title: 13C NMR study of the ion-binding selectivity of a new ammonium ionophore.
abstract: A bicyclic peptide, cyclo (L-Glu(1)-D-Leu(2)-Aib(3)-L-Lys(4)-D-Leu(5)-D-Ala(6))-cyclo-(1gamma-4epsilon) (I), was designed and synthesized to provide an ammonium ion complexation site in a tetrahedral geometry. Molecular modeling, dynamics and electrostatic studies for I indicated that it exhibits some selectivity for ammonium ions over potassium and sodium ions. NMR measurements in CDCl(3)/CD(3)OD (1:1) show that for those carbonyl groups involved in cation binding, (13)C resonances shifted downfield with increasing cation concentration. The resonance that exhibited the largest change in chemical shift between uncomplexed and complexed forms was used to determine the selectivity. Selectivity values obtained were logK(NH(4) (+), Na(+) ) = - 2.4 and logK(NH(4) (+), K(+) ) = - 0.6.
authors.affiliation: Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, USA.
authors.forename: W Grant
authors.initials: WG
authors.lastname: McGimpsey
authors.forename: Ernesto
authors.initials: E
authors.lastname: Soto
authors.forename: Peter F
authors.initials: PF
authors.lastname: Driscoll
authors.forename: Cheryl
authors.initials: C
authors.lastname: Nowak
authors.forename: John S
authors.initials: JS
authors.lastname: Benco
authors.forename: Christopher G F
authors.initials: CG
authors.lastname: Cooper
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Lambert
mesh_terms: D002247:Carbon Isotopes; D003198:Computer Simulation; D007477:Ions / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods* / Q000592:standards; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry*; D011188:Potassium / Q000737:chemistry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012015:Reference Standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012964:Sodium / Q000737:chemistry; D012995:Solubility; D055672:Static Electricity
chemical_list: D002247:Carbon Isotopes; D007477:Ions; D010456:Peptides, Cyclic; D000644:Quaternary Ammonium Compounds; D012964:Sodium; D011188:Potassium