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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2445 |
| Date | 15 May 2009 |
| Creators | Green, Kayla Nalynn |
| Contributors | Darensbourg, Marcetta Y. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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