Ligand and Metal Effects of the Co-Release Reactivityof Metal Acireductione and Flavonolate Complexes

• Main Author: Grubel, Katarzyna
• Format: Others
• Published: DigitalCommons@USU 2011
• Subjects: Metal Acireductione; Flavonaolate Complexes; Ligand and Metal Effects; Co-Realse Reactivity; Chemistry
• Online Access: https://digitalcommons.usu.edu/etd/1031; https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2038&context=etd

The research reported herein involves synthetic metal complexes of relevance to dioxygenase enzymes (Ni(II)-containing acireductone dioxygenase (Ni(II)-ARD) and quercentinase (2,4-flavonol dioxygenase) that promote oxidative carbon-carbon bond cleavage and CO release. The experiments focus on the elucidation of structure-reactivity relationships and evaluation of the conditions under which CO is generated. It had been proposed that hydrogen bond donors in the secondary environment of the active site metal center in Ni(II)-ARD influence the coordination of the acireductone substrate on the nickel center. To evaluate this proposal, we investigated the Ni(II) coordination chemistry of an acireductone-type enolate anion using a supporting chelate ligand having two internal hydrogen bond-donors. The resulting complex exhibited differences in terms of the organic product distribution in a CO release reaction resulting from oxidative C-C bond cleavage of the enolate ligand relative to this reported for the iv hydrophobic, 6-Ph2TPA-supported (6-Ph2TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)- N-((2-pyridyl)methyl)amine) analogue. In another study, we found that changes in the supporting chelate ligand or metal center influenced the coordination chemistry of the acireductone-type enolate anion. This chemistry highlighted the propensity of the enolate to undergo isomerization without CO release in the presence of water. Rigorously excluding water enabled the isolation of a Ni(II) enolate complex of the 6-PhTPA ligand and examination of its oxidative CO release chemistry, as well as the spectroscopic characterization of the first Co(II) complex of an acireductone-type enolate. To elucidate factors influencing the CO-release reactivity of metal-flavonoid complexes, some of which have relevance to quercentinase enzymes, we synthesized and characterized the first series of structurally-related metal-flavonolate complexes [(6- Ph2TPA)M(3-Hfl)]X (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II); X = OTfor ClO4 - ). Exposure of these complexes to UV light initiated photooxidative carboncarbon bond cleavage and CO release in a metal-dependent manner, with closed-shell d 10 metals giving rise to the highest rate of CO release. These studies suggest that metal flavonolate species may be useful as a new type of photo-induced CO release molecules (CORMs). Such species are of current interest for possible therapeutic applications.