Immobilized metallodithiolate ligand supports for construction of bioinorganic model complexes

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Title: Immobilized metallodithiolate ligand supports for construction of bioinorganic model complexes
Author: Green, Kayla Nalynn
Abstract: 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 ? -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 ? -Ni (CGC )2 - . Furthermore , infrared studies and NAA experiments have been used to identify and quantify ? - 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 .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2445
Date: 2009-05-15

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Immobilized metallodithiolate ligand supports for construction of bioinorganic model complexes. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2445 .

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