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Type: Journal article
Title: Phosphodiester cleavage properties of copper(II) complexes of 1,4,7-triazacyclononane ligands bearing single alkyl guanidine pendants
Author: Tjioe, L.
Joshi, T.
Forsyth, C.
Moubaraki, B.
Murray, K.
Brugger, J.
Graham, B.
Spiccia, L.
Citation: Inorganic Chemistry: including bioinorganic chemistry, 2012; 51(2):939-953
Publisher: American Chemical Society
Issue Date: 2012
ISSN: 0020-1669
Statement of
Linda Tjioe, Tanmaya Joshi, Craig M. Forsyth, Boujemaa Moubaraki, Keith S. Murray, Joël Brugger, Bim Graham, and Leone Spiccia
Abstract: Three new metal-coordinating ligands, L¹·4HCl [1-(2-guanidinoethyl)-1,4,7-triazacyclononane tetrahydrochloride], L²·4HCl [1-(3-guanidinopropyl)-1,4,7-triazacyclononane tetrahydrochloride], and L³·4HCl [1-(4-guanidinobutyl)-1,4,7-triazacyclononane tetrahydrochloride], have been prepared via the selective N-functionalization of 1,4,7-triazacyclononane (tacn) with ethylguanidine, propylguanidine, and butylguanidine pendants, respectively. Reaction of L¹·4HCl with Cu(ClO₄)₂·6H₂O in basic aqueous solution led to the crystallization of a monohydroxo-bridged binuclear copper(II) complex, [Cu₂L¹₂(μ-OH)](ClO₄)₃·H₂O (C1), while for L² and L³, mononuclear complexes of composition [Cu(L(2)H)Cl(2)]Cl·(MeOH)(0.5)·(H(2)O)(0.5) (C2) and [Cu(L(3)H)Cl(2)]Cl·(DMF)(0.5)·(H(2)O)(0.5) (C3) were crystallized from methanol and DMF solutions, respectively. X-ray crystallography revealed that in addition to a tacn ring from L(1) ligand, each copper(II) center in C1 is coordinated to a neutral guanidine pendant. In contrast, the guanidinium pendants in C2 and C3 are protonated and extend away from the Cu(II)-tacn units. Complex C1 features a single μ-hydroxo bridge between the two copper(II) centers, which mediates strong antiferromagnetic coupling between the metal centers. Complexes C2 and C3 cleave two model phosphodiesters, bis(p-nitrophenyl)phosphate (BNPP) and 2-hydroxypropyl-p-nitrophenylphosphate (HPNPP), more rapidly than C1, which displays similar reactivity to [Cu(tacn)(OH(2))(2)](2+). All three complexes cleave supercoiled plasmid DNA (pBR 322) at significantly faster rates than the corresponding bis(alkylguanidine) complexes and [Cu(tacn)(OH(2))(2)](2+). The high DNA cleavage rate for C1 {k(obs) = 1.30 (±0.01) × 10(-4) s(-1) vs 1.23 (±0.37) × 10(-5) s(-1) for [Cu(tacn)(OH(2))(2)](2+) and 1.58 (±0.05) × 10(-5) s(-1) for the corresponding bis(ethylguanidine) analogue} indicates that the coordinated guanidine group in C1 may be displaced to allow for substrate binding/activation. Comparison of the phosphate ester cleavage properties of complexes C1-C3 with those of related complexes suggests some degree of cooperativity between the Cu(II) centers and the guanidinium groups.
Keywords: Copper (II) complexes
Rights: © 2011 American Chemical Society
DOI: 10.1021/ic2019814
Grant ID: ARC
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