The acetyl CoA synthase paradigm for hybrid bio-organometallics: Quantitative measures for resin-bound Ni-Rh complexes
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abstract
The active site of Acetyl CoA Synthase utilizes a square planar NiN2S2 complex in the form of NiII(CGC)2- (CGC = the cysteine-glycine-cysteine tripeptide motif within the protein) to serve as a bidentate sulfur-donor ligand to chelate a second, catalytically active Ni atom responsible for the C-C and C-S coupling reactions for the production of Acetyl CoA. Metalloenzymes, such as this, which house stable catalytic complexes within intricately designed pockets accessible by solvent channels, have inspired design of resin-bound complexes. Through the use of TentaGel S-RAM resin beads, the O-Ni(CGC)2- ligand has been synthesized and derivatized with the RhI(CO)2 moiety. The identification of the O - Ni(CGC)Rh(CO)21 - adduct on these resin beads is afforded by attenuated total reflectance FTIR spectroscopy in the (CO) region and compared to solution analogues. The goal of this study is to establish a quantitative measure of the loading of nickel and rhodium on the tripeptide modified resin beads, O-(CGC). The extent of CGC derivatization was determined by Fmoc cleavage of the Fmoc protected O-(CGC). Nickel and rhodium loading were determined by Neutron Activation Analysis. This work provides evidence that the TentaGel S-RAM resin beads greatly decrease the air sensitivity of the Ni-Rh complex as compared to the unsupported solution phase analogue. The derivatized beads have also been studied for their ability to withstand a number of physical stresses, i.e., for leaching. 2006 Elsevier B.V. All rights reserved.
