title: Energetics of phosphate binding to ammonium and guanidinium containing metallo-receptors in water.
abstract: The design and synthesis of receptors containing a Cu(II) binding site with appended ammonium groups (1) and guanidinium groups (2), along with thermodynamics analyses of anion binding, are reported. Both receptors 1 and 2 show high affinities (10(4) M(-1)) and selectivities for phosphate over other anions in 98:2 water:methanol at biological pH. The binding of the host-guest pairs is proposed to proceed through ion-pairing interactions between the charged functional groups on both the host and the guest. The affinities and selectivities for oxyanions were determined using UV/vis titration techniques. Additionally, thermodynamic investigations indicate that the 1:phosphate complex is primarily entropy driven, while the 2:phosphate complex displays both favorable enthalpy and entropy changes. The thermodynamic data for binding provide a picture of the roles of the host, guest, counterions, and solvent. The difference in the entropy and enthalpy driving forces for the ammonium and guanidinium containing hosts are postulated to derive primarily from differences in the solvation shell of these two groups.
authors.affiliation: Department of Chemistry and Biochemistry, The University of Texas, Austin, TX 78712, USA.
authors.forename: Suzanne L
authors.initials: SL
authors.lastname: Tobey
authors.forename: Eric V
authors.initials: EV
authors.lastname: Anslyn
mesh_terms: D001665:Binding Sites; D040761:Biomimetic Materials / Q000737:chemistry; D002151:Calorimetry; D003300:Copper / Q000737:chemistry*; D019791:Guanidine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D011956:Receptors, Cell Surface / Q000737:chemistry; D055672:Static Electricity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D009942:Organometallic Compounds; D010710:Phosphates; D000644:Quaternary Ammonium Compounds; D011956:Receptors, Cell Surface; D014867:Water; D003300:Copper; D019791:Guanidine