coupling of two equivalent the coupling of two equivalent 1414N nuclei from the N nuclei from the nitrosyl and one nitrosyl and one 1414N from the imidazole ligand.N from the imidazole ligand.

[G]3250 3260 3270 3280 3290 3300 3310

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

[*10^ 3]

[G]3410 3415 3420 3425 3430 3435 3440 3445 3450

-30

-20

-10

0

10

20

30[*10^ 3]

EPR in THFEPR in THF

g = 2.035

Preliminary EPR SimulationPreliminary EPR Simulation

UV-Vis SpectroscopyUV-Vis Spectroscopy

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

Molar Absorption Coefficient

y = 7269.5x - 0.003

R2 = 0.9836

0

0.5

1

1.5

2

2.5

3

3.5

0 0.0001 0.0002 0.0003 0.0004 0.0005

Concentration (M)

Abs

orpt

ion

Probable MLCT

Fe(NO)Fe(NO)22(1-MeIm)(1-MeIm)22

• Fe(NO)Fe(NO)22(1-MeIm)(1-MeIm)22 has been characterized by has been characterized by

FT-IR and EPR spectroscopy.FT-IR and EPR spectroscopy.

• IR frequencies of nitrosyls in Fe(NO)IR frequencies of nitrosyls in Fe(NO)22(CO)(CO)22

(1810 and 1767 cm(1810 and 1767 cm-1-1) shifted upon the addition ) shifted upon the addition of 1-MeIm (1673 and 1616 cmof 1-MeIm (1673 and 1616 cm-1-1), suggesting the ), suggesting the role of 1-MeIm as a σ-donorrole of 1-MeIm as a σ-donor..

• Fe(NO)Fe(NO)22(CO)(CO)22 gave a broad peak with g = gave a broad peak with g =

2.0275 at 298 K. The addition of 1-MeIm gave a 2.0275 at 298 K. The addition of 1-MeIm gave a signal at g = 2.0151 at 240 Ksignal at g = 2.0151 at 240 K

EPR EPR

• This signal was further resolved to a well-split, This signal was further resolved to a well-split, nine-line spectrum yielding a structure of nine-line spectrum yielding a structure of Fe(NO)Fe(NO)22(1-MeIm)(1-MeIm)22

++..

SynthesisSynthesis

• Synthesize iron dinitrosyl complexes with 5,6-Synthesize iron dinitrosyl complexes with 5,6-dimethylbenzimidazole (Medimethylbenzimidazole (Me22BzIm) and 4-BzIm) and 4-

methylimidazole (4-MeIm) with similar reaction methylimidazole (4-MeIm) with similar reaction conditionsconditions

N

HNCH3

CH3

5,6-dimethylbenzimidazole (Me2BzIm)

N

HN

CH3

4-methylimidazole (4-MeIm)

Fe(NO)Fe(NO)22(L)(L)22 Reactions Reactions

• Reaction SchemeReaction Scheme

FeNO

NO CO

CO

+

N

HNCH3

CH3

2 CO N

NH

CH3

CH3

Fe

ON

ON

HN

N

H3C

CH3

2

+

N

HN

CH3

FeNO

NO CO

CO

+

2 CO Fe

ON

ON

N

HN

CH3

HN

N

H3C

2

+

CharacterizationCharacterization

• FT-IRFT-IR: To prove the carbonyl substitution by : To prove the carbonyl substitution by ligands ligands

• UV-VisUV-Vis: To study the electronic behavior: To study the electronic behavior

• NMRNMR: To decipher the structure in the absence : To decipher the structure in the absence of a crystal structure of a crystal structure

• EPREPR: To examine the biological non-heme : To examine the biological non-heme relevancerelevance

• Cyclic VoltammetryCyclic Voltammetry: To study the redox : To study the redox behavior behavior

• NO Releasing KineticsNO Releasing Kinetics: By photolysis of products: By photolysis of products

Cyclic VoltammetryCyclic Voltammetry

• Can be used to study the binding mechanism of Can be used to study the binding mechanism of Fe to the ligandsFe to the ligands

• React constant number of React constant number of moles of Fe(NO)moles of Fe(NO)22(CO)(CO)22 with with

varying moles of the ligandsvarying moles of the ligands

http://nanonet.rice.edu/research/CVtutorial2/sld011.htm

RecrystallizationRecrystallization

• Use a soluble solvent to dissolve the productUse a soluble solvent to dissolve the product• Filter through gravity filtrationFilter through gravity filtration• Collect filtrate in a vial and add a few drops of a Collect filtrate in a vial and add a few drops of a

non-soluble solventnon-soluble solvent• Place the vial at considerably low temperaturePlace the vial at considerably low temperature• Vapor diffusion techniques may be usedVapor diffusion techniques may be used

ConclusionsConclusions

• From the preliminary data, it is established that From the preliminary data, it is established that the reaction of dinitrosyl dicarbonyl iron with the reaction of dinitrosyl dicarbonyl iron with ligands containing the imidazole moiety gives ligands containing the imidazole moiety gives Fe(NO)Fe(NO)22(L)(L)22 or [Fe(NO) or [Fe(NO)22(L)](L)]44 type complexes type complexes

• These complexes are easy to characterize to These complexes are easy to characterize to study their electronic and binding behaviorstudy their electronic and binding behavior

• NO releasing kinetics can be easily studied from NO releasing kinetics can be easily studied from these complexesthese complexes

AcknowledgementsAcknowledgements

Dr. Lijuan LiDr. Lijuan Li

Dr. Ximeng WangDr. Ximeng Wang

Howard Hughes Medical InstituteHoward Hughes Medical Institute