This document discusses modeling the active site of the metalloenzyme nickel acireductone dioxygenase (Ni-ARD) using novel nickel and zinc complexes. A family of pyridyl and phenoxy-containing nickel and zinc complexes were synthesized and characterized as models of the Ni-ARD active site. Small modifications were made to the ligand backbone in the metal complexes to analyze resulting structural and electronic changes and better understand the enzyme's structure-function relationship. Future work will involve synthesizing assigned metal complexes, spectroscopically analyzing the compounds, and testing their reactivity.

1. Biomimetic Inorganic Chemistry:
Modeling Ni-ARD using novel Ni-N,O and
Zn-N,O complexes
By Jean-Marc Choufani

2.  Nickel is not a common element naturally
available due to its reactivity with oxygen;
however it serves an important role as the
metal center for a metalloenzyme, Nickel
Acireductone Dioxygenase (Ni-ARD)
 Fe-ARD vs Ni-ARD

3.  Protein does not have a preference to either transition metal
 May not be a difference in binding modes of ARD and ARD’, although
ARD’ has one additional intermediate step
 Disproving of the old hypothesis which stated that the mechanistic
difference between ARD and ARD’ was caused due to the way either
protein bound to the substrate. Both form 6 membered ring via 2 oxygen
atoms
 In one proposed mechanism, a reduced, redox active metal is used to
activate dioxygen for oxidation of the substrate. In the other proposed
mechanism, the metal serves to activate the substrate toward reaction with
O_2 by acting as a Lewis acid (Ni-ARD) [Fe-ARD’ much relies on transient
redox chemistry while Ni-ARD acts a Lewis acid]
Metal-Dependent Activity of Fe and Ni AcireductoneDioxygenases: How Two Electrons Reroute the Catalytic Pathway,
Volume 425?, 2013, pg. 3007
Acireductone Dioxygenase- (ARD-) Type Reactivity of a Nickel(II)Complex Having Monoanionic Coordination of a
Model Substrate:Product Identification and Comparisons to Unreactive Analogues, Volume 46, 2007, pg. 5499

4. Nickel Acireductone dioxygenase (Ni-ARD)
• The structure and function of the enzyme are determined partially by the center’s
active site.
• A family of related pyridyl and phenoxy containing Ni and Zn complexes are to be
synthesized and characterized as models of the active site of Ni-ARD.
• Better understanding of Ni-ARD can be made through small modifications of the
ligand backbone in the metal complex, and analyzing the structural and electronic
changes that result from these alterations.
NiII
H2O
H2O NHis
NHis
NHis
OGlu

5.  A family of related pyridyl and phenoxy containing Ni and Zn
complexes were synthesized and characterized as models of the
active site of Ni-ARD ([ZnII(OHMe26-H-DPPN)](OTf)2, and
[NiII(OHMe26-H-DPPN)](OTf)2).
 Through small modifications of the ligand backbone in the metal
complex, and analyzing the structural and electronic changes that
result from these alterations, a better understanding of the structure-
function relationship of the active site of Ni-ARD is being pursued.
N
Zn
N
N
O
N
+
[ZnII
(OMe2
6-H-DPPN)]+
N
Ni
N
N
O
N
[NiII
(OMe2
6-H-DPPN)]+
+
Chai et al. (2008). Characterization of Metal Binding in the Active Sites of Acireductone Dioxygenase Isoforms from
Klebsiella ATCC 8724. Biochemistry, (47), 2428-2438.

6. Ligand synthesis [N,N-bis(2-pyridilmethyl)propane-1,2-diamine]
(6-H-DPPN)
NH2
NH2
NH2
NHBoc
iii N
NH2
N
N
N
NH
N
N
O
O
i ii
n=0,1 n=0,1
n=0,1 n=0,1
i.- BOC 0.2 eq, DCM, 6hr addition, 24 hr rt ;
ii.-2-picolyl chloride hydrochloride 1.7eq, 5M NaOH , rt 3d (CC 100% Acetone);
iii.- Trifluoroacetic acid xcess, DCM, rt, 24 hr
100% 65%
75%
n=0 6-H-DPEN
n=1 6-H-DPPN
i.-Kilburn, J. Chem. Eur. J. 2002, 8,1300-1310
ii.-Bernal, I. et al. J. Chem. Soc. Dalton Trans. 1995, 3667-3675
iv.-Shinkai, S. Chem. Lett. 1998, 915-916

8. 1H-NMR of [N,N-bis(2-pyridilmethyl)propane-1,2-diamine] (6-H-DPPN)
in CDCl3

9. Future work
Proceed with synthesis of assigned metal complexes and spectroscopical
analysis of compounds, and test reactivity
[ZnII(OHMe26-H-DPPN)](OTf)2, and [NiII(OHMe26-H-DPPN)](OTf)2,
N
Zn
N
N
O
N
+
[ZnII
(OMe2
6-H-DPPN)]+
N
Ni
N
N
O
N
[NiII
(OMe2
6-H-DPPN)]+
+