title: Large pKa shifts of alpha-carbon acids induced by copper(II) complexes.
abstract: A series of synthetic receptors (4-6) incorporating metal ions, specifically copper(II), were examined for their ability to enhance the acidity of active methylene compounds. The copper(II) complexes were observed to reduce the pKa of 1,3-diketone carbon acids in acetonitrile by as much as 12 pKa units. The relatively large pKa reduction achieved by the complex is attributed to the electrostatic interaction between the anionic pi system of the enolate and the copper(II) ions. The cage structure and hydrogen bonding sites in receptors 4 and 5 lead to a very modest further enhancement of the acidity relative to that with 6. This study provides insight into the way in which metalloenzymes stabilize an enolate intermediate.
authors.affiliation: The Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station A5300, Austin, TX 78712, USA.
authors.forename: Zhenlin
authors.initials: Z
authors.lastname: Zhong
authors.forename: Brenda J
authors.initials: BJ
authors.lastname: Postnikova
authors.forename: Robert E
authors.initials: RE
authors.lastname: Hanes
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Lynch
authors.forename: Eric V
authors.initials: EV
authors.lastname: Anslyn
mesh_terms: D000143:Acids / Q000138:chemical synthesis / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons; D013057:Spectrum Analysis; D017186:Titrimetry
chemical_list: D000143:Acids; D011522:Protons; D002244:Carbon; D003300:Copper