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Description:
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The A -cluster active site in acetyl coA synthase exploits a Ni (CGC )2 -
metallopeptide as a bidentate ligand to chelate the catalytically active square -planar
nickel center used to produce acetyl coA . As Nature utilizes polypeptides to isolate and
stabilize the active sites , we have set out to immobilize biomimetic complexes to
polyethylene -glycol (PEG ) rich polystyrene polymer beads (TentaGel ) . The PEG rich
resin -beads serve to imitate the peptidic superstructure of enzyme active sites as well as
to protect the resin -bound models from O2 decomposition . As a model of the NiN2S2
ligand observed in the A -cluster of acetyl coA synthase , the CGC tripeptide was
constructed on resins using Merrifield solid phase peptide synthesis and then metallated
with NiII to produce bright orange beads . Derivatization with M (CO )x (M = Rh , W )
provided qualitative identification of Ο -Ni (CGC )M (CO )x
n - via ATR -FTIR .
Additionally , Neutron Activation Analysis (NAA ) and UV -vis studies have determined
the concentration of Ni and CGC , and qualitatively identify Ο -Ni (CGC )2 - . Furthermore ,
infrared studies and NAA experiments have been used to identify and quantify Ο -
Ni (CGC )Rh (CO )2
1 - . The S -based reactivity of Ni (ema )2 - , a good model of Ni (CGC )2 - , toward
oxygenation and alkylation has been pursued and compared to neutral NiN2S2
complexes . The spectroscopic , electrochemical and structural effects of these
modifications will be discussed and supported using DFT computations and electrostatic
potential maps of the resulting Ni (ema )*O2
2 - and Ni (ema )* (CH2 )3 complexes .
Having firmly established the synthesis , characterization and reactivity of
NiN2S2
2 - systems in solution and resin -bound , CuIIN2S2 analogues were explored . The
synthesis and identification of solution complexes , Cu (ema )2 - , Cu (emi )2 - , and Cu (CGC )2 -
via UV -Vis , EPR , and –ESI -MS will be discussed in addition to their S -based reactivity
with Rh (CO )2
+
. Furthermore , the resin -bound Cu (CGC )2 - complex has been produced
and characterized by EPR and its Rh (CO )2 adduct identified by ATR -FTIR and
compared to the analogous NiN2S2
2 - systems .
As the active site of [FeFe] Hydrogenase utilizes a unique peptide -bound propane
dithiolate bridge to support the FeFe organometallic unit , [FeFe]Hydrogenase models
have been covalently anchored to the resin -beads via similar carboxylic acid
functionalities . The characterization (ATR -FTIR , EPR , Neutron Activation Analysis ) ,
stability and reactivity of the immobilized models complexes are discussed as well as
work toward establishing the microenvironment of resin -bound complexes . |