A dinuclear zinc(II) complex of a new unsymmetric ligand with an N(5)0(2) donor set; A structural and functional model for the active site of zinc phosphoesterases
2014 (English)In: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 132, 6-17 p.Article in journal (Refereed) Published
The dinuclear complex [Zn-2(DPCPMP)(pivalate)](C10(4)), where DPCPMP is the new unsymmetrical ligand [2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin2-y1)methyl)amino)acetic acid], has been synthesized and characterized. The complex is a functional model for zinc phosphoesterases with dinuclear active sites. The hydrolytic efficacy of the complex has been investigated using bis-(2,4-dinitrophenyl)phosphate(BDNPP), a DNA analog, as substrate. Speciation studies using potentiometric titrations have been performed for both the ligand and the corresponding dizinc complex to elucidate the formation of the active hydrolysis catalyst; they reveals that the dinuclear zinc(II) complexes, [Zn-2(DPCPMP)](2) and [Zn-2(DPCPMP)(OH)1 predominate the solution above pH 4. The relatively high pKa of 8.38 for water deprotonation suggests that a terminal hydroxide complex is formed. Kinetic investigations of BDNPP hydrolysis over the pH range 5.5-11.0 and with varying metal to ligand ratio (metal salt:ligand = 0.5:1 to 3:1) have been performed. Variable temperature studies gave the activation parameters triangle H double dagger = 95.6 kJ mol(-1), triangle S double dagger = 44.8 J mo1(-1) K-1, and 6,triangle G double dagger = 108.0 kJ mo1-1. The cumulative results indicate the hydroxido-bridged dinuclear Zn(II) complex [Zn-2(DPCPMP)(mu-OH)] (+) as the effective catalyst. The mechanism of hydrolysis has been probed by computational modeling using density functional theory (DFF). Calculations show that the reaction goes through one concerted step (S(N)2 type) in which the bridging hydroxide in the transition state becomes terminal and performs a nucleophilic attack on the BDNPP phosphorus; the leaving group dissociates simultaneously in an overall inner sphere type activation. The calculated free energy barrier is in good agreement with the experimentally determined activation parameters.
Place, publisher, year, edition, pages
2014. Vol. 132, 6-17 p.
Zinc phosphoesterases, Dinuclear active sites, DNA analog, Transition state
IdentifiersURN: urn:nbn:se:su:diva-102972DOI: 10.1016/j.jinorgbio.2013.08.001ISI: 000333443800003OAI: oai:DiVA.org:su-102972DiVA: diva2:714559
FunderKnut and Alice Wallenberg FoundationGöran Gustafsson Foundation for Research in Natural Sciences and MedicineSwedish Institute