Issue 6, 2012
From the journal:

Dalton Transactions

The role of Zn–OR and Zn–OH nucleophiles and the influence of para-substituents in the reactions of binuclear phosphatase mimetics†

Lena J. Daumann,a   Kristian E. Dalle,a   Gerhard Schenk,a   Ross P. McGeary,a   Paul V. Bernhardt,a   David L. Ollisb  and  Lawrence R. Gahan*a  

* Corresponding authors

a School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Australia
E-mail: gahan@uq.edu.au

b Research School of Chemistry, Australian National University, Canberra, Australia

Abstract

Analogues of the ligand 2,2′-(2-hydroxy-5-methyl-1,3-phenylene)bis(methylene)bis((pyridin-2-ylmethyl)azanediyl)diethanol (CH3H3L1) are described. Complexation of these analogues, 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-methylphenol (CH3HL2), 4-bromo-2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (BrHL2), 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-nitrophenol (NO2HL2) and 4-methyl-2,6-bis(((2-phenoxyethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (CH3HL3) with zinc(II) acetate afforded [Zn2(CH3L2)(CH3COO)2](PF6), [Zn2(NO2L2)(CH3COO)2](PF6), [Zn2(BrL2)(CH3COO)2](PF6) and [Zn2(CH3L3)(CH3COO)2](PF6), in addition to [Zn4(CH3L2)2(NO2C6H5OPO3)2(H2O)2](PF6)2 and [Zn4(BrL2)2(PO3F)2(H2O)2](PF6)2. The complexes were characterized using 1H and 13C NMR spectroscopy, mass spectrometry, microanalysis, and X-ray crystallography. The complexes contain either a coordinated methyl- (L2 ligands) or phenyl- (L3 ligand) ether, replacing the potentially nucleophilic coordinated alcohol in the previously reported complex [Zn2(CH3HL1)(CH3COO)(H2O)](PF6). Functional studies of the zinc complexes with the substrate bis(2,4-dinitrophenyl) phosphate (BDNPP) showed them to be competent catalysts with, for example, [Zn2(CH3L2)]+, kcat = 5.70 ± 0.04 × 10−3 s−1 (Km = 20.8 ± 5.0 mM) and [Zn2(CH3L3)]+, kcat = 3.60 ± 0.04 × 10−3 s−1 (Km = 18.9 ± 3.5 mM). Catalytically relevant pKas of 6.7 and 7.7 were observed for the zinc(II) complexes of CH3L2− and CH3L3−, respectively. Electron donating para-substituents enhance the rate of hydrolysis of BDNPP such that kcatp-CH3 > p-Br > p-NO2. Use of a solvent mixture containing H2O18/H2O16 in the reaction with BDNPP showed that for [Zn2(CH3L2)(CH3COO)2](PF6) and [Zn2(NO2L2)(CH3COO)2](PF6), as well as [Zn2(CH3HL1)(CH3COO)(H2O)](PF6), the 18O label was incorporated in the product of the hydrolysis suggesting that the nucleophile involved in the hydrolysis reaction was a Zn–OH moiety. The results are discussed with respect to the potential nucleophilic species (coordinated deprotonated alcohol versus coordinated hydroxide).

Graphical abstract: The role of Zn–OR and Zn–OH nucleophiles and the influence of para-substituents in the reactions of binuclear phosphatase mimetics

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Article information

DOI
https://doi.org/10.1039/C1DT11187F
Article type
Paper
Submitted
23 Jun 2011
Accepted
04 Oct 2011
First published
15 Dec 2011

Dalton Trans., 2012,41, 1695-1708

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The role of Zn–OR and Zn–OH nucleophiles and the influence of para-substituents in the reactions of binuclear phosphatase mimetics

L. J. Daumann, K. E. Dalle, G. Schenk, R. P. McGeary, P. V. Bernhardt, D. L. Ollis and L. R. Gahan, Dalton Trans., 2012, 41, 1695 DOI: 10.1039/C1DT11187F

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