Structural Characterization and
Electronic Properties of a Cyclic
Non-heme-iron-dinitrosyl
Complex: [Fe(NO)2Imidazole]4
Eric Sundberg and Lijuan Li
California State University, Long Beach
Nitric Oxide Chemistry
• 30 Years ago:
– A major contributor to smog
– An ingredient in cigarette smoke and
automobile exhaust
– A suspected carcinogen
– An ozone depleting agent
– Toxic, noxious chemical
Koshland, D. E., Jr. Science 1992, 258, 1861-1902
Nitric Oxide Chemistry
• In 1992, it was named the “Molecule of the
Year” by the journal Science in an article
titled, “NO News is Good News”
• In 1998 three gentlemen were awarded the
nobel prize in medicine and physiology for
their work involving the biological aspects
of nitric oxide
Nitric Oxide Chemistry
Furchgott
Ignarro
Murad
Discovered that nitric oxide works as a signaling
molecule in the cardiovascular system
http://www.nobel.se/medicine/laureates/1998/index.html
Nitric Oxide Chemistry
Numerous Physiological Functions
• Maintains blood
pressure by dilating
blood vessels
• Kills foreign invaders
• Involved in
neurotransmission
• Involved in learning
and memory processes
• Controls platelet
aggregation
• Stimulates penile
erections
Feldman, P. L.; Griffith, O. W.; Stuehr, D. J. Chem Eng. News 1993, 71 (Dec), 26-38
Heme Versus Non-heme
• Nitrosyl (NO) on a
hemoglobin molecule
• Nitrosyl attached to a
non-heme molecule
CH3
+ NO
NO
CH3
N
N
NO
Fe
N
Fe
N
CH3
CH3
NO
L
Fe
COOH
COOH
L
NO
Muller, B.; kleschyov, A. L.; Stoclet, J. C. Br. J. Pharm. 1996, 119, 1281-1285
Outline
Non-heme iron Dinitroyls
Synthesis
Characterization
FT-IR
X-ray
Crystallography
Classification
EPR
and
NMR
Stability
UV-vis
Electrochemistry
Density Functional Theory
Synthesis
Fe(CO)2(NO)2 + C3H4N2
O
O
N
N
NH
Fe
C
O
C
O
Starting Material:
Dicarbonyldinitrosyliron(0)
N
Ligand:
Imidazole
Synthesis
• After 2 Hours:
O
• After 24 Hours:
O
N
N
Fe
N
HN
C
O
N
80
C
N
%T
1 00
Fe
C
O
O
60
O
60
N
Fe
N
1731.01
%T
N
C
40
HN
1686.63
O
1982.50
Fe (CO)(NO)2(Im)
80
1757.57
O
1806.83
O
2031.69
Fe (CO)2(N O)2
2088.01
Characterization
O
20
%T
1796.78
20
1725.95
Fe (NO)2(I m)2
15
10
2 600
2 400
2 200
2 000
W ave num bers (c m-1 )
1 800
1 600
Characterization
• X-ray
Crystallography
shows a cyclic
compound with an
acetone molecule
trapped inside
Materials and Methods
• Recrystallized [Fe(NO)2Im]4
• Nuclear Magnetic Resonance
– Dissolved 50mg of sample into 2 mls of deuterated
THF and transferred to a NMR tube
– AC200 Spectrometer
• Electron Paramagnetic Resonance
– Dissolved 2 mg of sample into degassed 1 ml of THF
and transferred to EPR tube
– Brooker EMX Model EPR Spectrometer
Materials and Methods
• Electrochemistry
– 3 electrode system with a gold
working electrode
– THF was used as the solvent
– Scan Rate of 100 mV sec-1
– 10mM [Fe(NO)2(Imidazole)]4
solution and a 0.1M electrolyte
solution, (tetrabutylammonium
perchlorate)
– Computer Controlled
Electrochemical Analyzer
Autolab Electrochemical Insturments
http://www.ecochemie.nl/
Materials and Methods
• UV-vis Spectroscopy
– Varian 300 Bio UV-vis spectrophotometer
– Dilution Series in THF: 0.1-0.8 mM
Cary Uv-vis
Spectrometer
www.varianinc.com
Materials and Methods
• Stability
– FT-IR spectroscopy (Nicholet 380
Spectrometer)
– 0.2mM in THF at 15 and 30 minutes
• Spin Density Functional Theory
– Performed using X-ray crystallographic
coordinates
– Dr. Fu-Ming Tao at Cal. State Univ. Fullerton
Nuclear Magnetic Resonance
1H
H1
NMR
(H2&H3)
(H1)
9.0
H2&H3
8.0
7.0
6.0
5.0
4.0
ppm
3.0
2.0
1.0
0
Nuclear Magnetic Resonance
13C
C1
NMR
C2&C3
C2&C3
C1
240
210
180
150
120
ppm
90
60
30
Electron Paramagnetic Resonance
g=2.03
20G
Hyperfine Structure
Electrochemistry
UV-vis Spectroscopy
MLCT
d-d transitions
Stability under Oxygen
Fe (NO)2(I m )2
23
22
21
20
19
17
1796.78
16
15
14
13
12
11
1725.95
%Transmi ttance
18
10
9
3 400
3 200
3 000
2 800
2 600
2 400
2 200
W ave num bers (c m -1 )
2 000
1 800
1 600
1 400
1 200
Spin Density Functional Calculations
• Will provide wavefunction analysis of the
molecule
–  = a + b + c…
– A diagram of the electron density on the
molecule
N
80
C
N
%T
1 00
Fe
C
O
O
60
O
60
N
Fe
N
1731.01
%T
N
C
40
HN
1686.63
O
1982.50
Fe (CO)(NO)2(Im)
80
1757.57
O
1806.83
O
2031.69
Fe (CO)2(N O)2
2088.01
Spin Density Functional Calculations
O
20
%T
1796.78
20
1725.95
Fe (NO)2(I m)2
15
10
2 600
2 400
2 200
2 000
W ave num bers (c m-1 )
1 800
1 600
Spin Density Functional Calculations
SingleSubstituted
Product
N:
Fe
N:
Fe
:N
O
:N
O
HN
Cyclic
Product
N
Fe
+
Conclusion
• [Fe(NO)2Im]4 has been characterized by
– X-ray Crystallography and FT-IR Spectroscopy
– NMR and EPR techniques
• Electrochemistry showed 2 chemically
reversible reductions
• UV-vis spectroscopy showed MLCT and dd orbital transitions
Conclusion
• Low stability of compound in solution when
exposed to oxygen
• Spin Density Functional Theory showed
excess electronic density on the imidazole
• Potential Medicinal Applications
Future Studies
• Mass spectrometry
• Elemental analysis
• NMR studies of decomposed sample
• Laser flash photolysis
Acknowledgements
• Dr. Lijuan Li
• Dr. Ximeng Wang
• The Beckman Scholars Foundation
• Howard Huges Medical Institute